Nobuko Yoshimoto

Anodic behavior of aluminum in organic solutions with different electrolytic salts for lithium ion batteries

The anodic polarization behavior of aluminum (Al) as a current collector of lithium (Li) ion battery has been investigated in organic electrolyte solutions containing different lithium salts. The Al current collector has suffered serious corrosion in the solution containing Li(CF3SO3)2N (LiTFSI) under an anodic polarization condition, whereas, it was anodically stable in the LiPF6 solution. In the solution of Li(C2F5SO2)2N (LiBETI), the Al anode showed an intermediate character between those in the LiPF6 and LiTFSI solutions. The corrosion behavior of the Al electrode was much influenced by its surface condition. The addition of LiPF6 in the imide-salts (LiTFSI and LiBETI) solutions suppressed the anodic corrosion of Al. The results of electrochemical quartz crystal microbalance (EQCM) experiments proved that the anodic processes on Al in the organic electrolytes consist of the formation of surface films and their dissolution. The X-ray photoelectron spectroscopy (XPS) analysis suggests that the anodic stability of the Al electrode in the imide-salts solutions containing LiPF6 is associated with the formation of a fluoride (AlF3)-rich film on the Al surface.

A Raman spectroscopic study of organic electrolyte solutions based on binary solvent systems of ethylene carbonate with low viscosity solvents which dissolve different lithium salts

The ionic structure of organic electrolyte solutions has been investigated, by means of Raman spectroscopy for mixed aprotic solvents that dissolve lithium salts. The solutions consisted of binary solvent systems of a high permittivity solvent (ethylene carbonate, EC) mixed with low viscosity alkyl carbonates (dimethyl carbonate, DMC, and diethyl carbonate, DEC) or a linear alkyl ether (1,2-dimethoxyethane, DME) and of LiCF3SO3, LiPF6 and LiN(C2F5SO2)2 as the solute. The Raman shifts based on the solvents varied with the sort of dissolved lithium salts and their concentration. The ion solvation was estimated from the side-bands of the Raman scattering for the C–O stretch of single bonds of the carbonate groups and for the symmetric ring deformation of EC. The number of EC molecules interacting with the lithium cation (Li+) was higher than that of DMC in a mixed EC+DMC (50:50 by volume) system. The apparent solvation number of Li+ in 1.5 mol dm-3 LiCF3SO3 solution was about 2.8 in EC+DMC, whereas that in 1.5 M LiPF6 solution was about 3.9. Specific solvation of Li+ was distinguished in EC+DME (50:50), where DME predominantly coordinates to Li+. However, it was also confirmed that EC, which has a lower donicity, interacts with Li+ even in the EC+DME system. That is, the solvation number of EC in LiCF3SO3/(EC+DME) remained ca. 1.0 even in high salt concentrations.

Ionic conductance behavior of polymeric composite solid electrolytes containing lithium aluminate

Abstract Polymeric electrolytes consisting of poly(ethylene oxide)-grafted polymethacrylates, lithium salts and ceramic filler (LiAlO 2 ) have been prepared. The addition of a small amount of LiAlO 2 increased the ionic conductivity of the polymeric electrolyte system containing LiClO 4 salt over an ambient temperature range. Conductivity of 3.5×10 −5 S cm −1 at 333 K (60°C) was obtained for the composite without any low molecular weight liquid component. The addition of the ceramic filler scarcely influenced the thermal properties of the polymeric electrolyte. XRD and 7 Li NMR experiments showed that the ionic mobility can be enhanced in the composites by adding LiAlO 2 . For the polymeric electrolyte system containing LiCF 3 SO 3 salt, however, the addition of the ceramic filler showed little influence on the ionic conductivity.

Anodic behavior of aluminum current collector in LiTFSI solutions with different solvent compositions

The anodic behavior of aluminum (Al) current collector of Li-ion batteries has been investigated in organic electrolyte solutions containing lithium bis[trifluoromethylsulfonyl]imide (Li(CF3SO2)2N: LiTFSI) with different compositions of solvents. The Al anode was subjected to anodic corrosion in the LiTFSI solution, but the degree of the corrosion depended on the solvent composition. The surface of Al pre-treated by mechanical polishing has suffered serious corrosion in the mixed solvent solution of ethylene carbonate (EC) and dimethyl carbonate (DMC), whereas the Al surface pre-treated by electro-polishing was relatively stable in the mixed solvent of g-butyrolactone (GBL) and DMC. The results of electrochemical quartz crystal microbalance (EQCM) experiments showed that the mass change of the Al surface during the potential cycling in GBL þ DMC was much different from that in the EC þ DMC solution. Scanning electron microscope (SEM) observation proved that the corrosion pits evolved on the electro-polished Al surface after potential cycling, but GBL resulted in a smaller amount of the corrosion product on the Al surface. # 2003 Elsevier Science B.V. All rights reserved.

Rechargeable magnesium batteries with polymeric gel electrolytes containing magnesium salts

Abstract Novel polymeric gel electrolytes consisting of poly(ethylene oxide)–modified poly(methacrylate) (PEO–PMA) with magnesium imide (Mg[(CF 3 SO 2 ) 2 N] 2 ) as the electrolytic salt and mixed alkyl carbonates as the plasticizer have been prepared by photo-induced radical polymerization. The polymeric gel film was flexible and self-standing with proper mechanical strength. The ionic conductivity of the polymeric gel film was about 10 −3 S cm −1 at room temperature. The ionic conductivity increased with the content of the plasticizer, ethylene carbonate (EC) and dimethyl carbonate (DMC), in the complex, while the mechanical strength of the gel film decreased with the increase in the plasticizer. The highest conductivity was obtained for the composition of 75 wt.% of the plasticizing component, EC+DMC dissolving Mg[(CF 3 SO 2 ) 2 N] 2 in the gel. The applicability of the present gel film to a rechargeable battery system was examined by a prototype cell consisting of Mg-doped V 2 O 5 and V 2 O 5 (or MnO 2 ) as the negative and positive electrodes, respectively.

