Carbon Nanocomposites for Electrochemical Capacitors - Science Direct

0 downloads 0 Views 1MB Size Report
nanocomposites application as the basis for supercapacitors electrodes with ... vehicles, fault-free engine starting devices for motor and railway transport, as.

Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 113 (2015) 511 – 518

International Conference on Oil and Gas Engineering, OGE-2015

Carbon nanocomposites for electrochemical capacitors Surovikin Yu.V.а,b * a

Institute of Hydrocarbons processing SB RAS, Neftezavodskaya st. 54, Omsk 644040, Russian Frderation b Omsk State Technical University, 11, Pr. Mira, Omsk 644050, Russian Federation

Abstract Carbon-carbon (C/C) nanocomposites based on nanodispersed carbon black and pyrolytic carbon obtained with matrix synthesis are investigated. The work presents the results of electrochemical tests on prototype samples of C/C nanocomposites as the components of electrochemical capacitors electrodes with the solutions of sulphuric acid (H2SO4) in water and tetraethylammonium tetrafuoroborate (TEABF4) in acetonitrile acting as electrolytes. The research demonstrated the interrelation of the electrode components size factor and the supercapacitor electrochemical properties, and also the prospects of C/C nanocomposites application as the basis for supercapacitors electrodes with high-energy electrolytes. © 2015 2015Published The Authors. Published by Elsevier Ltd. © by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Omsk State Technical University. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University Keywords: carbon nanocomposites; matrix synthesis; supercapacitror; size factor; porous structure; electrolyte

1. Introduction Recently, the attention of numerous scientists has been directed to development of more efficient autonomous electrochemical equipment (batteries, power cells, power sources, etc. ) to generate and store electrical energy. Nowadays, electrochemical capacitor with double electric layer, or supercapacitor, is considered as a promising rechargeable power source, the supercapacitor being the most suitable unit for storing and delivery of electrical energy. Due to high operational parameters of the supercapacitors, such application areas as storage devices of abnormal amount of energy, hybrid vehicles, fault-free engine starting devices for motor and railway transport, as well as the usage of combined power facilities have developed extensively. Also military equipment, aerospace and medicine industries are among the promising application areas [1].

* Corresponding author. Tel.: +7-381-256-0287; fax: +7-381-256-0211. E-mail address: [email protected]

1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University

doi:10.1016/j.proeng.2015.07.344

512

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

Electrochemical capacitors production is a dynamically developing area of worldwide industry of electrochemical power supplies production and it is notable for the variety of design and end-product properties. That is mainly connected to the usage of a wide range of the supercapacitors basic elements (electrode and electrolyte) properties [2, 3]. The variety of electrode materials and electrolytes calls for selecting special material combinations and allows to achieve the necessary parameters of the end-product specific energy and capacity (Fig. 1a, b). As a whole, the main purpose of the supercapacitors specific energy properties improvement is the replacement of aqueous electrolyte with organic one, and, as well, optimization of active mass couples properties, such as porous structure and surface chemistry of carbon porous material. Whereby the most relevant investigations are those focused on the search for new types of electrolytes with improved operational characteristics (non-toxic, with operating voltage not less than 3.5 V, wide operating temperature range, etc.) The use of new high-energy electrolytes will result in sufficient increase of specific energy properties of the supercapacitors till 40 kJ/kg and specific capacity up to 20 kW/kg. Activated Carbon

70

Separator----------------

60

Ionic liquids

Е, W-h/kg

50

Al current collector

1 2

40 30 20 10

Organic electrolytes Aqueous

0

Electrolyte__

[MeBuIm]BF4 a

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5

U, V b

Fig. 1. (a) Supercapacitor schematic diagram; (b) The dependence of specific energy on operating voltage: 1 - theoretical model, 2 - actual supercapacitor [4]

The most promising in developing supercapacitors of new generation and the substitution of traditionally used electrolytes (TEABF4/acetonitrile) are ionic liquids (IL) [4-6]. However, despite high individual operational characteristics of IL ([МеBuIm]BF4), its combination with standard active carbons does not result in maximum efficiency of a double electrical layer. It mainly depends on the size factor, i.e. the ratio between the pore size and the electrolyte cations and anions sizes (Fig. 2). 2. Experimental In developing ideal supercapacitor of new generation, the electrode material selection is determined by the size factor, and the requirements for carbon component porous structure parameters can differ significantly due to the electrolyte type [7-9]. In this regard there is the task for developing a new generation of nanostructured carbon materials with predetermined porous structure and surface chemistry through their controlled synthesis with the use of algorithms based on molecular-dynamic modeling of a dual electric layer. Such material are to be optimized for usage with high-energy electrolytes based on ionic liquids and achievement of maximum value of dual electrical layer surface.

