PVC–PMMA composite electrospun membranes as polymer electrolytes for polymer lithium-ion batteries

Composite nanofibrous membranes based on poly (vinyl chloride) (PVC)?Cpoly (methyl methacrylate) (PMMA) were prepared by electrospinning and then they were soaked in liquid electrolyte to form polymer electrolytes (PEs). The introduction of PMMA into the PVC matrix enhanced the compatibility between the polymer matrix and the liquid electrolyte. The composite nanofibrous membranes prepared by electrospinning involved a fully interconnected pore structure facilitating high electrolyte uptake and easy transport of ions. The ion conductivity of the PEs increased with the increase in PMMA content in the blend and the ion conductivity of the polymer electrolyte based on PVC?CPMMA (5:5, w/w) blend was 1.36?×?10^?3 S cm^?1 at 25?°C. The polymer electrolyte based on PVC?CPMMA (5:5, w/w) blend presented good electrochemical stability up to 5.0?V (vs. Li/Li⁺) and good interfacial stability with the lithium electrode. The promising results showed that nanofibrous PEs based on PVC?CPMMA were of great potential application in polymer lithium-ion batteries.     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

Study on ionic conductivity of polymer electrolyte plasticized with PEG–aluminate ester for rechargeable lithium ion battery

We have synthesized poly(ethylene glycol) (PEG)-aluminate ester as a plasticizer for solid polymer electrolytes. The thermal stability, ionic conductivity and electrochemical stability of the polymer electrolyte which consist of poly(ethylene oxide) (PEO)-based copolymer, PEG–aluminate ester and lithium bis-trifluoromethanesulfonimide (LiTFSI) were investigated. Addition of PEG–aluminate ester increased the ionic conductivity of the polymer electrolyte, showing greater than 10^− 4 S cm^− 1 at 30 °C. The polymer electrolyte containing PEG–aluminate ester retained thermal stability of the non-additive polymer electrolyte and exhibited electrochemical stability up to 4.5 V vs. Li⁺/Li at 30 °C.     

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g^?1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.     

Electrochemical properties of stacked-nanoflake Li4Ti5O12 spinel synthesized by a polymer-pyrolysis method

Stacked-nanoflake Li₄Ti₅O₁₂ spinel was synthesized via the pyrolysis of a Li–Ti copolymeric precursor formed by in situ polymerization of LiOH and [Ti(OC₄H₉)₄] and acrylic acid. XRD and SEM characterization shows that the powders calcined at 700 °C for 3 h was well-crystallized particles with submicron diameter. Charge–discharge measurement showed the Li₄Ti₅O₁₂ electrode had displayed excellent rate capability and delivered reversible capacity of 171, 158, 148, 138 and 99 mAh g⁻¹ at rates of 0.1C, 0.5C, 1C, 2C and 4C, respectively. The test electrode also showed excellent cyclability as the capacity retains 96.1% after 60 cycles between 0.5 and 2.5 V.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Exceptional electrochemical performance of two-year aged V2O5 nanowires for lithium storage

Vanadium pentoxide nanowires (VONs) with a uniform thickness of 15 nm were synthesized to use as an electrode for reversible lithium storage. The VONs after two years of aging time exhibit a high reversible lithium storage capacity and an excellent rate capability at a current density of 37 mAg⁻¹ and 74–740 mAg⁻¹, respectively, in the test voltage range of 0.1–3.0 V versus Li/Li⁺. Moreover, the VONs show a constant reversible specific capacity ∼945 mAhg⁻¹ after 50 cycles at 74 mAg⁻¹. The good electrochemical performances of VONs are attributed to the robust interlayer structure and improved electrical conductivity. These aging effects in VONs can be exploited to fabricate one-dimensional electrode materials for high-performance Li-ion batteries.     

