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Alar Jänes
Institute of Chemistry, University of Tartu, Tartu, Estonia

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Original paper
Published: 28 August 2021 in Journal of Solid State Electrochemistry
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Asymmetrical Zn thin foil|carbon cloth two-electrode cells based on 1 M Zn(ClO4)2 aqueous solution have been tested using cyclic voltammetry, constant current charge/discharge, and electrochemical impedance methods. The Ragone plots have been calculated from constant power measurements data. Very high gravimetric and volumetric energy densities at moderate gravimetric and volumetric power densities have been calculated, nearly 2–3 times higher than those for the best sol–gel method prepared two carbon electrode single cells. It was found that even at high power density (10 kW kg−1), the energy density values are comparable with the results for best CDC and sol–gel methods prepared carbon materials based supercapacitors. It has been observed that studied asymmetrical two-electrode cells demonstrated higher energy densities (~ 70 W h kg−1) than the ionic liquid based symmetrical cells what show energy density up to 47 W h kg−1 and capacitance ~ 120 F g−1. However, the power densities and relaxation times for Zn(ClO4)2 aqueous electrolyte based supercapacitors still need to be increased and decreased, respectively, to meet the needs of very quick short pulses high power energy storage applications.

ACS Style

Jaanus Eskusson; Thomas Thomberg; Tavo Romann; Karmen Lust; Enn Lust; Alar Jänes. Zn(ClO4)2 aqueous solution–based Zn thin foil|carbon cloth two-electrode single-cell characteristics. Journal of Solid State Electrochemistry 2021, 1 -12.

AMA Style

Jaanus Eskusson, Thomas Thomberg, Tavo Romann, Karmen Lust, Enn Lust, Alar Jänes. Zn(ClO4)2 aqueous solution–based Zn thin foil|carbon cloth two-electrode single-cell characteristics. Journal of Solid State Electrochemistry. 2021; ():1-12.

Chicago/Turabian Style

Jaanus Eskusson; Thomas Thomberg; Tavo Romann; Karmen Lust; Enn Lust; Alar Jänes. 2021. "Zn(ClO4)2 aqueous solution–based Zn thin foil|carbon cloth two-electrode single-cell characteristics." Journal of Solid State Electrochemistry , no. : 1-12.

Journal article
Published: 01 July 2021 in Journal of The Electrochemical Society
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In this work we have studied the effect of 1 M bis(trifluoromethanesulfonyl)imide metallic salts in acetonitrile (1 M MeTFSI, where Me = Li, Na, K, Cs or Mg) as an electrolyte for electrochemical capacitors (ECs), using computational quantum mechanical modelling, Raman analysis, cyclic voltammetry, electrochemical impedance spectroscopy and constant power methods. Also, the ionic conductivities of 1 M MeTFSI in AN have been measured and discussed. The ECs based on the 1 M KTFSI in AN electrolyte deliver the higher power density and energy density compared to other MeTFSI based electrolytes and showing excellent characteristics applicable in high energy and power EC devices.

ACS Style

T. Romann; J. Eskusson; T. Thomberg; E. Lust; A. Jänes. Bis(trifluoromethanesulfonyl)imide Metallic Salts Based Electrolytes for Electrochemical Capacitor Application: Theoretical vs Experimental Performance. Journal of The Electrochemical Society 2021, 168, 070528 .

AMA Style

T. Romann, J. Eskusson, T. Thomberg, E. Lust, A. Jänes. Bis(trifluoromethanesulfonyl)imide Metallic Salts Based Electrolytes for Electrochemical Capacitor Application: Theoretical vs Experimental Performance. Journal of The Electrochemical Society. 2021; 168 (7):070528.

Chicago/Turabian Style

T. Romann; J. Eskusson; T. Thomberg; E. Lust; A. Jänes. 2021. "Bis(trifluoromethanesulfonyl)imide Metallic Salts Based Electrolytes for Electrochemical Capacitor Application: Theoretical vs Experimental Performance." Journal of The Electrochemical Society 168, no. 7: 070528.

Journal article
Published: 20 March 2021 in C
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Quick characterization methods to determine the structure of carbon materials are sought after for a wide array of technical applications. In this study we present the combined analysis of the structure of carbide-derived carbons (CDCs) with Raman spectroscopy and wide-angle X-ray scattering (WAXS) methods. We present the optimal deconvolution method to be used for the detailed analysis of Raman spectroscopy data of CDCs and comparison to corresponding WAXS results is made. For a broad set of CDCs both WAXS and Raman spectroscopy data showed that the average graphene layer extent increases with synthesis temperature of CDC, while the coherent domain lengths obtained from Raman spectroscopy higher by an average of 4.4 nm. In addition, the presence of correlations between the parameters (D-band width and the parameter A ∑D/A ∑G) from Raman spectroscopy and the synthesis temperature are established. Based on the WAXS and Raman spectra data analysis the strong influence of the precursor carbide structure on the graphitization pathway is shown.

ACS Style

Riinu Härmas; Rasmus Palm; Heisi Kurig; Laura Puusepp; Torben Pfaff; Tavo Romann; Jaan Aruväli; Indrek Tallo; Thomas Thomberg; Alar Jänes; Enn Lust. Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis. C 2021, 7, 29 .

