Carbons in Electric Double Layered Capacitor

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1 212/11/13 第 4 講義 Now and Future of Capacitance Carbons in Electric Double Layered Capacitor Seong-Ho Yoon IMCE, Kyushu University Kasuga, Fukuoka, Japan Power density (W/kg) Current Capacitor Electro chemical Mateiral Surface Our Resaerh (Current) Ni- MH Pb Ni-Cd Liion Energy density (Wh/kg) Our Resaerh (Expect) Principle for Epoc-making Performance NMR Mechanism Knowledge.1 Power IAMS, Kyushu University 1 IAMS, Kyushu University 2 Relathip between Organic Capacitance and Surface Area 1M Et 4 NBF 4 /PC, 2.7V, Capacitance per Volume Electric Storage of EDLC Targets Larger Capacity per Volume High Rate of Charge-Discharge Better Carbon Electrode, Guideline? More Adsorption at Large Rate in the Adsorbent of Limited Volume Wetting to Carbon Surface Penetration into Pores Adsorption on Wall Surface Polarized Charge Outlet from Pore Discharge /Desorption First Cycle Sizes of Electrolyte vs. Pore for Penetration Invasion into Matrix or very narrow pore of wall Density Change or Expansion of Matrix, Volumetric Change of Electrode Mobility and Adsorbed Amount of Electrolyte as well as Structure of Electrode May Change under Electric Field IAMS, Kyushu University 3 4 1

2 212/11/13 Conjecture of pore size using capacitance data EDLC with organic electrolytes EDLC with inorganic electrolytes Electrolyte:Et 4 NBF 4 Electrolyte:H 2 SO 4 Cation((C 2 H 5 ) 4 N) Anion(SO 2-4 ) Stokes diameter :.676nm e- - Stokes diameter :.517nm e- e- e- e nm e e- e- e- e Ideal Model for capacitor 1.34nm M. Endo et al., J. Electrochem. Soc., 148 (8) A (21). Porous carbon In using Et 4 NBF 4 as an electrolyte, at least pore size larger than 1.3nm is necessary to have electric double layered capacitance. Capacity governing factors Surface area Pore size and its distribution Surface (Edge and Basal, Heterogeneous atom functional groups) Crystallinity of carbons (Resistivity) In using H 2 SO 4 as an electrolyte, pore size of about 1.nm is enough to have electric double layered capacitance. 5 6 Best Carbon Characterizat of Pitch and PAN based ACFs Pore structure: Right pore exclusively» Too large or small pores are useless Pore wall : Hexagonal edge» Graphitizable carbon (Higher conductive) Density : Least closed pore» Finer particles are desirable, but packing density should be maximized in the electrode Functional groups : Effectiveness» Oxygen functional groups have to be minimized» Other heterogeneous groups are still on studying. Va / cm 3(STP)g-1 dvp dv p 細孔径分布 (NL-DFT method) OG5A OG7A N 2 p / p p / p OG1A OG15A OG2A W / nm Va / cm 3(STP)g-1 dvp p FE2 FE1 FE3 FE W / nm 細孔特性表 (t -plot) Surface area (m 2 /g) Pore volume (cm 3 /g) Pore width (nm) A total A external A micro A meso V total V micro V meso W micro W meso OG-5A OG-7A OG-1A OG-15A OG-2A FE FE FE FE

3 212/11/13 CV results of Pitch & PAN based ACFs Pore size vs. Capacitance (Non-organic system) OG series 最適化された細孔サイズが存在 FE series 窒素官能基の影響 in H 2 SO Pore size vs. Capacitance (Organic system) 2D NMR (Non-organic system) OG series FE series 細孔サイズより相対的に大きいサイズを持っている電解イオンは 細孔内に浸透不可能 OG-5A Free electrolyte OG-15A Free electrolyte CM Adsorbed electrolyte 吸着された電解イオン CM OG 5A & FE 1 OG 15A & FE 3 H3O 電解イオン in Et 4 NBF 4 /PC D2SO4 D 4 D2SO4 D Chemical Shift Shift (ppm) (ppm) FE-1 FE-1 FE-3 FE-3 Somewhat broadened More than deshielded FE-1 吸着された電解イオン CM CM D2SO4 D 2SO 4 D2SO4 D 2SO

