V2O5 nanocomposites as cathode materials for rechargeable lithium batteries

Electrochimica Acta 50 (2005) 4627–4636

Electrochemical properties of microwave irradiated synthesis of poly(3,4-ethylenedioxythiophene)/V2O5 nanocomposites as cathode materials for rechargeable lithium batteries A. Vadivel Murugan ∗ Centre for Materials for Electronics Technology (C-MET), Department of Information Technology, Govt. of India, Dr. Homibhabha Road, Panchawati, Pune 411008, India Received 11 August 2004; received in revised form 23 December 2004; accepted 13 February 2005 Available online 20 March 2005

Abstract A series of poly(3,4-ethylenedioxythiophene) (PEDOT)/V2 O5 nanocomposites are prepared via the redox intercalative polymerization reaction of 3,4-ethylenedioxythiophene (EDOT) monomer and crystalline V2 O5 within 10 min by using rapid 2.45 GHz microwave irradiation with full power (800 W). The unique properties of the resultant nanocomposites are investigated by various characterization techniques using powder XRD, TGA/DTA and four-point probe conductivity analysis supports the intercalation of polymer nanosheet between V2 O5 layers leading to enhanced bi-dimensionality. X-ray photoelectron spectroscopy analysis clearly shows the presence of mixed valent V4+ /V5+ in the V2 O5 framework after the redox intercalative polymerization which also confirms charge transfer from the polymer to the V2 O5 framework. The application potential of these composites as cathode materials in rechargeable lithium batteries is also demonstrated by the electrochemical intercalation of lithium into the PEDOT/V2 O5 nanocomposites, where an enhancement in the discharge capacity (370 mAh/g) is observed compared to that of crystalline V2 O5 . © 2005 Elsevier Ltd. All rights reserved. Keywords: Microwave preparation; Redox intercalative polymerization; PEDOT/V2 O5 ; Lithium batteries

1. Introduction Recently, novel routes for the preparation of cathode materials for rechargeable lithium ion batteries have attracted increased important as power sources for a multitude of portable consumer electronics and electric vehicles [1]. In particular, the microwave-assisted route is yet another novel method of synthesis and is a very rapidly developing area of materials research. Several reports have appeared where conventional preparative techniques are substituted by the microwave method [2,3]. For example vanadium pentoxide is one of the layered cathode materials for rechargeable lithium ∗

Tel.: +91 20 25898390; fax: +91 20 25898180. E-mail addresses: [email protected], [email protected] (A.V. Murugan). 0013-4686/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2005.02.020

batteries because of its high-energy storage capacities. It has been demonstrated that the specific energy density of V2 O5 is higher than that of presently available cathode materials. However, the poor capacity retention of V2 O5 electrode upon cycling (capacity fading) limits its use in practical batteries [4]. Consequently, several groups have focused efforts on the synthesis of new cathode materials to ameliorate these limitation [5–10]. More significantly, conducting polymers based nanocomposites with inorganic transition metal oxides which are promising electrodes for electrochemical power sources. Indeed, the field has expanded in such a way that several recent reports focus only on specific preparation of conducting polymer nanocomposite and their functional properties particularly on the possibility of enhancing the energy storage characteristics for lithium batteries [5–10]. However, the preparation of many of these hybrid

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nanocomposite materials often involves lengthy procedures with several steps and needs more time before the formation of the organic–inorganic hybrid functional nanocomposite. It is, therefore, necessary to develop more efficient methods of synthesis involving simplified preparation procedures and short time, and the use of microwave-assisted synthesis is especially important in this regard. Here we report a new modified approach in the in situ intercalative microwave-assisted polymerization reaction which, for the first time, allows the intercalation of poly(3,4-ethylene dioxythiophene) PEDOT into the van der Waals gap of crystalline V2 O5 to produce new nanocomposites and it is also to understand the microwave assisted-redox intercalation reaction of EDOT with V2 O5 powder and the subsequent polymerization. This nanocomposite is characterized by powder X-ray diffraction, thermal analysis (TGA/DTA), X-ray photoelectron spectroscopy (XPS) and electronic conductivity measurements. Furthermore the application potential of this nanocomposite, displaying some unusual synergistic effects with respect to enhancement of electrochemical properties of V2 O5 by intercalation of PEDOT, has been demonstrated using this as a cathode material for rechargeable lithium batteries.

