Oligo(ethylene oxide)-functionalized trialkoxysilanes as novel electrolytes for high-voltage lithium-ion batteries

Oligo(ethylene oxide)-functionalized trialkoxysilanes were synthesized through hydrosilylation reaction by reacting trialkoxysilane with oligo(ethylene oxide) allyl methyl ether using PtO₂ as a catalyst. The physical properties of these compounds, such as viscosity, dielectric constant, and ionic conductivity, were characterized. Among them, [3-(2-(2-methoxyethoxy)ethoxy)-propyl]triethoxysilane (TESM2) exhibited a commercial viable ionic conductivity of 1.14 mS cm^?1 and a wide electrochemical window of 5.2 V. A preliminary investigation was conducted by using TESM2 as an electrolyte solvent for high-voltage applications in lithium-ion batteries. Using 1 M LiPF₆ in TESM2 with 1 vol% vinyl carbonate as an electrolyte, LiCoO₂/Li half-cell delivered a specific capacity of 153.9 mAh g^?1 and 90 % capacity retention after 80 cycles (3.0–4.35 V, 28 mA g^?1); Li_1.2Ni_0.2Mn_0.6O₂/Li₄Ti₅O₁₂ full cell exhibited the initial capacity of 161.3 mAh g^?1 and 86 % capacity retention after 30 cycles (0.5–3.1 V, 18 mA g^?1).     

Magnesium ion-conductive poly(ethylene carbonate) electrolytes

Magnesium (Mg) electrolytes are presently under investigation for their promising performance capabilities in the next generation of batteries. The present work studies Mg-ion transport in polymers using different types of Mg salts. Polymer electrolytes comprising poly(ethylene carbonate) (PEC) with Mg salts (MgX₂; X?=?TFSI, ClO₄) were prepared by solution casting. The structural, thermal, and electrochemical properties of flexible self-standing membranes were studied as potential Mg electrolytes. The impedance results at 90 °C found the highest conductivities of 6.0?×?10^?6 S cm^?1 for PEC-Mg(TFSI)₂, and 5.2?×?10^?5 S cm^?1 for PEC-Mg(ClO₄)₂, at 40 mol%. FT-IR measurements revealed changes in the peak fraction from the region of carbonyl group, which explain the interaction with Mg ions. The glass transition temperature of the TFSI system decreased with increasing salt concentration due to the plasticizing effect of TFSI anions. Thermal gravimetric analysis revealed that the highest values of the 5% weight-loss temperature at 40 mol% are 174 °C for PEC-Mg(TFSI)₂ and 160 °C for PEC-Mg(ClO₄)₂. The electrochemical stability of PEC-Mg(TFSI)₂ at 40 mol% was up to 2.2 V. To confirm the redox reaction of Mg ions in PEC, CV measurement was carried out using symmetrical cells with quasi Mg electrodes. Cathodic and anodic current peaks were clearly observed, and the presence of these peaks indicates Mg-ion conduction in PEC.     

Mixed solid electrolytes based on poly(ethylene oxide)

Polymer solid electrolytes from a PEO-NaI system were mixed with Nasicon and Al₂O₃ powders. As a result an increase of ionic conductivity exceeding 10^–1 S/cm at room temperature was observed for both cases. This increase was due to a higher concentration of amorphous phase which resulted apparently from a higher nucleation rate during the solidification process. The samples were studied using impedance spectroscopy, X-ray diffraction, electron microscopy, NMR, and other techniques.     

Conductance study of poly(ethylene oxide)- and poly(propylene oxide)-based polyelectrolytes

The ionic conductivity of poly(ethylene oxide) and poly(propylene oxide) in pure solution form, individually complexed with salts of Na⁺ and Li⁺, with and without plasticizer (propylene carbonate) and in blended form with individual salt with and without plasticizer, was studied. The conductance measurements were made at various concentrations of salt polymer complexes and at different temperatures. The effects of temperature and plasticizer concentration were measured from Arrhenius conductance plots. It is shown that the addition of salts in pure PEO increases conductance many times. The plasticizer has also same effect. The blending of PEO with PPO gives enhanced conductivity as compared to pure PEO. The activation energies were determined for all the systems which gave higher values for pure PEO and the value decreases with the addition of Li and Na salts and further decreases with the addition of plasticizer. The blending has also lowered the activation energy values which mean that incorporation of PPO in PEO has decreased crystallinity and the amorphous region has increased the local mobility of polymer chains resulting in lower activation energies.     

