No abstract

The growth processes and solvent effects on the two-dimensional structure of self-assembled monolayers (SAMs) formed by 6-mercaptohexanoic acid (MHA) on Au(111) were examined by scanning tunneling microscopy (STM) and contact angle (CA) measurements. The STM study revealed for the first time that the striped phases of 6-mercaptohexanoic acid (MHA) on Au(111) are preferentially formed near the step edges of gold terraces in the initial stage of SAM growth. In addition, it was found that MHA SAMs prepared from a polar aprotic solvent form a more well-ordered structure and a better hydrophilic surface than those prepared from a polar protic solvent. From this study, we clearly demonstrated that the properties of solvents are very important factors in controlling the two-dimensional structure of carboxylic acid-terminated SAMs.

Surface structures and adsorption states of self-assembled monolayers (SAMs) formed by COOH-terminated alkanethiols (ATs) with different alkyl chain lengths were examined by scanning tunneling microscopy (STM), contact angle measurement, and X-ray photoelectron spectroscopy (XPS). STM imaging reveals that COOH-terminated ATs with longer alkyl chains [HS(CH 2 ) n COOH, n ! 7] can easily form well-ordered SAMs, while COOH-terminated ATs with shorter alkyl chains hardly form ordered SAMs [HS(CH 2 ) n COOH, n 5]. From contact angle and XPS measurements, however, we found that the most surface characteristics, such as surface wettability as well as the adsorption state and the amount of adsorbed molecules, are independent of alkyl chain length. In this study, we elucidate that the intermolecular interaction between alkyl chains is a very important factor in obtaining two-dimensional well-ordered COOH-terminated SAMs.

We attempt to reveal how electrolyte additives affect the structural evolution of the solid electrolyte interphase (SEI) film on the anode surface of a lithium-ion secondary battery. Employing the hybrid Monte-Carlo/molecular-dynamics method, we theoretically investigate the SEI film structures in organic liquid-electrolyte systems with and without an organosilicon additive. The results show that the excessive growth of the SEI film is suppressed by introducing the organosilicon additives. It is further elucidated that the decomposition products of the organosilicon molecules are stably aggregated in the vicinity of the anode surface, and protect the electrolyte solvents and the lithium salts from the further reductive decomposition. These findings imply that the organosilicon additive possibly improves the cycle performance of LIBs owing to the formation of the effective SEI film.

Lithium ion batteries (LIBs) are one of the most versatile secondary batteries with high energy density and high power output.Recently the degradation of LIBs cycle durability has appeared to be one of the significant issues under the use of high voltage conditions.The capacity of LIBs is dramatically decreased after a cycle test in a range of 3.0-4.5 V. The additives for cathodes named “Multi Capture Powder (MCP)” have been developed herein.MCP is capable of capturing metal ions and refraining from cathode decompositions of fluorine compounds.Mechanisms of the effects of MCP on the improvement of LIBs’ cycle performance are different from those of cathode materials examined so far. In case of LiCoO2 (LCO) /graphite cells with 5% MCP added to the cathode, theircapacity retentions have increased by about 10% after 300 cycles under 2.5-4.35 V conditions. Electrochemical impedances between the LCO cathodes with MCP and the graphite anodes after the cycle tests were drastically decreased in comparison with the cells without MCP. In order to clarify the mechanism for the improvement of the capacity retention, the cathodes with/without MCP and the anodes were pulled out of the cells after the cycle tests.The capacity of both the LCO cathodes with /without MCP and the graphite anodes were measured before/after the cycle testsunder 0.2, 0.5 and 1.0 CA conditions with a Li counter electrode. According to the capacity measurements,  the cathode materials including MCP mitigate the capacity loss significantly although the dominent factor of the capacity loss of the cells results in the degradation of the cathodes with/without MCP. After the cycle tests, X-ray diffraction angles for the (003) plane of cathode active materials were shifted to lower than their initial ones before the cycle tests. The shift of the diffraction angles for the cathodes with MCP was smaller than that of those of the cathodes without MCP. MCP plays an important role in improving capacity retention under high voltage cycle test conditions.