In situ FTIR study of the Cu electrode/ethylene carbonate + dimethyl carbonate solution interface

The interfacial phenomena between Cu electrode and solution of lithium perchlorate in ethylene carbonate (EC)-dimethyl carbonate (DMC) have been investigated using in situ reflection absorption Fourier transform infrared (FTIR) spectroscopy and single reflection ATR-FTIR spectroscopy. The ATR spectra confirmed the bands due to free EC and DMC and the molecules solvated to lithium ions in the solution. The bands due to the result of the interaction between ClO₄⁻ and DMC in the mixture solution also appeared in the ATR spectra. In the FTIR spectra, the potential dependence on the concentration of EC and DMC in the vicinity of the Cu electrode was observed. It was understood that the reversible changes in the concentration of free EC and DMC and solvated EC and DMC in the diffuse double layer take place with changing in potential. As the potential decreased, the free EC and DMC concentrations increased, while the concentration of the EC and DMC solvated to lithium ions decreased. Thus, it can be concluded that the equilibrium shifts from Li⁺(EC)₂(DMC)₂ to Li⁺(EC)₂(DMC) + DMC or Li⁺(EC)(DMC)₂ + EC as the potential decreases. The bands due to (CH₂OCO₂Li)₂ and CH₃OCO₂Li were observed for an irreversible reaction.     

In situ FTIR spectra at the Cu electrode/propylene carbonate solution interface

In situ Fourier transform infrared spectroscopy (FTIR) spectra measurements were obtained for a Cu electrode/solution of lithium perchlorate in propylene carbonate (PC). The dependence of potential on the concentration of PC in the vicinity of the electrode was investigated. The bands due to free PC and PC solvated to lithium ions in the solution were distinguished by the single reflection attenuated total reflection (ATR) spectra. In the FTIR spectra, the reversible change in the concentration of free PC and solvated PC in the diffuse double layer was observed to be accompanied by a change in potential. As the potential decreased, the free PC concentration increased, while the concentration of the PC solvated to lithium ions decreased. Thus, it can be concluded that the equilibrium shifts from Li⁺(PC)₄ to Li⁺(PC)₃ + PC as the potential decreases. Furthermore, Li⁺(PC)₃ orientates itself so that it is parallel to the electrode surface.     

On the electric double-layer structure at carbon electrode/organic electrolyte solution interface analyzed by ac impedance and electrochemical quartz-crystal microbalance responses

ac impedance and electrochemical quartz crystal microbalance (EQCM) techniques have been applied to analyze the structure of electric double-layer formed at carbon/organic electrolyte solution interface using a sputtered carbon electrode. The mass changes caused by electrochemical adsorption (accumulation) of ions have been estimated in the solutions of propylene carbonate (PC) dissolving tetrafluoroborate (BF₄⁻) salts of lithium (Li⁺), tetraethylammonium (TEA⁺) and tetra-n-butylammonium (TBA⁺) cations. The observed mass changes during the cathodic polarization in the solutions containing TEA⁺ and TBA⁺ were well consistent with those expected by the calculation based on mono-layer adsorption of the cations with giving the consideration to the surface roughness. On the other hand, the mass change observed in the solution containing Li⁺ salt showed that the solvation of Li⁺ with three or four molecules of PC would be the charge compensation species at the interface. Comparison of the quantity of the electricity passed during the EQCM measurements with that from theoretical calculation with simple Helmholtz-layer model revealed that the major part of the double-layer capacitance would be based on the electrostatic polarization of the solvent molecule directly adsorbed at the carbon surface.     

Behaviour of highly crystalline graphitic materials in lithium-ion cells with propylene carbonate containing electrolytes: An in situ Raman and SEM study

