Chemically Reduced Organic Small-Molecule-Based Lithium Battery

Feb 27, 2015 - ABSTRACT: Organic lithium batteries are attractive because of the possibility of fabricating lightweight and flexible devices. However,...
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Chemically Reduced Organic Small Molecule based Lithium Battery with Improved Efficiency Manik E. Bhosale, and Kothandam Krishnamoorthy Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm5046786 • Publication Date (Web): 27 Feb 2015 Downloaded from http://pubs.acs.org on March 3, 2015

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Chemically Reduced Organic Small Molecule based Lithium Battery with Improved Efficiency Manik E Bhosale and Kothandam Krishnamoorthy* CSIR-Network Institute for Solar Energy, CSIR-National Chemical Laboratory, Dr Homi Bhabha Road, Pune 411008, Maharashtra, India. ABSTRACT: Organic lithium batteries are attractive due to the possibility of fabricating light weight and flexible devices. However, the organic lithium batteries have few drawbacks. The specific capacity is usually lower than the theoretical capacity, which further decreases upon cycling. Often, the specific capacity is very low compared to theoretical capacity while discharging the battery at moderate and high C rates. To circumvent this issue, we chemically reduced carboxylic acid functionality substituted perylene diimide (Benzoic-PDI) with hydrazine. Indeed, we found that the rate of redox reaction as well as the conductivity of the Benzoic-PDI increased upon chemical reduction. The battery comprising reduced Benzoic-PDI exhibit 100% coulombic efficiency and specific capacity while discharging at 20 C. The battery also exhibits very high specific energy (213 Wh/kg) and specific power (8548 W/kg). The control experiments confirm our hypothesis of using chemical reduction to improve the performance of organic lithium battery.

INTRODUCTION Lithium ion batteries are ubiquitous in consumer electronic devices due to good rechargeability and high gravimetric and volumetric energy densities.1-4 Due to light weight, flexibility and easy availability of organic materials, lithium ion batteries with organic cathodes are attractive. Conjugated polymers, 5-9 quinones,10-17 imides,18-21 trioxotriangulene,22 antiaromatic corroles,23 triazines24 and tetracyano quinodimethane25 have been explored as electrode material in lithium ion batteries. The interest in carbonyl containing molecules emanate from the relative ease of synthesis and availability from natural resources.26-28 Carbonyl moiety undergoes one electron reduction to enolate anion, which concurrently attracts lithium ion from the other electrode. Rylene imides with imide functionalities directly attached to the conjugated backbone are of special interest. Because, by modulating the conjugated backbone that is attached with the carbonyl moieties of the imide, the electron affinity (EA) of the molecule could be altered.29 For example, while going from pyromellitic diimide (PMDI) to naphthalene diimide (NDI) and further to perylene diimide (PDI), the LUMO energy decreases, which increases the EA.29 The increase in EA is expected to increase the average discharge voltage, hence PDI is attractive over other rylene imides (PMDI and NDI). Derivatives of PDI have been explored as cathode in lithium ion batteries. One of the early attempts was the use of perylene dianhydride (PDA) and sulphur as cathode.30 Later, a PDI polymer-CNT composite was synthesized by reacting PDA with ethylene diamine in presence of single wall carbon nanotubes.20 Recently, a series of PDI polymers were synthesized by reacting PDA with variety of diamines.31 So far, the polymeric forms of PDIs have been used to decrease the solubility of the active materials in battery electrolyte. However, the polymeric form complicates lithium ion transport.31 Often the specific capacity of organic cathode based lithium batteries decrease rapidly upon charge-discharge cy-

cling. Furthermore, the low specific capacity at moderate and high C-rates is also a problem. Polymerization of rylene imides in presence of functionalized graphene was proposed to prepare lithium batteries with fast charge-discharge capabilities.32,33 Although, it was possible to prepare batteries with specific capacities close to the theoretical capacities at low Crates (0.1 C), the specific capacity was 50% of theoretical capacity at high C-rates.32,33 In an interesting approach, pyrene4,5,9,10-tetraone was covalently connected as pendant moiety on poly(methyl methacrylate) to fabricate high capacity batteries.34 From the discussion, it is clear that fabrication of organic cathode based lithium batteries, which can exhibit theoretical capacity at high C rates is a challenge. In fact, it is essential to build batteries with high specific power and specific energy densities along with the ability to charge-discharge at high Crates. We hypothesized that a chemical reduction, which is commonly known as n-doping in the organic semiconductor literature, could pre-condition the molecules for faster lithium ion association and disassociation. Furthermore, the n-doping will increase the conductivity of the carbonyl containing mol-

Scheme 1. a) Cartoon showing the lithium battery fabrication procedure using reduced Benzoic-PDI. b) Synthesis of Benzoic-PDI and Phenyl-PDI.