SiMn–Graphite composites as anodes for lithium ion batteries

Two Si–Mn–C composites were obtained by sequentially ball milling the mixture of the silicon and manganese powders (atomic ratio of 3:5), followed by addition of 20 wt.% and 10 wt.% graphite, respectively. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electromicroscopy (SEM). The results of XRD show that there is no new alloy phase in the composite obtained by mechanical ball milling. SEM micrographs confirm that the particle size of the Si–Mn–C composite is about 0.5–2.0 μm and the addition of graphite restrains the morphological change of active center (Si) during cycling. The Si–Mn particles are dispersed among the carbon matrix homogeneously, which ensures a good electrical contact between the active particles. Electrochemical tests show that the Si–Mn–C composite achieves better reversible capacity and cycleability. The Si–Mn–20 wt.% C composite electrode annealed at 200 °C for 2 h reveals an initial reversible capacity of 463 mAh·g^− 1 and retains 387 mAh·g^− 1 after 40 cycles.     

A free-standing and thermostable polymer/plastic crystal electrolyte for all-solid-state lithium batteries

All-solid-state lithium batteries using flexible solid electrolytes instead of combustible organic liquid electrolytes are the ultimate solution to address the safety problem of commercialized lithium ion batteries. In this study, a free-standing and thermostable polymer/plastic crystal composite electrolyte (PPCE) based on polymerized trimethylolpropane trimethacrylate (TMPTMA)-1, 6-hexanediol diacrylate (HDDA) matrix, and plastic crystal electrolyte was prepared for all-solid-state lithium batteries. The polymerized TMPTMA-HDDA-based matrix of a porous network structure coupled with plastic crystal electrolyte (PCE) in the pores reveals good compatibility. The as-synthesized PPCE possesses excellent flexible performance, thermostability, and high conductivity, showing that PPCE can reach 8.53 × 10^?4 S cm^?1 with 7.5 wt% monomers (PPCE-7.5%) at 25 °C under a stability electrochemical window above 5.2 V. The assembled lithium batteries Li|PPCE|LiFePO₄ exhibit high capacity and highly cycling stability at room temperature, indicating great potential of all-solid-state lithium batteries.     

Charge/discharge characteristics of sulfur composite electrode at different temperature and current density in rechargeable lithium batteries

The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different current densities. The composite presented the discharge capacities of 854 and 632 mAh g⁻¹ at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g⁻¹ at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g⁻¹ at 55.6 and 667 mA g⁻¹, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g⁻¹.     

PEO-based composite lithium polymer electrolyte, PEO-BaTiO3-Li(C2F5SO2)2N

Polyethylene oxide (PEO) based polymer electrolytes with BaTiO₃ as filler and Li(C₂F₅SO₂)₂N as salt have been examined in lithium polymer batteries. The aluminum disolution potential in PEO-Li(C₂F₅SO₂)₂N was estimated to be 4.1 V vs. Li/Li⁺ at 80 °C, which was compared to that of 3.8 V vs. Li/Li⁺ in PEO-Li(CF₃SO₂)₂N. The electrical conductivity of the system was measured as a function of O/Li ratio. The highest conductivity was observed in O/Li=8. The conductivity was 1.65×10⁻³ S/cm at 80 °C and 1.5×10⁻⁵ S/cm at 25 °C. The interfacial resistance of Li/polymer electrolyte/Li annealed at 80 °C for 15 days was lower than 100 Ωcm². Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Enhanced electrochemical performance of unique morphological LiMnPO4/C cathode material prepared by solvothermal method

The LiMnPO₄/C composite material with ordered olivine structure was synthesized in 1:1(v/v) enthanol–water mixed solvent in the presence of cetyltrimethylammonium bromide (CTAB) at 240 ^°C. Rod-like particle morphology of the resulting LiMnPO₄/C powder with a uniform particle dimension of 150 × 600 nm was observed by using scanning electron microscope and the amount of carbon coated on the particle surface was evaluated as 2.2wt% by thermogravimetric analysis, which is reported for the first time to date for LiMnPO₄/C composite. The measurement of the electrochemical performance of the material used in rechargeable lithium ion battery shows that the LiMnPO₄/C sample delivers an initial discharge capacity of 126.5 mA h g^?1 at a constant current of 0.01 C, which is 74% of the theoretical value of 170 mA h g^?1. The electrode shows good rated discharge capability and high electrochemical reversibility when compared with the reported results, which is verified further by the evaluation of the Li ion diffusion coefficient of 5.056×10^?14 cm²/s in LiMnPO₄/C.     

