Solid polymer electrolytes with sulfur based ionic liquid for lithium batteries

The electrochemical properties of a solid hybrid polymer electrolyte for lithium batteries based upon tri-ethyl sulfonium bis(trifluorosulfonyl) imide (S₂TFSI), lithium TFSI, and poly(ethylene oxide) (PEO) is presented. We have synthesized homogenous freestanding films that possess low temperature ionic conductivity and wide electrochemical stability. The hybrid electrolyte has demonstrated ionic conductivity of 0.117 mS cm⁻¹ at 0 °C, and 1.20 mS cm⁻¹ at 25 °C. At slightly elevated temperature ionic conductivity is on the order of 10 mS cm⁻¹. The hybrid electrolyte has demonstrated reversible stability against metallic lithium at the anodic interface and >4.5 V vs. Li/Li⁺ at the cathodic interface.     

Enhanced electrochemical performance of porous NiO-Ni nanocomposite anode for lithium ion batteries

The nickel foam-supported porous NiO-Ni nanocomposite synthesized by electrostatic spray deposition (ESD) technique was investigated as anodes for lithium ion batteries. This anode was demonstrated to exhibit improved cycle performance as well as good rate capability. Ni particles in the composites provide a highly conductive medium for electron transfer during the conversion reaction of NiO with Li⁺ and facilitate a more complete decomposition of Li₂O during charge with increased reversibility of conversion reaction. Moreover, the obtained porous structure is benefical to buffering the volume expansion/constriction during the cycling.     

Advanced,high-performance composite polymer electrolytes for lithium batteries

Progress in lithium battery technology may be achieved by passing from a conventional liquid electrolyte structure to a solid-state, polymer configuration. In this prospect, great R&D effort has been devoted to the development of suitable lithium conducting polymer electrolytes. The most promising results have been obtained with systems based on blends between poly(ethylene oxide) and lithium salts. In this work we show that the transport and interfacial properties of these electrolytes may be greatly enhanced by the dispersion of a ceramic filler having an unique surface state condition. The results, in addition to their practical reflection in the lithium polymer electrolyte battery technology, also provide a valid support to the model which ascribes the enhancement of the transport properties of ceramic-added composites to the specific Lewis acid–base interactions between the ceramic surface states and both the lithium salt anion and the PEO-chains.     

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO₄ reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10⁻⁵ S cm⁻¹ at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO₂ cathode were assembled and their cycling performances were evaluated at 40 °C.     

New electrolytes for lithium ion batteries using LiF salt and boron based anion receptors

The thermal and electrochemical stability, as well as compatibility with various bench mark cathode and anode materials of two new lithium fluoride salt (LiF) based electrolytes have been studied. These two new electrolytes are formed by using boron-based anion receptors, tris(pentafluorophenyl) borane (TPFPB), or tris(2H-hexafluoroisopropyl) borate (THFPB) as additives, which were designed and synthesized at Brookhaven National Laboratory (BNL), to dissolve the LiF salt in carbonate solvents. The transference number of Li⁺ for these electrolytes is as high as 0.7 and the room-temperature conductivity is around 2 × 10⁻³ S cm⁻¹. The electrolytes containing propylene carbonate (PC) show superior low-temperature conductivity properties. The electrochemical window is approaching 5.0 V. It was also found that the new electrolytes work well with LiCoO₂ or LiMn₂O₄ cathodes. However, when PC containing electrolytes were used, PC co-intercalation is still a problem for graphite anodes. The formation of a stable solid electrolyte interface layer on the surface of anode in this type of electrolyte needs to be studied further.     

Composite gel-type polymer electrolytes for advanced,rechargeable lithium batteries

The main goal of this work was to determine whether the dispersion of ceramic fillers have any promotion effect on the properties of solid-like, gel-type lithium conducting polymer electrolytes. Using a series of different but complementary techniques, which included SEM analysis, voltammetry and impedance spectroscopy, we demonstrate that the dispersion of surface functionalized fumed silica and alumina, respectively, to PVdF–carbonate solvent–lithium salt systems, while not greatly influencing the transport properties, does stabilize the lithium metal interface and the mechanical properties of the resulting composite GPE electrolytes. The relevance of these features in view of practical application is here demonstrated by the response of lithium batteries based on selected GPEs.     