AMA Style

Riinu Härmas, Rasmus Palm, Heisi Kurig, Laura Puusepp, Torben Pfaff, Tavo Romann, Jaan Aruväli, Indrek Tallo, Thomas Thomberg, Alar Jänes, Enn Lust. Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis. C. 2021; 7 (1):29.

Chicago/Turabian Style

Riinu Härmas; Rasmus Palm; Heisi Kurig; Laura Puusepp; Torben Pfaff; Tavo Romann; Jaan Aruväli; Indrek Tallo; Thomas Thomberg; Alar Jänes; Enn Lust. 2021. "Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis." C 7, no. 1: 29.

Journal article
Published: 09 September 2020 in Journal of Energy Storage
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Development of high efficiency energy storage systems is increasingly important as these systems enable utilize energy from renewable sources and reduce greenhouse gas evolution caused by fuel combustion technologies in the same time. Electricity storage in the supercapacitor containing neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid or mixture of ionic liquids (EMImBF4 with addition of 5 wt% 1-ethyl-3-methylimidazolium iodide (EMImI)) has been studied in the two- and three-electrode systems using high porosity carbon electrode material with specific surface area of 2090 m2 g-1, micropore surface area of 2060 m2 g-1 and total pore volume of 1.085 cm3 g-1. Based on electrochemical characterization data (cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power discharge), the asymmetrical capacitor with ionic liquid mixture of 5 wt% EMImI in EMImBF4 shows increase in cell capacitance 5 F g-1 and specific energy about 3.5 W h kg-1 as well as in specific power, compared with the data for symmetrical capacitor system based on neat EMImBF4. However, electrochemical stability, i.e. the potential region of ideal polarizability for the ionic liquid mixture based capacitor is lower and therefore the coulombic and energy efficiencies calculated are also smaller.

ACS Style

T. Thomberg; E. Lust; Alar Jänes. Iodide ion containing ionic liquid mixture based asymmetrical capacitor performance. Journal of Energy Storage 2020, 32, 101845 .

AMA Style

T. Thomberg, E. Lust, Alar Jänes. Iodide ion containing ionic liquid mixture based asymmetrical capacitor performance. Journal of Energy Storage. 2020; 32 ():101845.

Chicago/Turabian Style

T. Thomberg; E. Lust; Alar Jänes. 2020. "Iodide ion containing ionic liquid mixture based asymmetrical capacitor performance." Journal of Energy Storage 32, no. : 101845.

Paper
Published: 27 May 2020 in RSC Advances
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A synthesis method has been developed to turn peat, cheap biomass into hard carbons that demonstrate high capacity and excellent sodium storage capability as anode material in sodium-ion batteries.

ACS Style

Anu Adamson; Ronald Väli; Maarja Paalo; Jaan Aruväli; Miriam Koppel; Rasmus Palm; Eneli Härk; Jaak Nerut; Tavo Romann; Enn Lust; Alar Jänes. Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries. RSC Advances 2020, 10, 20145 -20154.

AMA Style

Anu Adamson, Ronald Väli, Maarja Paalo, Jaan Aruväli, Miriam Koppel, Rasmus Palm, Eneli Härk, Jaak Nerut, Tavo Romann, Enn Lust, Alar Jänes. Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries. RSC Advances. 2020; 10 (34):20145-20154.

Chicago/Turabian Style

Anu Adamson; Ronald Väli; Maarja Paalo; Jaan Aruväli; Miriam Koppel; Rasmus Palm; Eneli Härk; Jaak Nerut; Tavo Romann; Enn Lust; Alar Jänes. 2020. "Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries." RSC Advances 10, no. 34: 20145-20154.

Journal article
Published: 05 May 2020 in Journal of The Electrochemical Society
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Various carbon materials have been synthesized applying hydrothermal carbonization process and subsequent ZnCl2 activation step using different mass ratios of activating reagent. The resulting powder materials were characterized physically and electrochemically in a two-electrode cell configuration using 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid. Activated materials porosity was highly dependent on the activation conditions i.e. on the ratio of ZnCl2 used in the activation process. The best material having Brunauer–Emmett–Teller specific surface area S BET = 2320 m2 g−1, micropore surface area S micro = 1510 m2 g−1 and total pore volume V tot = 1.01 cm3 g−1 where the highest amount of ZnCl2 was used for the synthesis of carbon material. High specific parallel capacitance (140 F g−1), a wide region of ideal polarizability (ΔV ≤ 3.0 V), short characteristic relaxation time (2.12 s), and high energy density (48 W h kg−1) values have been established for material with the highest porosity showing great potential for these supercapacitor systems to be used in practical application as energy storage devices.

ACS Style

Meelis Härmas; Thomas Thomberg; Alar Jänes. Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid. Journal of The Electrochemical Society 2020, 167, 080533 .

AMA Style

Meelis Härmas, Thomas Thomberg, Alar Jänes. Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid. Journal of The Electrochemical Society. 2020; 167 (8):080533.

