Mechanism of high ionic conductivity in elastomeric networks

The viscoelastic properties and the ionic conductivity of polyether-polyurethane networks containing alkali metal salts have been studied at various temperatures, salt concentrations and network structures. The reduced temperature, TT_g, is the predominant parameter which governs the viscoelastic behaviour and the ionic conductivity of these networks. Using the free volume concept an expresssion is derived for the ionic conductivity, irrespective of the macrostructure involved. The logarithm of the reduced conductivity, σ_T/σ_TR (which is the ratio of the conductivity at a given temperature to that at the reference temperature), is a linear function of the shift factor, log a_T, given by the dynamic mechanical properties. A comparison is made between the WLF parameters C₁ and C₂, obtained from conductivity and viscoelastic measurements.     

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.     

Ionanofluid plasticized electrolyte with improved electrical and electrochemical properties for high-performance lithium polymer battery

Herein, the electrochemical characteristics of Li/LiFePO₄ battery, comprising a new class of poly (ethylene oxide) (PEO) hosted polymer electrolytes, are reported. The electrolytes were prepared using lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dopant salt and imidazolium ionic liquid-based nanofluid (ionanofluid) as the plasticizer. Morphological, thermophysical, electrical, and electrochemical properties of these newly developed electrolytes were studied. Using FT-IR spectroscopy, the interactions between dopant salt plasticizers and the host polymer, within the electrolytes, were evaluated. The optimized 30 wt% ionanofluid plasticized electrolyte exhibits a room temperature ionic conductivity of 6.33 × 10⁻³ S cm⁻¹, wide electrochemical voltage window (~4.94 V vs Li/Li⁺) along with a moderately high value of lithium-ion transference number (0.47). The values are substantially higher than that of similar wt% IL plasticized electrolyte (7.85 × 10⁻⁴ S cm⁻¹, ~4.44 V vs Li/Li⁺ and ~ 0.28, respectively). Finally, the Li/LiFePO₄ battery, comprising optimized 30 wt% ionanofluid plasticized electrolyte, delivers 156 mAh g⁻¹ discharge capacity at 0.1 C rate and able to retain its 92% value after 50 cycles. Such a superior battery performance as compared to the IL plasticized electrolyte cell (137 mAh g⁻¹ and 84% after 50 cycles at the same current rate) would endow this ionanofluid a very promising plasticizer to develop electrolytes for next-generation lithium polymer battery.     

Good prospect of ionic liquid based-poly(vinyl alcohol) polymer electrolytes for supercapacitors with excellent electrical,electrochemical and thermal properties

Poly(vinyl alcohol) (PVA)/ammonium acetate (CH₃COONH₄)/1–butyl–3–methylimidazolium chloride (BmImCl) based polymer electrolytes were prepared by solution casting method. The ionic conductivity increased with temperature as shown in temperature dependent-ionic conductivity study. The maximum ionic conductivity of (7.31 ± 0.01) mS cm⁻¹ was achieved at 120 °C upon adulteration of 50 wt% of BmImCl. The samples obeyed Vogel–Tamman–Fulcher (VTF) relationship. The glass transition temperature (T_g) of the polymer matrix was reduced by doping it with salt and ionic liquid as shown in differential scanning calorimetry (DSC). Supercapacitor was thus assembled. Wider potential stability range has been observed with addition of ionic liquid. Inclusion of ionic liquid also improved the electrochemical behavior of EDLC. The capacitance of supercapacitor were determined by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tester. The cell also illustrated energy density of 2.39 Wh kg⁻¹ and power density of 19.79 W kg⁻¹ with Coulombic efficiency above 90%.     