2. Experimental PEDOT/V2 O5 nanocomposite, where prepared by dissolving a given amount of EDOT and crystalline vanadium pentoxide in doubly distilled water were treated in a double walled Teflon-lined digestion vessel and placed on a turn-table for uniform heating using a microwave digestion system (MLS-120 Mega, GmbH, Germany). The molar ratio of EDOT/V2 O5 was varied from 0.015 to 0.65 in five different compositions. Computer-controlled microwavehydrothermal treatments were conducted for fixed time (10 min) using 2.45 GHz microwave radiation with full power (800 W). When, the reaction mixture was exposed to microwave radiation, the microwaves induced rotation of the dipoles within the liquid, forcing the polar molecules to align and relax in the field of oscillating electromagnetic radiations, causing the liquid to become hot. After the microwave irradiation, the solid was filtered off and washed repeatedly with water and ethanol until the initial light yellow color in the filtrate was totally absent, and the bluish black powder was dried in air. The powder X-ray diffraction analysis was carried out using a Rigaku X-ray diffractometer (Rigaku miniflex) ˚ radiation and a equipped with a Ni filtered Cu K␣ (1.542 A) graphite crystal monochromator. X-ray photoemission spectra (XPS) was carried out on VG Microtech Multilab ESCA 3000 spectrometer using a non-monochromatized Al K␣ Xray source (hν = 1486.6 eV). The base pressure in the analysis chamber was maintained in the 10−10 Torr range. The energy resolution of the spectrometer was set at 1.1 eV with Al K␣ radiation at a pass energy of 50 eV. Binding energy

(BE) calibration was performed with Au 4f7/2 core level at 83.9 eV. The error in all the BE values reported here is within ±0.1 eV. Thermogravimetric analysis (TGA/DTA) was performed with a Shimadzu TGA-50 thermal analysis system using dry oxygen as a carrier gas. The TGA experiments were conducted from room temperature to 800 ◦ C at a linear heating rate of 10 ◦ C min−1 . Electronic conductivity measurements were made on compaction of powder in pellet form by using a four-point probe conductivity method. Elemental analysis was carried out using inductively coupled plasma optical emission spectroscopy (ICP–OES, Perkin-Elmer, 1000) and using a CE-Instruments-EA-1110 CHNO-S analyser. The electrochemical measurements were performed using a button-type cell configuration with the aid of a computer-controlled PGS201T (Tacussel) potentiostat/galvanostat system. The pristine crystalline V2 O5 and oxidized PEDOT/V2 O5 composite cathodes were made by intimately mixing 70% (by weight) active material, 25% of Ketjenblack, and 5% of PTFE. The surface area of electrodes and weight of the active material were adjusted to ∼1 cm2 and ∼20 mg respectively, for reproducibility. These electrodes were dried under vacuum at ∼80 ◦ C for more than 3 h, and introduced into an argon-filled glovebox without any exposure to air. The electrolyte was 1 M LiClO4 in 1:1 mixture (by volume) of EC/DMC, and a lithium foil was used as an anode. For charge/discharge experiments, a constant current of 15 mA/g was applied between 2.0 and 4.4 V (versus Li+ /Li) at C/2. For cyclic voltammetry of both crystalline V2 O5 and PEDOT/V2 O5 nanocomposites has been measured by the voltage was cycled between 2.2 and 3.8 V at a sweep rate of 0.5 mV s−1 .