The microcrystalline flaked graphites SFG6 and SFG44 were evaluated with regard to their compatibility with propylene carbonate (PC) by in situ Raman microscopy and postmortem scanning electron microscopy (SEM) study. PC is employed as electrolyte component in lithium-ion batteries. However, when used with certain types of graphitic materials, exfoliation occurs. To compare the effects of exfoliation, the first lithium insertion properties of these graphitic materials were measured with in situ Raman microscopy. Lithium half-cells containing either 1 M LiClO₄ 1:1 (w/w) ethylene carbonate (EC):dimethyl carbonate (DMC) or 1:1 (w/w) EC:PC were investigated. The commencement of the exfoliation process was detected in SFG44 EC:PC by the appearance of a shoulder band at 1597 cm⁻¹ on the G-band (1584 cm⁻¹) below 0.9 V versus Li/Li⁺. The band (assigned as the exfoliation or E-band) at higher wavenumbers (1597 cm⁻¹) corresponded to solvated lithium ions intercalated into graphite. The in situ Raman spectra of SFG6 in EC:DMC or EC:PC and SFG44 in EC:DMC did not show the E-band and instead displayed regular lithium intercalation spectra.In situ Raman microscopy and SEM were further employed to study the exfoliation process observed for SFG44 in 1:1 (w/w) EC:PC, when the potential was held under steady-state conditions at 0.8, 0.6 and 0.3 V, respectively. A blue-shift in the E-band from 1597 to 1607 cm⁻¹ was observed as the potential was lowered. SEM images showed dissimilar degrees of exfoliation at these three potentials.     

Ion-pairing effects and ion-solvent-polymer interactions in LiN(CF3SO2)2-PC-PMMA electrolytes: a FTIR study

FTIR spectroscopic investigations coupled with ionic conductivity and viscosity measurements on lithium imide (LiN(CF₃SO₂)₂)-propylene carbonate (PC)-poly(methyl methacrylate) (PMMA) based liquid and gel electrolytes over a wide range of salt (0.025-3 M) and polymer (5-25 wt.%) concentration range furnish a novel insight into the ion-ion and ion-solvent-polymer interactions. Vibrational spectral data for LiN(CF₃SO₂)₂-PC electrolytes reveal that the solvation of lithium ions manifests from Li⁺OC and Li⁺O (ring oxygens) interactions as the ν_s(CO), the ring breathing and the δ(CH) modes of the pentagonal solvent ring are strongly perturbed for all salt concentrations. The split of the ν(SO₂) mode (that appears at 1355 cm⁻¹ for the “free imide ion”) into two components at 1337 and 1359 cm⁻¹ confirms the existence of contact ion-pairs possessing two different stable optimized geometries wherein the Li⁺ ion coordinates in a bidentate fashion in liquid and gel electrolytes of 3 M LiN(CF₃SO₂)₂-PC strength. Perturbations observed for the ν_a(SNS) and ν_s(SNS) modes of the imide ion and the symmetric ring deformation mode of PC confirms the presence of ion-pairs in both 2 and 3 M electrolytes. Incorporation of even upto 25 wt.% of PMMA in a solution of LiN(CF₃SO₂)₂-PC of 3 M strength results in an insignificant conductivity decline (as σ₂₅>10⁻³ S cm⁻¹) which is simultaneously accompanied by a massive increase in its macroscopic viscosity (as η₂₅>10⁸ cSt). Gels containing 25 wt.% of PMMA exhibit a complex pattern of Li⁺-PMMA interactions through the carbonyl oxygen of its ester group which is evidenced from the perturbations observed for the ν_s(CO) mode of PMMA. Ionic conductivity decline that occurs at salt concentrations ≥1.25 M LiN(CF₃SO₂)₂-PC in both liquid and gel electrolytes, is therefore attributable to (i) ion-pairing phenomenon and (ii) an enhancement in the solution viscosity due to a high salt proportion.     

Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions

The potentiometric response of the Li⁺ ion-selective electrode based on the fast ion conductor Li_3xLa_2/3−xTiO₃ (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li⁺ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li⁺ activity in anhydrous solutions through a Li⁺ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li⁺ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li⁺ exchange reaction. An apparent standard current density of 12 μA/cm² and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li⁺ ion exchange mechanism in Li⁺ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti-O]⁻ with H₂O and/or to the formation of a water layer on the oxide surface.     