4 212/11/13 NMR (Organic system) 19F NMR ACF の細孔内電解イオン挙動に関する 2 H 固体 NMR 解析 (T 1 値 / 水系 ) OG-5A OG-15A Free electrolyte Free electrolyte Adsorbed electrolyte 吸着された電解イオン PTFE PTFE ( バインダー as binder) OG 5A & FE 1 OG 15A & FE 3 BF4 - 電解イオン OG5A T1 (sec) for OG series OG15A CM CM Free Adsorbed Free Adsorbed Free Adsorbed Free Adsorbed T1 (sec) OG5A Free Adsorbed OG15A Et4NBF4/PC 4NBF 4/PC Et4NBF4/PC 4NBF 4/PC. CM CM FE-1 FE-3 More de-shielded than More OG-15A deshielded 吸着された電解イオン FE1 T1 (sec) for FE series FE3 CM CM T1 (sec) FE1 Free Adsorbed FE3 Free Adsorbed Free Adsorbed Free Adsorbed Free Adsorbed Et4NBF4/PC Et4NBF4/PC 4NBF 4/PC 4NBF 4/PC CM CM 1. 緩和時間 T 1 は短いほどより強く吸着をしていることを意味する 2. T 1 の値は 充電の前に比べて充電後に より短くなる 3. 全体的に OGシリーズに比べてFEシリーズのT 1 値が短い Pores vs. capacitances Model structures of pores Yoon group of Kyushu university, Langmuir, 29, in press DOI: 1.121/la To examine the effect of pore size and surface composition of activated carbon fibers on EDLC To draw out the best pore and surface images of ACFs for better performance Conventional Hierarchical Structure Model After mild activation After mild activation Proposed Structure Model Model of adsorbed on the surface of OG and FE series Microdomain unit After severe activation After severe activation OG-5A FE-1 OG-15A FE-3 Non-solvated Ion size (nm) Solvated with solvent (PC) Reference (CH3CH2)4N BF Carbon. 22, 4, 2613 (CH3CH2)4N.68 BF Science. 26, 313,176 Et4N 4PC 1.35 J. Electrochem. Soc. 24, BF4-8PC , E199 Cf. Hydrate sulfate ion size of SO 2-4 (H 2 O) 12 :.53 nm J. Electrochem. Soc. 21,148(8), A Under mild activation condition, each of the microdomains on the uppermost surface contains the slitshaped micropores, leading to micropore-rich. 2. With increase of activation degrees, the size of uppermost microdomains reduces and the pore width of micropores becomes widened. Simultaneously, micropores are freshly generated in core part. 4

5 212/11/13 Two kinds of pores Removal of pores from inter-domain nucleation Maxsorb-III (Kansai coke and chemicals Co.) derived from petroleum coke high surface area (over 3 m 2 /g) M-3 (Osaka gas chemicals Co.) derived from mesophase carbon micro beads high surface area (over 3 m 2 /g) 1. Novel pore structures of activated carbons, also, were suggested with microdomain units through the interand intra-particular mechanism. 2. From this idea, ball mill treatment on ACs can bring the selective removal of inter-particle pores without destroying the intra-particle pores. 3. We tried to elucidate the roles of the inter- and intraparticle pores on capacitance with two super-activated carbons (with high surface area over 3 m 2 /g) in organic and inorganic electrolytes. Maxsorb-III (Kansai coke and Chemicals Co.) Ball-mill (for 1, 3, 5, 1 and 2 days) Physical Properties SEM, N2 adsorption/desorption at 77 K, Elemental analysis M-3 (Osaka gas chemicals Co.) Milling condit : at 2 rpm of pot mill rotator (ASH, AV-4) with zirconia balls (each 5 / 1 mm in diameter) Electrochemical Properties Cyclic voltammetry in.5 M H2SO4 and 1 M Et4NBF4/PC Structural Characteristics of MSCIII & M3 SEM images of ball-milled Maxsorb-III series As-received For 5 days For 1 days For 2 days MSCIII: Raw materials: resin Microdomain Domain M3: Raw materials: Mesophase Microdomain << Domain 19 5