Effect of nanoscopic confinement on improvement in ion conduction and stability properties of an intercalated polymer nanocomposite electrolyte for energy storage applications

Nanoscopic confinement of a cation coordinated polymer in the channels of organo-modified montmorillonite clay results in substantial improvement in conductivity, cation transport and stability properties required for energy storage/conversion devices. X-ray diffraction analysis confirms composite formation as evidenced by: (i) intercalation of PEO₈-LiClO₄ into the clay channels for clay loading ≥7.5 wt.% and (ii) partial intercalation/exfoliation for a lower clay loading (≤5 wt.%). Transmission electron microscopy analysis corroborates these findings as indicated by an enhancement in clay gallery width from 6 to 9 Å for 20 wt.% clay providing evidence for intercalation at higher clay loadings. Energy dispersive X-ray dot-mapping images confirm the homogeneous distribution of clay in nanocomposites. Thermal analysis indicates a strong dependence of thermodynamic parameters, e.g., glass transition (T_g), crystalline melting (T_m), melting enthalpy, glass transition width (ΔT_g), and thermal relaxation strength (ΔC_p), on clay concentration. These observations agree well with changes in electrical properties on nanocomposite formation. Substantial enhancement in ambient conductivity (∼208 times) occurs in a nanocomposite film (2 wt.% clay) relative to a clay-free film. The temperature dependence of conductivity obeys Arrhenius behaviour below T_m and the VTF (Vogel-Tamman-Fulcher) relationship above T_m. The ionic transport number (∼99.9%) confirms ionic charge transport with a cation contribution (tLi⁺)∼0.5 for 2 wt.% clay. It represents an increase by ∼65% in comparison with PEO₈-LiClO_4. Improvement in voltage and thermal stability is also observed with the nanocomposites.     

Effect of Li2CO3 and LiOH on the ionic conductivity of BaCe0.9Y0.1O3 electrolyte in SOFCs with a lithium compound electrode

The effects of Li₂CO₃ and LiOH on the ionic conductivity of BaCe_0.9Y_0.1O₃(BCY)-x%Li₂CO₃ (x = 0, 5, 10 and 30) and BCY-y%LiOH (y = 0, 2, 5 and 8) composite electrolytes were investigated. Symmetrical cells with the structure of foam Ni–Ni_0.8Co_0.15Al_0.05LiO₂ (NCAL)?BCY-x%Li₂CO₃ or y%LiOH?foam Ni-NCAL and Pt?BCY-x%Li₂CO₃ or y%LiOH?Pt were prepared with NCAL-coated foam Ni and porous Pt as symmetrical electrodes, respectively. The ionic conductivity test results of the cells with Pt as the symmetrical electrode showed that the addition of LiOH did not improve the ionic conductivity of the BCY electrolyte, while the addition of Li₂CO₃ could significantly improve the ionic conductivity of the BCY electrolyte. The maximum power density of the cells with the structure of foam Ni-NCAL?BCY-x%Li₂CO₃ or y%LiOH?foam Ni-NCAL decreases with the increase in the amount of Li₂CO₃ or LiOH, which indicates that adding Li₂CO₃ or LiOH to BCY via mechanical mixing did not improve the electrochemical performance of the cells with NCAL as the electrode, and the NCAL electrode has the greatest impact on the performance of the cells. The interface of Li₂CO₃ and BCY should be a high-speed channel for ion conduction. Increasing the effective area of the interface between BCY and Li₂CO₃ and optimizing its continuity in the electrolyte should be the main development direction for improving the ionic conductivity.     

Formation of the high lithium ion conducting phase from mechanically milled amorphous Li2S-P2S5 system

The fast ionic conducting structure similar to thio-Lithium Super Ionic Conductor (LISICON) phase is synthesized in the Li₂S-P₂S₅ system. The Li₂S-P₂S₅ glass-ceramics with the composition of xLi₂S·(100−x)P₂S₅ (75 ≤ x ≤ 80) are prepared by the heat-treatment of mechanically milled amorphous sulfide powders. In the binary Li₂S-P₂S₅ system, 78.3Li₂S·21.7P₂S₅ glass ceramic prepared by mechanical milling and subsequent heat-treatment at 260 °C for 3 h shows the highest conductivity of 6.3 × 10⁻⁴ S cm⁻¹ at room temperature and the lowest activation energy for conduction of 30.5 kJ mol⁻¹. The enhancement of conductivity with increasing x up to 78.3 is probably caused by the introduction of interstitial lithium ions at the Li sites which affects the Li ion distribution. The prepared electrolyte exhibits the lithium ion transport number of almost unity and voltage stability of 5 V vs. Li at room temperature.     