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ecules, which is an added advantage. Electrodes with these advantages are expected to respond to faster C-rates. It is essential to note that the discharge voltage is likely to be different between the first and the subsequent cycles of the reduced PDIs. In the first cycle, the electron is injected to radical anion of PDI. Thus, the number of electron transferred is one. However, in the subsequent cycles, the electrons are injected to neutral PDI, hence the number of electrons transferred is two. We have chosen carboxylic acid containing perylene diimide (Benzoic-PDI) (Scheme 1) as the organic cathode due to the following reasons, (i) the carboxylic acid is hydrophilic that decreases the solubility of the Benzoic-PDI in organic electrolyte solution used in the battery, (ii) the Benzoic-PDI with higher EA is expected to deliver better voltage during discharge, (iii) the n doping can be carried out using hydrazine and it may increase the charge carrier mobility/conductivity of Benzoic-PDI and (iv) the hydrazine reduced Benzoic-PDI is expected to be stable in ambient conditions. While this work was in progress, a paper was published on small molecules with lithium salt of carboxylic acid to decrease the solubility of the active material.35 In this paper, we show that the chemical reduction of Benzoic-PDI with hydrazine facilitates the fabrication of lithium battery with specific capacity equivalent to theoretical capacity at a high C rate (20 C). The specific capacity didn’t decrease upto 200 cycles. Furthermore, the coulombic efficiency is 100% over 200 cycles. Overall, the battery exhibited a specific energy of 213 Wh/kg and specific power of 8548 W/kg at 200th cycle. RESULTS AND DISCUSSION The Benzoic-PDI was synthesized by reacting pamino benzoic acid with perylene dianhydride (Scheme 1).36 The Benzoic-PDI was found to be insoluble in methanol, ethanol, acetone, acetonitrile, toluene, tetrahydrofuran, chloroform and dichloromethane. However, Benzoic-PDI was found to be sparingly soluble in dimethylformamide, N-methylpyrrolidone and dimethylsulfoxide. Thus, the absorption spectra of Benzoic-PDI was recorded using dilute dimethylformamide solution. The peaks at 458, 487, 523 and 581 are due to π-π* transitions.37 Upon addition of hydrazine, new peaks emerged at 700, 795 and 954 that are due to the formation of radical anion (Figure S1).37 The peaks due to the formation of radical anions could be observed even after several hours, while leaving the solution to stand quiescent in atmospheric condition. The stable nature of the radical anion is a desirable feature for the

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Figure 1. a) EPR spectra of reduced and untreated BenzoicPDI. b) SEM image of untreated Benzoic-PDI. c) SEM image showing the morphological change of Benzoic-PDI upon chemical reduction. d) IV curve of Benzoic-PDI showing the effect of chemical reduction.

fabrication of lithium battery. In order to further confirm the formation of radical anion, ESR spectra of reduced and untreated Benzoic-PDI were recorded. The g-tensor value of 2.003 for reduced Benzoic-PDI indicates the formation of radical anion. We didn’t observe any discernible peaks for the untreated Benzoic-PDI (Figure 1a). The CVs of both reduced and untreated Benzoic-PDI were recorded in the battery configuration with respect to Li/Li+ electrode. The ∆Ep was found to be 1 V with reduction peak at 1.7 V and oxidation peak at 2.7 V for untreated Benzoic-PDI (Figure S6). While using reduced Benzoic-PDI, a reduction peak was observed at 2 V vs Li/Li+ in the forward scan and corresponding oxidation peak was observed at 2.7 V vs Li/Li+ during the reverse scan (Figure S7). Thus the ∆Ep is 0.7 V. The decreased ∆Ep is due to the increased rate of the redox process, which confirms our hypothesis that the chemical reduction would enhance the rate of reduction of carbonyl moiety. PDI derivatives are known to self assemble into variety of structures depending on the functionalities on the imide nitrogen and bay position.38-43 Although synthesis and photophysical properties of Benzoic-PDI have been reported,36 information on the self assembly and morphological properties

Figure 2. a) Charge-discharge curve of Benzoic-PDI showing single plateau during the discharge (5C rate). b) Charge-Discharge curves of reduced Benzoic-PDI at 20 C rate. c) Plot showing the variation in coulombic efficiency and specific capacity as a function of cycle numbers.

