Per Jacobsson

The effect of nano-particle TiO2 fillers on structure and transport in polymer electrolytes

Nano-particle oxide fillers including TiO2, SiO2 and Al2O3 have previously been shown to have a significant affect on the properties of polymer electrolytes, especially those based on polyether–lithium salt systems. In some cases, conductivity increases of more than one order of magnitude have been reported in crystalline PEO-based complexes. In this work, we report on the effects of TiO2 on a completely amorphous polyether-based system to remove the complication of multiple phases presented by the semi-crystalline nature of PEO. Multinuclear magnetic resonance spectroscopy has shown that the lithium ion environment is changed by the addition of filler. Vibrational spectroscopy shows that the filler influences the disordered-longitudinal acoustic modes (DLAM) in the case of an amorphous polyether and suggests an interaction between the filler surface and the polymer. Positron annihilation lifetime spectroscopy indicates an increase in free volume upon addition of filler to an amorphous polyether–salt complex, coinciding with an apparent increase in polymer mobility as determined from 1H T2 NMR measurements. Impedance spectroscopy has shown clear evidence of an inter-phase region that may be more or less conductive than the bulk polymer electrolyte itself. The data support a model which includes conduction through an interfacial region in addition to the bulk polymer

A FTIR and Raman study of spontaneous reactions occurring at the LiNiyCo(1-y)O2 electrode/non-aqueous electrolyte interface

Spontaneous reactions occurring at the surface of LiNiyCo(1−y)O2-based electrodes during contact with non-aqueous organic electrolytes have been investigated by FTIR and Raman spectroscopy. It is found that several types of compounds and/or functional groups are formed on the electrode surface and that these compounds appear to be dependent on the type of electrolyte used. Thus, for a LiClO4-propylene carbonate (PC) electrolyte, the main reaction is formation of Li-carbonate, whereas in the case of LiPF6-ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte formation of P-, O- and F-containing compounds dominate. Spectroscopic data also show a variation of the LiNi(1−y)CoyO2 crystalline structure during storage in an electrolyte which probably is due to a spontaneous deintercalation of the Li ions. An analysis of the newly formed species is presented and possible reaction mechanisms are discussed.

Enhancement of ion dynamics in PMMA-based gels with addition of TiO2 nano-particles

Solvent and ion dynamics in PMMA based gels have been investigated as a function of the loading of nanosized TiO2 particles. The gels have a molar ratio of 46.5:19:4.5:30 of ethylene carbonate (EC), propylene carbonate (PC), lithium perchlorate and PMMA, respectively. A series of samples with 0, 4, 6 and 8 wt.% TiO2 filler were investigated. The diffusion coefficients for the lithium ions and for the two solvents (EC and PC) were investigated by pfg-NMR. It was shown that the addition of filler to the gel electrolytes enhances the diffusion of the cations, while the diffusion of the solvents remains constant. Raman measurements show no significant changes in ion–ion interactions with the addition of fillers, while the ionic conductivity is seen to decrease. However, the sample with 8 wt.% TiO2 had a conductivity close to that of the unfilled sample.

Phase behavior and ionic conductivity in lithium bis(trifluoromethanesulfonyl)imide-doped ionic liquids of the pyrrolidinium cation and Bis(trifluoromethanesulfonyl)imide anion.

The phase behavior and the ionic conductivity of ionic liquids (ILs) of the N-alkyl-N-alkylpyrrolidinium (PYR(xy)) cation and the bis(trifluoromethanesulfonyl)imide (TFSI) anion are investigated upon addition of LiTFSI salt. We compare the case of two new ILs of the PYR(2y) cation (where 2 is ethyl and y is butyl or propyl) with that of the PYR(14) (where 1 is methyl and 4 is butyl). We find that the addition of LiTFSI increases the glass transition temperature, decreases the melting temperature and the heat of fusion and, in the ILs of the PYR(2y) family, suppresses crystallization. In the solid state, significant ionic conductivities are found, being as high as 10(-5) S cm(-1), strongly increasing with Li(+) concentration. The opposite trend is found in the liquid state, where the conductivity is on the order of 10(-3)-10(-2) S cm(-1) at room temperature. A T(g)-scaled Arrhenius plot shows that the liquid-state ionic conductivity in these systems is mainly governed by viscosity and that the fragility of the liquids is slightly influenced by the structural modifications on the cation.

Reactivity of lithium battery electrode materials toward non-aqueous electrolytes: spontaneous reactions at the electrode-electrolyte interface investigated by FTIR

Abstract Spontaneous reactions occurring at the surface of LiNi 0.8 Co 0.2 O 2 and LiMn 2 O 4 -based electrodes during the storage in organic non-aqueous electrolytes have been investigated by diffuse reflectance FTIR technique. It is found that both materials spontaneously form different inorganic and organic compounds on their surface when in contact with electrolyte solutions. The nature of these self-acting reactions is moreover found to be similar to that of the processes occurring during electrochemical cycling of the electrodes. Reaction mechanisms and the final products depend on both electrode surface chemistry and the nature of electrolyte used. It appears that the spontaneous reactions are initiated by lithium deintercalation from the electrode active material. The influence of different factors, e.g. degree of lithiation of the active material, roughness of the electrode surface and temperature on the reaction rate is discussed.

