AC Hybrid Supercapacitor combining High Power of Supercapacitor and High Energy of Li-ion battery

AC Hybrid Supercapacitor combining High Power of Supercapacitor and High Energy of Li-ion battery

Available online at www.sciencedirect.com ScienceDirect Materials Today: Proceedings 18 (2019) 2625–2631 www.materialstoday.com/proceedings ICMPC-2...

2MB Sizes 0 Downloads 27 Views

Available online at www.sciencedirect.com

ScienceDirect Materials Today: Proceedings 18 (2019) 2625–2631

www.materialstoday.com/proceedings

ICMPC-2019

Li4Ti5O12/AC Hybrid Supercapacitor combining High Power of Supercapacitor and High Energy of Li-ion battery Hari Raja, Sobhit Saxenab*, Anjan Silc a,c

Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee-247667, India b School of Electronics & Electrical Engineering, Lovely Professional University, Punjab-144411,India

Abstract Spinel lithium titanate (Li4Ti5O12) has been synthesized by solid state route. Prepared Li4Ti5O12 powder was characterized by Xray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) for phase purity and particle size estimation respectively. Hybrid supercapacitor consisting of activated carbon and synthesized Li4Ti5O12 as electrodes is assembled inside the glovebox filled with argon gas. Electrochemical characteristics of hybrid supercapacitor are observed by constant current charging-discharging cyclic voltammetry. Activated carbon based electric double layer capacitor (EDLC) was also prepared and electrochemically characterized for comparison. Hybrid supercapacitor shows better discharge capacities of 12 and 10 mAhg-1 at 0.5C and 1C (1C = 100mAhg-1) compared to 9 and 3 mAhg-1of EDLC respectively. Cyclic performances are also observed for 80 cycles at 2C. The capacity retention of hybrid supercapacitor is >86% compared to 80% of EDLC. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: EDLC; Hybrid supercapacitor; Li4Ti5O12; Activated Carbon; Solid State Reaction.

1. Introduction Increasing greenhouse gas (GHG) emission has made essential of a clean energy source which can full-fill the demand of energy and power [1-3]. Compared to all available energy storage technologies such as storing kinetic energy, chemical energy, potential energy, magnetic energy and thermo-chemical energy, electrochemical energy storage is most beneficial technology. Electrochemical energy storage devices i.e. batteries, fuel cells and electrochemical capacitors or supercapacitors covers large area of applications from portable electronics (notebooks, mobile phones, * Corresponding author. Tel.: +91-9412002515; E-mail address: [email protected]

