CARBON ELECTRODE FROM SPENT HONEYCOMB FOR AQUEOUS AND NON¬AQUEOUS SUPERCAPACITOR AND LITHIUM-ION BATTERY
FIELD OF INVENTION
The invention relates to energy storage devices and in particular to hybrid devices with the synergistic effect of battery-type and capacitor-type electrode material which can bridge the gap between battery and supercapacitor. Further, the invention relates to the use of naturally available materials such as spent honeycomb and the activated carbon derived from it used as anode material for lithium-ion battery and as electrodes for ultracapacitor in aqueous and non-aqueous electrolyte.
BACKGROUND OF INVENTION
The development of energy storage devices in general have gained significance to meet the energy demands of the modern life. In particular, hybrid energy storage devices and their production from recyclable sources has gained particular attention. The usage of Lithium ion is increasing for everyday applications and are widely used in the portable electronics. The Lithium ion batteries have a very dominant usage in certain application areas.
As with the characteristic of the ever-evolving market requirements, the battery manufacturers are continuously working on developing batteries with high energy density, power density and long cycle-life with short charging time.. Thus, it is indispensable to develop high energy density hybrid energy storage devices which are also capable of delivering peak power demand. The most desirable energy storage device for various consumer electronics applications must have features of the batteries and that of the supercapacitors in a single platform. In this regard, there is more focus on energy storage devices using Li-ion hybrid capacitors and Li-ion battery.
However, almost all the commercial Li-ion batteries utilizes graphitic carbon as the anode material and as electrodes for ultracapacitor in aqueous and non-aqueous electrolyte owing to the favourable properties such as high conductivity, low voltage hysteresis, good rate capability etc. The objective of the invention is to propose a novel and hybrid energy storage device. Yet another object of the invention is to propose the manufacturing of the aforesaid

hybrid energy storage devices with improved performance levels and to reduce the use of natural resources such as carbonic graphite.
A further object of the invention is to propose sustainable approach for generating electrode materials to be used in the aqueous hybrid Li-ion capacitor and Li-ion battery. The activated carbon derived from the spent honeycomb is used anode material for lithium-ion battery and as electrodes for ultracapacitor in aqueous and non-aqueous electrolyte.
SUMMARY OF THE INVENTION
Hybrid energy storage devices with higher performance potentials are disclosed. In some embodiments, the energy storage devices comprise a positive electrode comprising aqueous Li-ion hybrid capacitor and Li-ion battery using LiCo02 and negative electrodes, comprising activated carbon extracted from carbonizing spent honeycomb material are disclosed. Fabrication processes for manufacturing the hybrid energy storage devices are disclosed.
The other objectives and advantages of the device of the present disclosure will be further appreciated and understood when considered in combination with the following description and accompanying drawings. While the following description may contain specific details describing particular embodiments of the device of the present disclosure, this should not be construed as limitations to the scope of the device of the present disclosure but rather as an exemplification of preferable embodiments. For each aspect of the device of the present disclosure, many variations are possible as suggested herein that are known to those of ordinary skill in the art. A variety of changes and modifications may be made within the scope of the present disclosure without departing from the spirit thereof.
BRIEF DESCRIPTION OF THE DRAWING
FIG. la, lb and lc are the XRD patterns and Raman spectrum and FT-IR spectrum that were recorded for the extracted spent honeycomb-derived activated carbon.
FIG. 2 (a-g) are the SEM images recorded for spent honeycomb-derived precarbonized carbon and the activated carbon.

FIG. 3 (a-f) are HR-TEM images and SEAD pattern recorded for the spent honeycomb-derived activated carbon.
FIG. 4 (a) is the CV curves at scan rate of 0.1 mVs-1, (b) is the Galvanostatic charge-discharge profiles at different C-rates and (c), die Cycle-life data as well as Coulombic efficiency recorded on the CR-2032 coin cell consisting of.the spent honeycomb-derived activated carbon as anode and lithium counter electrode in 1M LiPF6.
FIG. 5 (a) is the Nyquist plots obtained for the CR-2032-coin cell containing the spent honeycomb-derived activated carbon as anode and lithium counter electrode in 1M LiPF6 at as-assembled and after 210 charge-discharge cycle.
FIG. 6 (a) Galvanostatic charge-discharge profiles at 0.2 C-rate, (b) Energy density,
and (c) Cycle-life data as well as Coulombic efficiency recorded for the CR-2032 coin cell
(carbon | LiPF61 LiCoCh).
FIG. 7 (a) Cyclic voltammetry curves recorded at various scan rates, (b) Galvanostatic charge-discharge profiles at different current densities and (c) Variation of specific capacitance on current density and (d) cycle life data as well as Coulombic efficiency recorded for the spent honeycomb derived activated carbon in three electrode cell in 1M H2S04.
FIG. 8 (a) and 8 (b) are the cyclic voltammetry curves at different potential windows, (c) and (d) are the CV curves at various scan rates and (e) and (f) are the Galvanostatic charge-discharge profiles at different current densities recorded for the aqueous (left) and non¬aqueous (right) ultracapacitor devices.
Fig.9. (a, b) are the Ragone plots and (c, d) are the cycle-life data recorded for the aqueous (left) and the non-aqueous symmetry ultracapacitor devices contain the spent honeycaomb-derived activated carbon electrodes.