6 212/11/13 N 2 adsorption/desorption of ball-milled Maxsorb-III series N 2 adsorption/desorption of ball-milled M-3 series N2 adsorption/desorption isotherms at 77 K Pore size distribut N2 adsorption/desorption isotherms at 77 K Pore size distribut Va/cm 3 (STP)g -1 As-received 1 day 5 days 1 days 2 days dvp Va/cm 3 (STP)g -1 As-received 1 day 5 days 1 days dvp Selectively decreased inter particular pores by ball-mill treatment 2 days P/P W/nm P/P W/nm m 2 /g cm 3 /g nm m 2 /g cm 3 /g nm Area (total) Area (external) Area (micro) Vol (total) Vol (micro) W (micro) As-received Ball-milled for 1 day Ball-milled for 3 days Ball-milled for 5 days Ball-milled for 1 days Ball-milled for 2 days Area (total) Area (external) Area (micro) Vol (total) Vol (micro) W (micro) As-received Ball-milled for 1 day Ball-milled for 3 days Ball-milled for 5 days Ball-milled for 1 days Ball-milled for 2 days By ball-mill treatments, the inter-particle pores (cylinder-like mesopores) were selectively removed without destroying the intra-particle pores (slit-like micropores). 2. Such novel pore models may be proved from N2 adsorption/desorption isotherm at 77K by ball-mill treatment. 1. Both novelpore structures of M-3, inter- and intra-particle pore, were simultaneouslydecreasedby ball-mill treatments. 2. Dramatical decrease of both pore structures in M-3 may be caused by much smaller micrographitic units derived from mesophasecarbon micro beads (MCMB) which are easy to loss especiallytheir inter-particle pores by ball-milling. Cyclic voltammograms of ball-milled AC series Specific capacitances of ball-milled Maxsorb-III series 5 Maxsorb-III 5 M-3 In inorganic electrolyte (.5 M H2SO4) In organic electrolyte (1 M Et4NBF4/PC) in.5 M H 2 SO 4 as-received ball-milled for 1 day ball-milled for 3 days ball-milled for 5 days ball-milled for 1 days ball-milled for 2 days in.5 M H 2 SO 4 as-received ball-milled for 1 day ball-milled for 3 days ball-milled for 5 days ball-milled for 1 days ball-milled for 2 days F/m Capacitance (F/m 2 ) Capacitance (F/m 2 ) E / V (vs. Ag/AgCl) E / V (vs. Ag/AgCl) F/m as-received ball-milled for 1 day -3 ball-milled for 3 days in 1 M Et 4 NBF 4 / PC ball-milled for 5 days -4 ball-milled for 1 days ball-milled for 2 days E / V (vs. Ag/AgCl) in 1 M Et 4 NBF 4 / PC as-received ball-milled for 1 day ball-milled for 3 days ball-milled for 5 days ball-milled for 1 days ball-milled for 2 days E / V (vs. Ag/AgCl) 1. The capacitances in inorganic electrolyte with smaller size than intra-particle pores (micropores) were gradually decreased with increase of ball-mill times. 2. The capacitances in organic electrolyte with relatively larger ion size than that of inorganic electrolyte were steeply decreased up to 5 days and then continuously kept, with increase of ball-mill times. 3. From harsh decrease of capacitance in 1 M Et4NBF4/PC, we found out that the inter-particle pores selectively removed by ball-milling play an important role for EDLC in organic electrolyte. 6

