Effect of additives in PEO/PAA/PMAA composite solid polymer electrolytes on the ionic conductivity and Li ion battery performance

Polyethylene oxide (PEO) based-solid polymer electrolytes were prepared with low weight polymers bearing carboxylic acid groups added onto the polymer backbone, and the variation of the conductivity and performance of the resulting Li ion battery system was examined. The composite solid polymer electrolytes (CSPEs) were composed of PEO, LiClO_4, PAA (polyacrylic acid), PMAA (polymethacrylic acid), and Al₂O₃. The addition of additives to the PEO matrix enhanced the ionic conductivities of the electrolyte. The composite electrolyte composed of PEO:LiClO₄:PAA/PMAA/Li_0.3 exhibited a low polarization resistance of 881.5 ohms in its impedance spectra, while the PEO:LiClO₄ film showed a high value of 4,592 ohms. The highest ionic conductivity of 9.87 × 10⁻⁴ S cm⁻¹ was attained for the electrolyte composed of PEO:LiClO₄:PAA/PMAA/Li_0.3 at 20 °C. The cyclic voltammogram of Li⁺ recorded for the cell consisting of the PEO:LiClO₄:PAA/PMAA/Li_0.3:Al₂O₃ composite electrolyte exhibited the same diffusion process as that obtained with an ultra-microelectrode. Based on this electrolyte, the applicability of the solid polymer electrolytes to lithium batteries was examined for an Li/SPE/LiNi_0.5Co_0.5O₂ cell.     

Recent developments in the ENEA lithium metal battery project

Solvent-free P(EO)₂₀LiTFSI + PYR₁₄TFSI polymer electrolyte films with PYR₁₄⁺/Li⁺ mole ratios ranging from 0.96 to 3.22 were prepared by hot-pressing mixtures composed of PEO, LiTFSI and PYR₁₄TFSI of selected stoichiometries. The PYR₁₄TFSI room temperature ionic liquid (RTIL) is homogeneously incorporated into the P(EO)₂₀LiTFSI membrane without phase separation. For a PYR₁₄⁺/Li⁺ mole ratio of 3.22, the ionic conductivity was about 2 × 10⁻⁴ S/cm at 20 °C, i.e., more than one order of magnitude higher than that of the RTIL-free electrolyte. The electrochemical stability window of the polymer electrolyte containing the RTIL was about 6 V (versus Ag/Ag⁺). Li/V₂O₅ cells with the polymer electrolyte (PYR₁₄⁺/Li⁺ = 1.92) showed a 60% capacity retention after 80 cycles at 40 °C (the initial capacity was 210 mA h/g). Li/V₂O₅ cells (PYR₁₄⁺/Li⁺ = 1.28) held at 30 °C delivered about 93 mA h/g (at 0.057 mA/cm²), which corresponds to approximately 34% utilization of the active material. These results suggest that the incorporation of the RTILs into PEO-based polymer electrolytes is very promising for the future realization of solid-state lithium metal polymer batteries operating near ambient temperatures.     

Effects of polymer matrix and salt concentration on the ionic conductivity of plasticized polymer electrolytes

Two polar polymers with different dielectric constants, poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO), were each blended with a chlorine-terminated poly(ethylene ether) (PEC) and one of the two salts, LiBF₄ and LiCF₃CO₂, to form PEC plasticized polymer electrolytes. The room-temperature ionic conductivity of the PEC plasticized polymer electrolytes reached a value as high as 10^?4 S/cm. The room-temperature ionic conductivity of the PVDF-based polymer electrolytes displayed a stronger dependence on the PEC content than did the PEO-based polymer electrolytes. In PVDF/PEC/LiBF₄ polymer electrolytes, the dynamic ionic conductivity was less dependent on temperature and more dependent on the PEC content than it was in PEO/PEC/LiBF₄ polymer electrolytes. The highly plasticized PVDF-based polymer electrolyte film with a PEC content greater than CF4 (CF4 defined as the molar ratio of the repeat units of PEC to those of PVDF equal to 4) was self-supported and nonsticky, while the corresponding PEO-based polymer electrolyte film was sticky. In these highly plasticized PVDF-based polymer electrolytes, the curves of the room-temperature ionic conductivity vs. the salt concentration were convex because the number of carrier ions and the chain rigidity both increased with increase of the salt content. The maximum ionic conductivity at 30°C was independent of the PEC content, but it depended on the anion species of the lithium salts in these highly plasticized polymer electrolytes. © 1995 John Wiley & Sons, Inc.     

