Yoshiharu Matsuda

In situ scanning vibrating electrode technique for lithium metal anodes

The effect of the inorganic additives to electrolytes, aluminum iodide (AII 3 ) and tin(II) iodide, on the charge/discharge coulombic efficiency of a lithium (Li) metal anode has been investigated in binary solvent systems, i.e., propylene carbonate (PC) mixed with 2-methyltetrahydrofuran (2Me-THF) containing litnium perchlorate (LiClO 4 ), PC + 2Me-THF/LiClO 4 , and PC mixed with 1,2-dimethoxyethane (DME) containing LiClO 4 , PC + DME/LiClO 4 . AII 3 improved the coulombic efficiency of the Li metal anode in both the binary solvent systems. Two-dimensional Li ionic currents at the interface of the Li metal anode were monitored by using in situ scanning vibrating electrode technique (SVET) in the representative binary system, PC + 2Me-THF/LiClO 4 , in the absence and presence of the additives. The relationship between the coulombic efficiency and the Li ionic current distribution on the anode was discussed.

Solvation of Lithium Ions in Mixed Organic Electrolyte Solutions by Electrospray Ionization Mass Spectroscopy

In the studies of secondary lithium batteries, solvation of lithium ions in mixed organic electrolyte solutions has been an important problem in view of the development of advanced batteries. The formation of ion-permeable film at the interface between the negative electrodes and electrolyte solutions of secondary lithium batteries has been reported. 1-4 In such process, the solvent molecules react with the negative electrode and also probably react with the positive electrode. In mixed organic electrolyte solutions, solvent molecules which are solvated preferentially to lithium ions would react with the electrodes and the chemical species near the electrodes. Therefore, the solvated molecules to lithium ions would concern the film formation at the interface between the electrode and the electrolyte and affect the composition of the film formed. 4 As to the solvation of lithium ions in the organic electrolyte solutions some papers have been reported. In these previous papers, 5-12 Raman spectroscopy, nuclear magnetic resonance, and conductivity measurement varying the composition of the solutions were applied to study the solvation. The results were somewhat different for the mixed solvent systems depending on the measuring methods. Electrospray ionization-mass spectroscopy ~ESI-MS! emerged as a powerful technique for producing intact ions in vacuo from large and complex species in solution and was first applied to mass spectrometric analysis to large and fragile polar biomolecules in the gas phase. 13 In the paper, 13 nonvolatile small molecules and large biomolecules were diluted at concentrations from 2 to 100 ppm in 50:50 methanol:water. Then it spread to analytical studies of alkali metal cations solvent complexed with 18-crown-6, 14 transition-metal ion complexed with solvent, 15 and alkali metal cations/solvent binding. 16 In a previous paper, 17 ESI-MS was first introduced into the estimation of solvation number of solvents to lithium ion in single aprotic solvents containing lithium salts. At the present time, ESI-MS is used widely in the investigation of ionic species of molecular weight of ca. 50. In view of preferential solvation of solvent molecules to a cation in mixed organic electrolyte solutions, the donor number of the solvent has been considered to be a measure of solvent/cation interaction, 18-21 but the solvation of lithium ions in mixed organic electrolyte solutions has not been studied actively. In the present work, the solvation of lithium ions in mixed organic electrolyte solutions in which the structure of solvated lithium ions had not been investigated was studied by means of ESI-MS to clarify the solvation of lithium ions in the electrolyte solution of secondary lithium batteries and very interesting results were obtained. Experimental Sample solutions were prepared using LiClO4 ~reagent grade!, diethyl carbonate ~DEC!, dimethyl carbonate ~DMC!, ethylene carbonate ~EC!, g-butyrolactone ~GBL!, propylene carbonate ~PC!, ~lithium battery grade, Ube Industries!, and methanol ~MeOH !~ reagent grade!. The dilute solutions were prepared by mixing the binary mixed aprotic solvent containing 0.5 3 10 26 mol/L LiClO4 and methanol in the volumetric ratio of 1:20, because a low viscous solution is necessary for passing the solution through the feeding nozzle of electrospray ionization mass spectrometer. The details of ESI-MS have been presented in a previous paper. 17 The instrument was a mass spectrometer ~JEOL-D300! furnished with an electrospray ionization interface. Samples diluted with methanol were introduced at a rate of 2.5 mL/min to the injector whose nozzle was equipped with a conductor connecting to a high voltage direct current ~dc! source. High dc voltage applied on the nozzle and the samples contained in methanol were positively charged. The lithium ions solvated to the aprotic solvent molecules were introduced together with methanol, through a path of which temperature was controlled by heated nitrogen gas, to a skimmer, and methanol and free aprotic solvents were stripped there. Then the solvated lithium ions were injected into the mass analyzer.

Studies on Solvation of Lithium Ions in Organic Electrolyte Solutions by Electrospray Ionization-Mass Spectroscopy

Solvation of lithium ions in organic electrolyte solutions, ethylene carbonate ~EC!, propylene carbonate ~PC!, and g-butyrolactone ~GBL! containing LiClO4, for lithium batteries was studied by electrospray ionization-mass spectroscopy ~ESI-MS!. The mass spectrograms showed that a lithium ion solvated with two or three solvent molecules.