Investigation on porous MnO microsphere anode for lithium ion batteries

MnO microspheres with and without carbon coating are prepared as anode materials for lithium ion batteries. The MnO microsphere material shows a reversible capacity of 800 mAh g⁻¹ and an initial efficiency of 71%. It can deliver 600 mAh g⁻¹ at a rate of 400 mA g⁻¹. Results of Mn K-edge X-ray absorption near-edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS) confirm further the conversion reaction mechanism, indicate that pristine MnO is reduced to Mn⁰ after discharging to 0 V and part of reduced Mn⁰ is not oxidized to Mn²⁺ after charging to 3 V. This explains the origin of the initial irreversible capacity loss partially. The quasi open circuit voltage and the relationship between the current density and the overpotential are investigated. Both indicate that there is a significant voltage difference between the charging and discharging profiles even when the current density decreases to zero.     

Electrochemical characterization of electrolytes for lithium-ion batteries based on lithium difluoromono(oxalato)borate

The salt lithium difluoromono(oxalato)borate (LiDFOB) showed some promising results for lithium-ion-cells. It was synthesized via a new synthetic route that avoids chloride impurities. Here we report the properties of its solutions (solvent blend ethylene carbonate/diethyl carbonate (3:7, mass ratio), including its conductivity, cationic transference number, hydrolysis, Al-current collector corrosion-protection ability and its cycling performance with some electrode materials. Some Al-corrosion studies were also performed with the help of our recently developed computer controlled impedance scanning electrochemical quartz crystal microbalance (EQCM) that proofed to be a useful tool for battery material investigations.     

Comb-like copolymer-based gel polymer electrolytes for lithium ion conductors

A comb-like polymer was prepared by copolymerization of acrylonitrile and poly(ethylene glycol-methyl methacrylate) (PEGMEM). The copolymer was mixed with a propylene carbonate plasticizer and LiClO₄ to form a gel polymer electrolyte (GPE). ⁷Li solid-state NMR analysis was used to elucidate interactions between the lithium ions and unpaired electrons on the gel polymer groups. ⁷Li magic-angle spinning NMR and Fourier-transform infrared spectroscopy revealed that the PEGMEM segment could promote dissociation of the lithium salt. Differential scanning calorimetry was used to study the thermal behavior of GPEs of different compositions. The conductivity increased with PEGMEM content. Furthermore, the conductivity of GPE based on a comb-like copolymer exceeded that based on polyacrylonitrile (PAN) with the same composition (polymer/plasticizer 50:50 wt.%). Notably, the highest conductivity of the copolymer/plasticizer 50:50 wt.% system (2.51 × 10⁻³ S cm⁻¹) was close to that for the PAN/plasticizer 20:80 wt.% system (1.90 × 10⁻³ S cm⁻¹).     

Electrochemical stability of lithium bis(oxatlato) borate containing solid polymer electrolyte for lithium ion batteries

The electrochemical stability of lithium bis(oxatlato) borate (LiBOB) containing solid polymer electrolyte has been evaluated both by inert electrode and real cathodes. Enhanced intrinsic anodic stability and decreased interface impedance, are obtained by addition of nano-sized MgO to PEO₂₀-LiBOB. It is also found that the LiBOB-containing SPEs exhibit prominent kinetic stability between 3.0 and 4.5 V. For cells using SPEs as the separators, good cycling performance is obtained for real 4 V class cathodes material LiNi_1/3Co_1/3Mn_1/3O₂ and LiCoO₂. The Li|PEO₂₀-LiBOB|LiNi_1/3Co_1/3Mn_1/3O₂ cell takes an initial capacity of 156.8 mAh g⁻¹, with retention of 142.5 mAh g⁻¹ after 20 cycles at 0.2C-rate. The cell also works well up to 1C-rate. The addition of nano-sized MgO into PEO₂₀-LiBOB readily reduces the irreversible capacity per cycle, both for LiNi_1/3Co_1/3Mn_1/3O₂ and LiCoO₂ cathodes. In addition, the critical role of LiBOB in obtaining kinetic stability and passivating ability towards cathodes are specially discussed.     