Improvement of electrochemical properties of PEO–LiTFSI electrolyte by incorporation of boroxine polymers with different backbone lengths

A series of boroxine polymers (BP) with different backbone lengths were synthesized. Polymer electrolytes prepared by blending poly(ethylene oxide) (PEO) and BP with Li(N(SO ₂CF₃)₂) (LiTFSI) were evaluated. Better performance was observed by addition of BP in the PEO based polymer electrolyte. The effect of the backbone length of BP on electrochemical properties of PEO–BP–LiTFSI electrolyte systems was investigated. Compared with the PEO–LiTFSI system, about five times higher ionic conductivity at low temperature and five times higher lithium ion transference number at 70°C were achieved by incorporation of long chain BP in the electrolyte. Short chain BP exhibited outstanding performance in decreasing interfacial resistances on both anode and cathode surfaces. Good battery performance was also observed for these BP containing hybrid polymer electrolytes.     

Effect of grafting degree and side PEO chain length on the ionic conductivities of NBR-g-PEO based polymer electrolytes

Comb-shaped graft polymers were synthesized and complexed with a LiCF₃SO₃ salt to form a new class of polymer electrolytes. The polymers based on an acrylonitrile-butadiene copolymer (NBR) have pendant, short-chain poly(ethylene oxide) (PEO) grafted onto a butadiene unit. The characteristics of these polymer electrolytes were investigated in terms of number of pendant EO groups and grafting degree in the graft copolymer. The maximum conductivity was observed at the optimum side PEO chain length, and the PEO chain length for the maximum conductivity decreased with an increase in the grafting degree. And a solid ⁷Li NMR relaxation technique was used to study the local environments and dynamics of the ions in the polymer electrolytes. The maximum conductivity value obtained from our study was three orders of magnitude higher than that of classical PEO-based electrolytes at ambient temperature. These improved low temperature conducting polymers with higher relative mechanical strength are expected to be suitable for practical applications, such as in rechargeable lithium batteries or electrochromic devices.     

Novel PEO-based solid composite polymer electrolytes with inorganic–organic hybrid polyphosphazene microspheres as fillers

Novel solid-state composite polymer electrolytes based on poly (ethylene oxide) (PEO) by using LiClO₄ as doping salts and inorganic–organic hybrid poly (cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) microspheres as fillers were prepared. Electrochemical and thermal properties of PEO-based polymer electrolytes incorporated with PZS microspheres were studied. Differential scanning calorimetry (DSC) results showed there was a decrease in the glass transition temperature of the electrolytes and the crystallinity of the samples in the presence of the fillers. Maximum ionic conductivity values of 1.2 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.5 × 10⁻⁴ S cm⁻¹ at 80° were obtained and lithium ion transference number was 0.29. Compared with traditional ceramic fillers such as SiO₂, the addition of PZS microspheres increased the ionic conductivity of the electrolytes slightly and led to remarkable enhancement in the lithium ion transference number.     

Improving electrochemical properties of room temperature ionic liquid (RTIL) based electrolyte for Li-ion batteries

Room temperature ionic liquids (RTILs) with high safety characteristic usually have high viscosity and melting point, which is adverse for the application of RTIL-based electrolytes in Li-ion batteries. In this investigation, a promising RTIL, i.e. PP13TFSI consisting of N-methyl-N-propylpiperidinium (PP13) cation and bis(trifluoromethanesulfonyl)imide (TFSI) anion is synthesized. The effect of the content of Li salt in the electrolytes containing PP13TFSI and LiTFSI on the ionic conductivity and cell performance is investigated. The electrolyte of 0.3 mol kg⁻¹ LiTFSI/PP13TFSI is recommended for its higher lithium transference number and discharge capacity in the LiCoO₂/Li cell than other electrolytes. In addition, it is found that, by introducing 20% diethyl carbonate (DEC) as a co-solvent into pure RTIL electrolyte, the rate capability and low-temperature performance of the LiCoO₂/Li cells are improved obviously, without sacrificing its safety characteristics. It suggests that a component with low viscosity and melting point, i.e. DEC, is necessary to effectively overcome the shortcomings of RTIL for the application in Li-ion batteries.     