DETAILED DESCRIPTION OF THE INVENTION
The invention aims to solve the technical problem of improving the performances of hybrid energy storage devices and to explore the readily available natural materials as the alternate carbon sources. The energy storage devices of the invention comprise a positive electrode comprising aqueous Li-ion hybrid capacitor and Li-ion battery using LiCo02 and negative electrodes, comprising activated carbon extracted from carbonizing spent honeycomb material are disclosed. Provided herein are carbon and LiCo02 based materials, fabrication processes, and Li-ion devices with improved performance.
The hybrid energy storage device of the invention, the Li-ion hybrid capacitors use battery-type and capacitive-type electrode materials, which results in overall enhancement of electrochemical energy storage. Generally, in Li-ion hybrid capacitor, a lithium-rich material is used as positive electrode and a capacitive material is used as the negative electrode. In particular, the concept of intercalation/de-intercalation of Li ions paved the way for the use of the carbon-based anode material in place of the Li metal. All the available commercial Li-ion batteries utilizes graphitic carbon as the anode material and there is a need to explore alternate carbon resources that can be derived from naturally occurring materials.
For achieving the above-identified objectives, a hybrid energy device is designed and the fabrication process of the same is disclosed. Activated carbon derived from carbonizing spent honeycomb material and its used as negative electrodes are disclosed. The spent honeycomb was collected, cleaned and dried. For carbonization process, a portion of the cleaned honeycomb was initially precarbonized in a muffle furnace at a range of about 200- 400 °C for a time period of about two hours. Then, the precarbonized sample was homogeneously mixed with the requisite amount of KOH and in the subsequent step, the mixture was transferred into an alumina boat and kept in tubular furnace at a range of about 400 - 600 °C in Ar atmosphere for a time period of about four to six hours for activation. After the treatment, the obtained sample was washed several times subjected to acidic (HC1) and distilled water treatment. The samples then are dried in vacuum desiccator to obtain the final activated carbon
In this context, few embodiments of the invention are described in detail and it is to be understood that the invention is not limited in its application to the details of construction, [ ^ arrangements pfjthe components^the steps bg w>ichja;partipujar hybrid device, is

manufactured and the analysis techniques as set forth in the following description or illustrated in the drawings. It is entirely possible that the invention is capable of other embodiments and of being practiced and carried out in various other ways. Also, the phrases and terminologies as used herein are for the purpose of the description and should not be regarded as limiting.
The following steps explains in detail, the hybrid energy storage device, its composition and its fabrication details:
Energy Storage Device Composition and Fabrication
Activated carbon generation and characterization
A spent honeycomb was carefully collected, cleaned and then dried. For carbonization process, a portion of the cleaned honeycomb was initially precarbonized in a muffle furnace at a range of about 200- 400 °C for a time period of about two hours. Then, the precarbonized sample was homogeneously mixed with the requisite amount of KOH and in the subsequent step, the mixture was transferred into an alumina boat and kept in tubular furnace at a range of about 400 - 600 °C in Ar atmosphere for a time period of about four to six hours for activation. After the treatment, the obtained sample was washed several times subjected to acidic (HC1) and distilled water treatment. The samples then are dried in vacuum desiccator to obtain the final activated carbon.
The obtained activated carbon was characterized by using powder X-ray diffraction (Bruker D8 advance Da vinci) employing Cu Ka radiation source (a = 1.5417A), Raman spectroscopy (Witec Confocal Raman instrument with Ar ion laser 718 nm CRM200), Fourier transformed infra-red (Nicolet 6700) spectroscopy by means of KBr pellet method and scanning electron microscope (SEM, Hitachi, Model: S-3400N). High-resolution transmission electron microscope (HR-TEM, JEOL JEM 2100) analysis of the prepared material was carried at an operating voltage of 200 kV.
Lithium-ion storage characterization:
Lithium-ion storage performance of the spent honeycomb-derived activated carbon was examined by fabricating a prototype, a CR2032-type coin cell. The working electrode fortius prototype, was prepared by mixing the active material, super P carbon and polyvinylidene
■ E tfMI? TO^WWt^0 &&°>W-FlI&Pk2- FT*1^(NM?) was
used as a solvent to prepare the slurry. The slurry thus prepared and was coated on a copper