Characterisation of the SEI formed on natural graphite in PC-based electrolytes

The origin of the different Li⁺ intercalation behaviour of raw and jet-milled natural graphite has been investigated. Jet-milled graphite is found to cycle reversibly in equal solvent mixture of propylene carbonate (PC) and ethylene carbonate (EC), whereas raw graphite does not. Using both Al Kα and synchrotron radiation (SR) Photoelectron Spectroscopy, new insight is obtained into the formation of the solid electrolyte interphase (SEI) on the two different graphite materials during electrochemical cycling in 1 M LiPF₆ in either PC:EC (1:1) or in PC with 5% vinylene carbonate (VC) as additive. Solvent reduction products are found at the surface of both raw and jet-milled graphite cycled in PC:EC (1:1), but differed in composition. The addition of VC reduces primarily the quantities of salt reaction products (LiF and Li_xPF_y compounds) and produces a mainly organic SEI layer. Electron diffraction from the edges for raw and jet-milled graphite particles shows a more disordered surface structure in the jet-milled particles than in the raw graphite. The more disordered surface structure can serve as a physical barrier hindering PC co-intercalation and facilitating the formation of a stable SEI layer.     

Properties of Li-graphite and LiFePO4 electrodes in LiPF6–sulfolane electrolyte

Sulfolane (also referred to as tetramethylene sulfone, TMS) containing LiPF₆ and vinylene carbonate (VC) was tested as a non-flammable electrolyte for a graphite |LiFePO₄ lithium-ion battery. Charging/discharging capacity of the LiFePO₄ electrode was ca. 150 mAh g⁻¹ (VC content 5 wt%). The capacity of the graphite electrode after 10 cycles establishes at the level of ca. 350 mAh g⁻¹ (C/10 rate). In the case of the full graphite |1 M LiPF₆ + TMS + VC 10 wt% |LiFePO₄ cell, both charging and discharging capacity (referred to cathode mass) stabilized at a value of ca. 120 mAh g⁻¹. Exchange current density for Li⁺ reduction on metallic lithium, estimated from electrochemical impedance spectroscopy (EIS) experiments, was j_o(Li/Li⁺) = 8.15 × 10⁻⁴ A cm⁻². Moreover, EIS suggests formation of the solid electrolyte interface (SEI) on lithium, lithiated graphite and LiFePO₄ electrodes, protecting them from further corrosion in contact with the liquid electrolyte. Scanning electron microscopy (SEM) images of pristine electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of SEI formation. No graphite exfoliation was observed. The main decomposition peak of the LiPF₆ + TMS + VC electrolyte (TG/DTA experiment) was present at ca. 275 °C. The LiFePO₄(solid) + 1 M LiPF₆ + TMS + 10 wt% VC system shows a flash point of ca. 150 °C. This was much higher in comparison to that characteristic of a classical LiFePO₄ (solid) + 1 M LiPF₆ + 50 wt% EC + 50 wt% DMC system (T_f ≈ 37 °C).     

FTIR studies of chitosan acetate based polymer electrolytes

Chitosan is the product when partially deacetylated chitin dissolves in dilute acetic acid. As such, depending on the degree of deacetylation, the carbonyl, CONHR band can be observed at ∼1670 cm⁻¹ and the amine, NH₂ band at 1590 cm⁻¹. When lithium triflate is added to chitosan to form a film of chitosan acetate-salt complex, the bands assigned to chitosan in the complex and the spectrum as a whole shift to lower wavenumbers. The carbonyl band is observed to shift to as low as 1645 cm⁻¹ and the amine band to as low as 1560 cm⁻¹. These indicate chitosan-salt interactions. Also present are the bands due to lithium triflate i.e. ∼761, 1033, 1182 and 1263 cm⁻¹. When chitosan and ethylene carbonate (EC) are dissolved in acetic acid to form a film of plasticized chitosan acetate, the bands in the infrared spectrum of the films do not show any significant shift indicating that EC does not interact with chitosan. EC-LiCF₃SO₃ interactions are indicated by the shifting of the CO bending band from 718 cm⁻¹ in the spectrum of EC to 725 cm⁻¹ in the EC-salt spectrum. The Li⁺-EC is also evident in the ring breathing region at 893 cm⁻¹ in the pure EC spectrum. This band has shifted to 898 cm⁻¹ in the EC-salt spectrum. CO stretching in the doublet observed at 1774 and 1803 cm⁻¹ in the spectrum of pure EC has shifted to 1777 and 1808 cm⁻¹ in the EC-salt spectrum.     