Composite polymer electrolytes based on electrospun thermoplastic polyurethane membrane and polyethylene oxide for all‐solid‐state lithium batteries

To improve the electrochemical properties and enhance the mechanical strength of solid polymer electrolytes, series of composite polymer electrolytes (CPEs) were fabricated with hybrids of thermoplastic polyurethane (TPU) electrospun membrane, polyethylene oxide (PEO), SiO₂ nanoparticles and lithium bis(trifluoromethane)sulfonamide (LiTFSI). The structure and properties of the CPEs were confirmed by SEM, XRD, DSC, TGA, electrochemical impedance spectroscopy and linear sweep voltammetry. The TPU electrospun membrane as the skeleton can improve the mechanical properties of the CPEs. In addition, SiO₂ particles can suppress the crystallization of PEO. The results show that the TPU‐electrospun‐membrane‐supported PEO electrolyte with 5 wt% SiO₂ and 20 wt% LiTFSI (TPU/PEO‐5%SiO₂‐20%Li) presents an ionic conductivity of 6.1 × 10^?4 S cm^?1 at 60 °C with a high tensile strength of 25.6 MPa. The battery using TPU/PEO‐5%SiO₂‐20%Li as solid electrolyte and LiFePO₄ as cathode shows an attractive discharge capacity of 152, 150, 121, 75, 55 and 26 mA h g^?1 at C‐rates of 0.2C, 0.5C, 1C, 2C, 3C and 5C, respectively. The discharge capacity of the cell remains 110 mA h g^?1 after 100 cycles at 1C at 60 °C (with a capacity retention of 91%). All the results indicate that this CPE can be applied to all‐solid‐state rechargeable lithium batteries. © 2018 Society of Chemical Industry     

Effect of surface modified porous inorganic-organic hybrid polyphosphazene nanotubes on the properties of polyethylene oxide based solid polymer electrolytes

2-(2-methyloxyethoxy)ethanol modified poly (cyclotriphosphazene-co-4,4′-sufonyldiphenol) (PZS) nanotubes were synthesized and solid composite polymer electrolytes based on the surface modified polyphosphazene nanotubes added to PEO/LiClO₄ model system were prepared. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were used to investigate the characteristics of the composite polymer electrolytes (CPE). The ionic conductivity, lithium ion transference number and electrochemical stability window can be enhanced after the addition of surface modified PZS nanotubes. The electrochemical investigation shows that the solid composite polymer electrolytes incorporated with PZS nanotubes have higher ionic conductivity and lithium ion transference number than the filler SiO₂. Maximum ionic conductivity values of 4.95 × 10⁻⁵ S cm⁻¹ at ambient temperature and 1.64 × 10⁻³ S cm⁻¹ at 80 °C with 10 wt % content of surface modified PZS nanotubes were obtained and the lithium ion transference number was 0.41. The good chemical properties of the solid state composite polymer electrolytes suggested that the inorganic-organic hybrid polyphosphazene nanotubes had a promising use as fillers in solid composite polymer electrolytes and the PEO₁₀-LiClO₄-PZS nanotubes solid composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

Li‐ion conductivity in PEO‐graphene oxide nanocomposite polymer electrolytes: A study on effect of the counter anion

Graphene oxide (GO) has been prepared by modified Hummer's method for their incorporation as nanofiller in designing nanocomposite polymer electrolytes (NCPEs). Prior to use the GO nanofillers has been characterized by TEM, FTIR, and Raman studies to elucidate their nanostructure, functionality, and purity. The various poly(ethylene oxide) (PEO)‐based NCPEs has been prepared by incorporating GO nanofillers in presence of three different lithium salts, viz., CF₃SO₃Li, LiTFSI, and LiNO₃ as the source of Li‐ions and then casted into free standing polymeric films. The change in PEO crystallinity has been studied considering their full width half maximum values of respective diffraction peaks in the XRD spectra. The Li‐ion conductivity of various NCPEs has been studied from impedance spectroscopy. All the NCPE films show optimum value of Li‐ion conductivity with 0.3% GO nanofiller content irrespective of the source of Li‐ions used. But, variation of the Li‐ion conductivity values is occurred for all the three studied lithium salts. Both LiTFSI and LiNO₃ salts display Li‐ion conductivity in the order of 10^?4 S cm^?1 whereas CF₃SO₃Li in the order of 10^?6 S cm^?1, all in presence of 0.3% GO nanofillers. The change in conductivity values of the NCPEs has been explained by correlating with Argand plots and also with change in PEO crystallinity, which occurs due to various relaxation processes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46336.     