foil (9 um thickness) by doctor blade method and dried at a temperature range of anout 60-150 °C for a time period of about 8-15 h under vacuum. After this, the coin cells were assembled in an Ar-filled glove box (NICHWELL a-1500u) using the Li-metal disc as the counter electrode and the activated carbon as anode for the Li half-cell. For Li-ion full cell, lithium cobalt oxide (LCO) coated on an aluminum foil as the cathode and the activated carbon on the copper foil as the anode were used. In both these cases, the electrolyte used was 1M LiPFe in ethylene carbonate (EC)/ dimethyl carbonate (DEC) (1:1 in volume). The cyclic voltammetry (CV) studies were carried out using electrochemical workstation (Biologic, SP-150) on the coin cells in the potential range of 0-3 V at a scan rate of 0.01 mV/s. The galvanostatic charge-discharge cyclings on the coin cells at different current rates were performed using the Neware battery analyzer (CT-4008). The potential window for the half-cell was 0-3 V and that for the full cell was 4.2-2.8 V. The electrochemical impedance on the coin cell was recorded in the frequency range of 0.1 Hz to 106 Hz using the same electrochemical workstation.
Ultracapacitor Characterization
The ultracapacitor studies of the activated carbon were done initially in a three-electrode cell comprising the derived activated carbon as the working electrode, platinum (Pt) as counter electrode and Ag/AgCl as reference electrode in 1M H2S04. Then, proto-type symmetric ultracapacitor device was fabricated using identical two activated carbon electrodes in the form of CR-2032-coin cell using Wattman filter paper as separator. The working electrode for this characterization study was prepared using the mixture of the activated carbon (80 wt.%), carbon black (10 wt.%) and polyvinylidene fluoridone (PVDF) (10 wt.%). The PVDF was used as the binder in electrode fabrication to bind the electrode material on to the surface of carbon cloth current collector. N-methyl-2-pyrrolidone (NMP) was used as a solvent to obtain slurry. The slurry thus obtained was pasted on to the carbon cloth (1 cm x 1 cm) and dried at a temperature range of about 80-120°C for overnight. The masses of the coated and uncoated electrodes were measured. The total mass loading of the electrode was calculated by measuring the difference between the mass of the coated and uncoated electrodes. The active mass of the electrode was found to be 4 mg cm'2. The cyclic voltammetry (CV) and galvanostatic charge-discharge studies were carried out in a three-electrode cell in 1M H2SO4 using the aforementioned electrochemical workstation. The ultracapactive performances of proto-type
symmetric devices were evaluated in 1M H2SO4 (aqueous) and 1M LiPFfi (non-aqueous) in r c w T 0 F F I C E_ C H E N N AI 08/O8//G19 1 1 '■ 5 b ethylene carbonate (EC}/ dimethyl carbonate (DEC) (1:1 in volume).

Results and Discussion
Crystal Structure and Morphology
Figure 1. (a) shows XRD pattern recorded for the spent honeycomb-derived activated carbon. The set of Bragg peaks located at the diffraction angles (20), 26.6, 43.4, 56.6 and 66.6° are indexed to graphitic carbon as per the JCPDS PDF # 89-8494. It is apparent that the XRD pattern is characterized with well-defined high intense Bragg peaks corresponding to the graphitic carbon and the absence of other noticeable peaks indicating that the material is devoid of any other impurities. To substantiate the XRD result, Raman and FT-IR spectral analysis were carried out for the activated carbon. The Raman shifts displayed in Figure 1(b) exhibits two broad peaks at 1325 and 1581 cm"1 corresponding to the D and G bands of carbon, respectively. The D band corresponds to the disorder graphitic domains, while the G band is attributed to the E2g mode of sp2 domain of the graphene carbon. The estimated (ID/IG) ratio for the prepared sample is greater than one (1.22) which clearly indicates the existence of graphitic carbon. Figure 1(c) shows the FT-IR spectrum of the obtained carbon sample. The spectrum consists of broad band in the range of 2800-3650 cm"1 which is ascribed to NH and OH stretching vibrations. The sample exhibits two sharp peaks at 1646 and 1559 cm"1 which are ascribed to the C=C and C=N bonds, respectively. The peak observed at 1115 cm"1 is due to C-N-C bond. The peak present at 1015 cm"1 corresponds to C-H bond. Thus, the results obtained from the FT-IR analysis further complements the conclusions derived from the XRD and Raman analysis, besides confirming the presence of OH, NH and CN bonds.
SEM and HR-TEM analyses were done to explore the surface morphology and chemical composition of the spent honeycomb-derived activated carbon. Figure 2 shows the SEM images of pre-carbonized sample and the activated carbon at different magnifications. It is obvious from Figure 2(a-c) that the surface of the carbonized sample has singularly smooth solid matrix without significant pores. Undoubtedly, the micrographs of the activated carbon demonstrate the complete transformation of the smooth surface to highly etched surface with noticeable pores (Figure 2 (d-g)). The presence of such pores is expected to facilitate rapid diffusion of ions during the electrochemical testing. The surface morphology was further substantiated by the HR-TEM and BET studies. Figure 3(a-e) shows the TEM images obtained for the activated carbon. The micrographs clearly show the presence of carbon sheets with
porous morphology. It is seen that the grains are of the irregular shape with pore size ranging
T F iu 7 ptFTrf f H F N N jft I Q ft '' 0 8 * 23 1 3 1 2 s 3 6 1 c rro'm 5*70 nm. If fe evident from Figure 3(f) that the SAED pattern exhibits bright spots and

