Papers by Alexander Teran
Macromolecules, 2014
Block copolymer/lithium salt mixtures are promising materials for lithium battery electrolytes. T... more Block copolymer/lithium salt mixtures are promising materials for lithium battery electrolytes. The growth of ordered lamellar grains after a block copolymer electrolyte was quenched from the disordered state to the ordered state was studied by depolarized light scattering. Three quench depths below the order-to-disorder transition temperature were studied: 6, 12, and 24°C. Regardless of quench depth, elongated ellipsoidal grains with aspect ratios between six and eight were formed during the initial stage of order formation. This was followed by a rapid reduction in aspect ratio; at long times, isotropic grains with aspect ratios in the vicinity of unity were obtained. Unusual grain growth kinetics were observed at all quench depths: (1) The average grain volume decreased with time after the early stage of grain growth. To our knowledge, a decrease in grain size has never been observed before in any quenched block copolymer system. (2) The volume fraction occupied by ordered grains of the shallowest quenched sample (quench depth of 6°C) was significantly less than unity even after waiting times approaching 400 min. This is consistent with recent theoretical and experimental work indicating the presence of a coexistence window between ordered and disordered phases due to the partitioning of the salt into the ordered domains. At quench depths of 12 and 24°C, which are outside the coexistence window, the grain volume fraction increases monotonically with time, and ordered grains occupy the entire sample at long times.
Block copolymer/lithium salt mixtures are promising materials for lithium battery electrolytes. T... more Block copolymer/lithium salt mixtures are promising materials for lithium battery electrolytes. The growth of ordered lamellar grains after a block copolymer electrolyte was quenched from the disordered state to the ordered state was studied by depolarized light scattering. Three quench depths below the order-to-disorder transition temperature were studied: 6, 12, and 24°C. Regardless of quench depth, elongated ellipsoidal grains with aspect ratios between six and eight were formed during the initial stage of order formation. This was followed by a rapid reduction in aspect ratio; at long times, isotropic grains with aspect ratios in the vicinity of unity were obtained. Unusual grain growth kinetics were observed at all quench depths: (1) The average grain volume decreased with time after the early stage of grain growth. To our knowledge, a decrease in grain size has never been observed before in any quenched block copolymer system. (2) The volume fraction occupied by ordered grains of the shallowest quenched sample (quench depth of 6°C) was significantly less than unity even after waiting times approaching 400 min. This is consistent with recent theoretical and experimental work indicating the presence of a coexistence window between ordered and disordered phases due to the partitioning of the salt into the ordered domains. At quench depths of 12 and 24°C, which are outside the coexistence window, the grain volume fraction increases monotonically with time, and ordered grains occupy the entire sample at long times.
ACS Macro Letters, Jan 25, 2012
The ionic conductivity of a block copolymer electrolyte was measured in an in situ small-angle X-... more The ionic conductivity of a block copolymer electrolyte was measured in an in situ small-angle X-ray scattering experiment as it transitioned from an ordered lamellar structure to a disordered phase. The ionic conductivity increases discontinuously as the electrolyte transitions from order to disorder. A simple framework for quantifying the magnitude of the discontinuity is presented. This study lays the groundwork for understanding the effect of more complex phase transitions such as order−order transitions on ion transport.
Macromolecules
The ionic conductivity and glass transition temperatures of
nanostructured block copolymer elect... more The ionic conductivity and glass transition temperatures of
nanostructured block copolymer electrolytes composed of polystyrene-b-poly(ethylene oxide) (SEO) doped with lithium bis-(trifluoromethanesulfone)imide (LiTFSI) were studied in the small molecular weight limit (between 2.7 and 13.7 kg mol−1). In this range, the annealed conductivity exhibits a nonmonotonic dependence on molecular weight, decreasing with increasing molecular weight in the small molecular
weight limit before increasing when molecular weight exceeds about 10 kg mol−1. We show that annealed electrolyte conductivity is affected by two competing factors: the glass transition temperature of the insulating polystyrene (PS) block and the width of the conducting poly(ethylene oxide) (PEO) channel. In the low molecular weight limit, all ions are in contact with both PS and PEO segments. The intermixing between PS and PEO segments is restricted to an interfacial zone of width, λ. Our experiments suggest that λ is about 5 nm. The fraction of ions affected by the interfacial zone decreases as the conducting channel width increases. We also study the effect of thermal history on the conductivity of the block copolymer electrolytes. Our data suggest that long-range order impedes ion transport.