7 212/11/13 Specific capacitances of ball-milled M-3 series Capacitance vs. defined surfaces In inorganic electrolyte (.5 M H2SO4) F/m Capacitance (F/m 2 ) In organic electrolyte (1 M Et4NBF4/PC) F/m2 Capacitance (F/m 2 ) Capacitance Structural or its derived factors SEM images of HOPG surface by mechanical polishing Surface chemistry PCNF Surface area & pore structure Surface state edge and basal Electrical conductivity Functional groups Hetero atoms on the surface Metal or metal oxide on the surface PCNF Capacitive performance : Edge surface > Basal plane Edge surface is more effective than basal plane by a factor of 3-5. N o n - p o la riz a tio n Well-defined CNF series P C N F 5 F / g.. HCNF HCNF H C N F 1. The capacitances of M-3 in.5 M H2SO4 were largely decreased with increase of ball-mill times because both of inter- and intra-particle pores were simultaneously decreased by ball-milling. 2. The capacitances of M-3 with smaller micrographitic units which are easily destroyed by severe ballmilling for 2 days, comparing with Maxsorb-III, were dramatically decreased in both of organic and inorganic electrolytes. Edge Basal TCNF TCNF T C N F E / V ( v s. A g / A g C l ) S.-H. Yoon et al. Carbon, 25, 43, 1828 T.G. Kim et al. Langmuir, 26, 22, 986 Surface-modified PCNF series Electrochemical oxidation by treatment PCNF GPCNF-NA axis GPCNF 5 nm Graphitic edge Dome-like basal plane GPCNF-EC Cyclic voltammogram of GPCNF series PCNF GPCNF -2 GPCNF-NA GPCNF-EC E / V (vs. Ag/AgCl) Elemental analysis of GPCNF series (1) In anode ( electrode), treated samples by different potentials Results of elemental analysis (%) Ratio of O/C H C N O (diff.) as-prepared V V V V (2) In cathode (- electrode), treated samples by different potentials Recovered graphitic edge Recovered graphitic edge Samples Elemental analysis (wt%) H C N O (diff.) PCNF GPCNF GPCNF-NA GPCNF-EC Results of elemental analysis (%) Ratio of O/C H C N O (diff.) as-prepared V V V V

8 212/11/13 Functional Groups vs. capacitance Polarized anodic HCNF by binderless polarization condition in 3 wt% H2SO4 Polarized HCNF under binderless condition in 3 wt% H 2 SO 4 Current (ma) Anode ( electrode) Potential (V) Reduced HCNF Polarized HCNF at 1. V Polarized HCNF at 1.5 V Polarized HCNF at 2. V Polarized HCNF at 2.5 V Current (ma) * According to increase of the potential, Cathode (- electrode) Potential (V) Reduced HCNF Polarized HCNF at 1. V Polarized HCNF at 1.5 V Polarized HCNF at 2. V Polarized HCNF at 2.5 V in anode, EDLC and pseudocapacitane increased. in cathode, capacitance decreased slightly. 29 Analysis of ion behaviors on the Different carbon surface using solid NMR 31 Solid-state NMR Preparation of PCNFs with edge and basal planes Organic electrolyte:et 4 NBF 4 Cation Anion JEOL ECA4 Tetra ethyl ammonium: TEA Tetra fluoroborate: TFB Kinetic diam.:.74 nm Kinetic diam.:.49 nm 11 B solid-state NMR ( 11 B:128.3 MHz) Anion behaviors in positive electrode at 3 kinds of electrode states 1 Impregnated state 2 Charged state 3 Discharged state 31 8

9 212/11/13 BF - 4 ion behaviors on the surface of GPCNFs ( 11 B-NMR NMR) GPCNF シリーズに対する BF - 4 イオンの吸着挙動モデル GPCNF (Basal) GPCNF-NA-H (Edge) More Deshielded!!! GPCNF Adsorbed BF 4 - GPCNF-NA-H Adsorbed BF 4 - Charged (at positive electrode) Free BF 4 - Free BF 4 - Impregnated Et 4 NBF 4 /PC More deshielded ACF vs. 19 F Solid NMR N (Organic) OG-5A OG-15A Free electrolyte Free electrolyte Adsorbed electrolyte ACF vs. 2 H Solid NMR (Inorganic) Free electrolyte OG-5A OG-15A Free electrolyte Adsorbed electrolyte CM CM PTFE as binder Et 4NBF 4/PC Et 4NBF 4/PC D 2SO 4 D 2SO FE-1 FE-3 More de-shielded than OG-15A FE-1 FE-3 Somewhat broadened than FE-1 CM CM Et 4NBF 4/PC Et 4NBF 4/PC D 2SO 4 D 2SO

