ELECTROLYTE CONTAINING IODITE

The invention refers to a high-energy electrochemical capacitor in mixed salt aqueous electrolyte. Technical field

Electrochemical capacitors, also known as supercapacitors, are characterized by their excellent cyclability and fast charge/discharge, giving high power in short periods of time, making them in particular an interesting choice for powering hybrid and electric vehicles. However, in general, they display lower energy density as compared to other commercially available energy storage devices, e.g. accumulators. Taking into account the equation E = ½ CU ² , the energy E stored in a capacitor highly depends on capacitance C and voltage U, the latter being controlled by the stability window of the electrolyte.

Commercially available electrochemical capacitors based on two activated carbon (AC) electrodes generally operate in organic electrolytes, e.g. TEABF ₄ in acetonitrile or propylene carbonate, and exhibit a high stability window, up to 2.7-2.8 V. However, due to the relatively high cost, environmentally unfriendly character and lower conductance (mainly due to lower dissociation) of organic electrolytes, alternative solutions, such as aqueous electrolytes, are highly desirable. Conventional aqueous electrolytes usually used in electrochemical power sources, like acids (H ₂ S0 ₄ ) and alkalis (KOH), display higher conductivity (up to ~1 S cm ^"1 ) and higher capacitance C values than organic electrolytes. However, their restricted stability window, about 0.7-0.8 V, and highly corrosive nature are a hindrance for their industrial viability.

Background art

EP2323146 discloses a water-based electrolyte for an electric double-layer capacitor comprising: a salt having a cation and an anion, wherein the cation is Li ⁺ , Na ⁺ , or K ⁺ , and the anion is CI ^" , S0 ₄ ^2" , P0 ₄ ^3" or N0 ₃ ^" ; and a second component having a cation and an anion, wherein the cation is Li ⁺ , Na ⁺ , or K ⁺ , and the anion is OH ^" .

The international publication WO2012126499 presents a supercapacitor with aqueous electrolyte comprising i.a. Li ₂ S0 ₄ , Na ₂ S0 ₄ , K ₂ S0 ₄ , Cs ₂ S0 ₄ , LiN0 ₃ , NaN0 ₃ and KN0 ₃ . In this document, as well as in M. Bichat, E. Raymundo-Pinero, F. Beguin, "High voltage supercapacitor built with seaweed carbons in neutral aqueous electrolyte", Carbon 48 (2010) 4351-4361 and L. Demarconnay, E. Raymundo-Pinero, F. Beguin, "A symmetric carbon/carbon supercapacitor operating at 1.6 V by using a neutral aqueous solution", Electrochem. Comm., 12 (2010) 1275-1278, it has been demonstrated that AC/ AC capacitors based on salt aqueous electrolytes exhibit excellent cyclability under galvanostatic charge/discharge up to 1.6 V.

In the publications Q. Gao, L. Demarconnay, E. Raymundo-Pinero, F. Beguin, "Exploring the large voltage range of carbon/carbon supercapacitors in aqueous lithium sulfate electrolyte", Energy & Environ. Set, 5 (2012) 9611-9617, K. Fic, G. Lota, M. Meller, E. Frackowiak, "Novel insight into neutral medium as electrolyte for high-voltage supercapacitors", Energy & Environ. Sci., 5 (2012) 5842-5850, as well as in Polish patent PL215699 (Application No. P.392742), it has been disclosed that even higher values, up to around 2 V, can be reached with AC/ AC capacitors using aqueous Li ₂ S0 ₄ . In all cases, such high voltage values are achievable owing to the high over-potential for di-hydrogen evolution at the negative electrode. It has to be mentioned that the research work carried out so far in activated carbon-based capacitors utilized gold current collectors in order to get rid of possible corrosive effects related with the use of the aqueous electrolytes.

Although L1 ₂ SO ₄ seems to be the electrolyte of choice for future AC/AC capacitor applications, due to its environment friendly character, large stability window and high solubility (up to 2.7 mol L ^"1 ), further optimization of salt aqueous electrolytes seems essential in order to realize economically viable electrochemical capacitors with enhanced performance.

As the need to provide a cheap and efficient capacitor delivering high power and energy still exists, the object of the invention is to provide a low-cost, low-toxicity and high-safety capacitor with a long-cycle life, having energy and power density comparable to organic electrolyte systems.