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are not available. In order to understand the effect of hydrazine on the morphology of Benzoic-PDI, scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Benzoic-PDI before and after hydrazine treatment was recorded. From the SEM and TEM images, we can conclude that the Benzoic-PDI forms polydispersed bricks (Figure 1b). On the other hand, the hydrazine reduced Benzoic-PDI forms fibers, which is different from that of the bricks morphology observed for untreated Benzoic-PDI (Figure 1c). The change in morphology is likely due to acid-base interaction between the carboxylic acid functionalities of BenzoicPDI and hydrazine. FTIR is a useful tool to study organic acidbase interactions. The hydrogen bonding peak of the carboxylic acid moiety is expected to be affected, if there is interaction between carboxylic acid moiety and hydrazine. The FTIR spectrum of untreated Benzoic-PDI showed clear hydrogen bonding peak in the region of 2500-3100 cm-1(Figure S36, Supporting Information). This peak disappeared in case of hydrazine treated Benzoic-PDI. Thus, the FTIR spectra indicate interaction between Benzoic-PDI and hydrazine. The interaction between the bifunctional Benzoic-PDI and hydrazine lead to a polymeric structure. Thus, the fibers in the SEM image of hydrazine treated Benzoic-PDI is the polymeric form. Although the fibers seem to be continuous, careful observation of the TEM images of the fibers reveal breaks in the nanofiber. However, the breakage didn’t occur at several places similar to another hydrazine reduced PDI derivative.44 Indeed, we were able to prepare thin film of the hydrazine reduced Benzoic-PDI on top of interdigitated parallel electrodes and measure the conductivity. The conductivity of reduced Benzoic-PDI (1 x 10-2 S/m) was found to be seven orders higher than the untreated Benzoic-PDI (2 x 10-9 S/m) (Figure 1d). It is necessary to note that the conductivity could have been higher, if the fibers were continuous. However, the discontinuous nanofiber is not an issue in the fabrication of lithium batteries because a binder and conducting filler will be used. With this observation, we proceeded to fabricate lithium ion batteries using the hydrazine reduced Benzoic-PDI. The batteries were fabricated by evaporating the solvent from the solution of reduced Benzoic-PDI. The dry powder was mixed with kynar and carbon black and ground to a paste in NMP solvent. The paste was used to prepare thin film on top of stainless steel disk current collector. The material coated stainless steel disk was placed in the Swagelok cell with lithium electrode. The two electrodes were separated by glass filter. The electrolyte LiPF6 was dissolved in ethylene carbonate and diethyl carbonate. The charge discharge experiment using reduced and untreated Benzoic-PDI was carried out at a slow C rate of C/10. The discharge curves showed single plateau indicating that the electron transfer happened in single step in the potential window (4.5 V and 1.5 V vs Li/Li+). PDI accepts two electrons to form dianion in this potential window.30 A representative discharge curve (5 C) is shown in Figure 2a. Then, we carried out deep discharge (until 0V) to check the reduction of the remaining two carbonyl moieties similar to a reported experiment.30 If that reduction occurs, another plateau should appear below 1.5 V. Indeed, second plateau appeared below 1.5 V indicating the reduction of remaining carbonyl moieties (Figure S39). However, at this potential the electrolytes and the organic matter are also irreversibly reduced, hence chargedischarge between 0 and 4.5 V is not possible.

Figure 3. a) Ragone plot showing the efficacies of reduced and untreated Benzoic-PDI. b) Impedance spectra of reduced Benzoic-PDI before and after 200 charge discahrge cycles. c) Charge discharge IV curves of reduced Phenyl-PDI recorded at 1C rate. d) UV-vis absorption spectra of Phenyl-PDI and Benzoic-PDI dissolved from glass membrane separator.

