Polymer Dynamics in Block Copolymer Electrolytes Detected by Neutron Spin Echo

Loo, Whitney S.; Faraone, Antonio; Grundy, Lorena S.; Gao, Kang; Balsara, Nitash P.

doi:10.1021/acsmacrolett.0c00236

Cited by 10 publications

(8 citation statements)

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“…The reduced local chain stretching of the normal-tapered PS-b-POEM also can make it more robust toward concentration polarization effects in a battery environment, in which an electrolyte with an initial ion concentration of [Li + ]/[EO] ∼ 0.05 may experience a concentration gradient of 0 < [Li + ]/ [EO] < 0.1 during concentration polarization. 82 Minimal domain spacing variance can enable the electrolyte to maintain its initial morphology, transport properties, and sufficient contact with the battery electrodes. Another method to quantify chain stretching is the calculation of the statistical segment length of POEM, b POEM , as shown in Figure S9b.…”

Section: ■ Discussionmentioning

confidence: 99%

Quantifying the Effects of Monomer Segment Distributions on Ion Transport in Tapered Block Polymer Electrolytes

et al. 2021

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Tapered block polymers, which contain modified monomer segment distributions at the chemical junction between homogeneous blocks, can offer improved local segmental mobility and ion transport in comparison to their non-tapered, conventional analogues. In this work, the effective Flory–Huggins interaction parameters (χeffs) and distributions of conductive monomer segments, two factors that influence the segmental mobility, were investigated in salt-doped, self-assembled non-, normal-, and inverse-tapered polystyrene-block-poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) electrolytes using X-ray reflectometry measurements and coarse-grained molecular dynamics simulations. The increased covalent S/OEM bonding in tapered specimens contributed to a decrease in χeff, but the increased S-ion contacts contributed to an increase in χeff, especially in the inverse-tapered system. More specifically, the OEM content closer to the PS/POEM domain interfaces, at which the most drastic reduction in POEM mobility was found, was minimized at high domain spacings and interfacial widths. This combination of characteristics was particularly apparent in the non- and normal-tapered polymers as the stretching of chains across a single domain enabled reduced relative ion and OEM content near the PS/POEM domain boundaries, resulting in favorable ion transport conditions. In contrast, most inverse-tapered chains bridged across multiple domains or folded across an interface, which decreased the segmental mobility. The normal-tapered electrolytes also demonstrated reduced local stretching of the POEM chains in comparison to non- and inverse-tapered electrolytes. Taken together, these results suggested that a high-molecular-weight normal-tapered electrolyte could have the desirable structural characteristics (i.e., low segregation strength relative to non-tapered systems, large domain spacings, wide interfaces, and minimal local POEM chain stretching) that maximize the ionic conductivity in nanostructure-forming block polymers.

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Section: ■ Discussionmentioning

confidence: 99%

Quantifying the Effects of Monomer Segment Distributions on Ion Transport in Tapered Block Polymer Electrolytes

et al. 2021

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“…The self-diffusion constant of ions in polymer electrolytes has been extensively studied as it can be directly obtained from experiments through pulsed field-gradient nuclear magnetic resonance and is easily calculated from equilibrium simulations . It is typically found that ion diffusion is strongly coupled with the polymer segmental relaxation rate (related to the glass transition temperature T g ) as the local friction ions experience is mainly controlled by the relaxation of polymers. − Thus, a major strategy to improve overall conductivity has been to increase polymer segmental mobility (or reduce T g ).…”

Section: Introductionmentioning

confidence: 99%

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Shen

Hall

2020

Macromolecules

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Salt-doped polymers without added solvents have the potential to be nonflammable, robust electrolytes for batteries but suffer from low ion conductivity. Using bulky anions with delocalized charge may reduce ion agglomeration and increase conduction. However, size asymmetry between ions may increase preferential solvation of cations versus the larger anions, lowering the transference number t + (fraction of conductivity contributed by the cation, relevant to battery performance). We use coarse-grained molecular dynamics simulations, including a 1/r 4 potential to capture size-dependent solvation effects, to relate polymer and ion chemistry to t + and overall conductivity. At low ion size disparity, increasing dielectric constant improves cation conduction due to the mitigation of ion aggregation and correlated cation–anion motion. However, at high ion size disparity, high dielectric medium results in strong preferential solvation of cations, reducing cation mobility and t +. The trade-off between better cation–anion separation and cation preferential solvation suggests that the strategy of developing high dielectric polymers may enhance performance only at low ion size disparity.

