Valentina Borgel

Comparison between Na-Ion and Li-Ion Cells: Understanding the Critical Role of the Cathodes Stability and the Anodes Pretreatment on the Cells Behavior

The electrochemical behavior of Na-ion and Li-ion full cells was investigated, using hard carbon as the anode material, and NaNi0.5Mn0.5O2 and LiNi0.5Mn0.5O2 as the cathodes. A detailed description of the structure, phase transition, electrochemical behavior and kinetics of the NaNi0.5Mn0.5O2 cathodes is presented, including interesting comparison with their lithium analogue. The critical effect of the hard carbon anodes pretreatment in the total capacity and stability of full cells is clearly demonstrated. Using impedance spectroscopy in three electrodes cells, we show that the full cell impedance is dominated by the contribution of the cathode side. We discuss possible reasons for capacity fading of these systems, its connection to the cathode structure and relevant surface phenomena.

Li4Ti5O12/LiMnPO4 Lithium-Ion Battery Systems for Load Leveling Application

A new type of lithium-ion cell based on the combination of spinel Li4Ti5O12 anode with a high voltage olivine LiMnPO4 cathode, which can be promising for load leveling applications, is demonstrated for the first time. The power and safety characteristics of this battery system were found to meet the requirement for this application. The structure, surface morphology, and the performance were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and standard electrochemical techniques. A stable reversible capacity up to 125 mAh g � 1 of the cathode in full cell could be measured at discharge potentials >2.5 V with a reasonable capacity retention during prolonged charge/discharge cycling. The thermal stability of pristine and electrochemically delithiated LiMnPO4-Li4Ti5O12 composite cathodes and anodes in contact with the electrolyte solution was investigated by differential scanning calorimetry (DSC). The electrodes were also studied by thermogravimetric analysis, coupled with mass spectrometry. We did not found appreciable changes in the thermal stability of the electrodes in their pristine and charged states, in contact with LiPF6 solution in mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC).

In Situ FTIR Spectroscopy Study of Li / LiNi0.8Co0.15Al0.05O2 Cells with Ionic Liquid-Based Electrolytes in Overcharge Condition

We developed a methodology of in situ Fourier transform infrared (FTIR) measurements of gaseous products formed in an electrochemical cell upon polarization. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes were explored at potentials of up to 5.5 V vs Li in the ionic liquid (IL)-based electrolyte solution, LiTFSI/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. The polarization of the NCA electrodes formed CO 2 and CO due to the liberation of oxygen and the parallel dissolution of nickel ions, which oxidizes the carbon black in the composite electrode. The oxygen was mostly liberated from the NCA and also due to minor contribution from the surface groups on the carbon black additive.