3. Results and discussion 3.1. X-ray diffraction and X-ray photoelectron spectroscopy studies Fig. 1 shows the powder XRD diffraction patterns (a) crystalline V2 O5 and (b–f) for the series of PEDOT/V2 O5 composites to demonstrate the continuous structural changes upon intercalation using microwave irradiation with fixed time (10 min). A systematic study of the synthesis of the nanocomposites by direct in situ reaction of 3,4ethylenedioxythiophene (EDOT) with crystalline V2 O5 fine powder shows that upon intercalation, the interlayer spacing ˚ of V2 O5 expands in two stages, i.e., first from 4.32 to 14.1 A ˚ The interlayer separation is consistent and further to 19.1 A. with the existence of two phases in the PEDOT/V2 O5 system corresponding to the intercalation of one and two monolayers of PEDOT, respectively, in the V2 O5 framework. The strongest peak observed at the low angle corresponding to the (0 0 1) plane of the layered V2 O5 structure is directly related to the interlayer spacing. The (0 0 1) spacing of PEDOT/V2 O5 ˚ is larger than those for pure crysnanocomposite (14.1 A) ˚ talline V2 O5 (4.3 A) although there are minor changes with

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Fig. 1. Powder XRD pattern of the (a) crystalline V2 O5 and PEDOT/V2 O5 nanocomposite synthesized with different ratios of EDOT/V2 O5 ; (b) 0.015, (c) 0.035, (d) 0.075, (e) 0.45, (f) 0.65, by a direct microwave irradiation at 10 min.

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Scheme 1. Schematic diagram of the in situ redox intercalative polymerization of EDOT monomer forms monolayer and double-layer nanosheet formation of PEDOT into V2 O5 layers by microwave irradiation.

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the nature of the incorporated polymer. The main features of the V2 O5 diffraction pattern are in the composites are clearly modified by the appearance of a sharp diffuse scattering feature and an increase in the intensity of (0 0 1) peak. Then, within the series of nanocomposites, a clear change in the position of the peak takes place, which marks a difference between samples. The samples ‘b’ to ‘d’ with EDOT/V2 O5 ratios of 0.015 to 0.075 present the (0 0 1) peak at 2θ value from 6.6◦ to 6.4◦ , which corresponds to an interlayer spacing ´˚ Thus upon polymer nanosheet intercalation, 13.8 to 14.1 A. the interlayer spacing of V2 O5 fine powder expands from ´˚ More interestingly, the samples ‘e’ to ‘f’ with 4.3 to 14.1 A. EDOT/V2 O5 ratios of 0.45 to 0.65 present the (0 0 1) peak has further shifted to lower angle, 5.0 to 4.5◦ corresponding to ´˚ which is substantially larger interlayer spacing 17.8 to 19.1 A than that found for the samples ‘b’ to ‘d’. There are two regions with qualitatively different features, which confirm the existence of phases with distinct structures. This suggests that PEDOT intercalation occurs in two steps, leading to the formation of two correspondingly different phases. The first ´˚ and can be one represents an expansion from 4.3 to 14.1 A, explained by the monolayer formation of PEDOT nanosheet. On the other hand, the formation of the second phase, associated with an additional expansion of the ‘c’ parameter ´˚ precisely indicates the double amount (two polyto 19.1 A mer nanosheets) of PEDOT between layers per V2 O5 unit. These results are also in excellent agreement with the recent reports on conducting polymer/V2 O5 nanocomposites [6,14]. Thus it is likely that these materials constitute a new PEDOT/V2 O5 phase consisting of a monolayer and double layer of PEDOT nanosheets intercalated within V2 O5 interlayer spacing by microwave irradiation has been illustrated in Scheme 1. These results are listed in Table 1 along with a comparison of the spacings calculated from lattice constants, electronic conductivities and electrochemical properties of nanocomposite. X-ray photoelectron spectroscopic is a surface-specific technique to study the polymer–V2 O5 interaction and presence of mixed vanadium (V5+ /V4+ ) oxidation state, after the redox polymer intercalation. XPS results from V 2p and O

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Fig. 2. X-ray photoelectron spectra of PEDOT/V2 O5 nanocomposite prepared form direct microwave irradiation for 10 min with EDOT/V2 O5 ratio of 0.015.

