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Papers by Joykumar Thokchom
Journal of the American Ceramic Society, 2007
This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li 2 ... more This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li 2 O. 9Al 2 O 3. 38 TiO 2. 39P 2 O 5 glass-ceramic and polyethylene. The processing involved tape casting of 14Li 2 O. 9Al 2 O 3. 38TiO 2. 39P 2 O 5 glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 9501-11001C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150-350 lm thick membranes were characterized and are discussed in this paper. The crystallites of the glass-ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO 4 at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity.
Journal of The Electrochemical Society, 2008
In this paper, processing and characterization of sheet, pellet, and membrane specimens based on ... more In this paper, processing and characterization of sheet, pellet, and membrane specimens based on the lithium aluminum germanium phosphate (LAGP) glassceramic system is reported. X-ray diffraction patterns exhibited the presence of as the primary phase. Increasing heat-...
Journal of Power Sources, 2008
Superionically conducting lithium aluminum germanium phosphate (LAGP) glass-ceramic and barium st... more Superionically conducting lithium aluminum germanium phosphate (LAGP) glass-ceramic and barium strontium titanate, Ba 0.6 Sr 0.4 TiO 3 (0.6BST)-doped specimens were processed and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance techniques. The XRD patterns exhibited the existence of LiGe 2 (PO 4) 3 as the primary phase with impurity phases AlPO 4 and Li 2 O. SEM images revealed the presence of large LAGP crystals. The highest conductivity (5.08 × 10 −3 S cm −1) at 27 • C was obtained for the glass-ceramic sheet specimen crystallized at 850 • C for 12 h. Pelletized specimens prepared from the glass-ceramic powder and sintered at 850 • C for 9 h exhibited a slightly lower conductivity (4.62 × 10 −3 S cm −1) at 27 • C. The nonlinearity in the Arrhenius plots of total conductivity was attributed to the impurity phases, AlPO 4 and Li 2 O and mediated the transport of lithium ion which is associated with higher activation energy. Doping of dielectric 0.6BST to the LAGP led to the shifting of the temperature of inflection towards the higher temperature in the Arrhenius plot of total conductivity and enhanced the space charge effect.
Solid State Ionics, 2006
Three different formulations of 14 Li 2 O•9 Al 2 O 3 •38 TiO 2 •39 P 2 O 5 composition (LATP) wer... more Three different formulations of 14 Li 2 O•9 Al 2 O 3 •38 TiO 2 •39 P 2 O 5 composition (LATP) were melted, cast and crystallized. As-cast glass was characterized by differential scanning calorimetry which exhibited a distinct and strong exothermic peak around 680°C. The peak was attributed to the crystallization of the glass. The crystallized glass (glass-ceramic) was further characterized by X-ray diffraction which showed the existence of Li 1 + x Al x Ti 2 − x (PO 4) 3 (x ⋍ 0.3)as the primary phase mixed with a small concentration of AlPO 4 and an unidentified phase. The scanning electron micrographs revealed the presence of the primary crystalline phase with an average grain size of 1 μm. Electrical characterization by AC impedance spectroscopy revealed grain and grain boundary contributions to the total conductivity. The effect of specimen processing parameters on conductivity is also investigated and discussed.
L'invention se rapporte a une cathode composite impregnee a semi-conducteurs. La cathode cont... more L'invention se rapporte a une cathode composite impregnee a semi-conducteurs. La cathode contient un materiau actif poreux fritte, dans lequel les pores du materiau poreux sont impregnes d'un electrolyte solide amorphe inorganique et ioniquement conducteur. Un procede de production de la cathode composite impregnee a semi-conducteurs consiste a former une granule contenant un materiau de cathode d'intercalation actif; a fritter la granule pour former une granule de cathode poreuse frittee; a impregner les pores de la granule de cathode poreuse frittee d'un precurseur liquide d'un electrolyte solide amorphe inorganique et ioniquement conducteur; et a durcir la granule impregnee pour produire la cathode composite.