Ternary polymer electrolytes containing pyrrolidinium-based polymeric ionic liquids for lithium batteries

The electrochemical properties of solvent-free, ternary polymer electrolytes based on a novel poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide polymeric ionic liquid (PIL) as polymer host and incorporating PYR₁₄TFSI ionic liquid and LiTFSI salt are reported. The PIL-LiTFSI-PYR₁₄TFSI electrolyte membranes were found to be chemically stable even after prolonged storage times in contact with lithium anode and thermally stable up to 300 °C. Particularly, the PIL-based electrolytes exhibited acceptable room temperature conductivity with wide electrochemical stability window, time-stable interfacial resistance values and good lithium stripping/plating performance. Preliminary battery tests have shown that Li/LiFePO₄ solid-state cells are capable to deliver above 140 mAh g⁻¹ at 40 °C with very good capacity retention up to medium rates.     

Investigation of the stability of chlorinated PVC-based polymer electrolytes for lithium batteries

By thermogravimetric analysis, impedance spectroscopy and potentiodynamic cycling, the thermal and electrochemical stability of polymer electrolytes based on PVC and its chlorinated derivatives have been studied. The methods used to modify the properties of these polymeric electrolytes and to provide them with electrochemical stability when used in lithium batteries where the cathode is based on natural, nanostructured, and thermally-sprayed pyrite have been demonstrated.     

Simultaneous improvement in ionic conductivity and mechanical properties of multi-functional block-copolymer modified solid polymer electrolytes for lithium ion batteries

Solid polymer electrolytes (SPEs) with high ionic conductivity and acceptable mechanical properties are of particular interest for increasing the performance of batteries. Our previous studies indicated that copolymers could be good candidates for SPE materials due to the variable properties contributed by each block. A series of copolymers applied in this research was poly(ethylene oxide)-block-polyethylene, PEO-b-PE, which contains a conductive block (PEO block) and a reinforcement block (PE block). This study examines the effects of composition and molecular weight of the copolymers on performance of the resulting SPEs. The ternary SPEs were prepared by addition of copolymers into PEO/LiClO₄. It was found that increasing the PE block percentage in the copolymer resulted in a significant increase in both ionic conductivity and mechanical properties. The SPEs that contained the highest percentage of PE block, 80 wt%, exhibits the best performances. The results showed an increase of more than two orders in ionic conductivity, about 350% increase in tensile modulus, and about 97% increase in ultimate tensile strength when the PE block increased from 50 wt% to 80 wt%. It was also observed that increasing the molecular weight of the copolymer resulted in better mechanical properties, and an identical ionic conductivity.     

UV-cured polymer electrolytes encompassing hydrophobic room temperature ionic liquid for lithium batteries

We demonstrate herewith the application of in situ one-shot free radical photo-polymerisation (UV-curing) process to incorporate room temperature ionic liquids (RTILs) into polymer membranes which can be used as electrolytes for lithium-based batteries. The reactive formulation for the preparation of the polymer membranes was based on a dimethacrylic oligomer (BEMA). The polymer electrolyte membranes were synthesized by UV radiating a mixture of BEMA and a proper radical photo-initiator with different compositions of 1-ethyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide [EMIPFSI] and, additionally, LiTFSI as lithium source.Stable and flexible polymer films with good mechanical integrity can easily be produced with varying the EMIPFSI content by using this method. Remarkable values of ionic conductivity were obtained even at ambient temperature. Galvanostatic charge/discharge cyclability tests were performed on the polymer electrolyte membranes by constructing a cell using LiFePO₄ as cathode and Li metal as anode. The preliminary results are interesting, exhibiting good reversibility and cyclability.     

Investigation on lithium/polymer electrolyte interface for high performance lithium rechargeable batteries

Performance data of several linear and cross-linked polymer electrolytes are reported and the electrochemical criteria for the selection of electrolytes to be used in electric vehicle lithium metal batteries are discussed. Further, laboratory lithium cells with LiMn₂O₄ composite cathode were tested to ascertain the effective viability of these polymer in solid-state batteries and preliminary results are reported. This study clearly demonstrates the importance of a broad-based electrochemical characterization in selecting an electrolyte for lithium metal batteries.     

