Monika Bakierska

Facile synthesis of C/Sn nanocomposite anode material for Li ion batteries

Abstract C/Sn nanocomposites were prepared in simultaneous pyrolysis and carboreduction process (700 and 800°C) of a nanometric tin oxide(IV), obtained by a modified reverse microemulsion method. The proposed method provided formation of tin nanograins encapsulated in conductive carbon layers. The obtained materials with different carbon loadings (13–26 wt-%) were characterised by X-ray diffraction (XRD), low temperature nitrogen adsorption method (N2-BET) and transmission electron microscopy. Galvanostatic discharge/charge tests, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) as well as electrical conductivity studies were used to characterise electrochemical properties of C/Sn nanocomposites. It was found that the electrochemical performance of C/Sn nanocomposites may be affected by carbon matrix morphology.

Enhancement of Electrochemical Performance of LiMn2O4 Spinel Cathode Material by Synergetic Substitution with Ni and S

Nickel and sulfur doped lithium manganese spinels with a nominal composition of LiMn2−xNixO4–ySy (0.1 ≤ x ≤ 0.5 and y = 0.01) were synthesized by a xerogel-type sol-gel method followed by subsequent calcinations at 300 and 650 °C in air. The samples were investigated in terms of physicochemical properties using X-ray powder diffraction (XRD), transmission electron microscopy (EDS-TEM), N2 adsorption-desorption measurements (N2-BET), differential scanning calorimetry (DSC), and electrical conductivity studies (EC). Electrochemical characteristics of Li/Li+/LiMn2−xNixO4–ySy cells were examined by galvanostatic charge/discharge tests (CELL TEST), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The XRD showed that for samples calcined at 650 °C containing 0.1 and 0.2 mole of Ni single phase materials of Fd-3m group symmetry and nanoparticles size of around 50 nm were obtained. The energy dispersive X-ray spectroscopy (EDS) mapping confirmed homogenous distribution of nickel and sulfur in the obtained spinel materials. Moreover, it was revealed that the adverse phase transition at around room temperature typical for the stoichiometric spinel was successfully suppressed by Ni and S substitution. Electrochemical results indicated that slight substitution of nickel (x = 0.1) and sulfur (y = 0.01) in the LiMn2O4 enhances the electrochemical performance along with the rate capability and capacity retention.

Nature of the Electrochemical Properties of Sulphur Substituted LiMn2O4 Spinel Cathode Material Studied by Electrochemical Impedance Spectroscopy

In this work, nanostructured LiMn2O4 (LMO) and LiMn2O3.99S0.01 (LMOS1) spinel cathode materials were comprehensively investigated in terms of electrochemical properties. For this purpose, electrochemical impedance spectroscopy (EIS) measurements as a function of state of charge (SOC) were conducted on a representative charge and discharge cycle. The changes in the electrochemical performance of the stoichiometric and sulphur-substituted lithium manganese oxide spinels were examined, and suggested explanations for the observed dependencies were given. A strong influence of sulphur introduction into the spinel structure on the chemical stability and electrochemical characteristic was observed. It was demonstrated that the significant improvement in coulombic efficiency and capacity retention of lithium cell with LMOS1 active material arises from a more stable solid electrolyte interphase (SEI) layer. Based on EIS studies, the Li ion diffusion coefficients in the cathodes were estimated, and the influence of sulphur on Li+ diffusivity in the spinel structure was established. The obtained results support the assumption that sulphur substitution is an effective way to promote chemical stability and the electrochemical performance of LiMn2O4 cathode material.

Multifunctional carbon aerogels derived by sol–gel process of natural polysaccharides of different botanical origin

In this manuscript, we describe the results of our recent studies on carbon aerogels derived from natural starches. A facile method for the fabrication of carbon aerogels is presented. Moreover, the complete analysis of the carbonization process of different starch aerogels (potato, maize, and rice) was performed using thermogravimetric studies combined with a detailed analysis of evolved decomposition products. The prepared carbon aerogels were studied in terms of their morphology and electrical properties to relate the origin of starch precursor with final properties of carbon materials. The obtained results confirmed the differences in carbon aerogels’ morphology, especially in materials’ specific surface areas, depending on the botanical origin of precursors. The electrical conductivity measurements suggest that carbon aerogels with the best electrical properties can be obtained from potato starch.

Effect of electrolyte composition on thermal stability and electrochemical performance of LiMn2O4-ySy cathodes for Li-ion batteries

Electrolytes are indispensable for the proper operation of every battery technology. Hence, in this paper, our major focus concerns identification of the most appropriate electrolyte composition in order to minimise the reactions on the electrode surface as well as enhance the electrochemical performance of Li-ion batteries containing as a cathode LiMn2O4-ySy (LMOS) spinel materials. For this purpose, thermal stability of LiPF6 and LiClO4 salts in a mixture of EC:DEC, TMS:EMC solvents towards LMOS cathode materials was investigated. All the electrolyte solutions were also tested in Li/Li+/LMOS cells. The electrochemical behaviour of electrolyte-cathode material systems was further examined by the electrochemical impedance spectroscopy. As demonstrated, LiMn2O3.99S0.01 (LMOS1) electrode exhibits remarkable thermal and electrochemical stability in LiPF6 solution of alkyl carbonates (EC:DEC). The satisfactory cycling performance is due to the development of highly stable passivating surface film on the LMOS1 cathode in aforementioned electrolyte that protects the active material from unfavourable reactions.

Study on Stability and Electrochemical Properties of Nano-LiMn1.9Ni0.1O3.99S0.01-Based Li-Ion Batteries with Liquid Electrolyte Containing LiPF6

Herein, we report on the stability and electrochemical properties of nanosized Ni and S doped lithium manganese oxide spinel LiMn1.9Ni0.1O3.99S0.01, LMN1OS in relation to the most commonly used electrolyte solution containing LiPF6 salt. The influence of electrochemical reaction in the presence of selected electrolyte on the LMN1OS electrode chemistry was examined. The changes in the structure, surface morphology, and composition of the LMN1OS cathode after 30 cycles of galvanostatic charging/discharging were determined. In addition, thermal stability and reactivity of the LMN1OS material towards the electrolyte system were verified. Performed studies revealed that no degradative effects, resulting from the interaction between the spinel electrode and liquid electrolyte, occur during electrochemical cycling. The LMN1OS electrode versus LiPF6-based electrolyte has been indicated as an efficient and electrochemically stable system, exhibiting high capacity, good rate capability, and excellent coulombic efficiency. The improved stability and electrochemical performance of the LMN1OS cathode material originate from the synergetic substitution of LiMn2O4 spinel with Ni and S.