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The degradation mechanism of a graphite negative-electrode in LiPF6-based electrolyte solution was investigated using the basal plane of highly oriented pyrolytic graphite (HOPG) as a model electrode. Changes in the surface morphology were observed by in situ atomic force microscopy. In the initial cathodic scan, a number of pits appeared at around 1.75 V vs. Li+/Li, and fine particles formed on the terrace of the HOPG basal plane at about 1.5 V vs. Li+/Li. The fine particles were characterized by spectroscopic analysis, such as X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. We added one of the components to LiClO4-based electrolyte solution, and successfully reproduced the formation of pits and fine particles on the basal plane of HOPG. Based on these results, the formation mechanisms of pits and fine particle layers were proposed. [ABSTRACT FROM AUTHOR]

The concentration of ions in the electrolyte solution in lithium ion batteries changes during operation, reflecting the resistance to ion migration and the positions of diffusion barriers. The change causes various negative effects on the performance of batteries. Thus, it is important to elucidate how the concentration changes during operation. In this work, the concentration change of ions in the electrolyte solution in deep narrow spaces in a realistic battery was studied by in situ ultrafine microprobe Raman spectroscopy. Graphite composite and LiCoO 2 composite electrodes, which are the most commonly used electrodes in practical batteries, were placed facing each other and their distance was set to 80 μm, which is close to the distance between electrodes in practical batteries. After repeated charge/discharge cycles, the concentration of ions increased and decreased greatly during charging and discharging, respectively. The maximum concentration was more than three-times higher than the minimum concentration. The rate of changes in concentration increased almost linearly with increase in current density. The results have important implications about concentration changes of ions occurring in practical batteries. [ABSTRACT FROM AUTHOR]

To ensure optimal operation of electrochemical energy storage devices, a precise design of the interfaces formed between the electrodes and the electrolyte is essential. Si is a promising anode active material for Li-ion batteries owing to its high theoretical capacity; however, the large volume change associated with Li absorption and release hinders its practical applications. The development of high-performance storage batteries depends on the construction of an electrode-electrolyte interface that facilitates Li + movement. To this aim, the authors have developed Si-specific interface observation methods. In this feature article, we review and discuss recent advances in the reaction behavior of Si-based anodes, particularly at the Si electrode-electrolyte interface.

We prepared composite electrodes using TiO 2 coated with chlorophylls a and b as photoelectric conversion material and MnO 2 as energy storage material and investigated their photoelectrochemical capacitor properties. The coating with the combination of chlorophylls a and b improved the photoelectric conversion function of TiO 2 , compared with the coating with each alone. Na + adsorption on MnO 2 was enhanced with increasing the chlorophyll coating amount. The reason is that more chlorophylls a and b absorb visible light in different wavelengths to promote an easier photoexcited electron transfer to MnO 2 , just as they improve the efficiency of photosynthesis reactions in nature.

Lithium-ion batteries are used in various extreme environments, such as cold regions and outer space; thus, improvements in energy density, safety, and cycle life in these environments are urgently required. We investigated changes in the charge and discharge properties of Si-based electrodes in ionic liquid electrolytes with decreasing temperature and the cycle life at low temperature. The reversible capacity at low temperature was determined by the properties of the surface film on the electrodes and/or the ionic conductivity of the electrolytes. The electrode coated with a surface film formed at a low temperature exhibited insufficient capacity. In contrast, a Si-only electrode precoated with the surface film at room temperature exhibited a cycle life at low temperatures in ionic liquid electrolytes longer than that in conventional organic liquid electrolytes. Doping phosphorus into Si led to improved cycling performance, and its impact was more noticeable at lower temperatures., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Silicon oxide (SiO x ) has been placed into practical use as an anode active material for next-generation Li-ion batteries because it has a higher theoretical capacity than graphite anodes. However, the synthesis method is typically vapor deposition, which is expensive, and the poor electron conductivity of SiO x restricts high performance. In this study, we prepared M /SiO x active materials consisting of SiO x and a third element ( M = Al, B, Sn) using a low-cost mechanical milling (MM) method and investigated their electrode properties as Li-ion battery anodes. Also, the authors added a third element to improve the conductivity of the SiO 2 matrix. Al, B, and Sn were selected as elements that do not form a compound with Si, exist as a simple substance, and can be dispersed in SiO 2 . As a result, we confirmed that SiO x has a nanostructure of nanocrystalline Si dispersed in an amorphous-like SiO 2 matrix and that the third element M exists not in the nanocrystalline Si but in the SiO 2 matrix. The electron conductivity of SiO x was improved by the addition of B and Sn. However, it was not improved by the addition of Al. This is because Al 2 O 3 was formed in the insulator due to the oxidization of Al. The charge-discharge cycle tests revealed that the cycle life was improved from 170 cycles to 330 or 360 cycles with the addition of B or Sn, respectively. The improvement in electron conductivity is assumed to make it possible for SiO 2 to react with Li ions more uniformly and form a structure that can avoid the concentration of stress due to the volume changes of Si, thereby suppressing the electrode disintegration., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

