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Lithium-ion batteries are widely available commercially and attempts to extend the lifetime of these batteries remain necessary. The energy storage characteristics of NbO2 with a rutile structure as a material for the negative electrode of lithium-ion batteries were investigated. When negative potential was applied to the NbO2 electrode during application of a constant current in a nonaqueous solution containing lithium ions, these ions were inserted into the NbO2. Conversely, upon application of positive potential, the inserted lithium ions were extracted from the NbO2. In situ X-ray diffraction results revealed that the variation in the volume of NbO2 accompanying the insertion and extraction of lithium was 0.14%, suggesting that NbO2 is a zero-strain (usually defined by a volume change ratio of 1% or less) active material for lithium-ion batteries. Moreover, the highly stable structure of NbO2 allows the corresponding electrode to exhibit excellent cycling performance and coulombic efficiency.

The solid electrolyte interphase formation on the negative electrodes of lithium secondary batteries has been considered as one of the principal issues limiting the performance of batteries. Si is an attractive electrode material for improving energy density of lithium secondary batteries because of its high specific theoretical capacity (4200 mAh g−1). However, solid electrolyte interphase formation on Si-based electrodes have not been clearly understood in spite of its significance. Herein, the solid electrolyte interphase formation on Si electrodes in electrolyte solutions containing ethylene carbonate or propylene carbonate was investigated by using in-situ atomic force microscopy. Large and irreversible capacity fade in SiO electrodes was confirmed in both electrolyte solutions through cyclic voltammetry and charge/discharge testing. The in-situ atomic force microscopy results indicated that the decomposition reaction occurred in the ethylene carbonate-based electrolyte solution at a potential of ~0.68 V, while the lithium alloying reaction occurred below 0.25 V during the first reduction process. The decomposition reaction was more vigorous and occurred at a higher potential in the propylene carbonate-based electrolyte solution, resulting in the formation of a thick solid electrolyte interphase film. These results suggest that the solid electrolyte interphase formation on Si electrodes is strongly influenced by the composition of the electrolyte solution.

This study aims to improve the electrochemical properties of lithium metal for application as a negative electrode in high-energy-density batteries. Lithium metal was heat-treated at varying temperatures to modify the native and solid electrolyte interphase (SEI) films, which decreased the interfacial resistance between the lithium electrode and electrolyte, thereby improving the cycling performance. Moreover, the influence of the native and SEI films on lithium metals depended on the heat-treatment temperature. Accordingly, X-ray photoelectron spectroscopy (XPS) was performed to investigate the chemical composition of the native and SEI films on the heat-treated lithium metals before and after immersion in an organic electrolyte solution. The XPS results revealed the high dependence of the chemical composition of the outer layer of the native and SEI films on the heat-treatment temperature, implying that the native and SEI films can be effectively modified by heat treatment.

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