Chicago/Turabian Style

Meelis Härmas; Thomas Thomberg; Alar Jänes. 2020. "Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid." Journal of The Electrochemical Society 167, no. 8: 080533.

Research article
Published: 09 November 2019 in Journal of Applied Electrochemistry
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Different micro–mesoporous carbons derived from d-glucose (GDC), granulated white sugar (WSDC) and highly decomposed Estonian peat (PDC) were synthesized using hydrothermal carbonization and direct activation methods. The resulting carbonaceous materials were activated using chemical (KOH and ZnCl2) and physical (CO2) activation methods. The electrochemical characteristics of the electrical double-layer capacitors (EDLCs) based on 1 M Et3MeNBF4 solution in acetonitrile and EtMeImBF4 were measured using two-electrode cells. The EDLCs assembled had specific capacitances from 20 up to 158 ± 18 F g−1 (in EtMeImBF4) and phase angle values from − 65° to − 88° (at low frequencies). The characteristic time constant values vary more than 10 times. Applying constant power discharge method, very high energy and power densities (34 W h kg−1 at 10 kW kg−1) for activated carbon powders-based EDLCs have been measured. Fitting of impedance data showed that enhanced mesoporosity reduces the adsorption and mass-transfer resistance values.

ACS Style

M. Härmas; Rasmus Palm; T. Thomberg; R. Härmas; M. Koppel; M. Paalo; I. Tallo; T. Romann; Alar Jänes; E. Lust. Hydrothermal and peat-derived carbons as electrode materials for high-efficient electrical double-layer capacitors. Journal of Applied Electrochemistry 2019, 50, 15 -32.

AMA Style

M. Härmas, Rasmus Palm, T. Thomberg, R. Härmas, M. Koppel, M. Paalo, I. Tallo, T. Romann, Alar Jänes, E. Lust. Hydrothermal and peat-derived carbons as electrode materials for high-efficient electrical double-layer capacitors. Journal of Applied Electrochemistry. 2019; 50 (1):15-32.

Chicago/Turabian Style

M. Härmas; Rasmus Palm; T. Thomberg; R. Härmas; M. Koppel; M. Paalo; I. Tallo; T. Romann; Alar Jänes; E. Lust. 2019. "Hydrothermal and peat-derived carbons as electrode materials for high-efficient electrical double-layer capacitors." Journal of Applied Electrochemistry 50, no. 1: 15-32.

Journal article
Published: 23 August 2019 in Journal of The Electrochemical Society
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The electrical double layer capacitors (EDLC) based on hierarchical micro-mesoporous sol-gel TiC derived carbon (SgTiC-CDC) electrodes and 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeImBF4) and 1M Et3MeNBF4 + acetonitrile (AN) as the electrolytes were tested to establish the electrochemical characteristics and region of ideal polarizability. The precursors for the micro-mesoporous carbon electrodes were synthesized via modified sol-gel synthesis process. Compared to traditional titanium carbide derived carbons, where precursor carbide is commercially available, the sol-gel TiC derived hierarchical carbon materials exhibit larger specific density functional theory (DFT) surface areas (up to 1700 m2 g−1) and an unique pore size distribution with more mesopores between 2 and 10 nm. The electrochemical properties of the EDLCs were investigated using the cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power discharge methods. The EDLCs demonstrated nearly ideal capacitive behavior even at very high charging/discharging currents (10 A g−1) and cell potential scan rates (500 mV s−1). The EDLCs completed from SgTiC-CDC materials and EtMeImBF4 and Et3MeNBF4 + AN show good energy efficiencies (varying from 93% to 95% at current 1 A g−1) and coulombic efficiency values exceeded 99%. Thus, the EDLCs completed are very promising devices for extremely high power/energy density applications.

ACS Style

M. Paalo; I. Tallo; T. Thomberg; A. Jänes; E. Lust. Enhanced Power Performance of Highly Mesoporous Sol-Gel TiC Derived Carbons in Ionic Liquid and Non-Aqueous Electrolyte Based Capacitors. Journal of The Electrochemical Society 2019, 166, A2887 -A2895.

AMA Style

M. Paalo, I. Tallo, T. Thomberg, A. Jänes, E. Lust. Enhanced Power Performance of Highly Mesoporous Sol-Gel TiC Derived Carbons in Ionic Liquid and Non-Aqueous Electrolyte Based Capacitors. Journal of The Electrochemical Society. 2019; 166 (13):A2887-A2895.

Chicago/Turabian Style

M. Paalo; I. Tallo; T. Thomberg; A. Jänes; E. Lust. 2019. "Enhanced Power Performance of Highly Mesoporous Sol-Gel TiC Derived Carbons in Ionic Liquid and Non-Aqueous Electrolyte Based Capacitors." Journal of The Electrochemical Society 166, no. 13: A2887-A2895.