A TiO 2 electrode was coated with chlorophyll a to regenerate nicotinamide adenine dinucleotide phosphate (NADPH), which can enhance the photovoltages of the electrodes for photoelectrochemical capacitors. The photovoltage of an uncoated TiO 2 electrode was high during the first cycle but then steadily reduced owing to the oxidization of NADPH in the electrolyte during the photo-charge-discharge cycling. By contrast, a chlorophyll a -coated TiO 2 electrode maintained high photovoltages for 100 cycles. Residual NADPH concentrations after 100 cycles increased from 73% to 90% because of the coating, demonstrating that NADPH was regenerated by photoexcited chlorophyll a similar to a photosynthetic reaction in nature.

We have reported the effects of substituting a transition metal in silicide on the electrochemical performance of the silicide/Si composite anode for lithium-ion batteries (LIBs); the Cr 0.5 V 0.5 Si 2 /Si electrode exhibited much better cyclability compared with CrSi 2 /Si and VSi 2 /Si electrodes. Herein, we investigated the electrochemical performance of a Cr x V 1- x Si 2 /Si slurry electrode for its application in LIBs, and the results obtained were compared to those of a gas deposition (GD) electrode, which was comprised of only active materials. The slurry electrode exhibited a superior cycling life as with the GD electrode. After charge-discharge cycles, the expansion of the electrode thickness of CrSi 2 /Si and Cr 0.5 V 0.5 Si 2 /Si was smaller than that of VSi 2 /Si, and VSi 2 was significantly pulverized compared with the other silicides. It is considered that VSi 2 deformed easily by the stress from Si expansion and pulverized because the hardness of VSi 2 was the smallest among the silicides used in this study. These results reveal that Cr 0.5 V 0.5 Si 2 /Si has great potential as an anode material for next-generation LIBs and hardness is an important property for compositing silicide with Si., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Mixed per-6-thio-beta-cyclodextrin (CD-SH)/pentanethiol (C(5)SH) monolayers were constructed by the sequential immersion of a Au(111) electrode into solutions of CD-SH, ferrocene, and a mixed solution of ferrocene and C(5)SH. Highly compact CD-SH self-assembled monolayers (SAMs) with the surface CD-SH density of 74.0 +/- 6.3 pmol cm(-2) on a true surface area basis were formed in 1 mM CD-SH with the immersion time of more than 48 h as confirmed by reductive desorption voltammetry. Based on the concentration dependence of the adsorption amount, a Langmuir adsorption coefficient was determined to be 1.9 x 10(7) M(-1). Chronocoulometry in a ferrocene solution at the CD-SH SAM and the mixed CD-SH/C(5)SH monolayers revealed the following inclusion properties. (1) All the CD-SH cavities can be used for the inclusion of a guest compound before and after the adsorption of C(5)SH, as shown by the fact that the maximum inclusion amounts of ferrocene, 68.0 +/- 3.4 and 73.0 +/- 2.0 pmol cm(-2) before and after the adsorption of C(5)SH, respectively, were very close to the surface CD-SH density. (2) The association constant between the surface-confined CD-SH and ferrocene (7.6 x 10(4) M(-1)) is greater than the corresponding association constant in solution. (3) The intermolecular vacancies between the adsorbed CD-SH molecules are completely filled with C(5)SH. This ensures that the CD cavities are the only accessible sites for guest compounds and any other reactants.