Preparation and characterization of solid polymer electrolytes based on PHEMO and PVDF-HFP

Polymer electrolyte membranes consisting of a novel hyperbranched polyether PHEMO (poly(3-{2-[2-(2-hydroxyethoxy) ethoxy] ethoxy}methyl-3′-methyloxetane)), PVDF-HFP (poly(vinylidene fluoride-hexafluoropropylene)) and LiTFSI have been prepared by solution casting technique. X-ray diffraction of the PHEMO/PVDF-HFP polymer matrix and pure PVDF-HFP revealed the difference in crystallinity between them. The effect of different amounts of PVDF-HFP and lithium salts on the conductivity of the polymer electrolytes was studied. The ionic conductivity of the prepared polymer electrolytes can reach 1.64 × 10^? 4 S·cm^? 1 at 30 °C and 1.75 × 10^? 3 S·cm^? 1 at 80 °C. Thermogravimetric analysis informed that the PHEMO/PVDF-HFP matrix exhibited good thermal stability with a decomposition temperature higher than 400 °C. The electrochemical experiments showed that the electrochemical window of the polymer electrolyte was around 4.2 V vs. Li⁺/Li. The PHEMO/PVDF-HFP polymer electrolyte, which has good electrochemical stability and thermal stability, could be a promising solid polymer electrolyte for polymer lithium ion batteries.     

Synthesis of selenium/EDTA-derived porous carbon composite as a Li–Se battery cathode

The carbon substrate with unique 3D macroporous structure has been prepared through the immediate carbonization of ethylenediaminetetraacetic acid (EDTA) and KOH mixture. The porous carbon composed of micro- and small mesoporous (2–5 nm) structure has a BET specific surface area of 1824.8 m² g^?1. The amorphous and nanosized Se is uniformly encapsulated into the porous structure of porous carbon using melting diffusion route, and the weight content of Se in target Se/C composite can be as high as ~50 %. As an Li–Se battery cathode, the Se/C composite delivers a reversible (2nd) discharge capacity of 597.4 mAh g^?1 at 0.24C and retains a discharge capacity of 538.4 mAh g^?1 at 0.24C after 100 cycles. Furthermore, the composite also has a stable capacity of 291.0 mAh g^?1 at a high current of 4.8C. The high specific area and good porous size of EDTA-derived carbon substrate may a be responsibility for the excellent electrochemical performances of Se/C composite.     

Study of a novel porous gel polymer electrolyte based on TPU/PVdF by electrospinning technique

Investigation on a new electrospun gel polymer electrolyte consisting of thermoplastic polyurethane (TPU) and poly(vinylidene fluoride) (PVdF) has been made. Its characteristics were investigated by scanning electron microscopy, FT-IR, Differential Scanning Calorimeter (DSC) analysis. This kind of gel polymer electrolyte had a high ionic conductivity about 3.2 × 10^− 3 S cm^− 1 at room temperature, and exhibited a high electrochemical stability up to 5.0 V versus Li⁺/Li, good mechanical strength and stability to allow safe operation in rechargeable lithium-ion polymer batteries. A Li/GPE/LiFePO₄ cell delivered a high discharge capacity when it was evaluated at 0.1 °C—rate at 25 °C (167.8 mAh g^− 1). And a very stable cycle performance also existed under this low current density.     