Disclosure of the invention

The invention provides an electrochemical capacitor comprising two electrodes made of high surface area carbon, placed in aqueous electrolyte, wherein one of the components of the mixed aqueous electrolyte is an iodide (T) containing salt in the concentration between 0.1 mol L ^"1 and 2 mol L ^"1 and another component is a sulphate (S0 ₄ ^2" ) anion salt with a cation selected among Li , Na , K , Rb , Cs , NH ₄ , Be , Mg , Ba , and Al or a nitrate (NO3 ^" ) anion salt with a cation selected among Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , NH ₄ ⁺ , Be ²⁺ , Mg ²⁺ ,

Ca , Sr , Ba , and Al , in the concentration from 0.1 mol L ^" up to 10 mol L ^" or up to 0.2 mol L ^"1 below the solubility limit. The high surface area carbon material of electrodes is preferably selected from activated carbon (AC), nanotubes, graphene, nanocones, carbon onions, carbon aerogels, or composites made from these materials, carbon cloth, carbon monolith, the most preferably activated carbon (AC).

Moreover, it is advisable that each electrode comprises a current collector, preferably from stainless steel or titanium or nickel and its alloys.

The electrochemical capacitor according to the invention in one of its preferred embodiments uses the aqueous electrolyte comprising potassium iodide (KI) and lithium sulfate (Li ₂ S0 ₄ ) _; preferably in the concentrations of 0.5 mol L ^"1 KI and 1 mol L ^"1 Li ₂ S0 _4. Alternatively, in another preferred embodiment the capacitor of the invention has the aqueous electrolyte comprising potassium iodide (KI) and sodium nitrate (NaN0 ₃ ), preferably in the concentrations of 0.5 mol L ^"1 KI and 1 mol L ^"1 NaN0 ₃ .

The capacitor of the invention exhibits a capacitance exceeding 250 F g ^"1 polarized up to 1.6 V with cycle stability over 10 000 cycles. The capacitor preferably exhibits a capacitance over 350 F g ^"1 . All values referring to mass, expressed as g ^"1 or kg ^"1 in the whole text mean per average mass of carbon material in one electrode.

The capacitor exhibits energy density over 25 Wh kg ^"1 , preferably over 30 Wh kg ^"1 of carbon material.

The further subject of the invention is the capacitor defined above connected to at least one accumulator or fuel cell or engine or an electric circuit or the grid.

The subject of the invention is also the use of the water based electrochemical capacitor defined above to accumulate electrical energy with a density over 30 Wh kg ^"1 of carbon material.

The capacitor of the invention can be used for energy storage and delivery in cars, buses, rail vehicles, emergency doors and evacuation slides in airplanes, UPS, transformer stations, cranes, elevators, wind farms and solar farms, etc.

The invention is based on the observation that the pseudocapacitance originating from Faradaic redox reactions at the electrode/electrolyte interface in AC-based capacitors greatly improves the capacitance. For example, in Electrochem. Commun. 11 (2009) 87 and in Polish Patent PL215046 (Application No. P.386352) it has been demonstrated that AC-based capacitors containing 1 mol L ^"1 potassium iodide (KI) exhibit higher capacitance values than with other salt electrolytes when operating up to 0.8 V.

No AC-based capacitor containing potassium iodide (KI) has been reported so far to be polarizable beyond 1 V. In this patent application, we propose to combine the advantages of sulfate or nitrate-based salts to enhance the voltage (owing to over-potential for di- hydrogen evolution) and iodide-based salts to enhance the capacitance (owing to pseudo- capacitance originating from redox reactions at the carbon/iodine interface), in order to get energy density values of AC/AC capacitors in the same range as industrial AC/AC capacitors in an organic electrolyte using the same type of carbon material for electrodes. Although in S. Senthilkumar, R. Selvan, Y. Lee, J. Melo, J. Mater. Chem. Al (2013) 1086- 1095 a mixed electrolyte combining Na ₂ S0 ₄ (1 mol L ^"1 ) and KI (0.08 mol L ^"1 ) has been disclosed, the system was never applied for polarization over 1 V to give high energy density values.

In our invention, mixed electrolytes which utilize the enlarged stability window of salt aqueous electrolytes based on sulfate or nitrate salts, and enhanced capacitance originating due to the 2I7I ₂ redox couple, have been used to develop AC/ AC symmetric capacitors capable of operating up to 1.6 V with optional current collectors made up of stainless steel or titanium or nickel and its alloys. Additionally, among the salts, both L1 ₂ SO ₄ and NaN0 ₃ are capable of giving highly concentrated aqueous solutions of up to 2.7 mol L ^"1 and 10 mol-L ^"1 , respectively, which are very favorable for low-temperature range. Moreover, as mentioned before, these electrolytes allow attaining energy density comparable to the one achieved in organic medium with the same electrode material.