10 212/11/13 ACF vs. 2 H Solid NMR (T 1 value) OG5A T1 (sec) of OG series OG15A CM CM Free Adsorbed Free Adsorbed Free Adsorbed Free Adsorbed FE1 T1 (sec) of FE series FE3 CM CM Free Adsorbed Free Adsorbed Free Adsorbed Free Adsorbed Small value of T1 means stronger adsorption 2. T1 goes to be short after charge. 3. T1 of FE series < T1 of OG series T1 (sec) T1 (sec) OG5A CM CM FE1 Free Adsorbed OG15A Free Adsorbed FE3 CM CM Steam activation vs. KOH activation Table BET surface area, elemental composition, and capacitance of ACs Activation method Surface Atomic ratios (%) Electrode Capacitance Code (Temp., KOH/S- area density H C N O Ash BEAPS ratio) (m 2 /g) (g/cm 3 ) F/cm 3 F/m 2 K1 KOH (8,, 2) S1 Steam (8 ) K2 KOH (6,, 6) S2 Steam (85 ) Adsorption amount of N (cm 2 3 /g) Fig. N 2 adsorption and desorption isotherms at 77 K of ACs :K1 :S Relative pressure, P/P Adsorption amount of N (cm 2 3 /g) :K2 :S Relative pressure, P/P Intensity Intensity 11 B solid-state NMR Impregnated Sharp peak K1 S1 Broad peak Chemical shift, δ (ppm) K2 S Chemical shift, δ (ppm) Intensity Intensity K1 S Chemical shift, δ (ppm) K2 S2 Charged Chemical shift, δ (ppm) A peak was adjusted at ppm. Sharp peak (A peak): on the free surface, weakly adsorbed Broad peak (B peak): on the pore wall, strongly adsorbed Intensity Intensity K1 S1 Discharged Chemical shift, δ (ppm) K2 S Chemical shift, δ (ppm) 39 Relaxation time, T1 Sharp peaks (A peaks) Broad peaks (B peaks) Relaxation time, T 1 Relaxation time, T 1 (sec) (sec) Impregnated, Charged, Discharged K1 S1 K2 S2 Impregnated Charged Discharged K1 S1 K2 S2 Fig. 5 Longitudinal relaxation time (T ( 1 ) of at various states 4 4 1

11 212/11/13 Discussion Effect of pore wall structure (Edge and Basal) Chemical shift Capacitance Ring current effect Edge Basal 41 Difference of KOH & steam activat In the case of low surface area ACs (K1 and S1), The activat were not much proceeded for both KOH and steam activat. Small and homogeneous pores. 42 Deshielding Lower MF In the case of high surface area ACs (K2 and S2), The activat were fully proceeded for both KOH and steam activat. Large and heterogeneous pores. KOH showed the more dispersion property than steam, resulted in many edges. Shielding Higher MF High capacitance Low capacitance T. Kim et al., Langmuir (26), 22(22), KOH activation Steam activation Ion adsorbed on the edge Low MF shift, High capacitance K2 (KOH activated) has more edge walls. Ion adsorbed on the basal High MF shift, Low capacitance S2 (steam activated) has less edges in pore walls. Result of experiment 1 44 Difference of KOH and steam activat 7 6 Quantitative analyses of ion behaviors on the different activated carbons using solid NMR absorbed volume [cc/g] Sample Relative pressure [P/P ] BET S.A. [m 2 /g] SK2 SH2 Atomic ratios[%] H C N O ash Electrode density [g/ml] SK Capacitance F/ml SH ratios (SK/SH) Electrolyte:Et4NBF4/PC SK SH

12 212/11/13 Results of experimental 1 45 Results of experiment M Et4NBF4/PC electrolyte, 19F-NMR 1 M Et4NBF4/PC electrolyte, 19F-NMR a A b B σ[ppm] Free or adsorbed ion on the external surface Adsorbed on the pore walls PTFE main peak による BF4- normallization Peak area ratio PTFE Peaks ch-dis SK/SH Main Peak SK2 imp SK2 ch SK2 dis SH2 imp SH2 ch SH2 dis σ[ppm] Relaxation time (T 1)[s] Sample a A b B SK2 ch SK2 dis SK2 imp SH2 ch SH2 dis SH2 imp