Journal article
Published: 02 August 2019 in Batteries
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Cost-effective methods need to be developed to lower the price of Na-ion battery (NIB) materials. This paper reports a proof-of-concept study of using a novel approach to the glycine-nitrate process (GNP) to synthesize sodium vanadium phosphate (Na3V2(PO4)3 or NVP) materials with both high-energy (102 mAh g−1 at C/20) and high-power characteristics (60 mAh g−1 at 20 C). Glucose-derived hard carbons (GDHCs) were optimized to reduce both sloping and irreversible capacity. The best results were achieved for electrodes with active material heat treated at 1400 °C and reduced Super P additive. Sloping region capacity 90 mAh g−1, irreversible capacity 47 mAh g−1, discharge capacity 272 mAh g−1 (of which plateau 155 mAh g−1) and 1st cycle coulombic efficiency (CE) 85% were demonstrated. GDHC||NVP full cell achieved 80 mAh g−1 (reversible) by NVP mass out of which 60 mAh g−1 was the plateau (3.4 V) region capacity. Full cell specific energy and energy density reached 189 Wh kg−1 and 104 Wh dm−3, respectively. After 80 cycles, including rate testing from C/20 to 10 C, the cell cycled at 65 mAh g−1 with 99.7% CE. With further optimization, this method can have very high industrial potential.

ACS Style

Ronald Väli; Jaan Aruväli; Meelis Härmas; Alar Jänes; Enn Lust. Glycine-Nitrate Process for Synthesis of Na3V2(PO4)3 Cathode Material and Optimization of Glucose-Derived Hard Carbon Anode Material for Characterization in Full Cells. Batteries 2019, 5, 56 .

AMA Style

Ronald Väli, Jaan Aruväli, Meelis Härmas, Alar Jänes, Enn Lust. Glycine-Nitrate Process for Synthesis of Na3V2(PO4)3 Cathode Material and Optimization of Glucose-Derived Hard Carbon Anode Material for Characterization in Full Cells. Batteries. 2019; 5 (3):56.

Chicago/Turabian Style

Ronald Väli; Jaan Aruväli; Meelis Härmas; Alar Jänes; Enn Lust. 2019. "Glycine-Nitrate Process for Synthesis of Na3V2(PO4)3 Cathode Material and Optimization of Glucose-Derived Hard Carbon Anode Material for Characterization in Full Cells." Batteries 5, no. 3: 56.

Journal article
Published: 07 May 2019 in Journal of The Electrochemical Society
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EDLCs based on micro-mesoporous carbon electrodes prepared from steam and CO2-steam co-activated SiC-CDCs and room-temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate as an electrolyte were tested to establish the electrochemical power and energy densities and region of ideal polarizability. Cyclic voltammetry, constant current charge/discharge (CC/CD), electrochemical impedance spectroscopy (EIS) and constant power discharging methods have been applied to establish the electrochemical characteristics of EDLCs completed. The highest capacitance value of 162 F g−1 at 3.6 V has been established by EIS for the SiC-CDC material, which was activated with steam at 1000°C and cleaned with molecular H2. The capacitance values for other materials prepared using the steam activation process at different temperatures were only slightly lower. The calculated coulombic efficiency values from constant current discharge/charge data for all the systems remained within the range from 97.0 to 98.5% and from 99.3 to 100% at current densities 0.1 A g−1 and 1 A g−1, respectively. The coulombic efficiencies calculated from integrated cyclic voltammetry plots varied from 97 to 98 and from 99 to 100% at potential scan rates 5 and 50 mV s−1, respectively, showing that the steam activated SiC-CDC materials are very promising for various high energy density storage/generation applications.

ACS Style

E. Tee; I. Tallo; E. Lust; A. Jänes; T. Thomberg. Electrical Double Layer Capacitors Based on Steam and CO2-Steam Co-Activated Carbon Electrodes and Ionic Liquid Electrolyte. Journal of The Electrochemical Society 2019, 166, A1558 -A1567.

AMA Style

E. Tee, I. Tallo, E. Lust, A. Jänes, T. Thomberg. Electrical Double Layer Capacitors Based on Steam and CO2-Steam Co-Activated Carbon Electrodes and Ionic Liquid Electrolyte. Journal of The Electrochemical Society. 2019; 166 (8):A1558-A1567.

Chicago/Turabian Style

E. Tee; I. Tallo; E. Lust; A. Jänes; T. Thomberg. 2019. "Electrical Double Layer Capacitors Based on Steam and CO2-Steam Co-Activated Carbon Electrodes and Ionic Liquid Electrolyte." Journal of The Electrochemical Society 166, no. 8: A1558-A1567.

Journal article
Published: 21 January 2019 in The European Physical Journal E
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The search for efficient energy storage devices has recently led to the introduction of a fluid electrode material employing electrochemical flow capacitors (EFC). Unlike the classical solid electrode film containing capacitors, where the electrode material is fixed to the current collectors and capacitance is therefore limited with an active surface area of porous electrode, the flow electrodes offer new design opportunities which enable fully continuous charging/discharging processes as well as easily scalable systems. Here we describe the successful incorporation of the carboxymethyl cellulose sodium salt (CMC-Na) assisted carbonaceous suspension electrode in aqueous media for the electrochemical flow capacitor concept and demonstrate the electrochemical charge storage in flowable electrodes using a cation conductive membrane as separator in a double-pipe flow-electrode module. Experimental results were combined with computer simulations (FEM) to specify limiting processes EFC charging. The flow-electrode slurry is based on 0.1 M Na2SO4, 3 wt% CMC-Na and activated carbon powder suspended in water. During continuous operation of the system, the capacitance of the flow electrode reached to 0.3 F/L providing the energy and current densities of 7 mWh/kg and 56 mW/L, respectively. Additionally, we report a 70% round trip efficiency calculated during charging and discharging of the cell between 0 V and +0.75 V, while applying the current density of 1.6 mA/kg. The double-pipe flow-electrode module is easily expandable for transportation of large volumes of electrode material.