Journal of Physical Chemistry B, Nov 15, 2013
Ion-containing block copolymers are of interest for applications such as electrolytes in recharge... more Ion-containing block copolymers are of interest for applications such as electrolytes in rechargeable lithium batteries. The addition of salt to these materials is necessary to make them conductive; however, even small amounts of salt can have significant effects on the phase behavior of these materials and consequently on their ion-transport and mechanical properties. As a result, the effect of salt addition on block copolymer thermodynamics has been the subject of significant interest over the past decade. This feature article describes a comprehensive study of the thermodynamics of block copolymer/salt mixtures over a wide range of molecular weights, compositions, salt concentrations, and temperatures. The Flory−Huggins interaction parameter was determined by fitting small angle X-ray scattering data of disordered systems to predictions based on the random phase approximation. Experiments on neat block copolymers revealed that the Flory−Huggins parameter is a strong function of chain length. Experiments on block copolymer/salt mixtures revealed a highly nonlinear dependence of the Flory−Huggins parameter on salt concentration. These findings are a significant departure from previous results and indicate the need for improved theories for describing thermodynamic interactions in neat and salt-containing block copolymers.
Solid State Ionics, 2011
The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromet... more The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfone) imide (LiTFSI) was measured as a function of molecular weight of the PEO chains, M, over the range 0.2-5000 kg/mol. Our data are consistent with an expression σ = σ 0 + K/M proposed by Shi and Vincent [Solid State Ionics 60 (1993)] where σ 0 and K are exponential and linear functions of inverse temperature respectively. Explicit expressions for σ 0 and K are provided.
Macromolecules, 2011
The primary challenges to commercialization of the high-energy-density lithium sulfur battery are... more The primary challenges to commercialization of the high-energy-density lithium sulfur battery are dendrite growth of the lithium metal at the anode and capacity fade due to loss of active mass through dissolution at the cathode. Nanostructured solid polymer electrolytes offer one potential solution to reduce the amount of capacity fade seen in lithium metal/sulfur batteries by keeping the active material localized at the cathode and to prevent the growth of dendrites at the anode due to their high shear moduli. The block copolymer electrolyte poly(styrene)-block-poly(ethylene oxide) (SEO) has shown acceptable ionic conductivity and sufficient shear modulus to retard lithium dendrite growth. The solubility of the lithium polysulfide reaction intermediates Li2Sx, where 1 <= x <= 8, was studied in SEO copolymers with a range of molecular weights and salt concentrations using small angle X-ray scattering, X-ray diffraction, and differential scanning calorimetery.
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Papers by Alexander Teran
nanostructured block copolymer electrolytes composed of polystyrene-b-poly(ethylene oxide) (SEO) doped with lithium bis-(trifluoromethanesulfone)imide (LiTFSI) were studied in the small molecular weight limit (between 2.7 and 13.7 kg mol−1). In this range, the annealed conductivity exhibits a nonmonotonic dependence on molecular weight, decreasing with increasing molecular weight in the small molecular
weight limit before increasing when molecular weight exceeds about 10 kg mol−1. We show that annealed electrolyte conductivity is affected by two competing factors: the glass transition temperature of the insulating polystyrene (PS) block and the width of the conducting poly(ethylene oxide) (PEO) channel. In the low molecular weight limit, all ions are in contact with both PS and PEO segments. The intermixing between PS and PEO segments is restricted to an interfacial zone of width, λ. Our experiments suggest that λ is about 5 nm. The fraction of ions affected by the interfacial zone decreases as the conducting channel width increases. We also study the effect of thermal history on the conductivity of the block copolymer electrolytes. Our data suggest that long-range order impedes ion transport.
nanostructured block copolymer electrolytes composed of polystyrene-b-poly(ethylene oxide) (SEO) doped with lithium bis-(trifluoromethanesulfone)imide (LiTFSI) were studied in the small molecular weight limit (between 2.7 and 13.7 kg mol−1). In this range, the annealed conductivity exhibits a nonmonotonic dependence on molecular weight, decreasing with increasing molecular weight in the small molecular
weight limit before increasing when molecular weight exceeds about 10 kg mol−1. We show that annealed electrolyte conductivity is affected by two competing factors: the glass transition temperature of the insulating polystyrene (PS) block and the width of the conducting poly(ethylene oxide) (PEO) channel. In the low molecular weight limit, all ions are in contact with both PS and PEO segments. The intermixing between PS and PEO segments is restricted to an interfacial zone of width, λ. Our experiments suggest that λ is about 5 nm. The fraction of ions affected by the interfacial zone decreases as the conducting channel width increases. We also study the effect of thermal history on the conductivity of the block copolymer electrolytes. Our data suggest that long-range order impedes ion transport.