rings, indicating high crystalline nature of the generated carbon. The rings and spots were indexed to (003) and (101) of carbon, substantiating the aforediscussed XRD data. Thus, from the results of analytical characterizations, it is confirmed that the carbonization of the spent honeycomb led transformation to porous activated carbon with high crystal Unity.
Performance Characteristics:
Performance of half-cell containing spent honeycomb-derived carbon anode:
To evaluate lithium storage features, electrochemical activity of the fabricated CR-2032 half-cell comprising the spent honeycomb-derived activated carbon anode and Li metal counter electrode was initially examined by means of cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) polarization and electrochemical impedance spectroscopy (EIS) studies.
Figure 4 (a) shows the CV curves recorded in the potential range of 0-3.0 V at a scan rate of 0.1 mV s*1. It is seen that in the first cycle, a broad peak appears in the cathodic direction at about 0.6 V, which is ascribed to the irreversible decomposition of the electrolyte leading to form stable solid-electrolyte interface (SEI) in the vicinity of the electrode/electrolyte. This broad peak disappears in the second and subsequent cycles, suggesting that the SEI has afforded good stability to the electrode surface. The formation of SEI layer is considered advantageous as it can act as a passivation layer and prevent the electrolyte further undergoing decomposition. It is apparent that the reduction peak near 0 V and its corresponding oxidation peak at about 0.3 V in all the cycles, are attributed primarily to the intercalation/deintercalation of lithium ions into/out of the carbon electrode. Interestingly, a small anodic peak at 2.7 V is observed in all the CV curves, which is also ascribed to the insertion of lithium ions into the carbon, as has been reported. Further, the CV profiles obtained from the 2nd and 3rd cycles exhibit good similarity, implying excellent reversibility of the following stabilized electrochemical lithium insertion /re-insertion reaction. Thus, the CV results suggest that the spent honeycomb derived carbon is capable of interaction/de-intercalating reversibly with lithium.
6C + xLi + xe- «-► LixC6 ...(1)
Thus, the CV results suggest that the spent honeycomb-derived carbon is capable of
interacting/de-intercalating reversibly with lithium can be used as anode for LIB.
P M T nPFTTF l"HF M hi A T l"l ft / fl ft / O fl 1 Q 1 > : < ft

Figure 4 (b) shows the representative cycle charge/discharge profiles recorded at Ope-rate in the potential range of 0.01-3 V for the half cell. The results are in consistent with the aforediscussed CV profiles. It is seen that the plateau observed about at 0.6 V in the first cycle discharge curve corresponds to the cathodic peak observed in the first cycle of the CV curves. It is seen that the initial discharge capacity is 1520 mA h g-1. Such a high discharge capacity is due to the formation of SEI. It is noted that the first cycle charge capacity is 790 mA h g-1 and its discharge capacity is about 1520 mA h g-1 giving low Coulombic efficiency of 66 %. Such a low Coulombic efficiency in the first cycle is ascribed to the formation of SEI and subsequent transformation of the pristine carbon electrode to a highly active Li storage host. In the second cycle, the carbon anode delivers a discharge capacity of 752 mA h g'1 with improved Coulombic efficiency as high as 95 %, indicating stabilized reversible capacity. The irreversible capacity observed in the present case is as high as 750 mA h g'1. Such high value is of no practical use and has been widely observed for the anode material of the Li ion batteries. Undoubtedly, the high Coulombic efficiency confirms that the spent honeycomb-derived activated carbon is highly susceptible for efficient Li+ insertion/re-insertion, demonstrating suitability for practical use. It is noticeable that beyond 3rd cycle, the carbon anode maintained almost a stable lithiation capacity and Coulombic efficiency as high as 95%. Undoubtedly, the charge-discharge profile recorded at 50th cycle and 210th cycles are nearly identical, implying robust stability of the carbon electrode.
The rate capability of the carbon anode was examined by means of galvanostatic charge-discharge cyclings at different C-rates from 0.2 to 1C. The obtained data are shown Figure 4(c). Remarkably, the carbon anode delivers excellent reversible capacity of 1520,485, 448, 391, 359 mA h g-1 corresponding to 0.2, 0.4, 0.6, 0.8 and 1 C-rates, respectively. It is noted that at each C-rate, a stable lithiation capacity with high Coulombic efficiency is observed. High reversible capacity at low C-rate and low capacity at high C-rate are seen, as usually reported for a battery electrode. Notably, even at high 1 C-rate, the half-cell delivers appreciably high discharge capacity of 360 mA h g-1 and this discharge capacity is retained for long cycles (over 300 cycles). Excellent repeatability of the discharge capacity is seen when the 0.2C-rate is repeated after operating different C-rates. The lithium storage performance of the carbon anode is compared with the carbon derived from other biomasses in Table #. A discharge capacity in the range of 300 mA h g-1 only reported for the carbon derived from other sources whereas, the lithium storage performance of the carbon anode derived from the
spent honeycomb in the present case, is exceptionally as high. It is noted that the spent
E [4 T OFFICE CHENNAI 08/08/201 9- 12= 3b honey comb-den ved carbon exhibits significantly higher discharge capacity than the theoretical