ACS Style

Janno Torop; Faiza Summer; Vahur Zadin; Tuomas Koiranen; Alar Jänes; Enn Lust; Alvo Aabloo. Low concentrated carbonaceous suspensions assisted with carboxymethyl cellulose as electrode for electrochemical flow capacitor. The European Physical Journal E 2019, 42, 8 .

AMA Style

Janno Torop, Faiza Summer, Vahur Zadin, Tuomas Koiranen, Alar Jänes, Enn Lust, Alvo Aabloo. Low concentrated carbonaceous suspensions assisted with carboxymethyl cellulose as electrode for electrochemical flow capacitor. The European Physical Journal E. 2019; 42 (1):8.

Chicago/Turabian Style

Janno Torop; Faiza Summer; Vahur Zadin; Tuomas Koiranen; Alar Jänes; Enn Lust; Alvo Aabloo. 2019. "Low concentrated carbonaceous suspensions assisted with carboxymethyl cellulose as electrode for electrochemical flow capacitor." The European Physical Journal E 42, no. 1: 8.

Journal article
Published: 13 December 2018 in Journal of The Electrochemical Society
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The electrochemical behavior of 2- and 3-electrode systems has been tested in potassium salts based (in particular KPF6) different non-aqueous electrolytes. For comparison LiPF6 and NaPF6 based electrolytes were investigated. Quantum chemical calculations showed that K+ cation has high solvation energy compared to Li+ and Na+ cations, which explains somewhat lower solubility in PC. However, most solvent molecules are removed from K+ solvation shell when it enters the pores of porous carbon as experimentally even higher capacitances than for Na+ and Li+ based salts were found. The capacitance values calculated from the slopes of charge (CC) and discharge (CD) curves shows that the decrease in CD value from 1st cycle to 5000th was 23.6% for 0.8 M KPF6 in PC being similar to Li+ and Na+ cation based electrolytes. The studied EDLC systems demonstrated good coulombic efficiency as the ratio of capacitances CD/CC remained >0.99 even after 5000 discharge/charge cycles. The energy and power densities per electrode, dependent on the cation solvation energy have been calculated and discussed.

ACS Style

T. Thomberg; R. Väli; J. Eskusson; T. Romann; A. Jänes. Potassium Salts Based Non-Aqueous Electrolytes for Electrical Double Layer Capacitors: A Comparison with LiPF6and NaPF6Based Electrolytes. Journal of The Electrochemical Society 2018, 165, A3862 -A3870.

AMA Style

T. Thomberg, R. Väli, J. Eskusson, T. Romann, A. Jänes. Potassium Salts Based Non-Aqueous Electrolytes for Electrical Double Layer Capacitors: A Comparison with LiPF6and NaPF6Based Electrolytes. Journal of The Electrochemical Society. 2018; 165 (16):A3862-A3870.

Chicago/Turabian Style

T. Thomberg; R. Väli; J. Eskusson; T. Romann; A. Jänes. 2018. "Potassium Salts Based Non-Aqueous Electrolytes for Electrical Double Layer Capacitors: A Comparison with LiPF6and NaPF6Based Electrolytes." Journal of The Electrochemical Society 165, no. 16: A3862-A3870.

Journal article
Published: 15 September 2018 in Journal of Power Sources
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Electrochemical behaviour of titanium carbide-derived carbon (TiC-CDC) electrodes in 1 M (C2H5)3CH3NBF4 + acetonitrile electrolyte has been studied using cyclic voltammetry, constant current charge-discharge, impedance and constant power methods. After step by step cell potential widening and repetitive cell potential cyclization up to 3.4 V, surface passivation, i.e. decrease of faradic reaction currents at potentials higher than 3.4 V, has been detected. Based on Raman spectroscopy data, the passivation effect has been explained by repetitive oxidation-reduction of more active carbon sites from the surface of TiC-CDC and exposition of the more stable graphitic regions. After very careful electrode surface passivation/modification, the region of ideal polarizability can be widened up to 3.7 V and nearly ideal capacitive behaviour with phase angle more negative than −88° and stable series capacitance (∼120 F g−1) have been obtained. Very high experimental energy densities (30 Wh kg−1) at power densities 40 kW kg−1 (ΔE ≥ 3.4 V) have been measured, comparable even with the sol-gel TiC-CDC/(acetonitrile + (C2H5)3CH3NBF4) two-electrode electrical double layer capacitor system. Much higher energy and power values have been achieved at ΔE = 3.7 V, being the maximal cell potential limit, where nearly ideal polarizability for few hundred cycles was achieved.