The study on the conductivity and morphology of polyurethaneurea electrolytes based on poly(ethylene glycol) 2000 and LiClO4

Polyurethaneureas (PUU), which were synthesized from 4,4′-diphenylmethane diisocyanate (MDI), poly(ethylene glycol) (PEG, MW=2000), and 3,5-diaminobenzoic acid, were used as the matrix of the polyelectrolytes in this study. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and ⁷Li magic angle spinning (MAS) solid-state NMR were used to monitor changes in the morphology of PUU electrolytes corresponding to the concentration of lithium perchlorate (LiClO₄) dopants. The results of DSC and FT-IR indicate the different polymer complexes formed by the interaction of the Li⁺ ions with the different coordination sites of PUU. The ⁷Li MAS solid-state NMR investigation of the PUU electrolytes points out that two different Li⁺ environments exist at lower temperature. The results of DSC and the ⁷Li MAS solid-state NMR show that Li⁺ ions are preferentially coordinated to the ether oxygen of the PEG soft-segment when the salt concentration is below 0.1 mmol LiClO₄(gPUU)⁻¹. Impedance spectroscopy measurements show that the conductivity behavior followed the Arrhenius equation and was influenced by the hard-segment T_g. One of the PUU electrolytes under the investigation has an ionic conductivity as high as 3.0×10⁻⁵ S cm⁻¹ at 30 °C.     

Lithium sulfonated styrene oligomer (LiSSO) as a new class of lithium salt for polymer electrolytes

Summary   A new class of lithium salt with single-ionic characteristics, lithium sulfonated styrene oligomer (LiSSO) [(CH₂CHC₆H₅)₇-(CH₂CHC₆H₄SO₃ ⁻Li⁺)₂], was synthesized and its complex with poly(ethylene oxide) (PEO) was prepared. The maximum ionic conductivity of the PEO/LiSSO complex at 65°C was 2.1×10⁻⁴S/cm at a salt concentration of [Li⁺]/[EO] = 0.20. The lithium cationic transference number (t ₊) of the PEO/LiSSO complex was found to be 0.95, and the polymer electrolyte was electrochemically stable up to 6.2V. Received: 2 April 2001/Revised version: 30 July 2001/Accepted: 30 July 2001     

Dye-sensitised photoelectrochemical solar cells with polyacrylonitrile based solid polymer electrolytes

Novel all solid state dye-sensitised photolectrochemical solar cells of the type, FTO-TiO₂-dye-PAN, EC, PC, Pr₄N⁺I⁻, I₂-Pt-FTO, have been fabricated and characterised using current-voltage characteristics and action spectra. Liquid electrolyte generally used for such solar cells has successfully replaced by a quasi solid electrolyte comprised of polyacrylonitrile (PAN) with ethylene carbonate (EC) and propylene carbonate (PC) as plasticisers and Pr₄N⁺I⁻/I₂ redox couple with tetrapropylammoniumiodide as the complexing salt. For the polymer electrolyte, the optimum conductivity of 2.95×10⁻³ S cm⁻¹ was obtained for the electrolyte composition, PAN:EC:PC=15:35:50 (wt.%). The short circuit current density (J_SC) and the open circuit voltage (V_OC) obtained for an incident light intensity of 600 W m⁻² were 3.73 mA cm⁻² and 0.69 V, respectively. This corresponds to an overall quantum efficiency of 2.99%. From the action spectrum, the maximum incident photon conversion efficiency (IPCE) of 33% was obtained for incident light of wavelength 480 nm.     

Boroxine ring compounds as dissociation enhancers in gel polyelectrolytes

In order to combine the advantages of both traditional gel electrolytes and polyelectrolytes, a novel polyelectrolyte which incorporates a boroxine ring-containing anion-trapping agent has been explored. Poly(lithium 2-acrylamido-2-methyl-1-propanesulfonate) (PAMPSLi), ethylene carbonate (EC) and tri(methoxyethoxyethoxyethoxy)boroxine (TME₃Bx) were combined to prepare various gel systems. The thermal properties and conductivities of these gels have been investigated. A conductivity of 10^−3.6 S cm⁻¹ at 20 °C has been achieved in a gel polyelectrolyte system with a molar ratio of [EC]:[TME₃Bx]:[Li⁺]=24:1.7:1. Temperature-dependent NMR measurements indicated that a significant interaction exists between the boroxine ring and the polyelectrolyte.     