2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019

2626

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

MP3 players), industry to hybrid electric vehicles (HEVs) [4-7]. Due to higher power density than battery and fuel cell, and larger energy density than normal capacitor, supercapacitor is widely used as energy storage device in high power applications [8]. Generally activated carbon (AC) is used as an electrode material for electric double layer capacitors (EDLC) or supercapacitors because of its very high surface area, and organic salt as an electrolyte. The charging-discharging process of an electrochemical double layer capacitor is purely electrostatic and charge is stored in the form of double layer, which builds up at the electrode/electrolyte interface. However, because of limited charge storage at the surface of the active material (AC), the energy density of electrochemical double layer capacitor is limited [9]. Moreover, because of higher theoretical capacity (175 mAhg-1) than activated carbon, recently lithium titanate (Li4Ti5O12) has been studied as an anode material for supercapacitor, which is called hybrid supercapacitor [10-12]. Hybrid supercapacitor combines high power density of non-faradic supercapacitor material (AC) to high energy density of faradic battery material (Li4Ti5O12) [13-15]. Spinel Li4Ti5O12 has superiority as an electrode material for hybrid supercapacitor due to high energy density and stability at high rate [16]. Present work deals with synthesis of Li4Ti5O12 by solid state route and comparison of electrochemical performances of EDLC (AC/AC) and hybrid supercapacitor (LTO/AC). 2. Experiment Procedure 2.1 Preparation of electrode material Lithium titanate (Li4Ti5O12) was prepared by solid state route using a mixture of TiOas2 (Anatase, 99%, Loba Chemie, India), and Li2CO3 (99%, Loba Chemie, India). TiO2 and Li2CO3 were taken according to stoichiometric ratio of Ti/Li (5/4). Pulverisette-7 planetary ball milling equipment was used at 900 rpm for 12 hr to mix TiO2 and Li2CO3 in ethanol solvent. Ball milling was performed in ZrO2 grinding jar of 80 ml capacity with ZrO2 balls of diameter 0.5 mm. The obtained slurry was dried at 100ºC and then calcined at 800ºC for 10 hr in air to get pure phase Li4Ti5O12. 2.2 Material Characterization X- ray diffraction (XRD) was performed on the synthesized powder for phase purity verification using Smart Lab, Rigaku, Japan with CuKα radiation (λ= 1.54 Å). Diffraction pattern was collected at room temperature at a scanning rate of 2º/min in the 2θ range of 15-85º. Particle size of activated carbon (AC) and synthesized Li4Ti5O12 powder were determined by field emission scanning electron microscopy (FE-SEM) using Ultra Plus, Zeiss, Germany. 2.3 Electrode Preparation and Cell formation The negative electrode (anode) of hybrid supercapacitor was prepared by lithium titanate (Li4Ti5O12), whereas, electrodes (negative and positive) of EDLC and positive electrode (cathode) of hybrid supercapacitor were prepared by activated carbon. The slurry was prepared with active material (Li4Ti5O12 or AC), conducting agent acetylene black and polyvinylidene fluoride (PVDF) as binder (with a weight ratios of 80:10:10 respectively) mixed in Nmethyl-2 pyrrolidone (NMP) as solvent. The obtained slurry was pasted on current collector (copper foil for negative electrode and aluminium foil for positive electrode) and dried at 80°C in air, pressed mechanically, then dried again in vacuum at 80°C for 4 hr to make it moisture free. Electrodes were cut into discs having a diameter of 1 cm. Cylindrical Teflon cell was used for the cell assembly and electrical connections are made to measure electrochemical characteristics. Polypropylene (Celgard 2300) was used as a separator to separate both the electrodes. The electrolyte used was 1M LiPF6 dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1, by volume). The separator and electrolyte both were ionically conductive to allow movement of Li+ ions and electronically insulating to prevent electrons movement. Sketches of EDLC and hybrid supercapacitor cell characterized in the present work are shown in Fig. 1(a-b). Cell fabrication was carried out inside Ar-filled glove-box (MBRAUN, MB 200G Unilab, Germany) which maintains < 1 ppm of O2 and moisture. Electrochemical measurements of all cells were performed by using Arbin Cycler (Arbin Instruments, USA).

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

2627

Fig. 1. Sketches of (a) EDLC, (b) Hybrid supercapacitor.

3. Results and Discussion 3.1 Characterization of Li4Ti5O12 Powder Fig. 2 shows XRD pattern of Li4Ti5O12 powdered sample prepared by solid state route. There was no extra peak traced except Li4Ti5O12 peaks, confirming the pure Li4Ti5O12 material. During heat treatment Li+ ion diffuse into TiO2 and formation of Li4Ti5O12 start from outer surface, therefore homogeneous and fine mixing of raw materials is very important for complete reaction (as shown in eq.1) [17]. For this purpose high speed planetary ball milling with fine ZrO2 balls of diameter 0.5 mm for 12 hr was used. eq.1

Fig. 2. XRD pattern of heat treated Li4Ti5O12 powder at 800°C for 10 hr.

Fig. 3 shows FE-SEM images of Li4Ti5O12 powder and activated carbon. Fig. 3(a) shows activated carbon has larger particle size in the range of 0.5-2 µm, whereas Li4Ti5O12 powder has particle size less than 500 nm as shown in Fig. 3(b).