ACS Style

M. Pohl; I. Tallo; A. Jänes; T. Romann; E. Lust. Increasing the stability of very high potential electrical double layer capacitors by operando passivation. Journal of Power Sources 2018, 402, 53 -61.

AMA Style

M. Pohl, I. Tallo, A. Jänes, T. Romann, E. Lust. Increasing the stability of very high potential electrical double layer capacitors by operando passivation. Journal of Power Sources. 2018; 402 ():53-61.

Chicago/Turabian Style

M. Pohl; I. Tallo; A. Jänes; T. Romann; E. Lust. 2018. "Increasing the stability of very high potential electrical double layer capacitors by operando passivation." Journal of Power Sources 402, no. : 53-61.

Journal article
Published: 01 September 2018 in Electrochimica Acta
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Influence of specific surface area (SDFT), total pore volume (Vtot) and other porosity characteristics on the electrochemical parameters and power density of two electrode electric double layer capacitors based on 1 M 3-ethyl-methylammonium tetrafluoroborate (Et3MeNBF4) solution in acetonitrile and on 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeImBF4) has been analysed. The pore size distribution data calculated from nitrogen, CO2 and Ar adsorption isotherms using mainly Carbon 2D non-local density functional theory for heterogeneous surface (2D-NLDFT-HS) model have been compared with crystallographic characteristics obtained by Raman, X-ray diffraction, photoelectron spectroscopy, etc. methods. It was shown that, chemical composition and crystallographic structure of precursor material, synthesis and activation conditions have decisive influence on the shape (spherical, cylindrical or slit-shape pores) and hierarchical porous structure and electrical conductivity of the carbon materials. Noticeable increase in series and parallel capacitances from 50 to 138 F g−1 in 1 M Et3MeNBF4 and up to 155 F g−1 in EtMeImBF4, gravimetric power density (up to 35 kW kg−1) and volumetric power density (up to 25 kW dm−3, both at discharge time 3.6 s in 1 M Et3MeNBF4 + AN electrolyte) for optimised EDLC has been demonstrated. For EtMeImBF4 based cells lower gravimetric (25 kW kg−1) and volumetric (10 kW dm−3) power densities have been achieved. For completing the EDLCs with high power and energy densities, highly micro-and mesoporous materials with optimum specific surface area (1200–1500 m2 g−1) but maximum (meso) pore volume (Vtot > 1.5 cm3 g−1) should be applied. Only for optimized EDLCs the very short characteristic charging/discharging times (lower than 0.3 s in Et3MeNBF4 + AN and 1.0 s in EtMeImBF4) can be achieved.

ACS Style

R. Härmas; R. Palm; M. Härmas; M. Pohl; H. Kurig; I. Tallo; E. Tee; I. Vaas; R. Väli; T. Romann; O. Oll; R. Kanarbik; K. Liivand; J. Eskusson; J. Kruusma; T. Thomberg; A. Jänes; P. Miidla; E. Lust. Influence of porosity parameters and electrolyte chemical composition on the power densities of non-aqueous and ionic liquid based supercapacitors. Electrochimica Acta 2018, 283, 931 -948.

AMA Style

R. Härmas, R. Palm, M. Härmas, M. Pohl, H. Kurig, I. Tallo, E. Tee, I. Vaas, R. Väli, T. Romann, O. Oll, R. Kanarbik, K. Liivand, J. Eskusson, J. Kruusma, T. Thomberg, A. Jänes, P. Miidla, E. Lust. Influence of porosity parameters and electrolyte chemical composition on the power densities of non-aqueous and ionic liquid based supercapacitors. Electrochimica Acta. 2018; 283 ():931-948.

Chicago/Turabian Style

R. Härmas; R. Palm; M. Härmas; M. Pohl; H. Kurig; I. Tallo; E. Tee; I. Vaas; R. Väli; T. Romann; O. Oll; R. Kanarbik; K. Liivand; J. Eskusson; J. Kruusma; T. Thomberg; A. Jänes; P. Miidla; E. Lust. 2018. "Influence of porosity parameters and electrolyte chemical composition on the power densities of non-aqueous and ionic liquid based supercapacitors." Electrochimica Acta 283, no. : 931-948.

Journal article
Published: 18 July 2018 in Journal of The Electrochemical Society
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Different mico-mesoporous silicon carbide-derived carbons (SiC-CDC) were synthesized via gas phase chlorination at 1100°C and thereafter activated at 900°C and 1000°C with H2O steam using Ar and CO2 as the carrier gases. The physical characterization data show that these materials are mainly amorphous, the structure does not change remarkably during the activation process and the surface chemistry of the differently activated and treated materials remains the same and there are no functional groups at the SiC-CDC surface. N2, Ar and CO2 sorption measurements indicate an increase in the specific surface area and pore size distribution with increasing the activation temperature, whereas the influence of the carrier gas during synthesis is minimal. Although the specific surface areas and pore size distributions differed, the electrochemical parameters in 1 M (C2H5)3CH3NBF4 acetonitrile solution for all SiC-CDC materials were similar - specific gravimetric capacitances 130 ± 18 F g−1 and volumetric capacitance 67 ± 14 F cm−3 were calculated. Absolute phase angle values from −85° to −88° at low frequencies and very high energy and power densities 22 Wh kg−1 at 20 kW kg−1 and 12 Wh dm−3 at 10 kW dm−3 have been achieved.