Room temperature molten salts as lithium battery electrolyte

In the present study, are reported investigations obtained with the room temperature molten salt (RTMS) ethyl-methyl-imidazolium bis-(trifluoromethanesulfonyl)-imide (EMI-TFSI) in order to use it as solvent in lithium battery. The thermal stability, viscosity, conductivity and electrochemical properties are presented. A solution of 1m lithium bis-(trifluoromethanesulfonyl)-imide (LiTFSI) in EMI-TFSI has been used to test the electrolyte in a battery with LiCoO₂ and Li₄Ti₅O₁₂ as respectively cathode and anode materials. Cycling and power measurements have been obtained. The results have been compared with those obtained with a molten salt formulated with a different anion, BF₄⁻ and with a conventional liquid organic solvent EC/DMC containing LiTFSI. The 1m LiTFSI/EMI-TFSI electrolyte provides the best cycling performance: a capacity up to 106 mAh g⁻¹ is still delivered after 200 cycles, with 1C rate at 25 °C.     

Ionic liquid electrolytes based on multi-methoxyethyl substituted ammoniums and perfluorinated sulfonimides: Preparation, characterization, and properties

New functionalized ionic liquids (ILs), comprised of multi-methoxyethyl substituted quaternary ammonium cations (i.e. [N(CH₂CH₂OCH₃)_4−n(R)_n]⁺; n = 1, R = CH₃OCH₂CH₂; n = 1, R = CH₃, CH₂CH₃; n = 2, R = CH₃CH₂), and two representative perfluorinated sulfonimide anions (i.e. bis(fluorosulfonyl)imide (FSI⁻) and bis(trifluoromethanesulfonyl)imide (TFSI⁻)), were prepared. Their fundamental properties, including phase transition, thermal stability, viscosity, density, specific conductivity and electrochemical window, were extensively characterized. These multi-ether functionalized ionic liquids exhibit good capability of dissolving lithium salts. Their binary electrolytes containing high concentration of the corresponding lithium salt ([Li⁺] >1.6 mol kg⁻¹) show Li⁺ ion transference number (tLi⁺) as high as 0.6-0.7. Their electrochemical stability allows Li deposition/stripping realized at room temperature. The desired properties of these multi-ether functionalized ionic liquids make them potential electrolytes for Li (or Li-ion) batteries.     

Lithium Diffusion in Lithium Niobate Crystals with Different Initial Li2O Content at High Temperature

Lithium diffusion in lithium niobate crystals with different initial Li₂O content (C_initial) was investigated under Li‐rich environment at 1100°C. Lithium niobate crystals with widely varying diffusion‐limited Li₂O content profiles were prepared through the vapor transport equilibration (VTE) technique using congruent lithium niobate crystals with different C_initial, and the profiles were measured through Curie temperature by a thermal analyzer. A Boltzmann‐Matano analysis was employed to those profiles to estimate the Li⁺ diffusivity as a function of Li₂O content in lithium niobate crystals. A trigonometric function method was applied to those profiles to correlate diffusion time and Li₂O content. The results show that at the same composition of lithium niobate crystals after diffusing treatment, the less the C_initial, the larger the Li⁺ diffusivity. The relation between diffusion time and Li₂O content of the samples which have different C_initial and thickness was derived. Based upon the Boltzmann‐Matano result, diffusion time can be estimated easily from the relation. It is concluded that increasing C_initial contributes to shorten the diffusion time for preparing near‐stoichiometric lithium niobate crystals through the VTE technique, especially for thick crystal wafers.     

Solvents in salt electrolyte: Benefits and possible use as electrolyte for lithium-ion battery

An EC/DEC [40:60% (v/v)] solvent mixture has been added in various amounts to the ionic liquid (IL) hexyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N₁₁₁₆-NTf₂) in the presence of LiNTf₂ (lithium bis(trifluoromethylsulfonyl)imide) as lithium salt for possible use as electrolytes in lithium-ion batteries. These electrolytes exhibit a larger thermal stability than the reference electrolyte EC/DEC [40:60] + LiNTf₂ 1 M when the percentage of the IL exceeds 30% (v/v). All studied electrolytes are glass forming ones with an ideal glass transition temperature of ca. −85 °C(±5 °C), which has been determined by application of the VTF theory to conductivity and viscosity measurements and confirmed by DSC (T_g = −90 ± 5 °C). An electrochemical window of about 5 V versus Li/Li⁺ was measured at a glassy carbon electrode. The cycling ability of the optimized electrolyte N₁₁₁₆-NTf₂/EC:DEC (40/60% (v/v)) + 1 M LiNTf₂ has been investigated at a titanate oxide (Li₄Ti₅O₁₂) and a cobalt oxide (Li_xCoO₂) electrodes. Cycling the positive and the negative electrodes was conducted successfully with a high capacity and without any significant fading.     