Characterization of poly(ethylene oxide) copper salt polymer electrolytes

The physico-chemical and electrochemical properties of a new class of polymer electrolytes formed by complexes of poly(ethylene oxide) and copper trifluorosulphonate salts have been investigated. The results suggest that these electrolytes are good copper ion conductors. Under particular conditions of concentration and temperature, and apparent electronic transport has also been evidenced.     

牛血清白蛋白对Pluronic聚合物胶团形成的影响研究

用吡啶作为荧光探针研究了嵌段共聚物PluronicF108胶团形成以及牛血清白蛋白(BSA)对嵌段共聚物胶团形成的影响。研究表明,BSA阻碍嵌段共聚物的胶团形成,BSA与嵌段共聚物疏水链段的疏水相互作用是其阻碍嵌段共聚物胶团形成的主要原因。     

Effect of vinyl ethylene carbonate on the compatibility between graphite and the flame-retarded electrolytes containing dimethyl methyl phosphonate

Effect of the content of vinyl ethylene carbonate (VEC) on the compatibility between the graphite anode and the electrolytes containing 10–30% dimethyl methyl phosphonate (DMMP) was investigated by cyclic voltammetry measurement. Impact of the contents of VEC and DMMP on the formation of the solid electrolyte interface layer was discussed, and a competitive mechanism between the destructive effect of DMMP decomposition and the positive effect of VEC was proposed. In the LiCoO₂/graphite cells, the electrolytes modified by DMMP and VEC exhibited satisfying cell performances, especially for the electrolyte with 10% DMMP and 2% VEC.     

Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains

A polyphosphazene [NP(NHR)₂]_n with oligo[propylene oxide] side chains − R = –[CH(CH₃)–CH₂O]_m–CH₃ (m = 6 – 10) was synthesized by living cationic polymerisation and polymer-analogue substitution of chlorine from the intermediate precursor [NPCl₂]_n using the corresponding primary amine RNH₂. The polymer had an average molecular weight of 3.3 × 10⁵ D. Polymer electrolytes with different concentrations of dissolved lithium triflate (LiCF₃SO₃) were prepared. Mechanically stable polymer electrolyte membranes were formed using UV radiation induced crosslinking of the polymer salt mixture in the presence of benzophenone as photoinitiator. The glass transition temperature of the parent polymer was found to be − 75 °C before cross linking. It increases after crosslinking and with increasing amounts of salt to a maximum of − 55 °C for 20 wt.% LiCF₃SO₃. The ionic conductivity was determined by impedance spectroscopy in the temperature range 0–80 °C. The highest conductivity was found for a salt concentration of 20 wt.% LiCF₃SO₃: 6.5 × 10^− 6 S·cm^− 1 at 20 °C and 2.8 × 10^− 4 S cm^− 1 at 80 °C. The temperature dependence of the conductivities was well described by the MIGRATION concept.     

Star-shaped oligo(ethylene glycol) ethers (OEGE) as a new type of plasticizer for polymer gel electrolytes