Li3V2(PO4)3 cathode material synthesized by chemical reduction and lithiation method

The monoclinic-type Li₃V₂(PO₄)₃ cathode material was synthesized via calcining amorphous Li₃V₂(PO₄)₃ obtained by chemical reduction and lithiation of V₂O₅ using oxalic acid as reducer and lithium carbonate as lithium source in alcohol solution. The amorphous Li₃V₂(PO₄)₃ precursor was characterized by using TG–DSC and XPS. The results showed that the V⁵⁺ was reduced to V³⁺ by oxalic acid at ambient temperature and pressure. The prepared Li₃V₂(PO₄)₃ was characterized by XRD and SEM. The results indicated the Li₃V₂(PO₄)₃ powder had good crystallinity and mesoporous morphology with an average diameter of about 30 nm. The pure Li₃V₂(PO₄)₃ exhibits a stable discharge capacity of 130.08 mAh g⁻¹ at 0.1 C (14 mA g⁻¹).     

LiNi1/3Co1/3Mn1/3O2/polypyrrole composites as cathode materials for high-performance lithium-ion batteries

Polypyrrole is successfully introduced to enhance the reaction stability and ionic conductivity of LiNi_1/3Co_1/3Mn_1/3O₂ material through an ultrasound dispersion method and applied as cathode materials for lithium-ion batteries. This polymer can significantly advance the electrochemical properties. Expectedly, the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole composite has lower mixing degree of Li⁺/Ni²⁺, higher c/a value, which delivers the first discharge capacity of 199.2 mAh g⁻¹, which abate to 121.3 mAh g⁻¹ in the 300th cycle at 0.2 C between 2.5 and 4.5 V. Even at 3 C, it continues to reveal a reversible capacity of 86.4 mAh g⁻¹ after 100 cycles. All the consequences implied that the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole verified a minor charge transfer resistance and better Li⁺ diffusion ability, hence establishing preferable rate and cycling performance compared with the primordial LiNi_1/3Co_1/3Mn_1/3O₂.     

High discharge capacity solid composite polymer electrolyte lithium battery

In this study, a series of nanocomposite polymer electrolytes (CPEs), PAN/LiClO₄/SAP, with high conductivity are prepared based on polyacrylonitrile (PAN), LiClO₄ and low content of the silica aerogel powder (SAP) prepared by the sol-gel method with ionic liquid (IL) as the template. The effect of addition of SAP on the properties of the CPEs is investigated by FTIR, AC impedance, linear sweep voltagrams and cyclic voltammetry measurements as well as the charge-discharge performance. It is found that the ionic conductivity of the CPE is significantly improved by addition of SAP. The maximum ambient ionic conductivity of CPEs is about 12.5 times higher than that without addition of SAP. The results of the voltammetry measurements of CPE-3, which contained 3 wt% of SAP, show that the anodic and cathodic peaks are well maintained after 100 cycles, showing excellent electrochemical stability and cyclability over the potential range between 0 V and 4 V vs. Li/Li⁺. Besides, the room temperature discharge capacity measured at 0.5C for the coin cell based on CPE-3 is 120 mAh g⁻¹ and the capacity is retained after 20 cycles discharge, indicating the potential for practical use. This is perhaps the first report of the room temperature charge-discharge performance on the solid composite polymer electrolyte to the best of our knowledge.     