Impedance study of protecting film formation on lithium and lithiated graphite induced by bis(fluorosulfonyl) imide anion

The process of Li⁺ reduction from room temperature ionic liquids consisting of N-methyl-N-propylpyrrolidinium cation (MPPyr⁺) and bis(fluorosulfonyl) imide (FSI⁻) or bis(trifluoromethanesulfonyl) imide (TFSI⁻) anions was studied with the use of impedance spectroscopy. Reduction was carried out on both metallic lithium (Li) and graphite (G) electrodes. It has been found that the FSI anion in high amounts is able to form a protective film on both graphite and metallic lithium. The Li⁺/Li couple should rather be represented by a Li⁺/SEI/Li system. The SEI structure depends on the manner of its formation (chemical or electrochemical) and is not stable with time. The rate constant for the Li⁺ + e⁻ → Li process at the Li/SEI/Li⁺ (in MPPyrFSI) interface is k_o = 4.2 × 10⁻⁵ cm/s. In the case of carbon electrodes (G/SEI/Li⁺ interface), lithium diffusion in solid graphite is the rate determining step, reducing current by ca. two orders of magnitude, from ca. 10⁻⁴ A/cm², characteristic of the Li/SEI/Li⁺ electrode, to ca. 10⁻⁶ A/cm².     

Electrochemical behavior of Ge and GeX2 (X = O, S) glasses: Improved reversibility of the reaction of Li with Ge in a sulfide medium

Sulfide glasses have been considered as new anode materials for lithium-ion batteries because their high ionic conductivity (approximately ≥10⁻⁴ S/cm) (more than one order of magnitude higher than oxide glasses (approximately ≤10⁻⁶ S/cm)) was expected to accelerate Li⁺ ion insertion into and extraction from anode materials during charge and discharge reactions. This intrinsic property can yield the reversible lithium-alloying reaction by minimizing the aggregation of lithium-alloy phases leading to the improvement of cycling behavior. To examine sulfide glasses as new anode materials, GeS₂ glass was chosen for study in this work due to its stability in air-atmospheres. The electrochemical properties of the GeS₂ glass were compared with those of the Ge metal and GeO₂ glass. The initial insertion of lithium into the GeX₂ (X = O, S) glasses leads to the formation of Li₂X (X = O, S) phases associated with the irreversible capacity on the first cycle. The improved reversibility of the reaction of lithium with Ge was observed in the Li₂S medium rather than Li₂O one, which leads to the improvement of cycle performance in the GeS₂ glass anode.     

Simple introduction of anion trapping site to polymer electrolytes through dehydrocoupling or hydroboration reaction using 9-borabicyclo[3.3.1]nonane

Organoboron-based anion trapping polymer electrolytes were synthesized through hydroboration or dehydrocoupling reaction between poly(propylene oxide) (PPO) oligomer (M_n = 400, 1200, 2000 and 4000) and 9-borabicyclo[3.3.1]nonane (9-BBN). Obtained oligomers were added various lithium salts (LiN(CF₃SO₂)₂, LiSO₃CF₃, LiCO₂CF₃ or LiBr) to analyze the ionic conductivity and lithium ion transference number (tLi⁺). The ionic conductivity of the oligomer in the presence of LiN(CF₃SO₂)₂ showed higher ionic conductivity than other systems, however, the tLi⁺ was less than 0.3. When LiSO₃CF₃ or LiCO₂CF₃, was added high tLi⁺ over 0.6 was obtained. Such difference in tLi⁺ can be explained by HSAB principle. Since boron is a hard acid, soft (CF₃SO₂)₂N⁻ anion can not be trapped effectively. High ionic conductivity of 1.3 × 10⁻⁶ S cm⁻¹ and high tLi⁺ of 0.73 was obtained when PPO chain length was 2000. These values of facilely prepared polymer electrolytes are comparable to those of the PPOs having covalently bonded salt moieties on the chain ends.