ACS Style

Ester Tee; Indrek Tallo; Thomas Thomberg; Alar Jänes; Enn Lust. Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors. Journal of The Electrochemical Society 2018, 165, A2357 -A2364.

AMA Style

Ester Tee, Indrek Tallo, Thomas Thomberg, Alar Jänes, Enn Lust. Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors. Journal of The Electrochemical Society. 2018; 165 (10):A2357-A2364.

Chicago/Turabian Style

Ester Tee; Indrek Tallo; Thomas Thomberg; Alar Jänes; Enn Lust. 2018. "Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors." Journal of The Electrochemical Society 165, no. 10: A2357-A2364.

Journal article
Published: 01 May 2018 in Joule
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Almost all practical composite battery electrodes experience volume changes during cycling, deteriorating their cycling performance. A new key element that the EQCM-D methodology introduces into the energy storage field is a general platform for quantification of high-frequency viscoelastic characteristics of high-strain composite electrodes correlated with their low-frequency resilience and toughness moduli. Fast relaxation ensures effective high-strain accommodation by softened binder in aprotic solution. In contrast, with excessively stiff binder in aqueous solution, the strong electrode/binder interactions tracked dynamically reflect the initial and advanced stages of the mechanical degradation of the polymeric binder up to its complete destruction. The discovered correlation between the fracture toughness of the binder and its high-frequency viscoelastic behavior will serve for a rational design of extremely strained composite alloy-type electrodes such as the Li-Si anode. The high phase-transformation strain developed upon intercalation in the host particles of a composite battery electrode affects the polymeric binder network mechanically, deteriorating the electrode cycling performance. Here, electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) is used to demonstrate a new strain-accommodation mechanism, in high-strain NaFePO4/PVdF electrodes, via relaxation of the binder network surrounding the intercalation particles. Complete mechanical degradation of the polymer network occurs during long-term cycling of NaFePO4 electrodes in aqueous solutions (hard and tough behavior). In contrast, in aprotic solutions, a softened binder easily accommodates the high transformation strain, ensuring excellent electrode cycling performance (soft and tough behavior). Quantification of the high-frequency viscoelastic properties of an operating composite electrode linked to the binder's fracture toughness ensures fast and facile screening of the optimal polymeric binder/electrolyte solution combinations. This methodology should be extremely important for optimization of cycling performance of Li-Si anodes undergoing huge volume changes during cycling.

ACS Style

Netanel Shpigel; Sergey Sigalov; Mikhael D. Levi; Tyler Mathis; Leonid Daikhin; Alar Jänes; Enn Lust; Yury Gogotsi; Doron Aurbach. In Situ Acoustic Diagnostics of Particle-Binder Interactions in Battery Electrodes. Joule 2018, 2, 988 -1003.

AMA Style

Netanel Shpigel, Sergey Sigalov, Mikhael D. Levi, Tyler Mathis, Leonid Daikhin, Alar Jänes, Enn Lust, Yury Gogotsi, Doron Aurbach. In Situ Acoustic Diagnostics of Particle-Binder Interactions in Battery Electrodes. Joule. 2018; 2 (5):988-1003.

Chicago/Turabian Style

Netanel Shpigel; Sergey Sigalov; Mikhael D. Levi; Tyler Mathis; Leonid Daikhin; Alar Jänes; Enn Lust; Yury Gogotsi; Doron Aurbach. 2018. "In Situ Acoustic Diagnostics of Particle-Binder Interactions in Battery Electrodes." Joule 2, no. 5: 988-1003.

Journal article
Published: 01 November 2017 in Electrochimica Acta
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ACS Style

Ronald Väli; Alar Jänes; T. Thomberg; E. Lust. Synthesis and characterization of d-glucose derived nanospheric hard carbon negative electrodes for lithium- and sodium-ion batteries. Electrochimica Acta 2017, 253, 536 -544.

AMA Style

Ronald Väli, Alar Jänes, T. Thomberg, E. Lust. Synthesis and characterization of d-glucose derived nanospheric hard carbon negative electrodes for lithium- and sodium-ion batteries. Electrochimica Acta. 2017; 253 ():536-544.

Chicago/Turabian Style

Ronald Väli; Alar Jänes; T. Thomberg; E. Lust. 2017. "Synthesis and characterization of d-glucose derived nanospheric hard carbon negative electrodes for lithium- and sodium-ion batteries." Electrochimica Acta 253, no. : 536-544.

Journal article
Published: 01 July 2017 in Chemical Engineering Journal
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ACS Style

Maarja Pohl; Heisi Kurig; Indrek Tallo; Alar Jänes; Enn Lust. Novel sol-gel synthesis route of carbide-derived carbon composites for very high power density supercapacitors. Chemical Engineering Journal 2017, 320, 576 -587.

AMA Style

Maarja Pohl, Heisi Kurig, Indrek Tallo, Alar Jänes, Enn Lust. Novel sol-gel synthesis route of carbide-derived carbon composites for very high power density supercapacitors. Chemical Engineering Journal. 2017; 320 ():576-587.