Performance of polymer electrolyte cells at +25 to +100°C

Solid state rechargeable polymer electrolyte batteries utilizing lithium anodes and V₆O₁₃ composite cathodes were investigated at 100°C. The polymer electrolyte was a complex formed between polyethylene oxide (PEO) and LiCF₃SO₃. Over a hundred cycles were obtained at the C/5 rate (45% depth of discharge) with greater than 75% of the initial capacity of V₆O₁₃ being maintained at cycle number one hundred. Cells made with propylene carbonate (PC) doped polymer electrolyte also showed good performance at room temperature.     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

First-principles study of C3N nanoribbons as anode materials for Li-ion batteries

The potential of C₃N nanoribbons used as anode material for lithium-ion batteries has been systematically investigated through first-principles calculations. The results suggest that C₃N nanoribbons have excellent mechanical properties (stiffness ranging from 286.28 to 412.69 N m⁻¹) and good electronic conductivity (with a bandgap of 0-0.31 eV). Further studies reveal that the H-passivated C₃N nanoribbons have high Li insertion capacity (708.60 mA h g⁻¹) and significantly enhanced Li binding strength (0.21-2.11 eV) without the sacrifice of Li mobility. The high stiffness, superior cycle performance, good electronic conductivity, and excellent Li migration capability indicate the great potential of C₃N nanoribbons to be an anode material. The calculated results provide the valuable insights for the development of high-performance C₃N nanoribbons electrode materials in lithium-ion batteries.     

Studies on lithium bis(oxalato)-borate/propylene carbonate-based electrolytes for Li-ion batteries

Lithium bis(oxalato)-borate (LiBOB) is a promising salt for Li-ion batteries owing to its various characteristics such as non-fluorine, non-toxicity, low cost, and safety. It has the unique merits such as the stability at high temperature and the film-forming characteristics in propylene carbonate (PC)-based electrolyte. In this work, the utilization of PC as the basal solvent and dimethyl carbonate, γ-butyrolactone and ethylene carbonate as co-solvents for LiBOB have been investigated. The results indicate that the co-solvent has conducive effects on the conductivities, viscosities, and battery performance. The conductivity and viscosity of 0.7 mol L⁻¹ LiBOB in PC+GBL+EC+DMC (1:1:1:1, v/v) are 6.22 mS cm⁻¹ and 3.74 mPa s, respectively, and it is very stable in 0–5 V range. The capacity of Li/LiFePO₄ battery is about 160 mAh g⁻¹ at 0.5 °C. Moreover, the battery has exhibited the excellent rate performance.     

Investigation of the optical absorption characteristics of slow-cooled LiF:Mg,Ti (TLD-100)

The optical absorption (OA) spectrum of LiF:Mg,Ti has been studied as a function of dose at two different cooling rates following the 400 °C pre-irradiation anneal in order to further investigate the role of cooling rate in the thermoluminescence (TL) mechanisms of this material. “Slow-cooling” following the pre-irradiation 400 °C anneal substantially decreases the OA bands at 3.25 eV and 4.0 eV, in agreement with the overall loss in TL peaks 2–5 intensity using slow-cooling routines. Slow-cooling appears to shift the maximum intensity of peak 5 to lower temperatures (a behaviour which has been attributed to an enhanced intensity of peak 5a), however, no difference in the shape of the 4.0 eV OA band is detected following “slow-cooling”. Apparently the OA band related to peak 5a is too close in energy to the peak 5 OA band to be observed due to lack of sufficient resolution and spectral deconvolution process or it is not present at room temperature (RT) and formed during heating of the sample. The intensity of the 4.0 eV OA band does not change if the sample (prior to irradiation to a standard dose of 200 Gy) is irradiated to 4 kGy followed by a 500 °C/1 h post-irradiation anneal. This result demonstrates that the loss of intensity at high levels of dose (so-called radiation damage) of TL glow peak 5 results from alteration of the LCs or to the creation of additional competitive centers and is not correlated with the dose behaviour of the TCs.