ACS Applied Energy Materials, 2021
ACS Applied Energy Materials
J Electrochem Soc, 2007
ABSTRACT In this paper, processing and properties of water durable solid electrolyte membranes pr... more ABSTRACT In this paper, processing and properties of water durable solid electrolyte membranes prepared from a glass-ceramic powder in the Li2O-Al2O3-TiO2-P2O5 system are reported. Specifically, ionic conductivity, microstructure, and water stability of 150 to 350 mu m thick membranes of the glass-ceramic and its composite with polyethylene are investigated and discussed. The grains (crystallites) of the glass-ceramic show liquidlike conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of about 3. The ratio between the grain and grain boundary conductivities in the temperature range of 213 to 300 K varies by a factor of 3 to 14. The lower the temperature, the larger the ratio. The difference in conductivities is explained on the basis of crystallographic mismatch and the existence of crystalline AlPO4 at the grain boundary. The membranes were very stable in tap water. The polyethylene infiltration further improved water stability with little impact on conductivity.
Solid State Ionics, 2005
ABSTRACT PEOx : LiN(SO2CF2CF3)2 polymer electrolytes and PEOx : LiN(SO2CF2CF3)2–Al2O3 composite e... more ABSTRACT PEOx : LiN(SO2CF2CF3)2 polymer electrolytes and PEOx : LiN(SO2CF2CF3)2–Al2O3 composite electrolytes were prepared by the energy milling process and characterized by means of AC impedance and differential scanning calorimetry (DSC) techniques. An optimized, free-standing electrolyte composition in the PEOx : LiN(SO2CF2CF3)2 system yields a conductivity value of 1.5 × 10− 4 S cm− 1 at ambient temperature. The ionic conductivity first increases with salt concentration, reaches a maximum value at x = 8.5, and subsequently decreases. The conductivity of the polymer electrolyte decreased after adding 5 and 10 wt.% Al2O3. DSC results revealed that the energy milling process of specimen preparation leads to the formation of complexes between the polymer and the lithium salt. Annealing of the energy milled specimens in the 100 to 200 °C temperature range provided a nearly complete amorphous phase. The high conductivities of the polymer electrolytes are attributed to the existence of the complete amorphous phase.
Journal of the American Ceramic Society, 2007
The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LA... more The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LATP) glass-ceramic, Al 2 O 3 , and Ba 0.6 Sr 0.4 TiO 3 (0.6 BST) exhibit an inflection or peak around 271C, which is interpreted as a signature of space charge. The space charge is formed by the adsorption of lithium ions onto the dielectric phases below 271C. The space charge is also a source of an electric field, which influences the transport of conducting ions. The adsorbed ions are desorbed above 271C, resulting in a reduction or elimination of the space charge effect. A high dielectric constant phase, 0.6 BST, retains the space charge effect even at temperatures greater than 271C.
Journal of the American Ceramic Society, 2008
This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)-Al 2 O 3 composite memb... more This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)-Al 2 O 3 composite membranes. The tape cast specimens were subjected to binder burnout (5001C) and sintering (15501C) processes to obtain 200-300 lm thick membranes. The ionic conductivity and microstructure of the membranes were characterized and are discussed in this paper. The ionic conductivity of the composite specimens was enhanced and was correlated with the number of charge carrier and their mobility. The solubility of Al 2 O 3 in YSZ was minimal and nanosize Al 2 O 3 of the batch sintered into microsize and existed as a distinct phase. The scanning electron microscopy micrographs revealed that YSZ and Al 2 O 3 grains were strained.
Journal of Power Sources, 2006
The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycryst... more The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycrystalline lithium aluminum titanium phosphate (LATP) glass-ceramic material with Al 2 O 3 and Ba 0.6 Sr 0.4 TiO 3 (0.6BST) additions were investigated. It was determined that blocking and space charge effects coexist in these heterogeneous solids. However, their magnitudes differ from one system to another. The most pronounced blocking effect was evident in the LATP-Al 2 O 3 system, whereas a dominant space charge effect was observed in the LiI-Al 2 O 3 system. The higher dielectric constant of 0.6BST enhanced space charge effect in the LATP-0.6BST system. The space charge effect was also found to be temperature dependent.
Journal of Power Sources, 2008
A heterogeneous electrolyte comprised of PEG(6000):LiClO 4 (8:1)-MgO (20 wt.%) was prepared and c... more A heterogeneous electrolyte comprised of PEG(6000):LiClO 4 (8:1)-MgO (20 wt.%) was prepared and characterized. The electrolyte was subjected to a DC potential of 10 mV and the effect of the potential on conductivity evolution was investigated. The DC potential enhanced the conductivity by a factor of 25. The enhancement in conductivity was due to the formation of space charge around MgO that resulted in the development of an internal field.
