Dr P W S K Bandaranayake (original) (raw)
Papers by Dr P W S K Bandaranayake
Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3 ). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and KahatagahaKolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types
Solid State Ionics, 1991
Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.
The Canadian Mineralogist, 2010
We report results on the physicochemical attributes and geological context of vein graphite from ... more We report results on the physicochemical attributes and geological context of vein graphite from the Bogala and Kahatagaha-Kolongaha mines, Sri Lanka, according to their morphology and texture. Each type has been characterized with means of X-ray diffraction, Raman spectrometry, oxyreactive and differential thermoanalysis, and measurements of the ratio of the carbon isotopes, 13 C/ 12 C. The carbon isotopic data for the Bogala graphite, expressed as d 13 C, are in the range of-8.3 and-10.4‰, and the data for the Kahatagaha-Kolongaha graphite are in the range of-7.9 and-9.3‰. These values of d 13 C values are not consistent with graphite mineralization due to granulite metamorphism, but rather with a magmatic origin. In a single vein of Bogala graphite, we can observe successive morphologies from the wallrock to the central part of the vein. In this textural transition, the d 13 C decreases as the carbon content increases from 93 to 98%.
Solid State Ionics
Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.
Physics and Chemistry of Glasses
Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic press... more Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic pressure (1×10−4–0·5 GPa) have been performed on ionic conductive, xP2O5–(1–x)Na2O, sodium phosphate glasses and on electronic conductive, xP2O5–(1–x)V2O5, phosphovanadate glasses with x=0·4 and 0·5. Isobaric variations for ionic conductivity with temperature are characteristic of an activated mechanism for charge carrier formation and migration. The associated activation enthalpy, ΔH * (around 0·7 eV), is found to be pressure independent. A low activation entropy, ΔS *, is found to decrease with increasing pressure. Isothermal logarithmic variations of the ionic conductivity as a function of pressure are linear with negative slopes. A positive ‘activation volume’, ΔV * (mean value of around 5 cm3 mol−1) is calculated from these slopes. Its increase with temperature can be thermodynamically correlated to a diminution of the activation entropy with pressure. Isobaric conductivity variations of...
Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and Kahatagaha-Kolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types
Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006
The performances of γ-MnO2 cathode in alkaline battery depend on the crystallochemical properties... more The performances of γ-MnO2 cathode in alkaline battery depend on the crystallochemical properties of MnO2 as well as of graphite used to improve electronic conductivity of the cathode mixture. In the present work we have studied the performances of Sri Lanka natural graphite in the reduction process of γ-MnO2 and compare it with the other synthetic and natural graphites. We also show how crystallochemical and electrochemical properties of the synthetic manganese dioxide depend on defects which are related to the structural parameters Pr and Tw. Where Pr is the rate of ramsdellite-pyrolusite intergrowth and Tw microtwinning which represents the creation of nanostructure aggregates during electrodeposition.
Solid State Ionics - Materials and Devices - Proceedings of the 7th Asian Conference, 2000
Solid State Ionics - Trends in the New Millennium - Proceedings of the 8th Asian Conference, 2002
A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhi... more A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO9:Cu(CF5SO3)2 made by complexing copper triflate (CuTf2) with PEO appears to show scientifically intriguing transport properties. Although copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the
Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006
Sri Lanka natural vein graphite has various morphologies with different structural and physical c... more Sri Lanka natural vein graphite has various morphologies with different structural and physical characteristics. The identified most abundant morphology, the shiny-slippery-fibrous (SSI) graphite found in two mines, Bogala and Kahatagaha-Kolongaha, has a very high purity over 98% and high crystallinity. The characterization of Li-graphite intercalation process was mainly performed with the initial discharge-charge profiles at the current rate of C/20 and C/40, and cycled between the initial open circuit voltage and 0.005 V vs. Li/Li + in lithium cells in 1M LiPF6 (EC/DMC; 1:1). The synthetic KS25 graphite showed much better rechargeability and higher intercalation rate of lithium ions than natural BSSI and KSSI graphite. The irreversible capacity loss of natural vein graphite was partly due to passivation and exfoliation. But the major irreversible capacity loss of the graphite (natural or synthetic) was mainly due to lithium trapping in the internal pore spaces of graphite material or electrode structure. Measurements of the open circuit voltage in lithium cells with graphite as working electrode were used to obtain the thermodynamic factors such as entropy, ∆S, and enthalpy, ∆H, of lithium intercalation into natural and synthetic graphite. These thermodynamic values were determined in discharging process of the lithium cells from 0.005 V to 1.50 V vs Li/Li + at C/5 rate. For all the types of graphite, initially large ∆S decreases with lithium concentration and then becomes negative and shows three entropy plateaus indicating the transition of stages in graphite-lithium intercalation compounds. For natural and synthetic graphite ∆H is negative and increases with lithium concentration and follows the staging process of lithium intercalation.