Ionic conductance of polymeric electrolytes consisting of magnesium salts dissolved in cross-linked polymer matrix with linear polyether

Abstract A novel polymeric electrolyte system has been developed using oligo(ethylene oxide)-grafted polymethacrylate matrix and linear polyether which dissolves magnesium salts. Thermal analyses showed that the obtained polymeric electrolytes have homogeneous and amorphous phases over a wide temperature range. The ionic structure of the polymeric system was examined by Raman spectroscopy. The ionic conductance behavior of the polymeric electrolyte was investigated as solid Mg 2+ -ion conductors. The conductivity depended mostly on the kind of the dissolved magnesium salt. The highest conductivity was obtained for the polymeric electrolytes containing Mg[(CF 3 SO 3 ) 2 N] 2 (about 10 −4 S cm −1 at room temperature). Addition of dimethyl formamide as a complex-forming liquid component in the polymeric electrolyte system enhanced the ionic conductivity. The dc polarization of an Mg/Mg cell using the polymeric electrolyte proved that Mg 2+ is mobile in the present polymeric system.

Ionic structure and conductance behavior of plasticized polymeric electrolytes containing multivalent cations

Polymeric electrolytes consisting of oligo(ethylene oxide)-grafted poly(methylmethacrylate), organic plasticizer and inorganic salts of multivalent cations (Mg 2+ , La 3+ , Ce 3 and Yb 3+ ) have been prepared. Their behavior as solid ion conductors has been examined. Thermal and X-ray analyses showed that the polymeric electrolytes were homogeneous and amorphous over a wide temperature range. Ionic conductivities of 10 -4 and 10 -5 S cm -1 were obtained at room temperature for the polymeric films containing Mg(ClO 4 ) 2 and Ce(ClO 4 ) 3 , respectively. The ionic conductivity depends critically on the composition of the polymer electrolytes. The ionic coordination in the polymeric electrolytes, as determined by Raman spectroscopy, is discussed in relation to the conductance behavior.

Proton conductance and spectroscopic characteristics of acid-doped polymer gels based on poly(ethylene oxide)-modified polymethacrylate

Proton-conducting polymeric gels have been prepared by swelling a polymethacrylate-based polymer matrix in aqueous solutions of inorganic and organic acids such as sulfuric (H2SO4), hydrochloric (HCl), phosphoric (H3PO4), acetic (HAc), and succinic acids (HSc). The polymer matrix was composed of cross-linked poly(ethylene oxide)-modified polymethacrylate (PEO–PMA) with different plasticizing components of poly(ethylene glycol) dimethylether (PEGDE), dimethylformamide (DMF), and propylene carbonate (PC). The polymeric gels were characterized by conductometric and spectroscopic measurements. High ionic (proton) conductivity in the range of 6.410 4 –4.210 2 Sc m 1 were obtained at room temperature (22 jC), depending on the dopant acids, the type of plasticizers, and the polymer composition. The H3PO4- and HAc-doped films exhibited thermal stability in the temperature range of 20–80 jC. Possible proton transport mechanisms in the PEO–PMA-based gels were discussed based on the spectroscopic results of FT-IR, UV/VIS, X-ray diffraction (XRD), and fluorescence spectroscopy. The effects of water molecule absorbed in the polymer, together with the entrapped plasticizer (PEGDE, DMF, and PC), play important roles in obtaining the high ionic conductivity, through the reduction in the local viscosity of the gel films. D 2003 Elsevier Science B.V. All rights reserved.

Ionic conductance behavior of polymeric electrolytes containing magnesium salts and their application to rechargeable batteries

Abstract Polymeric electrolytes consisting of oligo(ethylene oxide)-grafted polymethacrylate (PEO-PMA) matrix, linear polyether and magnesium salts have been prepared, and their electrochemical behavior as solid Mg 2+ ion conductors has been examined. Thermal analyses showed that the obtained polymeric electrolytes are homogeneous and amorphous over a wide temperature range. The conductivity depended much on the kind of the dissolved magnesium salt. The highest conductivity was obtained for the polymeric electrolyte containing Mg[(CF 3 SO 2 ) 2 N] 2 (>10 −4 S cm −1 at room temperature). The dc polarization of a Pt/Mg cell using the polymeric electrolyte proved that Mg 2+ is mobile in the present polymeric system. A prototype cell was constructed using the polymeric electrolyte with a Mg (or Li) anode and a V 2 O 5 cathode, where the intercalation–deintercalation of Mg 2+ occurred reversibly.

Ionic conductance of polymeric electrolytes containing lithium salts mixed with rare earth salts

Abstract Polymeric ion conductors consisting of poly(ethylene oxide)-grafted poly(methylmethacrylate) (PEO–PMMA) matrices that dissolve lithium salts and rare earth salts have been prepared by photo-induced radical polymerization of methacrylate monomers with a linear polyether (PEGDE). The ionic structure and conductance behaviour of the resulting electrolyte systems were investigated as a function of the electrolyte composition. Polymeric electrolytes containing lithium salts with rare earth cations showed higher ionic conductivity than that containing lithium salts only. The conductance behaviour of the mixed salt system is discussed from the experimental results of thermal analysis, Raman spectroscopy, transport number measurements and 7Li NMR.