Therefore, all the charge discharge experiments were carried out between 4.5 and 1.5 V vs Li/Li+. The hypothesis is that the chemical reduction should facilitate the reduction process and render the possibility of rapid charge discharge of the battery. Thus, the battery was charged and discharged at 1, 5, 10, 20 and 30C rates. The charge discharge process was monitored for 200 cycles. In case of 5C rate (reduced Benzoic-PDI based battery), the initial specific capacity (90 mAh/g, Table 1) was higher than the theoretical capacity (85 mAh/g), which was observed in other PDI derivatives also.31 Please note that the theoretical capacity calculation was based on the two electron transfer in this potential window. It is important to note that 88% of the theoretical capacity was retained even after 200 cycles (Figure S9). The coulombic efficiency remained unchanged at 100% at 200 cycles, which reveals the efficient charging and discharging of the reduced Benzoic-PDI battery. On the other hand, the initial specific capacity of untreated Benzoic-PDI battery was found to be 69% of theoretical capacity, which is significantly lower than that observed for reduced Benzoic-PDI battery. Furthermore, the specific capacity decreased to 50% at the completion of 50 cycles (Figure S21). These experiments indicate that the efficacy of reduced Benzoic-PDI is superior to that of untreated Benzoic-PDI based battery. In case of 10 C rate (reduced Benzoic-PDI battery), the specific capacity was 96% of the theoretical capacity at 200 cycles with 100% coulombic efficiency. Unlike other organic lithium batteries, the increase in C rate didn’t decrease the specific capacity and coulombic efficiency of reduced Benzoic-PDI battery. In the control experiment (untreated Benzoic-PDI battery), the initial specific capacity was 32%, which decreased to 29% at the end of 10th cycle. This further corroborates that the reduced Benzoic-PDI battery exhibits far superior performance over its untreated counterpart. Indeed, it is interesting to note that the specific capacity as well as coulombic efficiency was 100% for the reduced Benzoic-PDI batteries that are discharged at 20 C (Figure 2b and 2c). Contrary to this, untreated Benzoic-PDI battery discharged immediately. This confirmed our hypothesis that the chemical reduction of Benzoic-PDI could increase the efficiency of lithi-

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um batteries. For 30 C, the specific capacity was found to be 70% of theoretical capacity between 25 and 200 cycles, albeit the coulombic efficiency was found to be close to 100%. Thus, while using reduced Benzoic-PDI, the best performance was observed at 20 C. It is essential to look at the specific energy and specific power, which are the parameters to decide the efficacy of energy devices.45,46 The Ragone plot was obtained by calculating the specific energy (area under the discharge curve) and specific power (specific energy/time of the discharge curve). The plot of these two parameters as a function of C rate is shown in Figure 3a. At high C rates, the battery exhibits high specific power as well as specific energy indicating the superior performance of the reduced Benzoic-PDI based batteries. The Ragone plot for untreated Benzoic-PDI reveals far inferior performance of the battery. Impedance spectroscopy was used to study the change in conducting properties of the reduced and untreated Benzoic-PDI as a function of charge-discharge cycling. Therefore, the experiment was carried out using the fully fabricated battery with the material as the working electrode and the Li foil as reference and counter electrode. The untreated Benzoic-PDI based films resistance increased from 54 Ω to 103 Ω upon cycling. On the other hand, reduced Benzoic-PDI’s resistance decreased from 42 Ω to 24 Ω (Figure 3b). This indicates that the reduced Benzoic-PDI’s increase in conductivity upon reduction is not lost during the process of charge discharge cycling. Small molecules are known to dissolve in the organic electrolytes used in the lithium batteries. Therefore, polymerization of the small molecules has been proposed to circumvent the solubility issue.31, 34 Although this method is occasionally successful, the polymerization complicates the lithiation and delithiation process.31 Furthermore, polymerization compromises the advantages of small molecules such as precise molecular weight and purity. Thus, we have decided to stick to small molecules and circumvent the solubility issue by installing a hydrophilic functionality. As hypothesized, the carboxylic acid functionality decreases the solubility of BenzoicPDI in organic solvents. The decreased solubility reflects in the performance of batteries. Please note the 100% specific capacity as well as coulombic efficiency of Benzoic-PDI based batteries. To further understand the efficacy of this design, control experiments were carried out using Phenyl-PDI (Scheme 1). The absence of hydrophilic carboxylic acid functionality increases the solubility of Phenyl-PDI in organic solvents. Lithium batteries fabricated with reduced Phenyl-PDI exhibited a specific capacity of 100 mAh/g that is comparable to theoretical capacity. However, the specific capacity rapidly decreased in the subsequent cycles and reached 40 mAh/g in the 50th cycle indicating the possible dissolution of PhenylPDI in the electrolyte solution (Figure 3c). Indeed, this can be