Sri Lankan Journal of Physics, 2008
Intercalation cathode materials belonging to the 4-volt class electrodes, lithiated cobalt oxide ... more Intercalation cathode materials belonging to the 4-volt class electrodes, lithiated cobalt oxide LiCoO 2 and lithiated nickel cobalt oxide LiCo 0.4 Ni 0.6 O 2 , were synthesized by sol-gel technique. The structural characteristics of the compounds were studied using XRD, FTIR and DSC. The compounds were used as cathode materials for assembling rechargeable lithium-batteries and their electrochemical performances were studied. The potentiostat and galvanostat techniques were used to determine the electrochemical characteristics. The irreversible capacity loss of LiCoO 2 during the first charge-discharge is about 20% and for LiCo 0.4 Ni 0.6 O 2 is about 90% for two different current rates of 5 and 10 A kg-1. The overall electrochemical capacity of LiCo 0.4 Ni 0.6 O 2 has been drastically reduced due to the s-block or p-block metal substitution. Also the un-reacted materials remained as impurities gave a very poor cycleability. However more stable charge-discharge performances have been observed for LiCoO 2 at different current rates. Differences and similarities between these two cathode materials in batteries are also discussed. The Li-ion batteries were assembled using the sol-gel synthesized cathode materials, natural untreated vein graphite of Sri Lanka as the anode material and 1 M LiPF 6 in EC/DMC as liquid electrolyte, and their performances were tested.
Solid State Ionics, 1990
ABSTRACT
Solid State Ionics, 1990
Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measu... more Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measurements have been performed for the Na2S0.,-MgSO, binary system. The redetermined phase diagram shows that the solid solution of the high-temperature phase of Na*SO, is stable up to 35 mol% MgSO, at 680°C. The ionic conductivity in this phase increases rapidly with increasing MgSO, content, the maximum conductivity at 540°C is about 150 times larger than the conductivity of pure Na2S0,. For two intermediate compounds, Na2Mg(S04)2 and Na2Mg3(S04)4, the ionic conductivity is relatively low, 2x 10m4 and 4X 10-6fi-1 cm-' at 500°C.
Solid State Ionics, 1988
... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) ... more ... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) 699. [ 3l ] BN Mehrotra, Z. Kristallogr. 155 (1981) 159. [ 32 ] C). Toft Sorensen, Gh, Johannnesen and K. Clausen, in: Transport structure relations in fast ion and mixed conductors, eds. ...
Solid State Ionics, 1993
A range of stable solid solutions with "~-L1SICON type structure forms in the system Li4_2xGel_~x... more A range of stable solid solutions with "~-L1SICON type structure forms in the system Li4_2xGel_~xO4 for 0.08 < x < 0.42. This phase has high lithium ion conductivity with a maximum value (bulk) of ~ 1.85× l0-5 S cm-~ for x=0.20 at 27°C. The net pellet conductivity for this composition is ~ 1.00 × l 0-5 S cm-~ at 27 ° C, rising to ~ 0.04 S crn-~ at 300 ° C. Conductivity Arrhenius plots for different compositions in the "/-solid solution range exhibit markedly non-linear behaviour above ~ 300 o C. The activation energies below ~ 300 °C are in the range 0.50-0.60 eV. The)'-solid solutions are structurally related to orthorhombic 7-Li3PO4 and contain interstitial Li + ions; for x = 0.20, a = 6.253 (2) A, b = 10.828 (3) A, c = 5.114 (2) A, at room temperature. An approximate phase diagram for the Li4GeO4-Li2SO4 binary system is presented, together with lattice parameter data on the),-solid solutions.
Solid State Ionics, 1995
Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.