Novel ionic plastic crystal-polymeric ionic liquid all-solid-state electrolytes for lithium ion batteries

离子塑性晶体作为一类新型的固态电解质材料,近年来受到研究人员的极大关注。本文合成了一种新型离子塑性晶体：N,N-二甲基吡咯双氟磺酰亚胺（P₁₁FSI）,并将其与吡咯阳离子离子液体聚合物-聚二甲基二烯丙基铵双氟磺酰亚胺（PILFSI）和锂盐（LiFSI）复合制备了P₁₁FSI-PILFSI-LiFSI全固态电解质。采用差示扫描量热法、热重分析、阻抗测试、线性扫描伏安法及对称锂电池测试等一系列表征技术对全固态电解质的热性能和电化学性能进行了系统研究。所制备的电解质膜具有好的柔韧性和热稳定性,高的离子电导率和电化学稳定性,以及与金属锂良好的界面相容性。将全固态电解质应用于Li/LiFePO₄电池中,在50℃、0.2 C充放电倍率时,电池放电比容量在60次循环后仍可达151.1 mA·h/g,容量保持率为96.8%;且在0.5 C、1.0 C倍率下放电比容量仍然高达138.1 mA·h/g和128.1 mA·h/g,展现出高的放电比容量,好的循环性能和倍率性能,有望应用于全固态锂离子电池中。     

Gel-type polymer electrolytes with different types of ceramic fillers and lithium salts for lithium-ion polymer batteries

Gel-type polymer electrolytes are prepared using PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ mixed lithium salts and ceramic fillers such as Al₂O₃, BaTiO₃ and TiO₂. The electrochemical properties of these electrolytes, such as electrochemical stability, ionic conductivity and compatibility with electrodes are investigated in addition to the physical properties. The charge–discharge performances of lithium-ion polymer batteries using these get-type polymer electrolytes are investigated. The gel-type polymer electrolytes containing a mixed lithium salt of LiPF₆/LiCF₃SO₃ (10/1, wt.%) exhibit more stable ionic conductivity and lower interfacial resistance than those containing only LiPF₆. In addition, an Al₂O₃ filler improves interfacial stability between the electrode and the polymer electrolyte. Stacking cells (MCMB 1028/LiCoO₂, 8 cm × 13 cm × 7 ea) composed of gel-type polymer electrolytes based on PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ (10/1, wt.%) and Al₂O₃ filler maintain 95% of initial capacity after 100 cycles at a C/2 rate.     

Lithium ion conductivity of gel polymer electrolytes containing insoluble lithium tetrakis(pentafluorobenzenethiolato) borate

Lithium ion conducting gel polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato) borate (LiTPSB), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and ethylene carbonate–propylene carbonate mixed solvent (EC–PC) were prepared and their ionic conductivities and electrochemical stabilities were investigated. Ionic conductivity was largely dependent on the contents of EC–PC and LiTPSB. Gel polymer electrolyte containing optimized content of 50 (LiTPSB)–50 (PVDF-HFP/EC–PC (13:87 wt.%)) exhibited ionic conductivity of 4 × 10⁻⁴ S cm⁻¹ at 30 °C, lithium ion transference number of 0.33 and anodic oxidation potential of 4.2 V.     

Polymer electrolytes based on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) membrane for lithium batteries

Electrospinning parameters are optimized for the preparation of fibrous membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} that consist of layers of uniform fibres of average diameter 1 μm. Electrospinning of a 16 wt.% solution of the polymer in acetone/N,N-dimethylacetamide (DMAc) (7/3, w/w) at an applied voltage of 18 kV results in obtaining membranes with uniform morphology. Polymer electrolytes (PEs) are prepared by activating the membrane with liquid electrolytes. The fully interconnected porous structure of the host polymer membrane enables high electrolyte uptake and ionic conductivities of 10⁻³ S cm⁻¹ order at 20 °C. The PEs have electrochemical stability at potentials higher than 4.5 V versus Li/Li⁺. A PE based on a membrane with 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC), which exhibits a low and stable interfacial resistance on lithium metal, is evaluated for discharge capacity and cycle properties in Li/LiFePO₄ cells at room temperature and different current densities. A remarkably good performance with a high initial discharge capacity and low capacity fading on cycling is obtained.