Dedicated to mark the centenary of Acad. Evgeni Budevski's birth

Sofia Electrochemical Days
SED’22

11-14 May 2022, Sofia, Bulgaria

 

Book of Abstracts

 

A Study of Carbon Xerogel Additive on the Performance of Negative Electrode Lead Battery

A. Aleksandrova, M. Matrakova, A. Stoyanova, S. Veleva, L. Soserov, N. Rey-Raap, A. Arenillas

Carbon xerogels have been widely used as electrode materials and additives in electrochemical energy sources, supercapacitors, fuel cells and batteries.
The aim of the present study is to investigate the application of carbon xerogels (CX) as additive to Negative Active Mass (NAM) of lead batteries. Additions of different types of carbon materials to NAM have a pronounced beneficial effect on dynamic charge acceptance and cycle life of lead
batteries negative plates.
The impact of selected additive of carbon xerogels on the electrochemical behavior of the negative plate was investigated in the small-size laboratory lead-acid cell with one negative and two positive plates with nominal capacity of 115 mAh. For comparison control cell without carbon product and reference cell with commercially available carbon product PBX®51 (Cabot Corp., USA were tested. The concentration of the studied carbon samples in NAM was 0.5 % PBX®51 and 0.25% CX, respectively. The impact of the studied carbon additives on the discharge capacity of negative plates was estimated at C/20 discharge current rate. The effect of PBX®51 or CX addition in the negative plate on cycle life of lead-acid cells has been evaluated under simulated high-rate partial state-of-charge (HRPSoC) duty. The phase composition, microstructure and morphology of the carbonaceous materials were investigated by X-ray diffraction analysis, surface area measurements (BET method) and scanning electron microscopy.
The control cell – without carbon additive delivers only 600 micro-cycles. In contrast the reference cell with 0.5% PBX®51 in NAM completes about 3000 micro-cycles, while cell with 0.25 % CX in NAM endures about 1000 micro-cycles.
 

Effect of Ionic Liquids on the Supercapacitor Performances

B. Karamanova, A. Stoyanova, A. Arenilas, N. Ray

The accumulation and storage of energy is an area that successfully combines leading technology for the production of nanomaterials and electrolytes with innovative engineering solutions. Electrochemical capacitor is one of the most promising energy-storage devices that can successfully meet the demands of high-power supply and long cycle life.
Ionic liquids are becoming more common as electrolytes in supercapacitors and they provide a good solution for improving the properties of these systems. They are of intensive research interest due to a number of its unique properties, such as non-volatile, electrochemical and heat-resistant, suitable mechanical stability, flame retardant, etc.
The aim of this work is to investigate the applicability of some ionic liquids for use in supercapacitor systems, based on activated carbon YP-50F and carbon xerogel AX-GO. The combination of porosity with high electrical conductivity makes these carbon materials a good candidate for use as an active mass in symmetric supercapacitor systems.
Two ionic liquids have been selected: 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMITCB). Utilizing them, two- and threeelectrode supercapacitor cells were assembled and tested using electrochemical methods such as galvanostatic charge / discharge curves, long-term tests and CV curves at different potential limits and at different speeds.
The AX-GO carbon xerogel shows higher and stable capacitive characteristics compared to the YP-50F in the selected ionic liquids. Despite the lower specific surface of AX-GO, the presence of narrow mesopores seems to contributes to its better electrochemical parameters in the studied electrolytes. It was found that the difference in the properties of the ionic liquids used have a significant impact on the electrochemical characteristics of symmetric supercapacitors.

 

Supercapacitors Based on Activated Carbon Xerogel and Manganese Dioxide
Operating in Neutral Electrolyte

L. Soserov, B. Karamanova, S. Veleva, A. Arenilas, N. Ray, F. Lufrano, A. Stoyanova

The use of alkali sulfates as electrolytes in supercapacitors eliminates the known limitations related to corrosion in aqueous electrolytes, but also it provides an opportunity to obtain high energy density, simultaneously being more eco-friendly and cost effective and safe [1].
In present work, the electrochemical characteristics of symmetric and hybrid supercapacitors based on synthesized manganese dioxide and activated xerogel (AX 6.5, pH = 6.5) were studied. In order to obtain a material with desired specific properties, the synthesis of activated carbon was carried out using microwave radiation where adjusting the pH, dilution ratio and resorcinol/formaldehyde (R/F) molar ratio. The cells are assembled in configuration using two electrodes without current collectors. Exchange AquavionTM commercial membrane with superior cation conductivity, chemical and thermal stability of up to 230 ⁰C, is used as a separator and electrolyte.
The structure, morphology and porous texture properties of electrodes materials are analyzed respectively by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopes (TEM), and low-temperature nitrogen adsorption techniques. The electrochemical performances of the electrodes are determined by cyclic voltammetry, galvanostatic charge/discharge as well as long-term tests.
The obtained results are encouraging and demonstrates a stable cycling performance of the studied MnO₂/AX cell.

[1] Gao, Q., Journal of Energy Chemistry 38 (2019) 219-224

 

Preparation of Manganese Oxides as Electrode Materials in Energy Storage Systems

B. Mladenova, V. Ilcheva, A. Stoyanova, S. Diankov, K. Pashova

Manganese dioxide has been of great interest as a reliable electrode material in many different types of energy storage systems, such as alkaline batteries, lithium-ion batteries and supercapacitors. Its higher electrochemical theoretical capacity (1370 Fg^-1), natural abundance, acceptable and low cost as well as low toxicity are the main reasons for favoring this material. On the other hand, it has been found that electrochemical characteristics of MnO₂ depend strongly on its crystal structure, particle size and morphology.
This work presents several methods for the synthesis of MnO₂ - co-precipitation, hydrothermal and green. The aim is to prepare an α-MnO₂ phase with high surface area, and testing its applicability as an active material for supercapacitors purposes.
All studied materials were structurally and morphologically characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) methods. Electrochemical tests of selected materials were also performed.
It is established that chemical precipitation (CP) method leads to formation of α-MnO₂ particles, while the hydrothermal (HT) technique provides the growth of α-MnO2 and γ-MnO₂ nanocrystals.
The effect of the stirring time of the resulting suspension on the manganese dioxide morphology at CP prepared samples was monitored. It was found that the active surface area decreases with increasing the stirring time.
The obtained results demonstrate a clear dependence of the structure of the final material on the preparation technique and the experimental conditions. In particular, the sample, prepared hydrothermally at 140 ^oC possesses higher specific area compared to the sample, prepared at 330 ^oC and these, synthesized by other techniques, which could be related to the different type of the structural architecture of the MnO₂ particles.