2628

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

Fig. 3. FE-SEM images of (a) Activated carbon, (b) Li4Ti5O12 powder.

3.2 Electrochemical performances Charge-discharge behaviors of EDLC and hybrid supercapacitor were measured at different current rates (assuming 1C = 100 mAhg-1) in the voltage range of 0.5 V- 3.0 V. Discharge capacities of EDLC were 9 and 3 mAhg-1, and charge capacities were 13 and 7 mAhg-1 at 0.5C and 1C rate respectively, whereas discharge capacities of hybrid supercapacitor were 13 and 10 mAhg-1, and charge capacities were 17 and 12 mAhg-1 at 0.5C and 1C respectively as shown in Fig. 4(a, b). Charge-discharge capacities of EDLC were lower than hybrid supercapacitor, because less amount of charge was stored in double layer of EDLC due to limited surface area available for charge storage. But in hybrid supercapacitor stored charge was more due to double layer formation of PF6- on the surface of AC as well as by intercalation of Li+ ion in the lattice structure of Li4Ti5O12 material. This process can be explained by the following reactions [18]: · (Cathode) eq.2 0 3 3 (Anode) eq.3

Fig. 4. Charge-discharge curves of EDLC and hybrid supercapacitor at (a) 0.5C, and (b) 1C

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

2629

Charging-discharging curves showing variation voltage w.r.t. time of EDLC and hybrid supercapacitor at different C-rates viz. 0.5C, 1C, 2C and 5C was shown in Fig. 5 (a-b). EDLC discharges very fast with no discharge plateau compared to hybrid supercapacitor which shows discharge plateau indicating intercalation characteristic of battery material even at high C-rates.

Fig. 5. Charge-discharge curves at different C-rates from 0.5C to 5C, (a) EDLC, (b) Hybrid supercapacitor

Fig. 6 shows the capacity retention curve of EDLC and hybrid supercapacitor for 80 cycles at 2C current rate. The continuous loss in the discharge capacity of hybrid supercapacitor was observed as compared to EDLC due to battery material in hybrid supercapacitor.

Fig. 6. Discharge capacity retention curve of EDLC and hybrid supercapacitor at 2C

The cyclic voltammetry (CV) curves of EDLC and hybrid supercapacitor were shown in Fig. 7. CV was measured in the potential window of 0.5 V- 3.0 V at constant scan rate of 2 mVs-1. As we can see, both EDLC and hybrid supercapacitor have different electrochemical behavior. Fig. 7(a) did not show oxidation-reduction peaks i.e. AC

2630

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

electrode exhibits only electrostatic adsorbing–desorbing process of PF6− on AC surface. Therefore charge was stored in supercapacitor due to double layer formation. CV curve of hybrid supercapacitor showed broad oxidationreduction peaks due to intercalation of Li+ ion as well as double layer formation on AC surface as shown in Fig. 7(b) [19].

Fig. 7. CV curves of (a) EDLC and, (b) Hybrid supercapacitor at scan rate 2 mVs-1