Chicago/Turabian Style

Maarja Pohl; Heisi Kurig; Indrek Tallo; Alar Jänes; Enn Lust. 2017. "Novel sol-gel synthesis route of carbide-derived carbon composites for very high power density supercapacitors." Chemical Engineering Journal 320, no. : 576-587.

Journal article
Published: 14 April 2017 in Journal of The Electrochemical Society
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In this study, we report the results of electrochemical impedance spectroscopy data modelling of various battery half-cells with different alkali metal (Li, Na, K) salts. Test results of electrochemical half-cells were evaluated for the D-glucose derived hard carbon negative electrode in 1.0 M LiPF6 + EC:DMC (1:1 volume ratio), 1.0 M NaPF6 + EC:DMC (1:1), 1.0 M NaClO4 + PC, 0.8 M KPF6 + EC:DEC (1:1) and 0.8 M KPF6 + EC:DMC (1:1) solutions at 0.5 mV s−1 potential scan rate measured within the potential region from 0.05 V to 1.2 V (vs Me/Me+) (where Me is Li, Na or K). Modelling of electrochemical impedance spectroscopy data was employed to characterize alkali metal insertion processes in/on D-glucose derived hard carbon anode. Detailed analysis of impedance data shows that Newman equivalent circuit modified with a constant phase element can be applied for calculation of impedance spectra and fitting of calculated data to experimental ones, using non-linear least square root fitting method. Equivalent circuit fit parameters depend strongly on electrolyte composition. Very slow processes have been observed for KPF6 + EC:DEC based half-cell. Comparatively quick metal-cation reduction and accumulation processes have been observed in NaClO4 + PC and LiPF6 +EC:DMC based half-cell anodes.

ACS Style

R. Väli; A. Jänes; E. Lust. Alkali-Metal Insertion Processes on Nanospheric Hard Carbon Electrodes: An Electrochemical Impedance Spectroscopy Study. Journal of The Electrochemical Society 2017, 164, E3429 -E3437.

AMA Style

R. Väli, A. Jänes, E. Lust. Alkali-Metal Insertion Processes on Nanospheric Hard Carbon Electrodes: An Electrochemical Impedance Spectroscopy Study. Journal of The Electrochemical Society. 2017; 164 (11):E3429-E3437.

Chicago/Turabian Style

R. Väli; A. Jänes; E. Lust. 2017. "Alkali-Metal Insertion Processes on Nanospheric Hard Carbon Electrodes: An Electrochemical Impedance Spectroscopy Study." Journal of The Electrochemical Society 164, no. 11: E3429-E3437.

Journal article
Published: 28 September 2016 in Journal of The Electrochemical Society
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Graphene nanoplatelets have been used for synthesis of Fe3O4-graphene nanocomposite negative electrode. A high-resolution transmission electron microscopy measurements of the graphene areas surrounded by Fe3O4 nanoparticles show that the graphene has folded on itself and the edges have some amounts of waviness which could indicate existence of amorphous carbon. A high energy density hybrid capacitors (HC) have been completed based on 1 M Li2SO4, Na2SO4, Rb2SO4, Cs2SO4 and MgSO4 aqueous electrolytes and Fe3O4-graphene nanocomposite/few-layer graphene electrode materials. The optimal working potential region of each electrode has been regulated by optimized mass balance of the electrodes. After optimization the cell voltage increased up to 1.4 V and an energy density (maximal) up to 9.4 Wh kg−1 in 1 M Cs2SO4 electrolyte. The maximal power density 41.1 kW kg−1 has been calculated for 1 M Rb2SO4 aqueous electrolyte based HC. The energy and power density of completed HC cells decreased with solvation Gibbs energy of the cations. The cycling efficiency values have been calculated being highest for 1 M Rb2SO4 and 1 M Cs2SO4 electrolyte based systems, 98.4% and 99.9%, respectively. Thus, promising HC cells based on Fe3O4-graphene nanocomposite/few-layer graphene electrodes in different aqueous electrolytes have been developed and characterized.

ACS Style

J. Eskusson; Protima Rauwel; Jaak Nerut; Alar Jänes. A Hybrid Capacitor Based on Fe3O4-Graphene Nanocomposite/Few-Layer Graphene in Different Aqueous Electrolytes. Journal of The Electrochemical Society 2016, 163, A2768 -A2775.

AMA Style

J. Eskusson, Protima Rauwel, Jaak Nerut, Alar Jänes. A Hybrid Capacitor Based on Fe3O4-Graphene Nanocomposite/Few-Layer Graphene in Different Aqueous Electrolytes. Journal of The Electrochemical Society. 2016; 163 (13):A2768-A2775.

Chicago/Turabian Style

J. Eskusson; Protima Rauwel; Jaak Nerut; Alar Jänes. 2016. "A Hybrid Capacitor Based on Fe3O4-Graphene Nanocomposite/Few-Layer Graphene in Different Aqueous Electrolytes." Journal of The Electrochemical Society 163, no. 13: A2768-A2775.