513

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

Author name / Procedia Engineering 00 (2015) 000–000

3

Fig. 2. The effect of the size factor on supercapacitor capacity [9].

2.1. Carbon nanocomposites The application of new high-energy electrolyte calls for the use of nanostructured carbon materials with specified surface chemistry and porous structure parameters: high specific surface (not less than 1000 m2/g), optical microand mesopores ratio (0.7 - 2.0 nm and 2.0 - 6.0 nm) and the pore sizes adjusted to geometric sizes of cations (0.87 nm [MeBuIm]+) and anions (0.45 nm BF4–) of electrolyte [10]. Similar dedicated highly-porous materials can be synthesized on the basis of nanodispersed carbon black (NDCB) and pyrolytic carbon (PC) due to matrix synthesis technique. Matrix synthesis provides fine adjustment of technical process parameters for obtaining desired porous structure. The research findings demonstrate its universal prospects for targeted acquisition of various types of carbon-carbon (C/C) nanocomposites [11].

Fig. 3 Matrix synthesis of C/C nanocommposites based on NDCB and PC: 1 - NDCB generation, 2 - nanoporous systems formation, 3 - 3D pyrocarbon matrix formation, 4 - thermal oxidative and thermal treatment of C/C nanocomposite

The synthesis of such materials is a multi-stage technical process, specified final nanocomposite properties built up at each stage. Matrix synthesis diagram is shown in Fig. 3. Autonomous product with final properties can be obtained at each stage: x High temperature process of NDCB generation; formation of particles sizes, degree of branching for primary aggregates and chemical purity of the final nanocomposite; x Formation on the basis of NDCB of various nanoporous systems in the form of granules till specified fractional composition, form and density; formation of macro- and large mesopores and ultimate composition of final nanocomposite; x Formation of 3D pyrocarbon matrix in porous systems till the specified mechanical strength, thermal and chemical resistance of nanocomposite; formation of mesopores of various sizes and closed porosity; x Thermal oxidative and thermal treatment of C/C nanocomposite is the stage of final formation of textural characteristics - formation of micropores and development of fine mesopores; formation of the surface functional cover.

514

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

Fig. 4. Micrographs of C/C nanocomposite (a) after 3D pyrocarbon matrix formation stage (SEM), (b) after thermal oxidative treatment stage (ARM)

NDCB choice, C/C nanocomposite formation till specified ratio, reinforcing filler (NDCB/binder (3D PC matrix) and the degree of the following thermal oxidative treatment determine the parameters of porous structure C/C nanocomposite (pore-size distribution, micro- and mesopores ratio, total pore volume, specific surface). %

60

Adsorption branch of isotherm

50 Desorption branch of isotherm Ряд 2

40 30 20 10 0 0

3

5

7

10

13

20

27

40

55

80

Diameter of pores, nm

Fig. 5. Pore-size distribution for C/C nanocomposites after thermal oxidative treatment.

Fig. 4 shows micrographs of the microstructure characteristic of C/C nanocomposite after 3D pyrocarbon matrix formation and thermal oxidative treatment stage. Common pattern for pore-size distribution for C/C nanocomposites obtained with NDCB/3D PC matrix ratio < 1 and relative mass loss of C/C nanocomposite in the range of 0.2 - 0.7 after thermal oxidative treatment is shown in Fig. 5. Herein one can see pore-size distribution determined by nitrogen adsorption isotherms (77 K) characteristic of C/C nanocomposites based on NDCB with particles size of 10 - 50 nm. In all cases the pores with sizes from 3.0 to 5.0 nm prevail (up to 50% of the whole pores volume) and only in the usage of NDCB with the particles size of