Solid State Ionics, 1992
Lithium sulphate and a few other compounds have high temperature phases which are both solid elec... more Lithium sulphate and a few other compounds have high temperature phases which are both solid electrolytes and plastic crystals (rotor phases). Three types of experiments are here considered in order to test the validity ofa "paddie-wheei mechanism" that has been proposed for cation conductivity in these phases. A single-crystal neutron diffraction study has been performed for cubic lithium sulphate. The refinement of the data gives a very complex model for the location of the lithium ions. There is definitely a void at and near the octahedrai (1/2, 1/2, 1/2) position. 90% of the lithium ions are located at the tetrahedral 8c-sites (1/4, 1/4, 1/4), although significantly distorted in the directions of the four neighbouring sulphate ions. The remaining 10% of the lithium ions are termed as an evenly distributed spherical shell which is surrounding the sulphate ions. The lithium ions are transported along a slightly curved pathway of continuous lithium occupation corresponding to a distance of about 3.7 A. Thus, lithium transport occurs in one of the six directions [ 110 ], [ 1 i0 ], [ 101 ] etc. The electrical conductivity has been studied for solid solutions of lithium tungstate in cubic lithium sulphate. The conductivity is reduced in the one-phase region, while it is increased in a two phase (solid-melt) region. There are pronounced differences between the rotor phases and other phases concerning how partial cation substitution affects the electrical conductivity of solid solutions. Regarding self and interdiffnsion, all studied mono-and divalent cations are very mobile in the rotor phases, which lack the pronounced correlation with ionic radii that is characteristic for diffusion in other classes of solid electrolytes. The quoted studies are to be considered as strong evidence against a percolation model proposed by Secco.
Solid State Ionics, 1991
Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.
Solid State Ionics, 1996
Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all c... more Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques
Solid State Ionics, 2006
Glasses in the 3TeO 2 x Li 2 O(1-x)V 2 O 5 system have been synthesised for 0 ≤ x ≤ 1. Conductivi... more Glasses in the 3TeO 2 x Li 2 O(1-x)V 2 O 5 system have been synthesised for 0 ≤ x ≤ 1. Conductivity data obey an Arrhenius type behaviour between room temperature and the glass transition temperature. The isothermal conductivity curves exhibit a sharp minimum near x=0.5. Values of activation energies and pre-exponential factors in the V 2 O 5 rich region are lower compared to those in the alkali oxide rich region implying that the conductivity mechanisms in these two regions are different. Experimental values suggest that an electronic conductivity by polaron hopping between V VI and V V cations would prevail in the first region. In the alkali oxide rich region, ionic conductivity would operate by an interstitial pair mechanism between non-bridging oxygens. The very low conductivity expected for x=0.5 could be explained by assuming that, for this composition, both ionic and electronic paths would not percolate any more.
Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3 ). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and KahatagahaKolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types
Solid State Ionics, 1991
Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.
The Canadian Mineralogist, 2010
We report results on the physicochemical attributes and geological context of vein graphite from ... more We report results on the physicochemical attributes and geological context of vein graphite from the Bogala and Kahatagaha-Kolongaha mines, Sri Lanka, according to their morphology and texture. Each type has been characterized with means of X-ray diffraction, Raman spectrometry, oxyreactive and differential thermoanalysis, and measurements of the ratio of the carbon isotopes, 13 C/ 12 C. The carbon isotopic data for the Bogala graphite, expressed as d 13 C, are in the range of-8.3 and-10.4‰, and the data for the Kahatagaha-Kolongaha graphite are in the range of-7.9 and-9.3‰. These values of d 13 C values are not consistent with graphite mineralization due to granulite metamorphism, but rather with a magmatic origin. In a single vein of Bogala graphite, we can observe successive morphologies from the wallrock to the central part of the vein. In this textural transition, the d 13 C decreases as the carbon content increases from 93 to 98%.
Solid State Ionics
Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.
Physics and Chemistry of Glasses
Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic press... more Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic pressure (1×10−4–0·5 GPa) have been performed on ionic conductive, xP2O5–(1–x)Na2O, sodium phosphate glasses and on electronic conductive, xP2O5–(1–x)V2O5, phosphovanadate glasses with x=0·4 and 0·5. Isobaric variations for ionic conductivity with temperature are characteristic of an activated mechanism for charge carrier formation and migration. The associated activation enthalpy, ΔH * (around 0·7 eV), is found to be pressure independent. A low activation entropy, ΔS *, is found to decrease with increasing pressure. Isothermal logarithmic variations of the ionic conductivity as a function of pressure are linear with negative slopes. A positive ‘activation volume’, ΔV * (mean value of around 5 cm3 mol−1) is calculated from these slopes. Its increase with temperature can be thermodynamically correlated to a diminution of the activation entropy with pressure. Isobaric conductivity variations of...
Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and Kahatagaha-Kolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types
Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006
The performances of γ-MnO2 cathode in alkaline battery depend on the crystallochemical properties... more The performances of γ-MnO2 cathode in alkaline battery depend on the crystallochemical properties of MnO2 as well as of graphite used to improve electronic conductivity of the cathode mixture. In the present work we have studied the performances of Sri Lanka natural graphite in the reduction process of γ-MnO2 and compare it with the other synthetic and natural graphites. We also show how crystallochemical and electrochemical properties of the synthetic manganese dioxide depend on defects which are related to the structural parameters Pr and Tw. Where Pr is the rate of ramsdellite-pyrolusite intergrowth and Tw microtwinning which represents the creation of nanostructure aggregates during electrodeposition.
Solid State Ionics - Materials and Devices - Proceedings of the 7th Asian Conference, 2000
Solid State Ionics - Trends in the New Millennium - Proceedings of the 8th Asian Conference, 2002
A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhi... more A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO9:Cu(CF5SO3)2 made by complexing copper triflate (CuTf2) with PEO appears to show scientifically intriguing transport properties. Although copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the
Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006
Sri Lanka natural vein graphite has various morphologies with different structural and physical c... more Sri Lanka natural vein graphite has various morphologies with different structural and physical characteristics. The identified most abundant morphology, the shiny-slippery-fibrous (SSI) graphite found in two mines, Bogala and Kahatagaha-Kolongaha, has a very high purity over 98% and high crystallinity. The characterization of Li-graphite intercalation process was mainly performed with the initial discharge-charge profiles at the current rate of C/20 and C/40, and cycled between the initial open circuit voltage and 0.005 V vs. Li/Li + in lithium cells in 1M LiPF6 (EC/DMC; 1:1). The synthetic KS25 graphite showed much better rechargeability and higher intercalation rate of lithium ions than natural BSSI and KSSI graphite. The irreversible capacity loss of natural vein graphite was partly due to passivation and exfoliation. But the major irreversible capacity loss of the graphite (natural or synthetic) was mainly due to lithium trapping in the internal pore spaces of graphite material or electrode structure. Measurements of the open circuit voltage in lithium cells with graphite as working electrode were used to obtain the thermodynamic factors such as entropy, ∆S, and enthalpy, ∆H, of lithium intercalation into natural and synthetic graphite. These thermodynamic values were determined in discharging process of the lithium cells from 0.005 V to 1.50 V vs Li/Li + at C/5 rate. For all the types of graphite, initially large ∆S decreases with lithium concentration and then becomes negative and shows three entropy plateaus indicating the transition of stages in graphite-lithium intercalation compounds. For natural and synthetic graphite ∆H is negative and increases with lithium concentration and follows the staging process of lithium intercalation.
Sri Lankan Journal of Physics, 2008
Intercalation cathode materials belonging to the 4-volt class electrodes, lithiated cobalt oxide ... more Intercalation cathode materials belonging to the 4-volt class electrodes, lithiated cobalt oxide LiCoO 2 and lithiated nickel cobalt oxide LiCo 0.4 Ni 0.6 O 2 , were synthesized by sol-gel technique. The structural characteristics of the compounds were studied using XRD, FTIR and DSC. The compounds were used as cathode materials for assembling rechargeable lithium-batteries and their electrochemical performances were studied. The potentiostat and galvanostat techniques were used to determine the electrochemical characteristics. The irreversible capacity loss of LiCoO 2 during the first charge-discharge is about 20% and for LiCo 0.4 Ni 0.6 O 2 is about 90% for two different current rates of 5 and 10 A kg-1. The overall electrochemical capacity of LiCo 0.4 Ni 0.6 O 2 has been drastically reduced due to the s-block or p-block metal substitution. Also the un-reacted materials remained as impurities gave a very poor cycleability. However more stable charge-discharge performances have been observed for LiCoO 2 at different current rates. Differences and similarities between these two cathode materials in batteries are also discussed. The Li-ion batteries were assembled using the sol-gel synthesized cathode materials, natural untreated vein graphite of Sri Lanka as the anode material and 1 M LiPF 6 in EC/DMC as liquid electrolyte, and their performances were tested.
Solid State Ionics, 1990
ABSTRACT
Solid State Ionics, 1990
Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measu... more Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measurements have been performed for the Na2S0.,-MgSO, binary system. The redetermined phase diagram shows that the solid solution of the high-temperature phase of Na*SO, is stable up to 35 mol% MgSO, at 680°C. The ionic conductivity in this phase increases rapidly with increasing MgSO, content, the maximum conductivity at 540°C is about 150 times larger than the conductivity of pure Na2S0,. For two intermediate compounds, Na2Mg(S04)2 and Na2Mg3(S04)4, the ionic conductivity is relatively low, 2x 10m4 and 4X 10-6fi-1 cm-' at 500°C.