1s core level of the polymer intercalated nanocomposite are displayed in Fig. 2. The spectra are clearly shows after the removal of the O 1s X-ray satellite around 518–520 eV and after Shirley background subtraction. A low-BE feature is apparent along with V5+ species at 517.2 eV. Deconvolution of the V 2p core levels clearly shows the above low-BE feature at 515.7 eV, which is attributed to V4+ . The above BE values are in good correspondence with the standard compound [12]. Using the deconvoluted peak area and the photoionization cross section of the V 2p3/2 level, the amount of V4+ is calculated to be 19% in total vanadium. This clearly indicates a charge transfer from the polymer to V2 O5 , indicating the effectiveness of the interaction between the polymer and V2 O5 . It is speculated here that the above interaction might be through the S atom of the polymer, as it is electron-rich; however, the above suggestion could not be confirmed since the S 2p signal is hardly seen in XPS, perhaps due to the low photoionization cross section [13], and further work is in progress with different amounts of polymer incorporation into V2 O5 .

Table 1 Comparison of inter layer spacing, room temperature conductivity, discharge capacity, open-circuit voltage and thermal stability of V2 O5 and PEDOT/V2 O5 nanocomposits with the corresponding EDOT/V2 O5 ratio Name of the materials

Nominal ‘x’ (‘x’ EDOT:V2 O5 )

Interlayer ´˚ spacing (A)

Electronic conductivity, σ (S cm−1 ) (RT)

Discharge capacitiesa (mAh/g)

Open-circuit voltagea (V)

Thermal stability in air (◦ C)

(a) V2 O5 (b) PEDOT/V2 O5 (c) PEDOT/V2 O5 (d) PEDOT/V2 O5 (e) PEDOT/V2 O5 (f) PEDOT/V2 O5 (g) PEDOT

– 0.015 0.035 0.075 0.450 0.650 –

4.3 13.8 14.0 14.1 17.8 19.1 –

9.1 × 10−5 3.6 × 10−3 6.1 × 10−3 4.2 × 10−2 9.8 × 10−2 1.2 × 10−1 1.2 × 10−0

271 370 303 294 288 264 78

3.43 3.74 3.76 3.77 3.62 3.61 2.80

690 400 400 310–400 310 310 260

a

The discharge capacity and open-circuit voltage (OCV) were obtained from the charge–discharge measurements of V2 O5 and PEDOT/V2 O5 nanocomposites synthesized from EDOT/V2 O5 ratio from 0.015 to 0.65, as a cathode material by coupling with lithium metal anode using 1 M LiClO4 in a mixed electrolyte of ethylene and dimethyl carbonate.

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Fig. 3. TGA/DTA curves of the (a) crystalline V2 O5 and PEDOT/V2 O5 nanocomposite synthesized with different ratios of EDOT/V2 O5 ; (b) 0.015, (c) 0.035, (d) 0.075, (e) 0.45, (f) 0.65, by a direct microwave irradiation at 10 min.

3.2. Thermogravimetric analysis (TGA/DTA) Fig. 3a–f shows the thermogravimetric analyses performed on the pristine oxide and the series of nanocomposite stability was examined in air. Fig. 3a shows TGA/DTA plot of pristine crystalline V2 O5 has been observed that no phase transformation up to 650 ◦ C. A subsequent mass gain after 650 ◦ C can be attributed to the phase transformation (melting) of V2 O5 [9,11]. Indeed, further evidence from the DTA curve shows a relatively sharp endotherm at 680 ◦ C. However, in the case of organic–inorganic PEDOT/V2 O5 nanocomposites shows two distinct stages of weight loss are