Description of drawings

Non-limiting examples of the invention are described with reference to the accompanying drawings, wherein:

Figs. 1-8 refer to Example 1, in particular:

Fig. 1 presents cyclic voltammograms at 2 mV s ^"1 of an AC/ AC capacitor in 1 mol L ^"1 L1 ₂ SO ₄ + O.5 mol L ^"1 Kl up to 1.6 V,

Fig. 2 presents cyclic voltammograms at 2 mV s ^"1 of AC/ AC capacitors containing 1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol L ^"1 KI (full black) and 1 mol L ^"1 Li ₂ S0 ₄ (dashed black) up to (a) 0.8 V and (b) 1.6 V,

Fig. 3 illustrates the galvanostatic charge/discharge of an AC/ AC capacitor in 1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol-L ^"1 KI up to 1.6 V at various current loads (a) and up to various voltages at 0.2 A- g ^"1 (b),

Fig. 4 illustrates the discharge (0.2 A-g ^'1 ) capacitance and efficiency of AC/AC capacitors containing 1 mol -L ^"1 Li ₂ SC>4 + 0.5 mol-L ^"1 KI (full black) and 1 mol-L ^"1 Li ₂ SC>4 (dashed black) up to 1.6 V, Fig. 5 shows the potential extrema of each electrode evaluated from galvanostatic charge/discharge at 0.2 A-g ^"1 up to different voltage values (a) and cyclic voltammograms obtained at 2 mV s ^"1 within the determined potential limits (b) in a two-electrode AC/ AC cell containing 1 mol L ^"1 Li ₂ S0 ₄ + 0.5 mol L ^"1 KI and equipped with a reference electrode, Fig. 6 presents (a) Nyquist plots realized from electrochemical impedance spectroscopy in the frequency range between 1 mHz and 100 kHz and (b) capacitance values per mass of one electrode versus frequency from impedance data for an AC/ AC capacitor containing 1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol-L ^"1 KI,

Fig. 7 presents capacitance and resistance of AC/ AC capacitors containing 1 mol L ^"1 Li ₂ S0 ₄ + 0.5 mol L ^"1 KI (A) and 1 mol L ^"1 Li ₂ S0 ₄ (·) evaluated from galvanostatic

(1 A.g ^"1 ) discharge realized after successive two-hours floating periods at 1.6 V,

Fig. 8. illustrates Ragone plots comparing the performance of AC/ AC capacitors with

1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol L ^"1 KI (A), 1 mol L ^"1 Li ₂ S0 ₄ (·) and 1 mol L ^"1 TEABF ₄ in acetonitrile (■).

Figs. 9-15 refer to Example 2, in particular:

Fig. 9 presents cyclic voltammograms at 2 mV s ^"1 of an AC/ AC capacitor in 1 mol-L ^"1

NaNO ₃ + 0.5 mol-L ^"1 KI up to 1.6 V,

Fig. 10 presents cyclic voltammograms at 2 mV s ^"1 of AC/ AC capacitors containing 1 mol-L ^"1 NaN0 ₃ + 0.5 mol-L ^"1 KI (full black) and 1 mol-L ^"1 NaN0 ₃ (dashed black) up to a) 0.8 V and b) 1.6 V,

Fig. 11 illustrates the galvanostatic charge/discharge of an AC/ AC capacitor in 1 mol-L ^"1 NaN0 ₃ + 0.5 mol-L ^"1 KI up to 1.6 V at various current loads (a) and up to various voltages at 0.2 A.g ^"1 (b),

Fig. 12 illustrates the discharge (0.2 A g ^"1 ) capacitance and efficiency of AC/AC capacitors containing 1 mol-L ^"1 NaN0 ₃ + 0.5 mol -L ^"1 KI (full black) and 1 mol-L ^"1 NaN0 ₃ (dashed black) up to 1.6 V,