Investigation of the sudden drop of electrolyte conductivity at low temperature in ceramic fuel cell with Ni0·8Co0·15Al0·05LiO2 electrode

The sudden drop of ionic conductivity of GDC (Gd_0.1Ce_0·9O_1.95) electrolyte in ceramic fuel cells with NCAL (Ni_0·8Co_0·15Al_0·05LiO₂) as electrode at low temperature was studied. It is found that the peak power density (PPD) of the cell with GDC electrolyte decreases linearly with the decreasing of the operation temperature above 400 °C. However, when the operation temperature drops to 400 °C, the cell PPD decreases significantly. EIS results show that the ionic conductivity of the electrolyte decreases linearly with the decrease of cell operating temperature. When the temperature decreases to approximately 400 °C, the ionic conductivity of the electrolyte decreases from 0.251 S cm^?1 at 425 °C to 0.026 S cm^?1 at 400 °C. The rapid decrease of the electrolyte ionic conductivity is considered to be the direct cause of the sudden decrease of the PPD. According to the results of XPS, FTIR and TG-DSC, LiOH/Li₂CO₃ formed in the NCAL anode diffuses into the electrolyte and melts at 419 °C or above, which is the reason for the high ionic conductivity of the electrolyte. The reason for the sudden drop of ionic conductivity is that LiOH/Li₂CO₃ and other compounds solidify in molten salts below 419 °C.     

New Li ion-conducting ormolytes

The preparation and characterization of two new families of lithium-conducting solid-state electrolytes is reported. Both systems are silica (SiO₂) – polyethyleneglycol (PEG_n) hybrid materials with (type I) or without (type II) covalent organic-inorganic chemical bonds. Their electrical conductivity has been studied by complex impedance spectroscopy between 20°C and 100°C in the frequency range 1 Hz to 10 MHz as a function of the polymer chain length (200<n<1900), polymer concentration and lithium concentration (4<[O]/[Li]<80). The highest room-temperature ionic conductivity (σ6×10⁻² S cm⁻¹) has been found for type II material for ratios [O]/[Li]=15 and PEG₃₀₀/TEOS=1.0. The effect of the chain length on the polymer mobility has been studied by nuclear magnetic resonance by measuring the Li⁺ line widths and the spin-lattice relaxation time T₁ between -100°C and +100°C. The bonded chain mobility increases with the chain length (type II) while the opposite occurs with unbonded chain material (type I). Both types of materials present high ionic conductivity at room temperature and are adequate as Li⁺-conducting electrolyte in all solid-state electrochemical devices.     

Effect of ball milling on structural and electrochemical properties of (PEO)nLiX (LiX = LiCF3SO3 and LiBF4) polymer electrolytes

Polymer electrolytes consisting of poly(ethylene oxide) (PEO) and lithium salts, such as LiCF₃SO₃ and LiBF₄ are prepared by the ball-milling method. This is performed at various times (2, 4, 8, 12 h) with ball:sample ratio of 400:1. The electrochemical and thermal characteristics of the electrolytes are evaluated. The structure and morphology of PEO–LiX polymer electrolyte is changed to amorphous and smaller spherulite texture by ball milling. The ionic conductivity of the PEO–LiX polymer electrolytes increases by about one order of magnitude than that of electrolytes prepared without ball milling. Also, the ball milled electrolytes have remarkably higher ionic conductivity at low temperature. Maximum ionic conductivity is found for the PEO–LiX prepared by ball milling for 12 h, viz. 2.52×10⁻⁴ S cm⁻¹ for LiCF₃SO₃ and 4.99×10⁻⁴ S cm⁻¹ for LiBF₄ at 90 °C. The first discharge capacity of Li/S cells increases with increasing ball milling time. (PEO)₁₀LiCF₃SO₃ polymer electrolyte prepared by ball milling show the typical two plateau discharge curves in a Li/S battery. The upper voltage plateau for the polymer electrolyte containing LiBF₄ differs markedly from the typical shape.     