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Figure 4. a) Phenyl-PDI based cathode before charge discharge cycling. The dotted boxes show the brick type Phenyl-PDI on the surface of the electrode b) Phenyl-PDI based electrode after charge discharge cycling. There are no brick type Phenyl-PDIs on this electrode surface. c) Benzoic-PDI electrode before cycling and the dotted boxes point at the brick type Benzoic-PDI. d) The Benzoic-PDI electrode after charge discharge cycling and the dotted boxes indicate the presence of brick type Benzoic-PDI on the electrode surface.

visually observed by opening the battery and looking at the glass membrane separator. The separator was found to be red in color, which was milky white before the charge discharge experiment. To further confirm that the change in color of the separator is due to the Phenyl-PDI, the separator was placed in DMF solution comprising 33 µM cardiogreen dye. The cardiogreen dye absorbs at 800nm, which is about 200 nm higher than the absorption maxima of Phenyl-PDI. Due to the difference in absorption maxima, cardiogreen was chosen as internal standard. The Phenyl-PDI sticking on the separator dissolved in the DMF solution. The UV-vis absorption spectra of the DMF solution exhibited peaks at 458, 488 and 524 nm, which are the characteristic peaks of Phenyl-PDI (Figure 3d). On the other hand, in a similar experiment using Benzoic-PDI, extremely weak absorption peaks were observed (Figure 3d). The intensity of the peak due to cardiogreen dye is same for solutions containing Phenyl-PDI and Benzoic-PDI. Thus, the difference in peak intensity of Phenyl-PDI and Benzoic-PDI is absolute. This proved that the Benzoic-PDI dissolution is insignificant in the electrolyte, hence the electrode is stable and performs well during the charge discharge cycling. The elec-

Table 1. Lithium battery metrics for organic small molecules based cathode Reduced Benzoic-PDI 1C

5C

10C

20C

Untreated Benzoic-PDI 30C

1C

5C

10C

20C

Reduced Phenyl-PDI 1C

5C

10C

20C

Untreated PhenylPDI 0.5C

1C

5C

C

85

90

107

100

68

60

53

30

35

97

85

70

80

125

55

25

P

366

2160

4106

8442

12272

383

1985

3533

7165

197

987

1978

3961

215

441

2279

E

126

235

272

246

160

95

107

53

82

229

200

162

186

273

122

55

C - Specific Capacity (mAh/g), P - Specific Power (W/kg) and E - Specific Energy (Wh/kg)

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trodes were also subjected to SEM imaging to study the stability of Benzoic-PDI and Phenyl-PDI based electrodes. The low aspect ratio, micron size rods in the SEM image of PhenylPDI electrode are due to the presence of Phenyl-PDI on the electrode (Figure 4a). However, after the charge discharge cycling, these rods disappear that indicates the dissolution of the Phenyl-PDI in electrolyte solution (Figure 4b). On the other hand, the brick like Benzoic-PDI is present on the electrode before and after charge discharge cycling (Figure 4c and 4d). This further corroborates the importance of our design of installing hydrophilic functionality on the PDI molecules. Thus, it is essential to have a molecule that is insoluble in organic solvents and we could synthesize such a molecule by simple installation of hydrophilic carboxylic acid functionality. CONCLUSIONS In summary, a perylenediimide small molecule that is insoluble in the electrolytes used in lithium battery has been designed and synthesized. Although, the molecule is insoluble in the electrolyte solution, the lithium battery exhibited poor performance due to sluggish redox of the carbonyl moieties of the imide functionality. Chemical reduction increased the rate of redox process as well as the conductivity of the molecule. The increase in these two properties enhanced the performance of the lithium ion battery. The chemically reduced and electrolyte solution insoluble perylenediimide based battery exhibited 100% coulombic efficiency and specific capacity at high C rates. The specific power and energy of the battery was 8548 W/kg and 213 Wh/kg, respectively. Thus, chemical reduction improved all aspects of organic molecule based lithium ion battery. EXPERIMENTAL SECTION Synthesis of Benzoic-PDI: A mixture of 0.5 gm (1.27 mmol) of 3,4,9,10-perylene tetracarboxylic dianhydride, 0.436 gm (3.18 mmol) of 4-aminobenzoic acid, 20 gm of imidazole and 0.1 gm (0.456 mmol) of zinc acetate were heated at 100 ºC for 2h. Then the mixture was refluxed at 140 ºC for 20h under argon atmosphere. After that, the mixture was cooled to room temperature and acidified with 100 ml of 2N hydrochloric acid. The precipitate was collected by filtration. The precipitate was thoroughly washed with copious amount of water and methanol and dried under vacuum at 100 ºC. Synthesis of Phenyl-PDI: A mixture of 0.5 gm (1.27 mmol) of 3,4,9,10-perylene tetracarboxylic dianhydride, 0.296 gm (3.18 mmol) of aniline, 20 gm of imidazole and 0.1 gm (0.456 mmol) of zinc acetate were heated at 100 ºC for 2h. The mixture was refluxed at 140 ºC for 20h under argon atmosphere. Then the mixture was cooled to room temperature and acidified with 100ml of 2N hydrochloric acid. The precipitate was collected by filtration and washed with copious amount of water and methanol to remove impurities. The precipitate was finally dried under vacuum at 100 ºC. Electrode Preparation: Electrodes were prepared by mixing reduced active material (60 weight %) with carbon black (30 weight %) and Kynar (10 weight %). A paste of these materials was prepared using N-methyl-2-pyrrolidone (NMP) as a solvent. The paste was coated on stainless steel disk and then dried overnight at room temperature and then 130 °C for 3 h in argon filled glove box. The boiling point of hydrazine is