capacity of the graphite (372 mAhg-1) in particular at lower C-rates. Such high capacity could be due to the existence of hierarchically porous morphology which can facilitate insertion of more than 1 mole of lithium. From the capacity values, it is estimated that 1.1-1.3 mole of lithium is being intercalated/de-intercalated per six carbon (C6). micrographs as well as BET revealed the presence of pores in the size range of 5-70 nm. These macro-porous cores within the carbon sheets may serve as ion-buffering reservoirs, facilitating faster diffusion of Li ions, thereby supporting high rate capability. The EIS studies were carried out on the half-cell consisting of the carbon anode to get insights about ion transport properties before and after cycling.
Figure 5 shows the obtained Nyquist plots. It is evident that the Nyquist plots consists of a semicircle in the high frequency region owing to electrode resistance and a spike at the low frequency region which is attributed to Warburg element of diffusion-controlled lithium insertion process. The appearance of smaller semi-circle in the high frequency region for the as-fabricated half-cell indicates the intrinsic high conducting nature of the carbon anode. In contrast, for the cycled coin cell, the diameter of the semi-circle is much higher compared to the freshly prepared coin cell, implying increased resistance due to the formation of SEI upon charging/discharging. It is presumed that such increased resistance seems responsible for slight drift in the discharge capacity at higher cycles (200) onwards.
Performance of (Carbon I LiPFft I LiCoO?) full cell:
To demonstrate the practical application of the spent honeycomb-derived carbon for lithium-ion battery, a full cell was constructed using the derived carbon as anode and commercial lithium cobalt oxide (LCO) as cathode in the form CR-2032 coin cell using 1M LiPF6 electrolyte and celgard as separator. The mass loading ratio of the anode to cathode was optimized to 1:4. Such a high ratio has been often employed in the literature because, the half-cell capacity of the cathode is limited to only 140 mAh g"r. Then, the full cell was subjected to charge-discharge cycling at 0.2 C-rate.
Figure 6(a) shows the representative cycle charge-discharge profiles recorded for the
full cell. It is seen that clear plateau potential at about 4.0V is seen during charging and
discharging. As the number of cycles increases, the plateau potential decreases, may be due to
inherent nature of the electrodes. Undoubtedly, the charge-discharge profiles recorded at 10th,
E2(D0th ancf5O~0lhfeySle areHneafty^sirnilar, deMnstratmg'excellent1 cycling' stability which is

desirable for practical application. It is seen that the full cell consisting of the spent honeycomb-derived carbon anode and the LCO exhibits a first charge and discharge capacities of 485 and 474 mA h g"1, respectively with a Coulombic efficiency as high as 98 %. For practical implementation, the cell must operate reliably at variable discharge currents. Hence, the full cell was subjected to rate capability test at different C-rates. The obtained rate capability data along with Columbic efficiency recorded up to 500 long charge-discharge cycles are displayed in Figure 6(b).
It is seen that the discharge capacity at initial cycles is largely varying, and from 11th cycle onwards, nearly similar discharge capacity is seen, implying stability of lithium insertion/re-insertion reaction with high Columbic efficiency. The rate capability data implies that the discharge capacity observed at high C-rates is nearly similar to that observed at low C-rates, except at initial few cycles (- 10 cycles). This implies that the spent honeycomb-derived carbon electrode can deliver similar capacity even at high C-rates (high power). It is seen that the discharge capacity at 11th is about 140 mAh g"' and that at 500th cycle is 130 mAh g"1 Thus, undoubtedly, the full cell retains nearly similar discharge capacity for long cycles. The obtained value is based on the cathode mass and comparable with the previously reported full cell performance. An excellent recovery to the original capacity observed at O.lC-rate after operating the cell at different C-rates, confirms the robustness of the carbon electrode in retaining the lithium storage features.
Energy density of the full cell (Carbon f LiPF61 LCO) was calculated by using the following equation:
E = CV Wh kg-1 where, C is the cell capacity (C = i*t Ah g"1) and V is cell voltage (V). the obtained energy density in the representative C-rates. The energy density was found to be 1660 Wh kg'1 at 0.1C-rate which is higher than the theoretical energy density of the hard carbon. In addition, the obtained value is also higher than that of the reported values for Li ion batteries using carbon from other source.
The self-discharge characteristics of the full cell was examined. For this, the cell was subjected to charging at lC-rate up to 4.2 V. After complete charging, the cell was disconnected from the current source and there the potential decay was recorded with respect to time. The obtained self-discharge profile is shown in Figure 6 (c). It is seen that soon after disconnecting
from the current source, ,the cell, potential .drops from ,4=2 rtO| 4A Vi such potential drift is
TENT OFFICE LHbNNRi U6F/So'zbi^ n! K^