Dopant effect on Li+ ion transport in NASICON-type solid electrolyte: Insights from molecular dynamics simulations and experiments

The performance of sodium superionic conductor (NASICON)-type LiZr₂(PO₄)₃ (LZP) solid electrolytes for Li-ion batteries is dependent on their ion transportation properties. Therefore, to achieve high stability, ionic conductivity, and good compatibility with Li, the LZP solid electrolyte has chosen and doped with Al to improve aforesaid properties. Also, the effect of the dopant on various parameters has been investigated via MD simulations and experimentally. In this study, molecular dynamics (MD) simulations were used to investigate the effect of Al doping on the ion transport properties of Li_1+xAl_xZr_2?x(PO₄)₃ (LAZP, x = 0.0–1.0) solid electrolytes. A facile solid-state reaction was used to synthesize both pristine and Al-doped solid electrolytes and to estimate the effect of doping on the ionic conductivity and ion diffusion in LZP. Computational and experimental results provided strong evidence of improved ion conductivity and diffusion in LZP owing to the presence of the Al dopant. Furthermore, the computational results agreed well with the experimental results, thereby validating the computational model. A maximum ionic conductivity of σ_Li = 2.77 × 10^?5 S cm ^?1 (for x = 0.2) was obtained. Enhanced ionic conductivity was observed with Al dopants owing to the creation of interstitial Li ions through a reduction in grain boundary resistance. However, a further increase in the amount of dopant reduced the ionic conductivity of LZP owing to Li-ion trapping at the most stable and metastable sites around the Al insertions. Doped LZP solid electrolytes are suitable for use in energy storage devices because of their enhanced ionic conductivity compared to that of pristine LZP.     

Hybrid Poly(Ethylene Oxide)-Based composite polymer electrolyte for high-performance all-solid-state lithium batteries

Composite solid-state electrolytes (CSSEs) using solid-state lithium metal batteries (SSLMBs) are widely used as one among the primary technological paths aimed towards chemically necessary safety with acceptable energy density. Nevertheless, the unchecked growth of lithium dendrites and the sluggish transport of lithium ions impede the development of SSLMBs based on CSSEs. Herein, the simultaneous introduction of multilayer g-C₃N₄ and exceptionally thermally stable boron nitride (BN) into the PVDF/PEO system is presented. Benefitting from the unique trait and synergistic effect of g-C₃N₄ and BN in the synthesized CSSEs (g-C₃N₄/BN/PVDF/PEO-LiTFSI), the prepared CSSEs yield excellent Li⁺ transfer number (0.75), surprising thermal stability (shrinkage of only 14.13% after heated at 130 °C for 4 h), and high electrochemical stability window over 4.73 V vs. Li/Li⁺, which are much higher than those reported in the current literature PEO-based CSSEs. Moreover, the Li||CSSEs||LiFePO₄ cell applying the CSSEs attained outstanding cycling stability (capacity retention rate of 85% after 350 cycles) and excellent rate performance (58.6 mAh g⁻¹ at 5C). This study offers a simple, promising application, robust, and scalable manufacturing strategy to develop a dual role for stable and safe polymer-based all-solid-state lithium batteries.     

Nanocomposite polymer electrolytes for solid-state lithium-ion batteries with enhanced electrochemical properties

Solid-state polymer electrolytes (SPEs) have attracted significant attention owing to their improvement in high energy density and high safety performance. However, the low lithium-ion conductivity of SPEs at room temperature restricts their further application in lithium-ion batteries (LIBs). Herein, we propose a novel poly (ethylene oxide) (PEO)-based nanocomposite polymer electrolytes by blending boron-containing nanoparticles (BNs) in the PEO matrix (abbreviated as: PEO/BNs NPEs). The boron atom of BNs is sp²-hybridized and contains an empty p-orbital that can interact with the anion of lithium salt, promoting the dissociation of the lithium salts. In addition, the introduction of the BNs could reduce the crystallinity of PEO. And thus, the ionic conductivity of PEO/BNs NPEs could reach as high as 1.19 × 10⁻³ S cm⁻¹ at 60°C. Compared to the pure PEO solid polymer electrolyte (PEO SPEs), the PEO/BNs NPEs showed a wider electrochemical window (5.5 V) and larger lithium-ion migration number (0.43). In addition, the cells assembled with PEO/BNs NPEs exhibited good cycle performance with an initial discharge capacity of 142.5 mA h g⁻¹ and capacity retention of 87.7% after 200 cycles at 2 C (60°C).     