Fig. 13 shows the potential extrema of each electrode evaluated from galvanostatic charge/discharge at 0.2 A g ^"1 up to different voltage values (a) and cyclic voltammograms obtained at 2 mV s ^"1 within the determined potential limits (b) in a two-electrode AC/ AC cell containing 1 mol-L ^"1 NaN0 ₃ + 0.5 mol -L ^"1 KI and equipped with a reference electrode, Fig. 14 presents capacitance and resistance of AC/ AC capacitors containing 1 mol -L ^"1 NaN0 ₃ + 0.5 mol-L ^"1 KI (A) and 1 mol-L ^"1 NaN0 ₃ (·) evaluated from galvanostatic (1 A g ^"1 ) discharge realized after successive two-hours floating periods at 1.6 V, Fig. 15 illustrates Ragone plots comparing the performance of AC/ AC symmetric capacitors with 1 mol L^ NaNOs + 0.5 mol L^ KI (A), 1 mol L^ NaNOs (·) and 1 mol L ^"1 TEABF ₄ in acetonitrile (■).

Examples

Non-limiting examples of the present invention are described below Example 1

The electrochemical capacitor consisting of two electrodes made of activated carbon (AC) and an electrolytic mixture of 1 mol L ^"1 L1 ₂ SO ₄ and 0.5 mol L ^"1 potassium iodide (KI). The electrochemical capacitor electrodes were made of a composite consisting of 80 wt.% KOH activated carbon with BET specific surface area 2180 m ² g ^_1 , 10 wt.% polytetrafluoroethylene (PTFE) and 10 wt.% carbon black having good electrical conductivity. The electrodes in the form of pellets with a diameter of 10 mm, a weight of around 8-10 mg and a thickness of around 0.2-0.3 mm were pressed at 5 ton-cm ^"2 in a hydraulic press for 2 minutes. The pellets, after drying under vacuum at 110°C for 3 hours, were cooled down to room temperature and weighed.

Thus prepared two identical electrodes were separated with a porous glass fiber separator, and placed in a teflon vessel between two current collectors of stainless steel type 316L. The vessel was filled with a mixture containing 1 mol L ^"1 L1 ₂ SO ₄ + 0.5 mol L ^"1 potassium iodide (KI), and sealed.

The electrical conductivity of the 1 mol L ^"1 L1 ₂ SO ₄ + 0.5 mol L ^"1 KI electrolyte mixture was 94 mS cm ^"1 and pH = 6.3. The values of capacitance, efficiency and operating life were measured by cyclic voltammetry, galvanostatic charge/discharge and floating at constant voltage, and compared with those obtained in 1 mol L ^"1 Li ₂ S0 ₄ electrolyte. For the mixed salt aqueous electrolyte (1 mol L ^"1 Li ₂ S0 ₄ + 0.5 mol L ^"1 KI), a capacitance value of 366 F g ^"1 was measured using galvanostatic (0.2 A g ^"1 ) charge/discharge up to 1.6 V. By contrast, a capacitance value of 215 F g ^"1 was obtained in 1 mol L ^"1 L1 ₂ SO ₄ using galvanostatic (0.2 A g ^"1 ) charge/discharge up to 1.6 V. Further, capacitance and resistance were measured after successive two-hour periods of floating. Floating means keeping the cells for a certain time at a certain voltage, in this case, two hours at a voltage of 1.6 V at room temperature. A total of 60 floating periods (each for two hours) was used and each was interspersed by five galvanostatic charge/discharge cycles made to estimate the capacitance and resistance of the system from the 5 ^th discharge. In 1 mol L ^"1 Li ₂ S0 ₄ , used as a reference electrolyte during floating, the resistance increased from 1.52 Ω to 2.78 Ω, while the capacitance decreased from 188 F g ^"1 to 129 F g ^"1 . The increase in resistance could be due to corrosion products formed on the positive current collector, which perturb the electrical contact between the activated carbon electrode and the current collector made from stainless steel. By contrast, in the mixture of 1 mol L ^"1 L1 ₂ SO ₄ + 0.5 mol L ^"1 KI, the resistance is lower than in the solution without KI, and remains constant at around 1.2 Ω for 120 hours of floating. During 120 hours of floating at 1.6 V in the mixture of 1 mol L ^"1 L1 ₂ SO ₄ + 0.5 mol L ^"1 KI, capacitance values between 310-320 F g ^"1 were obtained with no decay in capacitance over the entire period of floating.