Preparation of α-LiFeO2-based cathode materials by an ionic exchange method

β-FeOOH prepared with an enhanced hydrolysis method had been subjected to H⁺/Li⁺ exchange with various lithium salts in ethanol for various duration. The effects of the kind of lithium salt used and the duration of ionic exchange on the composition, the crystalline structure, and the electrochemical properties of the prepared powders were investigated. It was found that α-LiFeO₂ can be prepared from β-FeOOH by an ionic exchange reaction with LiOH in ethanol at 85 °C. α-LiFeO₂ powders so prepared show electrochemical active properties with reversible capacity of 65–80 mAh g⁻¹. The in situ XRD patterns of the cycled α-LiFeO₂ cathode revealed that the crystalline structure remains unchanged while the lattice of cubic decreases and increases periodically upon charge/discharge cycling. The results of XANES suggest that the electrochemical reaction of the Fe³⁺/Fe²⁺ redox couple occurs as the prepared α-LiFeO₂ electrode is charge/discharge cycled.     

In situ preparation of poly(ethylene oxide)–SiO2 composite polymer electrolytes

Amorphous poly(ethylene oxide) (PEO)–SiO₂ composites are prepared by in situ reactions that involve the simultaneous formation of the polymer network and inorganic nanoparticles. The polymer matrix is formed by ultraviolet irradiation of a PEO macromer, and silica is produced in situ by the sol–gel method. The PEO–SiO₂ composite mixed with LiBF₄ is used as a lithium-ion conducting solid electrolyte and electrochemical transport properties such as ionic conductivity and Li⁺ transference number are measured. A significant increase in the Li⁺ transference number, up to 0.56, is found together with a slight decrease in the ionic conductivity. The results are interpreted in terms of interactions between the surface OH groups of the inorganic particles, the cations, the anions, and the ether oxygen atoms on the PEO backbone.     

Lithium conducting ionic liquids based on lithium borate salts

The simple reaction of trialkoxyborates with butyllithium resulted in the obtaining of new lithium borate salts: Li{[CH₃(OCH₂CH₂)_nO]₃BC₄H₉}, containing oxyethylene substituents (EO) of n = 1, 2, 3 and 7. Salts of n ≥ 2 show properties of room temperature ionic liquid (RTIL) of low glass transition temperature, T_g of the order from −70 to −80 °C. The ionic conductivity of the salts depends on the number of EO units, the highest conductivity is shown by the salt with n = 3; in bulk its ambient temperature conductivity is 2 × 10⁻⁵ S cm⁻¹ and in solution in cyclic propylene sulfite or EC/PC mixture, conductivity increases by an order of magnitude. Solid polymer electrolytes with borate salts over a wide concentration range, from 10 to 90 mol.% were obtained and characterized. Three types of polymeric matrices: poly(ethylene oxide) (PEO), poly(trimethylene carbonate) (PTMC) and two copolymers of acrylonitrile and butyl acrylate p(AN-BuA) were used in them as polymer matrices. It has been found that for systems of low salt concentration (10 mol.%) the best conducting properties were shown by solid polymer electrolytes with PEO, whereas for systems of high salt concentration, of the polymer-in-salt type, good results were achieved for PTMC as polymer matrix.     

Li–B–O–N electrolytes for all-solid-state thin film batteries

We report for the first time new Li⁺ ion conducting thin film solid electrolytes based on Li–B–O–N system. Substitution of oxygen in xLi₂O–B₂O₃ (x = 1, 3, 5) by nitrogen was successfully achieved by reactive sputtering under nitrogen plasma. FTIR and XPS analyses indicated that N atom was incorporated in the Li–B–O matrix film, and an increase in the composition of Li₂O together with N-substitution caused the structural conversion from ring-type borate to open structured one, where more free space and ionic bonding characteristic are offered for higher mobility of Li⁺ ions. A high ionic conductivity of ca. 2.3 × 10⁻⁶ S cm⁻¹ at room temperature was obtained from the thin film electrolyte of Li_3.09BO_2.53N_0.52 glass that was prepared using 3Li₂O–B₂O₃ target. Electrochemical analyses suggest the high Li⁺ ion conductivity is induced by the reduced activation energy through the control of the composition and the structure.     