Solid State Ionics, 1988
... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) ... more ... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) 699. [ 3l ] BN Mehrotra, Z. Kristallogr. 155 (1981) 159. [ 32 ] C). Toft Sorensen, Gh, Johannnesen and K. Clausen, in: Transport structure relations in fast ion and mixed conductors, eds. ...
Solid State Ionics, 1993
A range of stable solid solutions with "~-L1SICON type structure forms in the system Li4_2xGel_~x... more A range of stable solid solutions with "~-L1SICON type structure forms in the system Li4_2xGel_~xO4 for 0.08 < x < 0.42. This phase has high lithium ion conductivity with a maximum value (bulk) of ~ 1.85× l0-5 S cm-~ for x=0.20 at 27°C. The net pellet conductivity for this composition is ~ 1.00 × l 0-5 S cm-~ at 27 ° C, rising to ~ 0.04 S crn-~ at 300 ° C. Conductivity Arrhenius plots for different compositions in the "/-solid solution range exhibit markedly non-linear behaviour above ~ 300 o C. The activation energies below ~ 300 °C are in the range 0.50-0.60 eV. The)'-solid solutions are structurally related to orthorhombic 7-Li3PO4 and contain interstitial Li + ions; for x = 0.20, a = 6.253 (2) A, b = 10.828 (3) A, c = 5.114 (2) A, at room temperature. An approximate phase diagram for the Li4GeO4-Li2SO4 binary system is presented, together with lattice parameter data on the),-solid solutions.
Solid State Ionics, 1995
Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.
Solid State Ionics, 1992
Lithium sulphate and a few other compounds have high temperature phases which are both solid elec... more Lithium sulphate and a few other compounds have high temperature phases which are both solid electrolytes and plastic crystals (rotor phases). Three types of experiments are here considered in order to test the validity ofa "paddie-wheei mechanism" that has been proposed for cation conductivity in these phases. A single-crystal neutron diffraction study has been performed for cubic lithium sulphate. The refinement of the data gives a very complex model for the location of the lithium ions. There is definitely a void at and near the octahedrai (1/2, 1/2, 1/2) position. 90% of the lithium ions are located at the tetrahedral 8c-sites (1/4, 1/4, 1/4), although significantly distorted in the directions of the four neighbouring sulphate ions. The remaining 10% of the lithium ions are termed as an evenly distributed spherical shell which is surrounding the sulphate ions. The lithium ions are transported along a slightly curved pathway of continuous lithium occupation corresponding to a distance of about 3.7 A. Thus, lithium transport occurs in one of the six directions [ 110 ], [ 1 i0 ], [ 101 ] etc. The electrical conductivity has been studied for solid solutions of lithium tungstate in cubic lithium sulphate. The conductivity is reduced in the one-phase region, while it is increased in a two phase (solid-melt) region. There are pronounced differences between the rotor phases and other phases concerning how partial cation substitution affects the electrical conductivity of solid solutions. Regarding self and interdiffnsion, all studied mono-and divalent cations are very mobile in the rotor phases, which lack the pronounced correlation with ionic radii that is characteristic for diffusion in other classes of solid electrolytes. The quoted studies are to be considered as strong evidence against a percolation model proposed by Secco.
Solid State Ionics, 1991
Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.
Solid State Ionics, 1996
Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all c... more Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques
Solid State Ionics, 2006
Glasses in the 3TeO 2 x Li 2 O(1-x)V 2 O 5 system have been synthesised for 0 ≤ x ≤ 1. Conductivi... more Glasses in the 3TeO 2 x Li 2 O(1-x)V 2 O 5 system have been synthesised for 0 ≤ x ≤ 1. Conductivity data obey an Arrhenius type behaviour between room temperature and the glass transition temperature. The isothermal conductivity curves exhibit a sharp minimum near x=0.5. Values of activation energies and pre-exponential factors in the V 2 O 5 rich region are lower compared to those in the alkali oxide rich region implying that the conductivity mechanisms in these two regions are different. Experimental values suggest that an electronic conductivity by polaron hopping between V VI and V V cations would prevail in the first region. In the alkali oxide rich region, ionic conductivity would operate by an interstitial pair mechanism between non-bridging oxygens. The very low conductivity expected for x=0.5 could be explained by assuming that, for this composition, both ionic and electronic paths would not percolate any more.