Tomáš Kazda

Study of electrochemical properties and thermal stability of the high-voltage spinel cathode material for lithium-ion accumulators

This article deals with the properties of high-voltage cathode material LiNi0.5Mn1.5O4 synthesised by a solid-state reactions method. The sample—LiNi0.5Mn1.5O4—was synthesised by two steps of annealing process. A number of electrochemical and physical methods were used to analyse the samples. The obtained LiNi0.5Mn1.5O4 powder was characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and galvanostatic charge/discharge measurements at different loads and high temperature in lithium-ion cells with metal lithium as a counter electrode. All these analyses were used for confirmation of the structure of the material LiNi0.5Mn1.5O4 and for investigating its electrochemical properties. A special analysis was used for this paper to understand and confirm the function of this type of material. It is called electron paramagnetic resonance (EPR) spectroscopy, which is used in the field of lithium-ion batteries and also which is not common. This analysis is typically used to analyse free radicals. It is possible to study changes of valence in cathode materials during charging and confirming the valence change of Mn from Mn3+ to Mn4+ and of Ni from Ni2+ to Ni3+ and then to Ni4+ with EPR analysis. Thermogravimetric (TG) analysis of stability of the material LiNi0.5Mn1.5O4 with in situ observation of structural changes by SEM was used as the last analysis.

The influence of used precursors on the properties of high-voltage cathode materials

This article deals with the influence of precursors used in the high-voltage cathode material LiNi0.5Mn1.5O4 based on the LiMn2O4 material on its properties. Precursors with various sizes of particles were used for making the cathode material. Consequently, its influence on the stability during cycling, change of load, and the influence of higher temperatures during cycling were investigated. Produced materials were further analyzed to discover the influence of the change of the used precursor on the structure of the cathode material. The structure of the material deposited on Al foil was investigated by atomic force microscopy (AFM), and also X-ray photoelectron spectroscopy (XPS) analysis was performed. The materials were then observed by SEM and analyzed by the EDAX method. The results show that smaller particle size enhances the properties of cathode material both in the stability during cycling and higher capacity and also the potential under higher load.

Study of Stability and Structural Changes Occurring during High Thermal Load of the High Voltage Cathode Material by In Situ Scanning Electron Microscopy

One of the most progressive battery systems which are used in portable devices, electric vehicles and energy storage systems are Li-Ion batteries. However, currently used cathode materials are close to their limits and in the coming years they are no longer able to meet growing energy demands. Many research groups focus their interest on modifications of existing cathode materials in order to improve their parameters. Some of them search for new types of cathode materials which could replace currently used cathode materials. The result of one of those efforts was the development of the cathode material LiNi0.5Mn1.5O4 [1]. This material is based on the LiMn2O4 where manganese is partially replaced by nickel, this allows to charge the cathode material up to 5 V. Potential of LiNi0.5Mn1.5O4 against lithium is 4.7 V i.e. 1 – 1.5 V increase in respect to standard cathode materials. With this combination of high potential and theoretical capacity 148 mAh/g, LiNi0.5Mn1.5O4 exhibits high gravimetric energy density approaching 700 Wh/kg which is approximately 20 % more than gravimetric energy density of LiCoO2 and about 30 % more than in the case of the cathode material LiFePO4. Moreover, LiNi0.5Mn1.5O4 is also stable during long term cycling and exhibits good stability at higher current loads because of the spinel structure; however, it still suffers by dissolution of manganese into the electrolyte during cycling at higher temperatures which leads to defects in the structure and capacity decrease [2].

Finite Element Model of Discharging and Temperature Field of the Lithium Ion Battery

This paper deals with a possibility of numerical simulation of temperature profile by discharging of li-ion battery. The numerical model was prepared using SolidWorks and ANSYS Fluent software and it was compared by real measurement using electrical impedance spectroscopy and thermocamera imaging. The simulation was realised as transient real-time.