515

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

50 nm the pores with sizes from 5.0 to 20.0 nm appear, and the percent of pores with sizes from 3.0 to 5.0 nm decreases. The universal prospects of matrix synthesis allows to construct the end-product with various levels of structure organization (from atomic-molecular to permolecular) and to form its operating properties in a controlled way. Currently matrix synthesis of granuled carbon-carbon nanocomposites is one of the promising ways to produce new functional carbon material significantly surpassing traditional active carbons in mechanical, thermal and chemical resistance and the level of non-carbon impurities. 2.2. Electrochemical tests Present work contains the results of electrochemical tests of electrochemical capacitors electrodes prototype samples with the use of common electrolytes, such as aqueous solution of sulphuric acid (H2SO4) and tetraethylammonium tetrafuoroborate (TEABF4) solution in acetonitrile. Highly-porous C/C composites were used as an active electrode component. These C/C nanocomposites were obtained through matrix synthesis on the basis of NDCB with various particle sizes: 10-15 nm (SK 145); 20-25 nm (SK 865) and 40-50 nm (SK 770); with NDCB/3D PC matrix ratio < 1, and relative mass loss of C/C nanocomposite from 0.4 to 0.8. Porous structure parameters of the materials obtained due to low-temperature nitrogen adsorption (77 K) with the equipment "Sorptomatic 1900", "Carlo Erba Instruments", are provided in Table 1. Table 1. Characteristics of the electrode based on different active components Specific capacity Сsp, (F/g)

Porous structure parameters Sample code

SBET (m2/g)

VΣ** (cm3/g)

Vμ *** (cm3/g)

DBET (nm)

Ddes* (nm)

Dads* (nm)

Vμ/V∑ (%)

H2SO4

TEABF4

SK 865 -1

800

1.97

0.33

9.8

11.0

20.6

0.17

48.8

48.7

SK 863 -3

883

2.93

0.33

13.3

14.3

23.4

0.11

57.2

43.9

SK 145 -1

521

0.73

0.19

5.6

5.6

8.5

0.26

36.3

31.9

SK 145 -5

787

2.16

0.31

11.0

8.8

18.8

0.14

50.5

52.6

SK 770

418

0.86

0.18

8.2

7.0

12.2

0.21

30.5

30.6

Norit DLC Supra 30

1541

0.79

0.64

2.1

6.9

9.0

0.81



63.6

* Pore-size distribution was calculated by isotherms of nitrogen adsorption-desorption (77K) with Dollimore Heal method [12]; ** Total pore volume by nitrogen with Р/РS = 0.996; ***Micropores volume was calculated by Dubinin-Radushkevich equation of the theory of the volume filling of micropores (TVFM).

Electrochemical capacitors electrodes were produced by mixing highly-porous C/C nanocomposite powder (with particles size to 20 μm) and conductive filler (NDCB P 267-E) and polymer binder F-4D with subsequent multistage calendaring. Norit DLC SUPRA 30 active carbon powder applied in commercial supercapacitors production was used for comparison. The obtained electrodes were saturated with electrolyte solution (3М H2SO4; 1М TEABF4) and electrochemical tests were carried out. Capacity values were received in Swagelock-type doubleelectrode cell with Elins P-8 potentiostat by cyclic voltammetry. The results are shown in Fig. 6-8 and in Table 1. The obtained results demonstrate the interrelation of the electrode components size factor and the supercapacitor electrochemical characteristics. It was determined that, in

516

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

passing from sulphuric acid to organic electrolyte, the capacity changes slightly which proves good availability of C/C nanocomposites prototype samples pores both for sulphuric acid ions and larger organic salt ions. Also electrodes based on non-aqueous electrolytes and C/C nanocomposite with larger mesopores and lesser amount of micropores possess higher specific capacity values. In tests it was determined that potential scanning rate increase does not result in significant relative change in specific capacity (С,%) of the prototype electrodes and the least change is the case for the electrodes based on C/C nanocomposites with SK 865-3 type porous structure. Mention should be made of the fact that the electrodes based on C/C nanocomposites are notable for high specific characteristics and constant specific power efficiency with the increase in polarizing current. a

i, A/g

i, A/g

b

SK 145-1 SK 145-5 SK 865-1 SK 865-3 SK 770

SK 145-1 SK 145-5 SK 865-1 SK 865-3 SK 770

E, V

E, V

Fig. 6. Cyclic volt-ampere curves for the electrode based on C/C nanocomposites: (а) 3М H2SO4; (b) 1М TEABF4. Potential scanning rate is 20 mV/s

a

b

SK 145-1

SK 145-1

SK 145-5

SK 145-5

SK 865-1

SK 865-1

SK 865-3

SK 865-3

SK 770

SK 770

V, mV/s

V, mV/s

Fig. 7. Relative change in specific capacity of electrode based on C/C nanocomposites at potential scanning rate increase (а) 3М H2SO4; (b) 1М TEABF4

517

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

The comparison of electrochemical properties of the electrode based on standard microporous active carbon and the electrode based on C/C nanocomposite with a larger amount of mesopores proves the significant effect of size factor on efficiency of a double electric layer (Fig. 8b) With almost twofold difference in specific surfaces of Norit DLC SUPRA 30 active carbon ( SN2 =1541 m2/g) and С/С nanocomposite SK 145-5 (SN2 =787 m2/g), specific capacities of supercapacitor electrode does not differ more than 20%.