Star-shaped oligo(ethylene glycol) methyl ethers (three and four arm molecules of various molecular weights) were synthesized and characterized with regard to viscosity, thermal transitions, ability to solvate the electrolyte LiCF₃SO₃ and the ionic conductivity of their LiCF₃SO₃ solutions in comparison to linear oligo(ethylene glycol) methyl ethers. Polymer gel electrolytes were prepared by photopolymerization of tri(ethylene glycol) dimethacrylate (EG₃DMA) or its copolymerization with the polar comonomer cyanomethyl methacrylate (CyMA) in the presence of the oligo(ethylene glycol) ethers mentioned above and of the electrolyte LiCF₃SO₃. The gels were characterized concerning their thermal transitions, thermo-mechanical properties, their ability to solvate the electrolyte and their ionic conductivity. In comparison to the linear plasticizers the star-shaped ones show a distinctly lower tendency to crystallize, which is even completely suppressed in several cases. Intensified ion association was found in LiCF₃SO₃ solutions of the star-shaped plasticizers, if the number of the ethylene glycol units per arm was lower than 4. Therefore, the conductivity of the solutions and the gels was lower than that with linear plasticizers at room temperature. The modification of the polymer matrix by copolymerization with 20 mol% CyMA resulted in a maximum of the ionic conductivity σ≈1×10⁻⁵ S/cm of gels with star-shaped plasticizers at 25 °C.     

An experimental study on the effect of mesoporous silica addition on ion conductivity of poly(ethylene oxide) electrolytes

Solid polymer electrolyte (SPE) composites, which are composed of poly(ethylene oxide) (PEO), mesoporous silica (SBA-15), and lithium salt were prepared in order to investigate the influence of SBA-15 content on the ionic conductivity of the composites. The ionic conductivity of the SPE composites was monitored by frequency response analyzer (FRA), and the crystallinity of the SPE composites was evaluated by using XRD. As a result, the addition of SBA-15 to the polymer mixture inhibited the growth of PEO crystalline domain, due to the mesoporous structure of the SBA-15. Also, the PEO₁₆LiClO₄/SBA-15 composite electrolytes show an increased ion conductivity as a function of SBA-15 content up to 15 wt.%. These ion conductivity characteristics are dependent on crystallinity with SBA-15 content.     

共聚物Pluronic P103对牛血清白蛋白荧光光谱的猝灭

应用静态荧光光谱研究了嵌段共聚物PluronicP103对牛血清白蛋白(BSA)荧光光谱的猝灭。研究表明,PluronicP103对BSA的荧光有猝灭作用,动态猝灭是引起BSA荧光猝灭的主要原因。发现嵌段共聚物PluronicP103在水溶液中的蔟集状态影响其与BSA的相互作用,以胶团形式存在的PluronicP103对BSA的猝灭作用更强。     

Ultrasound-promoted tosylation of oligo(ethylene glycols)

A series of oligo(ethylene glycols) was efficiently tosylated by ultrasound procedure within dichloromethane in the presence of triethylamine. Results show that sonochemical synthesis of oligo(ethylene glycol) ditosylates has a double advantage since it does not use catalysts and it drastically reduces the reaction time. This straightforward method represents an eco-friendly alternative to the traditional tosylation by pyridine synthesis.     

Effects of preparation method on properties of lithium salt-poly(ethylene oxide) polymer electrolytes

The effects of using different sources of precursor poly(ethylene oxide) (PEO) and acetonitrile solvent on the physical and electrochemical properties of lithium salt-PEO polymer electrolytes were investigated. Although no differences were found due to the use of different types of PEO, the purity of the acetonitrile solvent was found to be critical in controlling the properties of the polymer product. Acetonitrile of nominally relatively low purity produced polymer electrolytes exhibiting largely crystalline type behaviour while the use of nominally high purity solvents gave polymers which were apparently completely amorphous at temperatures above about 50°C. Transport number measurements gave values for the lithium ions of 0.4 at 132°C for the largely crystalline materials and 0.3 at 112°C for the amorphous polymers. Analysis of the acetonitrile solvents revealed the presence of water in the nominally high purity grades and it has been confirmed that water contamination is responsible for the production of the low melting temperature form of the polymer complex.     

A phosphate additive for poly(ethylene oxide)-based gel polymer electrolytes

The influence of an organophosphosphate additive on poly(ethylene oxide) lithium bis(trifluoromethylsulfonyl)imide-based gel polymer electrolytes for secondary lithium battery applications is described. Tris(2-(2-methoxyethoxy)ethyl)phosphate, is compared to the well known gel-battery component, propylene carbonate, through a study of complex impedance analysis, differential scanning calorimetry, and limiting oxygen index combustion analysis. The conductivities of the gels at low concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (1.9–4.2 mol%) are higher to those of propylene carbonate-based systems with the same concentration. Despite micro-phase separation at high concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (7.0–14.9 mol%), the conductivities remain comparable to systems that use propylene carbonate. The addition of tris(2-(2-methoxyethoxy)ethyl)phosphate to poly(ethylene oxide) gives increased fire retardance, while the addition of propylene carbonate to poly(ethylene oxide) results in increased flammability.     