observed in the thermogravimetry and differential thermal analysis (TGA–DTA) curves as shown in Fig. 2b–f. The first step, up to 120 ◦ C, corresponds to the removal of the reversibly bound water, whereas the second step at ∼215 ◦ C corresponds to the loss of more strongly bound water perhaps bound between the layers. This is followed by a continuous weight loss between ∼ 250 and 400 ◦ C which could be attributed to the combustion of the organic polymer component, which is in good agreement with the exothermic peak in the DTA curve. A subsequent mass gain after 650 ◦ C can be attributed to the phase transformation (melting) of V2 O5 [9,11]. Indeed, further evidence from the DTA curve shows a rela-

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tively sharp endotherm at 650 ◦ C. However, Fig. 3b–c shows a small exothermic DTA peak observed at ∼400 ◦ C which could be attributed to the combustion of the organic polymer component are frozen and intact in between V2 O5 layers. Therefore, there is considerable bonding interaction between the organic and inorganic components to increase the thermal stability nanocomposite whereas, Fig. 3d–f the polymer concentration gradually increases with decreasing in decomposition temperature from ∼400 to ∼310 ◦ C which is in good agreement with the sharp exothermic peak in the DTA curve. 3.3. Electronic conductivity The electrical transport of nanocomposite can be understood by considering the insertion of poly(3,4-ethylenedioxythiophene) in V2 O5 as a composite system in which, two different types of low-dimensional electronic conductors coexist at the molecular level in a dimensionally constrained environment. Two types of charge carriers can be present in these materials, small polarons (electrons) associated with the d1 (V4+ ) centers on the vanadium oxide lattice, and large polarons (holes) on the poly(3,4-ethylene dioxythiophene) backbone [14]. The actual nature of charge transport would depend on the relative mobility of these two different types of carriers as demonstrated by the fact that the electronic conductivity of PEDOT/V2 O5 is about 104 times higher than that of pristine V2 O5. In all samples, the conductivity is almost exclusively electronic under our experimental conditions, and increases with temperature as has been observed in most intercalated compounds and conjugated polymers [15,16]. For similar PEDOT/V2 O5 nanocomposites synthesized with different nominal EDOT/V2 O5 ratios, the room temperature conductivity varies from 10−1 to 10−3 S cm−1 , which is substantially higher than the room temperature conductivity of pristine V2 O5 (10−5 S cm−1 ) and less than pristine PEDOT (1.2 S cm−1 ). Hence, it is evidences that PEDOT has a major contribution in conductivity of PEDOT/V2 O5 nanocomposites (see Table 1). In addition, the increase in conductivity is probably due to a continued process of growth of the organic polymer network and the conductivity increases as the length of polymer chain increases from (a) to (e) although the exact mechanism may be complex (see Table 1 and Fig. 4) involving percolation phenomena. 3.4. Cyclic voltammetry Fig. 5 shows comparative cyclic voltammograms of (a) crystalline V2 O5 , and two [(b) and (c)] PEDOT/V2 O5 nanocomposites respectively illustrating a drastic change in electrochemical properties induced by the polymer insertion. For example, during the first cathodic scan, from the opencircuit voltage to 2.2 V versus Li/Li+ , the crystalline V2 O5 undergoes a well-known phase transformation and the stabilization occurs after the third cycle (Fig. 5a). The irreversible shift in the cathodic peak from 2.65 V (first cathodic scan) to 2.82 V (third and following cathodic scans) suggests that the

Fig. 4. Four-probe, variable-temperature electrical conductivity of (a) crystalline-V2 O5 and all PEDOT/V2 O5 nanocomposites synthesized by a direct microwave irradiation at 10 min with different EDOT/V2 O5 ratios; (b) 0.015, (c) 0.035, (d) 0.75, (e) 0.45, (f) 0.65 and (g) PEDOT.