Journal of the American Ceramic Society, 2007
This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li 2 ... more This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li 2 O. 9Al 2 O 3. 38 TiO 2. 39P 2 O 5 glass-ceramic and polyethylene. The processing involved tape casting of 14Li 2 O. 9Al 2 O 3. 38TiO 2. 39P 2 O 5 glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 9501-11001C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150-350 lm thick membranes were characterized and are discussed in this paper. The crystallites of the glass-ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO 4 at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity.
Journal of The Electrochemical Society, 2008
In this paper, processing and characterization of sheet, pellet, and membrane specimens based on ... more In this paper, processing and characterization of sheet, pellet, and membrane specimens based on the lithium aluminum germanium phosphate (LAGP) glassceramic system is reported. X-ray diffraction patterns exhibited the presence of as the primary phase. Increasing heat-...
Journal of Power Sources, 2008
Superionically conducting lithium aluminum germanium phosphate (LAGP) glass-ceramic and barium st... more Superionically conducting lithium aluminum germanium phosphate (LAGP) glass-ceramic and barium strontium titanate, Ba 0.6 Sr 0.4 TiO 3 (0.6BST)-doped specimens were processed and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance techniques. The XRD patterns exhibited the existence of LiGe 2 (PO 4) 3 as the primary phase with impurity phases AlPO 4 and Li 2 O. SEM images revealed the presence of large LAGP crystals. The highest conductivity (5.08 × 10 −3 S cm −1) at 27 • C was obtained for the glass-ceramic sheet specimen crystallized at 850 • C for 12 h. Pelletized specimens prepared from the glass-ceramic powder and sintered at 850 • C for 9 h exhibited a slightly lower conductivity (4.62 × 10 −3 S cm −1) at 27 • C. The nonlinearity in the Arrhenius plots of total conductivity was attributed to the impurity phases, AlPO 4 and Li 2 O and mediated the transport of lithium ion which is associated with higher activation energy. Doping of dielectric 0.6BST to the LAGP led to the shifting of the temperature of inflection towards the higher temperature in the Arrhenius plot of total conductivity and enhanced the space charge effect.
Solid State Ionics, 2006
Three different formulations of 14 Li 2 O•9 Al 2 O 3 •38 TiO 2 •39 P 2 O 5 composition (LATP) wer... more Three different formulations of 14 Li 2 O•9 Al 2 O 3 •38 TiO 2 •39 P 2 O 5 composition (LATP) were melted, cast and crystallized. As-cast glass was characterized by differential scanning calorimetry which exhibited a distinct and strong exothermic peak around 680°C. The peak was attributed to the crystallization of the glass. The crystallized glass (glass-ceramic) was further characterized by X-ray diffraction which showed the existence of Li 1 + x Al x Ti 2 − x (PO 4) 3 (x ⋍ 0.3)as the primary phase mixed with a small concentration of AlPO 4 and an unidentified phase. The scanning electron micrographs revealed the presence of the primary crystalline phase with an average grain size of 1 μm. Electrical characterization by AC impedance spectroscopy revealed grain and grain boundary contributions to the total conductivity. The effect of specimen processing parameters on conductivity is also investigated and discussed.
L'invention se rapporte a une cathode composite impregnee a semi-conducteurs. La cathode cont... more L'invention se rapporte a une cathode composite impregnee a semi-conducteurs. La cathode contient un materiau actif poreux fritte, dans lequel les pores du materiau poreux sont impregnes d'un electrolyte solide amorphe inorganique et ioniquement conducteur. Un procede de production de la cathode composite impregnee a semi-conducteurs consiste a former une granule contenant un materiau de cathode d'intercalation actif; a fritter la granule pour former une granule de cathode poreuse frittee; a impregner les pores de la granule de cathode poreuse frittee d'un precurseur liquide d'un electrolyte solide amorphe inorganique et ioniquement conducteur; et a durcir la granule impregnee pour produire la cathode composite.