Specific power efficiency, W/kg

a

b

SK S K 145-1 145 14 1 455 4 45-1 SK 145-5 145 14 1 45-5 45 SK SK 865-1 865 86 8 655-1 6 SK SK 865-3 86 8 865 655-3 6 5 SK SK 770 SK 77 77

Specific energy, W-h/kg

Fig 8 (a) The dependence of specific power efficiency on specific energy for electrode based on C/C nanocomposite and TEABF4 in acetonitrile. (b) specific capacity of supercapacitor electrode based on various active components and TEABF4 in acetonitrile.

3. Conclusion The conducted investigations demonstrated the prospects for using C/C nanocomposites as supercapacitors electrode basis with non-aqueous electrolytes. It was shown that technical process of matrix synthesis of C/C nanocomposites allows variability in porous structure with predetermined parameters, and its universal potentials and obtained findings provide the basis for targeted synthesis of new nanostructured carbon materials with necessary properties to produce supercapacitors of a new generation with high electrical energy characteristics. References [1] K.K. Den'shhikov, B.V. Shherbina, Sostojanie tehniki i rynka superkondensatorov, izd-vo MGU, Moskva, 2004. (in Russian) [2] P. Simon, Yu. Gogotsi, Materials for electrochemical capacitors, Nature Materials. 7 (2008) 845–854. [3] A.G. Pandolfo, A.F. Hollenkamp, Carbon properties and their role in supercapacitors, J. Power Sources. 157 (2006) 11–27. [4] K.K. Den'shhikov, Predel'nye znachenija harakteristik dvojnoslojnyh superkondensatorov, v: «Jubilejnaja nauchnaja konferencija, posvjashhennaja 50-letiju OIVT RAN», OIVT RAN, Moskva, 2010, 348-351. (in Russian) [5] K.K. Denshchikov, M.Y. Izmaylova, A.Z. Zhuk, Y.S. Vygodskii, V.T.Novikov, F.Gerasimov, 1-Methyl-3-butylimidazolium tetraflouroborate with activated carbon for electrochemical double layer supercapacitors, Electrochim. Acta. 55 (2010) 7506–7510. [6] M.Ju. Izmajlova, K.K. Den'shhikov, V.T. Novikov, Primenenie ionnyh zhidkostej v kachestve jelektrolita jelektrohimicheskogo dvojnoslojnogo superkondensatora, Al'ternativnaja jenergetika i jekologija. № 11 (2009) 109–113. (in Russian) [7] C. Largeot, C. Portet, J. Chmiola, P.-L. Taberna, Yu. Gogotsi, P. Simon, Relation between the ion size and pore size for an electric doublelayer capacitor, J. Am. Chem. Soc. 130 (2008) 2730–2731.

518

Yu.V. Surovikin / Procedia Engineering 113 (2015) 511 – 518

[8] S. Kondrat, C.R. Perez, V. Presser, Y. Gogotsi, A.A. Kornyshev, Effect of pore size and its dispersity on the energy storage in nanoporous supercapacitors, Energy Environ. Sci. 5 (2012) 6474–6479. [9] J. Chmiola, G. Yushin, Yu. Gogotsi, C. Portet, P. Simon, P.-L. Taberna, Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer, Science. 313 (2006) 1760–1763. [10] Ya.S. Vygodskii, E.I. Lozinskaya, A.S. Shaplov, K.A. Lyssenko, M.Yu. Antipin, Ya.G. Urman, Implementation of ionic liquids as activating media for polycondensation processes, Polymer. 45 (2004) 5031–5045. [11] V.F. Surovikin, Ju.V. Surovikin, M.S. Cehanovich, Novye napravlenija v tehnologii poluchenija uglerod-uglerodnyh materialov. Primenenie uglerod-uglerodnyh materialov, Ros. him. zhurn. 41 (2007) 111–119. (in Russian) [12] D. Dollimore, G.R. Heal, An improved method for the calculation of pore size distribution from adsorption data, J. Appl. Chem. 14 (1964) 109–114.

Suggest Documents