attributed to the IR drop. Then, the cell reaches stable OCV at about 4.0 V and retains for more than 120 h which is desirable for a practical application.
Further, the fabricated full cell was examined for powering a consumer electronics, namely commercial green LED bulb. The full cell was subjected to galvanostatic charging up to 4.2 V at 0. lC-rate. Then, the green LED was connected to the charged coin cell. It was found that on single charge the coin cell could power the LED for more than 3 hours. This implies that the spent honeycomb-derived carbon can serve as practical anode for implanting in commercial lithium-ion battery with improved energy density and rate capability as well as stability. Notably, the source used here is mere agricultural waste. The honeycomb can be grown even domestically in large amount. Then, the spent honeycomb can be made as value added product sustainably to generate anode material for commercial LIB. The carbon anode generation process presented here is simple and can be scaled up for mass production.
Double layer capacitance of honeycomb-derived carbon:
Carbon-based materials are increasingly examined for charge storage in ultracapacitor which operates on the basis of charge separation at the electrode/electrolyte interface (electrical double layer formation). It was reported that the performance of ultracapacitors depends on the surface area of the carbon material used which in turn depends on the source of the carbon as well as method of activation. Hence, the spent honeycomb-derived activated carbon was also examined for ultracapacitor application in aqueous and non-aqueous electrolytes.
Initially, the charge storage properties of the activated carbon were examined in three electrode configurations in 1M H2SO4. Figure 7 (a) shows the CV curves recorded in the potential range of 0 - 1.0 V Vs Ag/AgCl in 1M H2SO4. The CV curves are nearly rectangular in shape, implying that the charge storage takes place by means of electrical double-layer formation. It is observed that die current response increases with the increase of scan rate, suggesting that the electrode is possessing excellent rate capability. It is noted that with increase of current response as scan rate increased, a pronounced anodic peak is seen in the CV curves at about 0.4 V, indicating existence of minor pseudo capacitance due to the occurrence of Faradic reaction at the carbon electrode surface where oxygen functional groups present. It has been documented that the OH or NH containing carbon materials are demonstrated to exhibit such minor pseudo capacitance owing to the redox reaction promoted by the lone pair electrons
associated with the heteroatoms.
ENT OFFICE CHENNAI 08 '06 / 2019 12=37

Further, the charge storage features of the carbon electrode were investigated by means of galvanostatic charge-discharge studies. Figure 7. (b) shows charge-discharge profiles of the activated carbon electrode recorded at various current densities in the potential range of 0-1.0 V. It is apparent that at each current density, the charge-discharge curves display nearly symmetrical which further confirms that the charge storage is highly reversible with high Columbic efficiency. From the charge-discharge profiles, the specific capacitance was calculated at each current density using the following equation:
O ((I*t))/((V*m)) F g1 (1)
where, C is specific capacitance (F g"1), I is discharge current (A), t is discharge time (s), V is potential window (V) and m is active mass of the electrode (g).
Figure 7 (c) shows the specific capacitance as a function of current densities. It is observed that at low current density, higher specific capacitance is delivered owing to the effective utilization of the active mass of the electrode, while a low specific capacitance is obtained at higher current density due to the fast charge-discharge rates which lead to poor utilization of the active material. It is seen that the activated carbon exhibits specific capacitance 260 F g'1 at a current density of 1.2 A g"1 and retains to 170 F g"' even at a high current density of 10 A g"1. Interestingly, the present carbon electrode exhibits high specific capacitance may be due to the presence of sheet-like carbon, high porosity, hierarchical pores and large surface area.
Figure 7 (d) shows the cycle life performance of the carbon electrode recorded at a current density of 10 Ag"' for 5000 charge-discharge cycles. It is seen that the carbon electrode delivers capacitance of 170 F g"' throughout the examined 5000 cycles, demonstrating the robustness stability of the honeycomb-derived carbon electrode for practical use. The Columbic efficiency was also found to be excellent throughout the cycle life. The nearly similar charge-discharge profiles recorded in the initial three cycles and the last three cycles shown in inset of Figure 7 (d) substantiate the 100% Columbic efficiency of the carbon electrode. Hence, the spent honeycomb-derived activated carbon can be a potential electrode for ultracapacitor.