Conductive performances of solid polymer electrolyte films based on PVB/LiClO4 plasticized by PEG200, PEG400 and PEG600

Solid polymer electrolyte (SPE) films consisting of polyvinyl butyral (PVB) as host polymer, LiClO₄ as alkali salt at mole ratio of [O]:[Li] = 8, and different molecular weight polyethylene glycol (PEG) including PEG₂₀₀, PEG₄₀₀, and PEG₆₀₀ as plasticizers are prepared by physical blending method. The dielectric relaxation and electrochemical impedance measurements reveal that the conductive performances are improved by adding PEG as plasticizers through the enhancement in the moving space for ions, and PEG₄₀₀ performs plasticizing effect superior to PEG₂₀₀ and PEG₆₀₀. Their conductivity is measured by using a sandwiched Pt/SPE/Pt cell model. SPE with 30% PEG₄₀₀ (wt%) of PVB exhibits the maximum conductivity at room temperature, and its conductivity increases linearly with temperatures from 303 to 333 K at two to three orders of magnitude higher than that of the other two SPEs containing 30% PEG₂₀₀ and 30% PEG₆₀₀, respectively. However, their conductivity does not increase linearly with the increase in heating temperatures until the temperature reaches around 333 K; the decrease in conductivity with heating from their maxima is attributed to the restriction of ion moving space because of the crosslinking reaction between hydroxyl and aldehyde groups. As observed from the XRD and the microscopy results, PEG₄₀₀ is more effective than others in enhancing the conductive performances of these SPEs through changing LiClO₄ from crystalline to amorphous state, increasing the flexibility of PVB, disturbing the short distance sequential order of PVB chains, and promoting the formation of ‘pathway’ for ions’ movement.     

The effect of nanosized TiO2 addition on poly(methylmethacrylate) based polymer electrolytes

The electrochemical, X-ray diffraction, thermal, rheological and spectroscopic studies have been carried out to examine the effect of nanosized TiO₂ addition in different concentration to polymethylmethacrylate (PMMA) based gel polymer electrolytes (GPE). This work demonstrates that with optimum concentration of TiO₂ loadings in GPE, the ionic conductivity enhances with negligible effect on other electrochemical properties. The obtained ionic conductivity value is >10⁻³ S cm⁻¹. An increase in viscosity by an order of magnitude is obtained which also restricts the flow property of GPE. The addition of TiO₂ retains the amorphicity of the GPE while the T_g increases. Enhanced mechanical stability of these composite polymer electrolytes (CPEs) with solid-like behavior is evident from their appearance. The activation energy has been calculated by fitting the conductivity profile in VTF equation, which decreases on the addition of fillers. FTIR characterization also confirms the interaction of filler with CO of PMMA. The capabilities and properties exhibited by these CPEs will be of immense interest for electrochemists to use them in solid-state devices.     

Effects of surface lithiated TiO2 nanorods on room-temperature properties of polymer solid electrolytes

Polymer solid electrolyte with high ionic conductivity at room-temperature is most likely to be widely used in solid-state lithium batteries. In this work, the novel surface lithiated TiO₂ nanorods were firstly used as ionic conductor in polymer solid electrolyte. The surface lithiated TiO₂ nanorods-filled polypropylene carbonate polymer composite solid electrolyte (CSE) has an uniform composite structure with a thickness of about 60 μm. The ionic conductivity at room-temperature is 1.21 × 10⁻⁴ S cm⁻¹ and the electrochemical stability window is up to 4.6 V (vs Li⁺/Li). The assembled NCM622/CSE/Li solid-state battery shows a stable cycle performance with a retention capacity of 120 mAh g⁻¹ after 200 cycles at the current density of 0.3 C and a high coulomb efficiency of 99%. Compared with TiO₂ particles, this novel surface lithiated TiO₂ nanorods can provide more continuous ion transport channels and more Lewis acid-base reactive sites, provide a novel way to enhance the lithium ion transport in polymer solid electrolyte.