Measurements conditions of Example 1 :

Supercapacitors body:

• Two-electrode cell, optionally with reference (teflon vessel)

• Current collectors: Stainless steel (316L)

• Separator: glass microfiber, thickness: 260μιη, pore size: Ι .όμιη

• Reference electrode: Ag wire

Electrolytes: aqueous solutions

1 mol L ^"1 L1 ₂ SO ₄ + 0.5 mol L ^"1 KI mixed electrolyte or

1 mol-L ^"1 L1 ₂ SO ₄

Characterization techniques:

The cyclic voltammetry measurements (CV) were performed in the voltage range from 0 to 1.6 V with a sweep rate of 2 mV s ^"1 for both two-electrode and two-electrode with reference electrode measurements.

The galvanostatic measurements were performed with specific current values between 0.2 A g ^"1 and 4.0 A g ^"1 _.

Impedance measurements were conducted over a frequency range of 1 mHz to 100 kHz. All measurements were realized at 25°C.

Figs. 1-8 of drawings present the measurements obtained in the electrochemical capacitor described in Example 1.

Example 2

The electrochemical capacitor consisting of two electrodes made of activated carbon (AC), with an electrolytic mixture of 1 mol-L ^"1 NaN0 ₃ and 0.5 mol-L ^"1 potassium iodide (KI).

The electrochemical capacitor electrodes were made of a composite consisting of 80 wt.% KOH activated carbon with BET specific surface area 2180 m ² g ^_1 , 10 wt.% polytetrafluoroethylene (PTFE) and 10 wt.% carbon black having good electrical conductivity. The electrodes in the form of pellets with a diameter of 10 mm and a weight of around 8-10 mg and a thickness of around 0.2-0.3 mm were pressed at 5 ton-cm ^"2 in a hydraulic press for 2 minutes. The pellets after drying under vacuum at 110°C for 3 hours were cooled down to room temperature and weighed.

Thus prepared two identical electrodes were separated with a porous glass fiber separator, and placed in a teflon vessel between two current collectors of stainless steel type 316L. The vessel was filled with a mixture containing 1 mol L ^"1 NaN0 ₃ + 0.5 mol L ^"1 KI, and sealed.

The electrical conductivity of the 1 mol L ^"1 NaN0 ₃ + 0.5 mol L ^"1 KI mixture was 105 mS cm ^"1 and pH = 6.5. The values of capacitance, efficiency and operating life were measured by cyclic voltammetry, galvanostatic charge/discharge and floating, and compared with those obtained in 1 mol L ^"1 NaN0 ₃ . For the mixed salt aqueous electrolyte (1 mol L ^"1 NaN0 ₃ + 0.5 mol L^ KI), a capacitance value of 378 F g ^"1 was measured using galvanostatic (0.2 A g ^"1 ) charge/discharge up to 1.6 V. By contrast, in 1 mol L ^"1 NaN0 ₃ , a capacitance value of only 159 F'g ^"1 was obtained using galvanostatic (0.2 A g ^"1 ) charge/discharge up to 1.6 V. Further, capacitance and resistance were measured after successive two-hour periods of floating, as defined in Example 1. A total of 60 (each for two hours) floating periods was used and each was interspersed by five galvanostatic charge/discharge cycles made to estimate the capacitance and resistance of the system from the 5 ^th discharge. In 1 mol L ^"1 NaN0 ₃ , used as a reference electrolyte during floating, the resistance increased from 1.29 Ω to 2.57 Ω, while the capacitance decreased from 111 F g ^"1 to 80 F'g ^"1 . The increase in resistance could be due to corrosion products formed on the positive current collector, which perturb the electrical contact between the activated carbon electrode and the current collector made from stainless steel. By contrast, in the mixture of 1 mol L ^"1 NaN0 ₃ + 0.5 mol L ^"1 KI, an initial increase in resistance from 1.38 Ω to 2.05 Ω was observed during the first 15 hours of floating; then the resistance remains almost constant at around 2.1 Ω until the end of floating. Upon floating at 1.6 V in the 1 mol L ^"1 NaN0 ₃ + 0.5 mol L ^"1 KI mixture, the capacitance values increase from 304 F'g ^"1 to 364 F'g ^"1 during the first 30 hours, and then they decrease to reach 227 F g ^"1 after 120 hours of floating.

Measurements conditions of Example 2

Supercapacitors body:

• Two-electrode cell, optionally with reference (teflon vessel)

• Current collectors: Stainless steel (316L)

• Separator: glass microfiber, thickness: 260μπι, pore size: 1.6μπι • Reference electrode: Ag wire

Electrolytes: Aqueous solutions

1 mol-L ^"1 NaN0 ₃ + 0.5 mol L ^"1 KI mixed electrolyte or

1 mol-L ^"1 NaN0 ₃

Characterization techniques:

The cyclic voltammetry measurements (CV) were performed in the voltage range from 0 to 1.6 V with a sweep rate of 2 mV s ^"1 for both two-electrode and two-electrode with reference electrode measurements.