structural change is permanent as reported elsewhere [17,18]. This type of voltammogram of crystalline V2 O5 is different from that of vanadium pentoxide xerogels V2 O5 ·nH2 O as reported by Anaissi et al. [19] since, amorphous xerogels are known to exhibit enhanced electrochemical behavior in terms of faradaic yields and reversibility. Further, the weak interactions between the interlamellar layer, allow fast insertion of Li+ ions between the polymer nanosheets rather than that in the channels of crystalline vanadium pentoxide [19]. In contrast, for the PEDOT/V2 O5 hybrids, there is no sign of any irreversible structural change (Fig. 5b and c), although the broad cathodic peak resembles that of 2D-V2 O5 compounds [20]. The broad and diffuse peak shape can, therefore, be correlated with the layer stacking derived by the polymer incorporation, as previously deduced from X-ray diffraction data. 3.5. Charge–discharge properties Fig. 6 demonstrates second discharge plot of potential versus discharge capacity carried out at 15 mA/g in the voltage range of 2.0–4.2 V (versus Li+ /Li) for V2 O5 and 2.0–4.4 V for the hybrids, corresponding to the uptake of ∼2 lithium per V2 O5 unit. The pristine V2 O5 shows distinctive plateau due to structural changes from ␣-V2 O5 to ␧-Lix V2 O5 , to δLix V2 O5, and then finally to ␥-Lix V2 O5 [21]. On the contrary, the potential decreases more smoothly down to ∼2.7 V for the hybrid samples. Similar continuous decrease in potential has also been observed for V2 O5 xerogel [22–25], 2D-V2 O5 [26] and polymer/V2 O5 xerogel hybrids, [11] of which the common structural feature is the separation of vanadium oxide layers owing to the presence of interlayer molecules. A plausible explanation is that the disturbed layer stacking derived by the separation of layers which would make structural disorders (e.g. reduced covalency of bondings between some

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Fig. 5. Cyclic voltammograms of (a) pristine V2 O5 , (b) PEDOT/V2 O5 nanocomposite synthesized with different EDOT/V2 O5 ratios; (b) 0.015, (c) 0.65 by direct microwave irradiation for 10 min at 0.5 mV/s between 2.2 and 3.8 V vs. Li+ /Li.

vanadium and oxygen atoms) thereby creating empty subbandgap V5+ :3d0 energy states rather uniformly distributed between ∼3.7 and ∼2.7 V [27,28]. The next lithium insertion into the pristine V2 O5 occurs at ∼2.3 V and is accompanied by the irreversible structural changes to ␥-Lix V2 O5 phase [17,18], leading to a transformation of curve shape in second cycle, while the hybrids display a plateau at ∼2.5 V like V2 O5 xerogel or 2D-V2 O5 . The fact that about 2.1 mol of lithium could be inserted per V2 O5 unit, similar to the case of 2D-V2 O5 compounds, also advocates the above-mentioned assertion. Although, samples (a)–(e) deliver 370, 303, 294, 288, and 264 mAh/g, respectively, the pristine V2 O5 produces 271 mAh/g on the second discharge. It is worth while to mention that (b) reveals a larger capacity in the first discharge. It would be accounted for the presence of V4+ , which can be easily oxidized by an electrochemical method, as already observed in the case of PPy/V2 O5 and PTh/V2 O5 hybrids [29]. Sample (b) shows the largest reversible capacity (∼370 mAh/g) among the hybrids, while sample (f) delivers the smallest value (∼264 mAh/g). It is probably due to the fact that the formula weight of sample (b)

