Li-salt concentration has been recently proposed as an important control parameter of reduction stability of electrolytes in lithium-ion battery (LIB). Here we theoretically investigated low (LC) and high (HC) concentration systems of LiN(SO2CF3)2 (Li-TFSA) salt in acetonitrile (AN) solution, to elucidate the mechanism of improving the low reduction stability of AN at the HC condition, by density functional theory based molecular dynamics (DFT-MD) sampling of the solvation character with extra electron(s). We demonstrated that TFSA anions sacrificially accept the reductive electron at the HC condition, which is ascribed to formation of specific network structure and the resulting shift of electron affinity of the anions. We also found that, even in the LC condition, TFSA eventually decomposes with one electron reduction. This sacrificial anion reduction hinders two electron reductive decomposition of AN, leading to improved electrochemical stability. The mechanism may give a guiding principle for the design of better LIB electrolytes.

We investigated stable structures and photoexcitation character of Ru N749 dye (black dye (BD)) adsorption to TiO 2 anatase (101) interface immersed in bulk acetonitrile (AN) solution, a most representative electrode interface in dye-sensitized solar cells (DSCs). Density-functional-theory-based molecular dynamics (DFT-MD) with explicit solvent molecules was used to take into account the fluctuations of solvation shells and adsorbed molecules. We demonstrated that BD adsorption via deprotonated carboxylate two anchors (d2) is the most stable at the interface, while the one protonated carboxyl anchor (p1) has the average energy only slightly higher than the d2. This indicates that the p1 state can still coexist with the d2 under equilibrium. It is in contrast with the calculated large stability of the p1 in vacuo. Inhomogeneous charge distribution and anchor fluctuation enhanced by AN solution causes this d2 stabilization. The calculated projected densities of states and the photoabsorption spectra clearly show that the d2 state has larger driving force of the electron injection into the TiO 2 , whereas the photoabsorption in the wavelength region over 800 nm, a characteristic of BD sensitizer, is mainly attributed to the p1 state even in the AN solution. Consequently, the better performance of BD DSC can be understood in terms of the cosensitizer framework of the d2 and p1 states.

Poly-paraphenylenevinylene (PPV), a material used in organic light-emitting diodes (OLEDs), for which improving the efficiency is an important issue. In general, the molecular orientations of organic compounds in the crystal form are an essential factor determining electron and hole transfer, which are closely related to the efficiency of OLEDs. We have investigated the effects of the rotation of each molecule and the intermolecular distance in the dimer system of PPV, which consists of donor and acceptor molecules, on its charge-recombination process by performing constrained density functional calculations. Starting from the structure of the crystal, it was clarified that the rotation of the donor decreases the charge-recombination factor, to nearly zero, while that of the acceptor increases it to about 10(6) s(-1). We found that this is caused by the repulsive interaction between the donor and acceptor molecules and the formation of a transport pathway resulting from the acceptor rotation.