4. Conclusion Spinel lithium titanate (Li4Ti5O12) has been synthesized by solid state route, using ball milling at 900 rpm for 12 hr. Prepared Li4Ti5O12 powder was characterized by X-ray diffraction for phase purity verification and field emission scanning electron microscopy for particle size estimation. Comparison between electrochemical characteristics of EDLC and hybrid supercapacitor has been done by charging-discharging, capacity retention and CV tests. Hybrid supercapacitor has shown discharge capacities of 13 and 10 mAhg-1 at current rates of 0.5C and 1C respectively, whereas EDLC has shown only 9 and 3 mAhg-1. Moreover, capacity retention of hybrid supercapacitor was higher than EDLC. Therefore hybrid supercapacitor has superiority over EDLC in electrochemical performance where high power and high energy is required. References [1] VanMierlo J, Favrel V, Meyer S, Hecq W. How to Define Clean Vehicles? Environmental Impact Rating of Vehicles. International Journal of Automotive Technology, 2003, 4(2): 77-86 [2] Pandolfo A G, Hollenkamp A F. Carbon properties and their role in supercapacitors, Journal of Power Sources, 2006, 157: 11–27 [3] Simon P, Gogotsi Y. Materials for electrochemical capacitors. Nature Materials, 2008, 7: 845–854 [4] Park K S, Benayad A, Kang D J, Doo S G. Nitridation-driven conductive Li4Ti5O12 for Lithium Ion batteries. Journal of American Chemical Society. 2008, 130: 14930-14931 [5] Scrosati B, Garche J. Lithium Batteries: Status, Prospects and Future. Journal of Power Sources, 2010, 195: 2419–30 [6] Perrin M, Saint-Drenan Y M, Mattera F, Malbranche P. Lead–acid batteries in stationary applications: competitors and new markets for large penetration of renewable energies. Journal of Power Sources, 2005, 144: 402-410 [7] Raj H, Saxena S, Sil A. Internal Hybrid System of Li-Ion Battery and Supercapacitor. Journal of Basic and Applied Engineering Research, 2015, 2(11): 937-940 [8] Winter M, Brodd, R. J. What are the batteries, Fuel cells and Super capacitors?. Chemical Reviews, 2004, 104: 4245–4269 [9] Cericola D, Novák P, Wokaun A, Kötz R. Hybridization of electrochemical capacitors and rechargeable batteries: An experimental analysis of the different possible approaches utilizing activated carbon, Li4Ti5O12 and LiMn2O4. Journal of Power Sources, 2011, 196: 10305– 10313 [10] Amatucci G G, Badway F, Shelburne J, Gozdz A, Plitz I, DuPasquier A, Menocal S G. The non-aqueous asymmetric hybrid technology: Materials. 18 electrochemical properties and performance in plastic cells, Proc. of 11th International seminar on double-layer capacitors, 2001, 16-24

H. Raj et al. / Materials Today: Proceedings 18 (2019) 2625–2631

2631

[11] Plitz I, DuPasquier A, Badway F, Gural J, Pereira N, Gmitter A, Amatucci G G. The design of alternative nonaqueous high power chemistries. Applied Physics A, 2006, 82: 615-626 [12] Amatucci G G, Badway F, DuPasquier A, Zheng T. An asymmetric hybrid nonaqueous energy storage cell. Journal of Electrochemical Society, 2001, 148(8): 930-939 [13] Conway B E, Pell W G. Peculiarities and advantages of hybrid capacitor devices based on combination of capacitor and battery type electrodes. Proc. of 12th International seminar on double-layer capacitors, 2002, 16-32 [14] Lu P, Xue D, Yang H, Liu Y. Supercapacitor and nanoscale research towards electrochemical energy storage. International Journal of Smart Nano Materials, 2013, 4: 2–26 [15] Shukla A K, Banerjee A, Ravikumar M K, Jalajakshi A. Electrochemical capacitors: Technical challenges and prognosis for future markets. Electrochimical Acta, 2012, 84: 165–173 [16] Hong M S, Lee S H, Kim S W. Use of KCL Aqueous Electrolyte for 2 V Manganese Oxide/Activated Carbon Hybrid Capacitor. Electrochemical Solid-State Letter, 2002, 5(10): A227 –A230 [17] Sandhya C P, John B, Gouri C. Lithium titanate as anode material for lithium-ion cells: a review. Ionics, 2014, 20: 601–620 [18] Lee B G, Yoon J R. Preparation and Characteristics of Li4Ti5O12 Anode Material for Hybrid Supercapacitor. Journal of Electrical Engineering & Technology, 2012, 7 (2): 207-211 [19] Hu X B, Huai Y J, Lin Z J, Suo J S, Deng Z H. A (LiFePO4–AC)/Li4Ti5O12 Hybrid Battery Capacitor. Journal of Electrochemical Society, 2007, 154 (11): 1026-1030