(∼185 g/mol) is smallest and that of sample (f) (∼217 g/mol) is largest. A more accurate inspection of insertion voltage is accomplished by the analysis of differential coulombic capacity profiles of the second discharge (inset Fig. 6). The sharp peaks of pristine V2 O5 are typical traits of the phase transformations, while on the contrary, the hybrids exhibit broad peaks, which would sustain our above argument on the sub-bandgap states V5+ :3d0 energy states rather uniformly distributed between ∼3.7 and ∼2.7 V [22–25]. Sample (b) shows three peaks at 2.9, 2.5 and 2.3 V analogous to PPy/V2 O5 and PAni/V2 O5 hybrids [29]. In the case of PAni/V2 O5 hybrids, the 2.3 V peak could be increased after appropriate oxygen treatment, which could be attributed to the polymer [6,30]. But in our case, the hybrids also display 2.3 V peak although PEDOT has no redox capacity around 2.3 V. We, therefore, suggest a possibility that the 2.3 V capacity might be from the synergetic interaction between V2 O5 layers and polymer chains, and not from the polymers alone. For sample (e), the 2.9 V peak shifts down to 2.7 V, and 2.3 V peak is less obvious, which also supports this thought. In order to clarify the role of the

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Fig. 6. Typical second discharge curves of (a) pristine crystalline V2 O5 and (b–f) PEDOT/V2 O5 nanocomposites have been prepared by a direct microwave irradiation at fixed time (10 min) with different EDOT/V2 O5 ratios; (b) 0.015, (c) 0.035, (d) 0.075, (e) 0.450, (f) 0.65 as a cathode material by coupling with lithium metal anode using 1 M LiClO4 in a mixed electrolyte of ethylene and dimethylcarbonate using constant current density of 15 mA/g and the electrode surface area is ∼1 cm2 . The potential range was set to 2.0–4.4 V vs. Li+ at discharge rate C/2. The insets show the corresponding differential capacity profiles of the second discharge.

polymer incorporation on the electrochemical performance for extended cycling, the variation of discharge capacities were measured on sample “a” pristine V2 O5 and nanocomposites “b” to “f”. In particular, nanocomposite samples “b” and “f” (ratios of EDOT/V2 O5 (b) 0.015 and (f) 0.65) as a representative for monolayer and double-layer incorporated system. Sample “b” maintains capacities over 300 mAh/g for 10 cycles. All the hybrids provide larger capacity and better cyclability than the pristine V2 O5 . The improved performances are presumably due to a higher electrical conductivity and to the separation between vanadium oxide layers, leading to an enhanced bi-dimensionality [14].

4. Conclusions We have found a novel rapid eco-friendly microwave irradiation method of interleaving poly(3,4-ethylenedioxythiophene) between the layers of V2 O5 with in 8 min. The reaction takes place with the in situ polymerization of EDOT within the framework of V2 O5 with different nominal EDOT/V2 O5 ratios to give two distinct phases. These two phases can be distinguished by the different interlayer spacing as detected from powder X-ray diffraction patterns. The fact that two distinct phases rather than a continuum of compositions is obtained in this system suggests the existence of a significant interaction between the host and guest beyond simple insertion into the van der Waals gaps and is closer to the formation of true compounds. Analysis of the experimental data presented here suggests that the polymer-

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ization proceeds concomitantly with the intercalation. The polymer chains appear fixed in the interlamellar space, and the ring flips observed in the bulk form of PEDOT are frozen in these materials. Therefore, there is considerable bonding interaction between the organic and inorganic components, probably due to hydrogen bonding. XPS results also do confirm the redox intercalation process and charge transfer from the polymer to the V2 O5 framework. According to electrochemical measurements, the hybrids show reversible specific capacities up to ∼370 mAh/g at 15 mA/g rate between 2 and 4.4 V versus Li+ /Li. This improvement of electrochemical performance compared with pristine V2 O5 is attributed to higher electric conductivity and enhanced bi-dimensionality. The influence of intercalants on Li+ diffusion rates and charge capacity in the PEDOT/V2 O5 nanocomposite is increased relative to that for V2 O5 . The results also suggest that, the polymer nanocomposite acts as a promising cathode material than the pristine V2 O5 material by enhancing lithium diffusion.

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