Raman, infra-red and d.s.c. studies of lithium coordination in a thermoplastic polyurethane

Abstract Fourier transform ( FT )-Raman and infra-red (i.r.) spectroscopy were utilized to monitor changes in the morphology of a commercial, phase-segregated thermoplastic polyurethane (TPU) as a function of LiClO 4 concentration (0.1 to 2.0mmol/g TPU). Significant changes in both the FT -Raman and the FT i.r. spectra were detected which suggest a competition between hydrogen bonding and lithium cation coordination, especially between the hard segments of the host polymer matrix. A loss in long-range ordering of the hard domain was observed by differential scanning calorimetry with an increase in salt concentration. The ionic conductivity (σ) was found to increase with increasing temperature and salt concentration. For the highest concentration used, σ ranged from a very low value of ∼ 1 × 10 −9 S cm −1 at room temperature to ∼ 1 × 10 −4 S cm −1 at 130°C

The molar conductivity behavior in polymer electrolytes at low salt concentrations; A Raman study of poly(propylene glycol) complexed with LiCF3SO3

Raman scattering measurements have been carried out on poly(propylene glycol) complexed with LiCF 3 SO 3 salt over a wide salt concentration range, the ether oxygen to alkali metal cation ratios (O : M) ranging from 4820 : to 12 :1. The relative concentrations of solvated anions, anion-cation pairs and ionic aggregates have been calculated from an analysis of the symmetric anion stretch. The degree of association is found to be almost constant in the O : M range 4820 : 1-40 : 1 whereafter it increases with increasing salt concentration. The results show that the dramatic increase reported for the molar conductivity in the O : M range 1000 : 1-40 : 1 cannot be explained by the redissociation of contact ion pairs or the formation of conducting triplets. Instead the major contribution to the conductivity increase seems to be a concentration dependent enhancement of the ionic mobility. A percolation based ionic hopping process involving exchange between ions in pairs and dissolved ions, either free or coordinated to ether oxygen sites, is advanced as a possible microscopic mechanism.

A Raman study of ion-polymer and ion-ion interactions in low molecular weight polyether - LiCF3SO3 complexes.

Abstract We report Raman scattering investigations of the stability of various ion—polymer interactions from studies of LiCF 3 SO 3 —polyethers. New results for endcapped polyethers of different molecular weights in the range of one to eight repeat units are compared with previous data from OH-terminated polyether salt complexes. We conclude that anions coordinated to OH-endgroups are more stable than cations forming crosslinks between oxygens of adjacent polymer chains which in turn are more stable than cations coordinated to single oxygens. It is the weak oxygen—cation bond which is causing the dramatic increase in ion—ion association as tempearature increases. OH—anion bonds are little affected by temperature.

NMR and Raman characterization of pressure polymerized C60

Bulk C60 has been treated at 1.1 GPa and 550–585 K, producing a dense insoluble material which on heating to above 600 K reverts to normal C60. Raman and IR studies on modified material show a larg ...

Ion transport in polymer electrolytes containing nanoparticulate TiO2: The influence of polymer morphology

Recent studies have shown that composite polymer electrolytes, formed by dispersing nanosized ceramic particles in polyether-based electrolytes, have improved ion transport properties as compared to their unfilled analogues. In the present study polymer electrolytes with different loadings of nano-sized ceramic particles (TiO2) and different polymer chemistry and morphology have been investigated. Of special interest are filler induced effects on polymer, solvent and cationic mobility. Partly crystalline polymer electrolytes based on poly(ethylene oxide) have been compared to fully amorphous polymer electrolytes based on a polyether urethane, as well as gel electrolytes based on PMMA. 7Li pfg-NMR, linewidth and spin–spin relaxation times as well as 1H pfg-NMR and spin–spin relaxation times, were measured as a function of temperature and composition. The 1H spin–spin relaxation measurements reveal increased average polymer mobility with the addition of filler up to a maximum at 4 and 8 wt.% TiO2 for the fully amorphous and the partly crystalline electrolytes, respectively. The 7Li linewidth measurements for the fully amorphous system show a broadening of the linewidth with addition of filler. Based on variable temperature measurements this broadening is interpreted as a result of the inhomogeneity introduced by the filler particles. Pulsed field gradient (pfg) diffusion measurements were employed to determine ion and solvent self-diffusion coefficients. In the case of the PMMA-based gel electrolyte and the fully amorphous electrolytes enhanced cation self-diffusion was observed upon addition of TiO2.