The galvanostatic measurements were performed with specific current values between 0.2 A g ^"1 and 4.0 A g ^"1 .

All measurements were realized at 25°C.

Figs. 9-15 of drawings present the measurements obtained in the electrochemical capacitor described in the Example 2.

The presented figures of drawings provide a report that contains capacitance, efficiency, resistance, electrodes potential range, charge propagation, energy and power density of capacitors realized by using 1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol-L ^"1 KI and 1 mol-L ^"1 NaN0 ₃ + 0.5 mol -L ^"1 KI mixed electrolytes and electrodes made of KOH activated carbon with pores of size ranging from 0.6 to 2.5 nm and with an average micropore size L ₀ = 1.55 nm. As presented on Fig. 1, 2, 4 and Fig. 9, 10, 12, they exhibit remarkable capacitance values of 366 F-g ^'1 and 378 F g ^"1 up to 1.6 V, respectively.

Aging tests under floating conditions show that the mixed electrolytes display excellent performance for a long period of time without losing efficiency. The capacitors realized by using mixed salt electrolytes and stainless steel current collectors exhibit energy density values of 30 Wh kg ^"1 and 34 Wh kg ^"1 for 1 mol-L ^"1 Li ₂ S0 ₄ + 0.5 mol-L ^"1 KI and 1 mol-L ^"1 NaN0 ₃ + 0.5 mol-L ^"1 KI, respectively, making them economically viable energy storage devices.

References

1. F. Beguin, E. Frackowiak, Supercapacitors: Materials, Systems and Applications, Ch. 2, Wiley- VCH, Weinheim, 2013, pp. 71-73.

2. B.E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and

Technological Applications, Kluwer Academic, New York, 1999, p. 549.

3. R. Kotz, M. Carl en, Principles and applications of electrochemical capacitors, Electrochim. Acta, 45 (2000) 2483-2498. 4. EP2323146 "Water-based electrolyte for electric double layer capacitor and electric double layer capacitor having the same" Taiwan Textile Research Institute

5. WO2012126499 "Electrochemical Capacitor" Francois Beguin (FR); Laurent Demarconnay (FR); Encarnacion Raymundo-Pinero (FR).

6. M. Bichat, E. Raymundo- Pinero, F. Beguin, High voltage supercapacitor built with seaweed carbons in neutral aqueous electrolyte, Carbon 48 (2010) 4351-4361. 7. L. Demarconnay, E. Raymundo-Pinero, F. Beguin, A symmetric carbon/carbon supercapacitor operating at 1.6 V by using a neutral aqueous solution, Electrochem. Comm., 12 (2010) 1275-1278.

8. Q. Gao, L. Demarconnay, E. Raymundo-Pinero, F. Beguin, Exploring the large voltage range of carbon/carbon supercapacitors in aqueous lithium sulfate electrolyte, Energy & Environ. Sci., 5 (2012) 9611-9617.

9. K. Fic, G. Lota, M. Meller, E. Frackowiak, Novel insight into neutral medium as electrolyte for high-voltage supercapacitors, Energy & Environ. Sci., 5 (2012) 5842-5850.

10. Wysokonapie iowy kondensator elektrochemiczny - High voltage electrochemical capacitor (2010) PL215699 (Appl. No P-392742) (E. Frackowiak, K. Fic, G. Lota)

11. E. Frackowiak, Q. Abbas, F. Beguin, Carbon/carbon supercapacitors, J. Energy Chem., 22 (2013) 226-240.

12. G. Lota, E. Frackowiak, Electrochem. Commun. 11 (2009) 87.

13. G. Lota, K. Fic, E. Frackowiak, Electrochem. Commun. 12 (2011) 38-41.

14. Kondensator elektrochemiczny pracuja y w roztworze jodku - Carbon electrode of the supercapacitor in the iodine solutions (2008) PL215046 (Appl. No P 386352) (E. Frackowiak, G. Lota, J. R. Miller)

15. E. Frackowiak, G. Lota, K. Fic, M. Meller, ChemSusChem 5 (2012) 1181-1185.

16. S. Senthilkumar, R. Selvan, Y. Lee, J. Melo, J. Mater. Chem. A 1 (2013) 1086-