Solid state NMR study of sodium thiocyanate/poly(ethylene oxide) electrolytes

¹H-, ¹³C-, ²³Na-solid state NMR measurements have been used to characterise the morphology and the dynamics of several NaSCN-PEO mixtures. Selective ¹³C-MAS experiments allowed to determine the composition of the (PEO)_nNaSCN samples in terms of the different phases present, as well as the real stoichiometry of the crystalline complex. ¹H- and ¹³C-spin-lattice relaxation times provided estimates of the dimensions of the different domains and gave information on the dynamics of the polymer chains. ²³Na-MAS spectra and 2D nutation experiments allowed to individuate the presence of different environments for the sodium cations on the basis of their quadrupolar interactions.     

Morphology and conductivity of electrolytes based on poly(ethylene oxide) - Eu(ClO4)3 films

Solid polymer electrolytes based on a poly(ethylene oxide), (PEO), host have been prepared using the solvent casting method and characterized by conductivity measurements and thermal analysis. The observed ionic conductivity of the novel system based on PEO and europium perchlorate was similar to that of other electrolytes based on the same polymer host with a different trivalent guest species [1]. The presence of the perchlorate anion widened the composition range of amorphous behaviour but limited the thermal stability of the electrolytes produced. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Identification of accidentally degenerate bands in UV photoelectron spectra of ethylene carbonate and propylene carbonate

High resolution photoelectron spectra of ethylene carbonate and propylene carbonate were taken, and analysis of vibrational structures was made for the     

Thermal history — conductivity relationship in lithium salt-poly (ethylene oxide) complex polymer electrolytes

A.C. conductivity measurements on a number of lithium salt-poly(ethylene oxide) (PEO) complex polymer electrolytes have been correlated with the results of D.S.C. analysis. An enhancement in the conductivity of compositions with O:Li ratios of greater than 6:1 on annealing at above 150°C was attributed to the melting of the polymer crystalline phase and the retention of an amorphous polymer structure in the electrolyte on cooling down to the crystallisation temperature of the pure PEO phase.     

Effects of inert fillers on the mechanical and electrochemical properties of lithium salt-poly(ethylene oxide) polymer electrolytes

The effects of adding an inert filler (α-alumina) to lithium perchlorate-poly(ethylene oxide) polymer electrolytes have been investigated. It was found that additions of 10 vol. % α-alumina had a negligible effect on the ionic conductivity of the polymer but gave a significant improvement in the mechanical stability of the material at temperatures in excess of 100°C. A.C. measurements on samples containing 0 and 10 vol. % α-alumina gave values of 0.2 to 0.3 for the transport number of the lithium ions between 110 and 130°C.     

Ionic conductivity of electrolytes based on star-branched poly(ethylene oxide) with high concentration of lithium salts

Electrolytes based on star-branched poly(ethylene oxide) with lithium bis(trifluoromethanesulfone)imide LiTFSI and lithium iodide salts were prepared by casting from solution. The electrical properties of electrolytes subjected to various heating and cooling runs were studied by impedance spectroscopy and impedance spectroscopy simultaneous with optical microscope observation. Differential scanning calorimetry was used for additional characterization. The results indicate that in electrolytes with high content of salt, values of ionic conductivity comparable to that of dilute electrolytes can be achieved. Moreover, electrolytes with high amount of salt seem to show weaker temperature dependence of conductivity. Promising results in terms of ionic conductivity were obtained for mixture of LiTFSI and lithium iodide. A few problems which may decrease the performance of studied system as a solid electrolyte were also identified, from which changes of physical properties of samples subjected to thermal cycles and aging seem to be the most important ones.