Effects of electrolyte composition on the charge and discharge performances of LiNiO2 positive electrode for lithium ion batteries

Charge and discharge behaviour of LiNiO2 positive electrode has been examined in organic electrolytes with different compositions. The discharge capacity of the oxide electrode at a moderate cycling rate varied with the electrolyte composition. Redox responses in potential sweep voltammetry also depended on the kind of lithium salt and solvent of the electrolyte. Electrolyte solutions of relatively low ionic conductivity generally gave lower voltammetric responses and rate capability. A.c. impedance analysis of the LiNiO2 electrode before and after the charge and discharge demonstrated that the surface chemistry of the oxide, depending on the electrolyte composition, has an important influence on the rate capability of the oxide electrode in organic electrolyte solutions.

Effect of organic additives in electrolyte solutions on behavior of lithium metal anode

Abstract Addition effect of polymer materials, polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN) and polyethylene oxide (PEO) in the electrolyte solutions, ethylene carbonate (EC)–propylene carbonate (PC) (1:1 vol.)/ 0.25xa0mol/l LiBF 4 or Li (CF 3 SO 2 ) 2 N, was investigated. In the electrolyte solutions containing PVP the charge–discharge current efficiency of lithium on Ni electrode was the highest and the interface resistance between a lithium metal electrode and the electrolyte solution was small during charge–discharge cycle.

Solvation of lithium ions in organic electrolytes of primary lithium batteries by electrospray ionization-mass spectroscopy

Abstract Solvation of lithium ions in the organic electrolyte solutions for primary lithium batteries was investigated by electrospray ionization-mass spectroscopy (ESI-MS). In LiBF 4 /γ-butyrolactone (GBL), lithium ions were solvated to GBL molecules in the form [Li(GBL) 2 ] + or [Li(GBL) 3 ] + , and in LiClO 4 / dimethoxyethane (DME)–propylene carbonate (PC), lithium ions were solvated mainly to DME and PC in the form [Li(DME)(PC)] + .

Effect of organic additives in electrolyte solutions on lithium electrode behavior

Abstract Charge–discharge behavior of Li and Li–Al anodes has been investigated by measurement of AC impedance and polarization resistance. The anodes showed lower interfacial resistance in ethylene carbonate (EC)–dimethyl carbonate (DMC)/1 M LiPF 6 than that in EC–diethyl carbonate (DEC)/1 M LiPF 6 . The interfacial resistance between Li–Al electrode and electrolyte solution decreased with content of Al in the alloy. Further, addition of 2-methylfuran (2MeF), 2-methyltetrahydrofuran (2MeTHF), 2-methylthiophene (2MeTp) and polyethylene oxide (PEO) in the electrolyte solutions decreased the polarization resistance.

Effects of the electrolyte composition on the electrochemical lithium-intercalation behavior of graphite-analysis by electrochemical quartz crystal microbalance technique

Abstract Electrochemical lithium intercalation into graphite and related carbonaceous materials has been investigated in ethylene carbonate (EC)-based organic electrolytes using electrochemical quartz crystal microbalance (EQCM). During constant-current charging (cathodic polarization), changes in the resonance frequency indicated the mass of the electrode increasing generally with an increase in charge passed. The mass change of the graphite per quantity of electricity (Δ m Δ Q −1 ) depended on the electrolyte composition in the potential range of 0.0–0.2 V versus Li/Li + as well as in the more positive potential range. Variations in Δ m Δ Q −1 with electrode potential revealed that the relative rate of electrolyte decomposition yielding precipitation on the graphite surface changes with electrode potential. For the artificial graphite, the mass change in EC + DMC (dimethyl carbonate) containing LiClO 4 was larger than that in EC + PC (propylene carbonate) containing LiClO 4 , which suggested that the process in EC + DMC is somewhat different from that in EC + PC. These results are discussed in connection with those obtained from conventional electrochemical and X-ray diffraction measurements.

Electrolyte solutions for anodes in rechargeable lithium batteries

Abstract The suitability of organic electrolyte systems for highly graphitized carbon anodes has been discussed by considering the stability of co-solvents included in ethylene carbonate-based electrolytes and the stability of lithium salts. The side-reaction and the film formation on the graphitized anodes were found to affect the discharge capacity of the graphitized anodes. With respect to the lithium salts, lithium bistrifluoromethylsulfonyl imide offered high and stable capacity. Furthermore, the electrochemical behavior of a surface film on a lithium metal anode was investigated at various operating temperatures. It was found that the operating temperature during charge/discharge cycling influences the morphology of the film on a lithium metal anode, resulting in the variation in charge/discharge coulombic efficiency of a lithium metal anode. The results are discussed in view of the stability of electrolyte solutions and the film formation between the negative electrode and the organic electrolyte solution.

Application of gel alkylene oxide electrolytes to rechargeable lithium batteries

Advanced gel polymer electrolytes of alkylene oxide system were prepared. The base polymer was random copolymer of alkylene oxide system (MW: 8000, ethylene oxide (EO): ca. 80%, propylene oxide (PO): ca. 20%, end functional group: acrylic group). The gel polymer electrolyte was prepared by mixing the base polymer, a solvent, a lithium salt and an initiator followed by UV irradiation. Ionic conductivity of gel polymer electrolyte was measured with ac method at temperature range between -20 and + 60°C. The ionic conductivity reached over 2.5 mS cm -1 at 20°C when LiBF 4 /γ-butyrolactone (GBL) solution was incorporated as an electrolyte. The discharge capacity with charge-discharge cycle of test cells, C n -Li/LiCoO 2 , with the gel polymer electrolyte was more stable during cycling than that with liquid organic electrolyte solution. It was affected by the kind of plasticizer in the gel electrolyte. The capacity of the test cell was limited by the weight of cathode active material (1.3 mAh). The highest discharge capacity was attained using C n -Li/the base polymer-GBL-LiBF 4 /LiCoO 2 and its utilization rate of the cathode material was 83%.