Performances of aqueous (Carbon IH2SO4 I Carbon) and non-aqueous (Carbon IL1PF61 Carbon) prototype ultracapacitor devices:
The aforesaid high capacitance and robust stability of the spent honeycomb-derived carbon electrode encouraged us to further investigate its performance in the form of proto-type symmetric ultracapacitor device. Thus, the symmetric ultracapacitor device in the form of CR-2032-coin cell was constructed by using identical two carbon electrodes in each of aqueous (1M H2SO4) and non-aqueous (1M LiPFe) electrolytes. It is known that the voltage window in aqueous electrolyte is limited to less than 2 V, whereas the use of non-aqueous electrolyte overcome the limit of low potential range as reasonably larger working potential range can be realized. The larger potential window is expected to deliver higher energy density. Hence, to optimize the suitable potential window, CV curves at different potential windows were recorded at a scan rate of 10 mV s"1.
Figure 8 (a, b) shows the obtained CV curves for the (carbon | H2SO41 carbon) and (carbon | LiPFe1 carbon) ultracapacitor devices. It is apparent that the CV curves of the symmetric device in both aqueous and non-aqueous electrolytes have characteristic rectangular shape having slight difference in the current response. The appearance of rectangular shape curves implies dominance of double layer mechanism for charge storage, as has already verified in three electrode configurations. It is pertinent to note that in the case of aqueous electrolyte, the comfortable working voltage range could be fixed to 0-1.6 V, beyond which, the decomposition of electrolyte takes place, leading to hydrogen evolution. As expected, in the case of the non-aqueous, the CV curves clearly demonstrate that the working potential window could be as high as 3.2 V which is more than double compared to the potential window of the aqueous electrolyte. Hence, the optimum potential windows for aqueous device and non¬aqueous device were fixed at 0-1.6 V and 0-3.2 V, respectively. Then, the scan rate dependent CV curves in the respective optimized potential windows were recorded for both devices and shown in Figure 8 (c, d). The CV curves of both the devices are unperturbed rectangular shape even at higher scan rates, suggesting an excellent electrochemical reversibility of the symmetric ultracapacitors with appreciable charge storage.
Further, the charge storage features of the ultracapacitors were characterized by examining galvanostatic charge-discharge cycling at various current densities in the respective
potential windows. The obtained profiles are displayed in Figure 8 (e, f).
fFNT OFFICE CHENNAI 08/G8/2fcTl9 12=37

The symmetric devices possess an excellent reversibility. It is evident that in both the electrolytes, the charge-discharge profiles are nearly symmetrical, in particular beyond 1 Ag"' current density, implying a rapid current-voltage response as well as excellent Coulombic efficiency.
The energy density and power density of the devices were calculated from the charge/discharge profiles using the following equations.:
E= 1/7.2 CV2 Whkg1 (1)
P = E x 3600 / At W kg'1 (2)
where, E is energy density (Wh kg"1), C is specific capacitance (F g*1), V is device voltage (V), P is power density (W kg"1) and At is discharge time (s).
The calculated energy density and the power density are displayed in Ragone plots shown in Figure 9 (a. b), The Ragone plot of the symmetric device in aqueous electrolyte shows a maximum energy density of 88 Wh kg-1 at a power density of 399 W kg-1, whereas the non¬aqueous device delivers an energy density of 72 Wh kg-1 at a power density of 350 W kg"'. At an energy density of 25 Wh kg-1, the symmetric non-aqueous device delivers power density of 4800 W kg-1. One of the vital features of the practical ultracapacitor, is its long-term stability. Hence, cycling stability of the symmetric devices in aqueous and non-aqueous electrolytes were carried out for long cycles and the obtained results are given in Figure 9 (c, d). The unperturbed nearly 100% Columbic efficiency for the examined long cycles suggests robustness stability of the proto-type devices. The high Columbic efficiency has been substantiated by the charge-discharge profiles shown in inset of Figure 9 (c, d). It is clear that the charge-discharge profiles recorded at initial three cycles and last three cycles are nearly identical.
In conclusion, the instant invention provides an excellent hybrid energy storage device that has the best features of a supercapacitor and a lithium ion battery. The development of hybrid energy storage device with high energy (100-125 Wh kg"1) and power densities (7-11 kW kg*1) and when connected in series or alone can power a wide variety of consumer electronics. Further, the aqueous Li-ion conducting electrolyte provides a wide potential window for the device operation and potential electrode material of Li-rich coated with carbon helps in reducing the capacity fading and thus improving the performance. More
important is the fact that the potential electrode materials for Li-ion capacitor and Li-ion
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battery are derived from recycling the disposed battery and hence provides an excellent alternative for sustainability, recycling and reducing e-wastes.
Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Any reference to "or" herein is intended to encompass "and/or" unless otherwise stated.
While the preferable embodiments of the current invention have been discussed and described as appropriate, it will be obvious to a person skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions are possible without departing from the scope of the present disclosure. Various alternatives to the embodiments of the present disclosure described herein may be employed while practicing the disclosure of the current invention. Further, it is intended that the following claims define the scope of the present disclosure and that methods and structures within the scope of these claims and their equivalents be covered thereby.
Also, throughout the disclosure of the current invention, the numerical features are presented in a way of range format. The description in range format is merely for suitability and convenience and should not be construed as an inflexible limitation on the scope of any of the embodiments of the current invention. Accordingly, the description of a range mentioned is to be considered as disclosing all the possible subranges as well as individual numerical values within that range to the tenth of the unit of the lower limit unless the context clearly dictates omerwise. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed subranges such as from 1 to 2, from 1 to 3, from 1 to 4, from 2 to 4, from 2 to 3, and from 3 to 4, as well as individual values within that range, for example, 1.1,2,2.3,4, and 4.9. This applies regardless of the breadth of the range. The upper and lower limits of these intervening ranges may independently be included in the smaller ranges, and are also encompassed within the present disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the present disclosure, unless the context clearly dictates otherwise.