Room-Temperature Solid-State Lithium Metal Batteries Using Metal Organic Framework Composited Comb-Like Methoxy Poly(ethylene glycol) Acrylate Solid Polymer Electrolytes

Solid polymer electrolyte with good thermal stability and flexibility is an excellent candidate for solid-state lithium metal batteries, while its low ionic conductivity caused by high crystallinity limits its application at ambient temperature. Here a metal organic framework (zeolitic imidazolate framework-8, ZIF-8) composited comb-like methoxy poly(ethylene glycol) acrylate polymer electrolyte (MCPE) with high ionic conductivity (9.96 × 10⁻⁵ S cm⁻¹ at 30 °C) is prepared by an in situ UV polymerization method. The as-prepared MCPE exhibits improved mechanical property due to the introduction of porous ZIF-8 nanofillers, which is beneficial to suppress the growth of lithium dendrites. Consequently, the LiFePO₄||MCPE||Li cells show a high capacity of 116 mAh g⁻¹ at 30 °C and 0.5 C, and maintain 89.4% of initial capacity after 150 cycles with the average Coulombic efficiency of 99.9%. These results demonstrate that the MCPE shows great potential in solid-state lithium metal batteries near room temperature.     

Rapid preparation and performances of garnet electrolyte with sintering aids for solid-state Li–S battery

Lithium-sulfur (Li–S) batteries are attractive due to their high theoretical energy density. However, conventional Li–S batteries with liquid electrolytes undergo polysulfide shuttle-effect and lithium dendrite formation during charge/discharge process, leading to poor electrochemical performance and safety issues. Garnet type Li₇La₃Zr₂O₁₂ (LLZO) solid-state electrolyte (SSE) restricts the penetration of polysulfides and exhibits high ionic conductivity at room temperature (RT). Herein, Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZNO) ceramic electrolyte using Li₃PO₄ (LPO) as sintering aids (LLZNO-LPO) is prepared by the rapid sintering method and is applied to construct a shuttle-effect free solid-state Li–S battery. The SSE displays high conductive pure cubic-LLZO phase; during the rapid sintering, LPO melts and junctions the voids between the grains, thus improves Li⁺ conductivity. As a result, the LLZNO-LPO ceramic electrolyte with Li⁺ conductivity of 4.3 × 10^?4 S cm^?1 and high critical current density (CCD) of 1.2 mA cm^?2 is obtained at RT. The Li–S solid-state battery which utilizes LLZNO-LPO ceramic electrolyte can deliver an initial discharge capacity of 943 mA h·g^?1 and 602 mA h·g^?1 retention after 60 cycles. In the same time, the initial coulombic efficiency is as high as 99.5%, indicating that the SSE can effectively block the polysulfide shuttle towards the Li anode and fulfill a shuttle-free Li–S battery.     

Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 enabled PEO-based solid composite electrolyte with high lithium ion transference number and cycling stability

Solid polymer electrolytes (SPEs) have attracted much attention because of their potential in improving energy density and safety. Vanadium doped ceramic matrix Li_6.7La₃Zr_1.7V_0.3O₁₂ (LLZVO) was synthesized by high-temperature annealing, and formed a composite electrolyte with polyethylene oxide (PEO). Compared with pure PEO electrolyte membrane, the composite electrolyte membrane exhibited better ionic conductivity (30 °C: 3.2 × 10^?5 S cm^?1; 80 °C: 3.6 × 10^?3 S cm^?1). The combination of LLZVO was beneficial to improve the lithium ion transference number (t_Li⁺) of SPE, which was as high as 0.81. The Li/SPE/LiFePO₄ battery shows good cycling ability, with a specific capacity of 142 mAh g^?1 after a stable cycle of 150 cycles. Meanwhile, the symmetrical lithium battery with composite electrolyte can work continuously for 1200 h without short circuit at the current density of 0.1 mA cm^?2 at 50 °C, and the capacity is 0.176 mAh. Vanadium doped ceramic matrix LLZVO as an active ionic conductor, improved the overall performance of solid electrolyte.     