114 °C, hence upon heating the electrode at 130 °C, excess hydrazine as well as NMP are removed from the electrode. Lithium foil was used as anode and glass membrane was used as separator. The preparation of Swagelok cell was carried out in argon filled glove box. The battery testing was carried out in atmospheric condition. Material and Device Characterization: The cyclic voltametry and the charge-discharge experiments were carried out using multi channel autolab MAC 80038 instrument in the potential range of 1.5 - 4.5 V vs Li/Li+ at different C-rate (for 1C rate current density is 170 mA/g). Electrochemical Impedance spectroscopy measurements were done in the frequency range of 10 mHz to 40 kHz using Biologic instrument. The cyclic voltammograms were recorded using the assembled batteries, Thus, the reference electrode was Li/Li+. Electron spin resonance (ESR) spectra were recorded at room temperature with JES – FA 200 ESR Spectrometer under the settings of center field, 337.227 G, microwave frequency, 9.45 GHz, power, 0.99 mW. ESR spectra of Benzoic-PDI and PhenylPDI were measured in DMF solutions (50 µM) with hydrazine reduction. Keithley 4200-SCS semiconductor analyser was used for conductivity measurements. The interdigitated microelectrodes were purchased from Fraunhofer IMS, germany. SPECORD 210 PLUS spectrophotometer was used to record absorption spectra. Specific capacity was calculated on the basis of the amount of the active material. Specific Capacity (mAh/g) was calculated by charge/weight of the active material. Specific energy (Wh/kg) was calculated by area under the discharge curve and Specific power (W/kg) was calculated by specific energy/time of the discharge curve.

ASSOCIATED CONTENT Supporting Information. Theoretical calculations, charge discharge curves, absorption, impedance and ESR spectra, cyclic voltammogram, electron microscopy images are in Supporting Information. “This information is available free of charge via the Internet at http://pubs.acs.org/”

AUTHOR INFORMATION Corresponding Author * [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT MEB acknowledges the scholarship from Council of Scientific and Industrial Research. KK thank Department of Science and Technology for Funding. Conductivity measurements by Mr Arulkashmir and cartoon by Ms Chayanika Das are acknowledged.

REFERENCES (1) Armand, M.; Tarascon, J.-M. Nature, 2008, 451, 652. (2) Choi, N.-S.; Chen, Z.; Freunberger, S. A.; Ji, X.; Sun, Y.K.; Amine, K.; Yushin, G.; Nazar, L. F.; Cho, J.; Bruce, P. G. Angew. Chem., Int. Ed., 2012, 51, 9994. (3) Novak, P.; Muller, K.; Santhanam, K. S. V.; Haas, O. Chem. Rev., 1997, 97, 207. (4) Luo, C.; Huang, R.; Kevorkyants, R.; Pavanello, M.; He, H.; Wang, C. Nano Lett., 2014, 14, 1596.

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Chemistry of Materials Table of Content

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