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“…Energy generation and storage in an LIB depend, in part, on the flux of lithium ions across the electrolyte, and several factors (e.g., polymer/ion chemistry, ion concentration) govern this lithium-ion transport. For example, the ratio of lithium ions, [Li + ], relative to ethylene oxide units, [EO], can modulate ion solvation by the polymer, chain stretching/stiffness, − and transient ion–polymer cross-linking . Thus, knowledge of local ion concentrations within a conducting domain becomes increasingly important for BP electrolytes, in which the presence of domain interfaces can create heterogeneities in the ion transport.…”

Section: Effects Of Synthesis and Formulation Variables On Intra-doma...mentioning

confidence: 99%

Nanostructured Block Polymer Electrolytes: Tailoring Self-Assembly to Unlock the Potential in Lithium-Ion Batteries

Ketkar

Epps

2021

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Ion-containing solid block polymer (BP) electrolytes can self-assemble into microphase-separated domains to facilitate the independent optimization of ion conduction and mechanical stability; this assembly behavior has the potential to improve the functionality and safety of lithium-ion batteries over liquid electrolytes to meet future demands (e.g., large capacities and long lifetimes) in various applications. However, significant enhancements in the ionic conductivity and processability of BPs must be realized for BP-based electrolytes to become robust alternatives in commercial devices. Toward this end, the controlled modification of BP electrolytes' intra-domain (nanometer-scale) and multi-grain (micrometer-scale) structure is one viable approach; intra-domain ion transport and segmental compatibility (related to the effective Flory−Huggins parameter, χ eff ) can be increased by tuning the ion and monomer-segment distributions, and the morphology can be selected such that the multi-grain transport is less sensitive to grain size and orientation.To highlight the characteristics of intra-domain structure that promote efficient ion transport, this Account begins by describing the relationship between BP thermodynamics (namely, χ eff and the statistical segment length, b, which is indicative of chain stiffness) and local ion concentration. These thermodynamic insights are vital because they inform the selection of synthesis and formulation variables, such as polymer and ion chemistry, polymer molecular weight and composition, and ion concentration, which boost electrolyte performance. In addition to its relationship with local ion transport, χ eff is also an important factor with respect to electrolyte processability. For example, a reduced χ eff can allow BP electrolytes to be processed at lower temperatures (i.e., lower energy input), with less solvent (i.e., reduced waste), and/or for shorter times (i.e., higher throughput) yet still form desired nanostructures. This Account also examines the impact of electrolyte preparation and processing on the ion transport across nanostructured grains because of grain size and orientation. As morphologies with a 3D-connected versus 2D-connected conducting phase show different sensitivities to conductivity losses that can occur because of the fabrication methods, it is necessary to account for electrolyte processing effects when probing ion transport. The intra-domain and micrometer-scale structure also can be tuned using either tapered BPs (macromolecules with modified monomer-segment composition profiles between two homogeneous blocks) or blends of BPs and homopolymers, independent of the BP molecular weight and composition, as detailed herein. The application of TBPs or BP/HP blends as ion-conducting materials leads to improved ion transport, reduced χ eff , and greater availability of morphologies with 3D connectivity relative to traditional (non-tapered and unblended) BP electrolytes. This feature results from the fact...

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Polymer Dynamics in Block Copolymer Electrolytes Detected by Neutron Spin Echo

Cited by 10 publications

References 64 publications

Quantifying the Effects of Monomer Segment Distributions on Ion Transport in Tapered Block Polymer Electrolytes

Quantifying the Effects of Monomer Segment Distributions on Ion Transport in Tapered Block Polymer Electrolytes

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Nanostructured Block Polymer Electrolytes: Tailoring Self-Assembly to Unlock the Potential in Lithium-Ion Batteries

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