Preparation of solid-state composite electrolytes based on organic/inorganic hybrid star-shaped polymer and PEG-functionalized POSS for all-solid-state lithium battery applications

A series of composite electrolytes (CEs) consisting of organic/inorganic hybrid star-shaped polymer (SPP13), plasticizer (PEG-functionalized POSS derivatives), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared to investigate the effects of the composite compositions and PEG chain length of PEs on the properties of CEs. SPP13 was prepared via ATRP from poly(ethylene glycol) methyl ether methacrylate (PEGMA) and methacryl-cyclohexyl-POSS (MA-POSS) using an octafunctional initiator, and the PEG-functionalized POSS derivatives were synthesized by the hydrosilylation reaction of octakis(dimethylsilyloxy)silsesquioxane (OHPS) and allyl-PEG. The CEs were found to be dimensionally-stable enough to separate the electrodes in batteries, but they still possessed high mobility of ion-conducting P(PEGMA) segments, as estimated by the low glass transition temperatures (T_g). The CEs having solid-state show quite high ionic conductivity (4.5 × 10⁻⁵ S cm⁻¹ at 30 °C) which is about three times of magnitude larger than that of the matrix polymer (SPP13) electrolyte (1.5 × 10⁻⁵ S cm⁻¹ at 30 °C). The CEs were electrochemically stable up to +4.2 V without the decomposition of electrolytes. An all-solid-state lithium battery prepared from the CEs exhibited larger discharge capacity than that prepared from the SPP13 electrolyte at 60 °C.     

Polymer Electrolytes Based on Polymeric Ionic Liquid Poly(methyl 2-(3-vinylimidazolidin-1-yl)acetate bis(trifluoromethane sulfonyl)imide)

A new kind of ionic liquid monomer methyl 2-(3-vinylimidazolidin-1-yl)acetate bromide (MVIm-Br) and polymeric ionic liquid (PIL), poly(methyl 2-(3-vinylimidazolidin-1-yl)acetate bis(trifluoromethanesulfonyl)imide) (PMVIm-TFSI), were synthesized and characterized. Different compositions of polymer electrolytes were prepared by blending PMVIm-TFSI and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with poly(methylmethacrylate-co-vinyl acetate) (P(MMA-VAc)). The thermal stability and ionic conductivity improved significantly when PMVIm-TFSI was added into P(MMA-VAc)/LiTFSI polymer. For the polymer electrolytes obtained, the highest ionic conductivity at 30 °C is 4.71 × 10⁻⁴ S cm⁻¹ and the corresponding decomposition temperature is ca. 308 °C. Moreover, P(MMA-VAc)/PMVIm-TFSI/LiTFSI electrolyte membrane (transmittance ≥90%) can be used as the ion-conductive layer material for electrochromic devices, which reveal excellent electrochromic performance.     

Effect of silica on the interfacial stability of the PEO-based polymer electrolytes

Summary In order to evaluate the effect of silica on stabilizing the interface of lithium metal electrode/solid polymer electrolyte, the cyclic behavior for silica-free and silica-containing polymer electrolyte under electrical stress was investigated using cyclic voltammetry. These electrolytes have an ionic conductivity of the order 10^-4 S/cm at above 60°C and most importantly the introduction of hydrophilic silica in PEO-based polymer electrolyte has brought about the enhanced stability of lithium metal electrode/polymer electrolyte interface especially under electrical stress. This in turn supports the suitability of the composite polymer electrolytes with hydrophilic silica for fabrication of enhanced rechargeable solid lithium polymer batteries. Received: 7 May 2002/ Revised version: 10 July 2002/ Accepted: 12 July 2002     

Alternating copolymers of carbon dioxide with glycidyl ethers for novel ion-conductive polymer electrolytes

To overcome the low ionic conduction of existing poly(ethylene oxide)-based polymer electrolytes, we consider polycarbonates obtained from the copolymerization of CO₂ and epoxy monomers. We synthesized four types of polycarbonates possessing phenyl, n-butyl, t-butyl and methoxyethyl side groups using zinc glutarate, and measured the ionic conductivity of their electrolytes, including 10 mol% of LiTFSI. The electrolyte possessing methoxyethyl side groups had the highest conductivity, of the order of 10⁻⁶ S cm⁻¹ at room temperature. The activation energy (E_a) for ionic conduction in the polycarbonate electrolytes was estimated from the VTF equation, and the E_a of the electrolyte possessing n-butyl side groups was almost the same with the polyether-based electrolytes. An interesting feature of our study is that the polycarbonate is a unique candidate for ion-conductive polymers because of its flexible and hydrophobic properties.