ACS Applied Energy Materials, 2021
ACS Applied Energy Materials
J Electrochem Soc, 2007
ABSTRACT In this paper, processing and properties of water durable solid electrolyte membranes pr... more ABSTRACT In this paper, processing and properties of water durable solid electrolyte membranes prepared from a glass-ceramic powder in the Li2O-Al2O3-TiO2-P2O5 system are reported. Specifically, ionic conductivity, microstructure, and water stability of 150 to 350 mu m thick membranes of the glass-ceramic and its composite with polyethylene are investigated and discussed. The grains (crystallites) of the glass-ceramic show liquidlike conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of about 3. The ratio between the grain and grain boundary conductivities in the temperature range of 213 to 300 K varies by a factor of 3 to 14. The lower the temperature, the larger the ratio. The difference in conductivities is explained on the basis of crystallographic mismatch and the existence of crystalline AlPO4 at the grain boundary. The membranes were very stable in tap water. The polyethylene infiltration further improved water stability with little impact on conductivity.
Solid State Ionics, 2005
ABSTRACT PEOx : LiN(SO2CF2CF3)2 polymer electrolytes and PEOx : LiN(SO2CF2CF3)2–Al2O3 composite e... more ABSTRACT PEOx : LiN(SO2CF2CF3)2 polymer electrolytes and PEOx : LiN(SO2CF2CF3)2–Al2O3 composite electrolytes were prepared by the energy milling process and characterized by means of AC impedance and differential scanning calorimetry (DSC) techniques. An optimized, free-standing electrolyte composition in the PEOx : LiN(SO2CF2CF3)2 system yields a conductivity value of 1.5 × 10− 4 S cm− 1 at ambient temperature. The ionic conductivity first increases with salt concentration, reaches a maximum value at x = 8.5, and subsequently decreases. The conductivity of the polymer electrolyte decreased after adding 5 and 10 wt.% Al2O3. DSC results revealed that the energy milling process of specimen preparation leads to the formation of complexes between the polymer and the lithium salt. Annealing of the energy milled specimens in the 100 to 200 °C temperature range provided a nearly complete amorphous phase. The high conductivities of the polymer electrolytes are attributed to the existence of the complete amorphous phase.
Journal of the American Ceramic Society, 2007
The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LA... more The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LATP) glass-ceramic, Al 2 O 3 , and Ba 0.6 Sr 0.4 TiO 3 (0.6 BST) exhibit an inflection or peak around 271C, which is interpreted as a signature of space charge. The space charge is formed by the adsorption of lithium ions onto the dielectric phases below 271C. The space charge is also a source of an electric field, which influences the transport of conducting ions. The adsorbed ions are desorbed above 271C, resulting in a reduction or elimination of the space charge effect. A high dielectric constant phase, 0.6 BST, retains the space charge effect even at temperatures greater than 271C.
Journal of the American Ceramic Society, 2008
This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)-Al 2 O 3 composite memb... more This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)-Al 2 O 3 composite membranes. The tape cast specimens were subjected to binder burnout (5001C) and sintering (15501C) processes to obtain 200-300 lm thick membranes. The ionic conductivity and microstructure of the membranes were characterized and are discussed in this paper. The ionic conductivity of the composite specimens was enhanced and was correlated with the number of charge carrier and their mobility. The solubility of Al 2 O 3 in YSZ was minimal and nanosize Al 2 O 3 of the batch sintered into microsize and existed as a distinct phase. The scanning electron microscopy micrographs revealed that YSZ and Al 2 O 3 grains were strained.
Journal of Power Sources, 2006
The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycryst... more The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycrystalline lithium aluminum titanium phosphate (LATP) glass-ceramic material with Al 2 O 3 and Ba 0.6 Sr 0.4 TiO 3 (0.6BST) additions were investigated. It was determined that blocking and space charge effects coexist in these heterogeneous solids. However, their magnitudes differ from one system to another. The most pronounced blocking effect was evident in the LATP-Al 2 O 3 system, whereas a dominant space charge effect was observed in the LiI-Al 2 O 3 system. The higher dielectric constant of 0.6BST enhanced space charge effect in the LATP-0.6BST system. The space charge effect was also found to be temperature dependent.
Journal of Power Sources, 2008
A heterogeneous electrolyte comprised of PEG(6000):LiClO 4 (8:1)-MgO (20 wt.%) was prepared and c... more A heterogeneous electrolyte comprised of PEG(6000):LiClO 4 (8:1)-MgO (20 wt.%) was prepared and characterized. The electrolyte was subjected to a DC potential of 10 mV and the effect of the potential on conductivity evolution was investigated. The DC potential enhanced the conductivity by a factor of 25. The enhancement in conductivity was due to the formation of space charge around MgO that resulted in the development of an internal field.