CLAIMS
1. A method of fabricating energy storage device comprising:
a) carbonization of the spent honeycomb
b) collecting the carbonized spent honeycomb and processing it to activated carbon on copper foil as the anode
c) using lithium cobalt oxide (LCO) coated on an aluminium foil and/or Li-metal discs as the cathode
d) fabricating the device comprising activated carbon on copper foil (or discs) as the negative electrode or anode, lithium cobalt oxide (LCO) coated on an aluminium foil and/or Li-metal discs, as the positive electrode or the cathode along with other components such as separators
2. The method of claim 1, wherein the processing of spent honeycomb to obtain activated
carbon comprises;
a) washing and drying the spent honeycomb
b) pre-carbonizing the washed honeycomb in a muffle furnace at a temperature range of 200-400 °C for a time period of at least two hours
c) mixing the pre carbonized sample with the requisite amount of KOH, subjecting the mixture to be transferred into an alumina boat and kept in tubular furnace at a temperature range of 400 - 600 °C in Ar atmosphere for a time period of about four to six hours
d) subjecting the obtained sample to be washed several times with acid (HC1) and distilled water
e) sample drying in vacuum desiccator to obtain activated carbon.
3. A hybrid Li-ion capacitor with the electrodes extracted by processing the spent honeycomb
comprising:
a) using a mixture of activated carbon and carbon black, with a binder such as polyvinylidene difluoride (PVDF), Polytetrafluoroethylene (PTFE), polysodium acrylate (PAA); and a
conductive additive such as -sp carbon, acetylene black, activated carbon;
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b) slurry was prepared by adding a solvent such as NMP, ethanol, water and coated on a current collector such as carbon cloth, nickel foam, stainless steel, copper foil and the slurry paste of the said electrodes applied on a substrate
c) separator between the negative electrode and the positive electrode
d) H2SO4 (aqueous symmetric capacitor) or LiPF^ (non-aqueous symmetric capacitor) as the electrolyte
4. A Li-ion battery with the activated carbon anode extracted from the spent honeycomb
material comprising:
a) lithium cobalt oxide (LCO) coated on an aluminium foil and/or Li-metal discs, the cathode comprising a binder such as polyvinylidene difluoride (PVDF), Polytetrafluoroethylene (PTFE), polysodium acrylate (PAA); and a conductive additive such as -sp carbon, acetylene black, activated carbon
b) slurry was prepared by adding a solvent such as NMP, ethanol, water and coated on a current collector such as carbon cloth, nickel foam, stainless steel, copper foil and the slurry paste of the said electrodes applied on a substrate
c) activated carbon derived from spent honeycomb material used as anode, and a separator between the anode and the cathode
d) LiPF4 in EC/DEC as the electrolyte

5. The Hybrid Lithium-ion capacitor of claim3, having a high energy density in the range of 100-125 Wh kg"1 (aqueous/non-aqueous symmetric capacitors) and power density in the range of 2-10 kW kg"1 (aqueous/non-aqueous symmetric capacitors)
6. The Lithium-ion battery of claim 4, having a storage capacity in the range of 130 mAh s~' to 200 mAh/g-'