Michał Świętosławski

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.

Morphology and electrical conductivity of carbon nanocoatings prepared from pyrolysed polymers

Conductive carbon nanocoatings (conductive carbon layers—CCL) were formed on α-Al2O3 model support using three different polymer precursors and deposition methods. This was done in an effort to improve electrical conductivity of the material through creating the appropriate morphology of the carbon layers. The best electrical properties were obtained with use of a precursor that consisted of poly-N-vinylformamide modified with pyromellitic acid (PMA). We demonstrate that these properties originate from a specific morphology of this layer that showed nanopores (3-4 nm) capable of assuring easy pathways for ion transport in real electrode materials. The proposed, water mediated, method of carbon coating of powdered supports combines coating from solution and solid phase and is easy to scale up process. The optimal polymer carbon precursor composition was used to prepare conductive carbon nanocoatings on LiFePO4 cathode material. Charge-discharge tests clearly show that C/LiFePO4 composites obtained using poly-N-vinylformamide modified with pyromellitic acid exhibit higher rechargeable capacity and longer working time in a battery cell than standard carbon/lithium iron phosphate composites.

Sol–gel synthesis, structural and electrical properties of Li2CoSiO4 cathode material

Polyanionic cathode materials for lithium-ion batteries start to be considered as potential alternative for layered oxide materials. Among them, Li2CoSiO4, characterized by outstanding capacity and working voltage, seems to be an interesting substitute for LiFePO4 and related systems. In this work, structural and electrical investigations of Li2CoSiO4 obtained by sol–gel synthesis were presented. Thermal decomposition of gel precursor was studied using EGA (FTIR)-TGA method. Chemical composition of the obtained material was confirmed using X-ray diffraction and energy-dispersive X-ray spectroscopy. The morphology of β-Li2CoSiO4 was studied using transmission electron microscopy. High temperature electrical conductivity of Li2CoSiO4 was measured for the first time. Activation energies of the electrical conductivity of two Li2CoSiO4 polymorphs (β and γ) were determined. The room temperature electrical conductivity of those materials was estimated as well.

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.

Preliminary study of structural changes in Li2MnSiO4 cathode material during electrochemical reaction

In this paper, we present exsitu observations of a structure of particular Li2MnSiO4 grains at different states of charge (SOC). The goal of these studies is structural analysis of Li2MnSiO4 cathode material for Li-ion batteries at different stages of electrochemical reaction using transmission electron microscopy. Performed analysis suggests that amorphization process of Li2MnSiO4 is not directly connected with lithium ions deintercalation but with additional electrochemical reactions running in the working cell.

C/Li2MnSiO4 Nanocomposite Cathode Material for Li-Ion Batteries

Technological development of portable devices, e.g, mobile phones, laptops, etc., as well as progress in electrical vehicles (EV) and hybrid electrical vehicles (HEV) technologies require batteries efficient in volumetric and gravimetric energy storage, exhibiting large number of charge/discharge cycles and being cheap and safe for users. Moreover, materials used in energy storage and conversion systems should be environmentally friendly and recyclable. Currently, rechargeable lithium-ion batteries (LIBs) are the most popular portable energy storage system, mostly due to their highest energy density among all others rechargeable battery technologies, like Ni-Cd or Ni-MH cells which reached the theoretical limit of performance. Commercially available LIBs are based on layered lithium cobalt oxide (LiCoO2) or related systems, which are expensive and toxic. These materials are unstable in an overcharged state, thus the battery safety is affected, especially in high power (20-100 kWh) applications for EV, HEV and renewable energy systems. The bigger battery capacity results in more energy accumulated, thus operational safety is a key issue. On the other hand, lifetime and capacity retention of LIBs in changeable operation conditions (from -30°C to +60°C, average lifetime 2-4 years) are a challenges to develop new materials and cell assembly technologies.

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.