Role of solvation site segmental dynamics on ion transport in ethylene-oxide based side-chain polymer electrolytes

Bennington, Peter; Deng, Chuting; Sharon, Daniel; Webb, Michael; Pablo, Juan J. de; Nealey, Paul F.; Patel, Shrayesh N.

doi:10.1039/d1ta00899d

Cited by 29 publications

(59 citation statements)

References 73 publications

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“…On the other hand, OE side chains are well known to be Li +ion conductors in disordered form. 81,82 Because doping is not able to induce significant crystallinity in the high OE fraction samples, we find that the ionic conductivity shows an opposite trend compared to the electronic conductivity. Higher OE fraction samples are the most disordered and thus show higher ionic conductivity.…”

Section: ■ Results and Discussionmentioning

confidence: 82%

Enhancing the Ionic Conductivity of Poly(3,4-propylenedioxythiophenes) with Oligoether Side Chains for Use as Conductive Cathode Binders in Lithium-Ion Batteries

et al. 2022

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Mixed electron- and ion-conducting polymers serve as excellent candidates for polymer binders in lithium-ion batteries (LIBs) because of an extension of functionality beyond simple mechanical adhesion. Such dual conduction was observed in our recent report on dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx2), which showed excellent performance as a cathode binder for LiNi0.8Co0.15Al0.05O2 (NCA). However, ionic conductivity was found to be significantly lower than that of its electronic counterpart. To enhance mixed conduction, here we report a family of synthetically tunable, electrochemically stable, random copolymers based on PProDOT-Hx2, in which the hexyl (Hex) side chains are replaced to varying extents with oligoether (OE) side chains, generating a series of (Hex:OE) PProDOTs. When OE content was varied from 5 to 35%, the resulting copolymers were insoluble in the battery electrolyte and were stable after 100 electrochemical doping/dedoping cycles. Electron paramagnetic resonance and electrochemical kinetics studies were performed to illustrate the reversible and fast electrochemical doping process of (Hex:OE) PProDOTs. Electronic and ionic conductivity measurements as a function of electrochemical potential show a decrease in electronic conductivity and a concurrent increase in ionic conductivity with increasing incorporation of OE side chains. X-ray scattering studies on electrochemically doped polymers indicate a decline in crystalline ordering with the increase in OE content of the (Hex:OE) PProDOTs, suggesting that decreasing crystallinity is responsible for both the increased ionic and reduced electronic conductivity. Compounding these structural changes, swelling studies show a linear mass increase with OE content upon electrolyte exposure, indicating that solvent-induced swelling and electrolyte uptake play a significant role in the ability of these polymers to conduct ions. Finally, rigorous cell testing was performed by employing electrochemical impedance spectroscopy, galvanostatic charge–discharge, rate capability tests, and differential capacity vs voltage analysis, using NCA cathodes to understand the role of these polymers as mixed electron- and Li+-ion-conducting polymer binders in LIBs in comparison to the commonly used polyvinylidene fluoride. It is observed that (75:25) PProDOT containing 25% of OE side chains achieves the highest rate capability and fastest charging and discharging under symmetric testing conditions. The synthetic flexibility to fine-tune electronic and ionic conductivity makes (Hex:OE) PProDOTs a promising new class of mixed conducting polymers for electrochemical energy-storage application.

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Section: ■ Results and Discussionmentioning

confidence: 82%

Enhancing the Ionic Conductivity of Poly(3,4-propylenedioxythiophenes) with Oligoether Side Chains for Use as Conductive Cathode Binders in Lithium-Ion Batteries

et al. 2022

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“…Therefore, the Li + transport models presented in what follows for miscible polymer mixtures share the same criteria for identifying viable solvation sites as used in a series of PEObased homopolymer hosts. 5,6,49,50 Here, we adopt the solvation-site connectivity protocol by Webb et al but in the context of miscible polymer mixtures. 7 Specifically, a viable solvation site in a PEO-based electrolyte is defined at the centroid of a set of five or more EO atoms, each within 3.7 Å of the centroid.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…To date, the most efficient polymer hosts for lithium-ion (Li + ) transport have been based on poly(ethylene oxide) (PEO) . The ionic transport mechanism in PEO-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is based on the hopping of Li + between solvation sites composed of five to six ether oxygens (EO). − The rate of hopping depends on the number of solvation sites, their connectivity, and segmental mobility. − To achieve a reasonable conductivity, PEO must operate in its rubbery state, above its melting temperature, and well above its glass-transition temperature . This is because fast transport of Li + relies on fast chain motions of the polymer host, which only occur when the polymer material is in the rubbery state.…”

Section: Introductionmentioning

confidence: 99%

Critical Percolation Threshold for Solvation-Site Connectivity in Polymer Electrolyte Mixtures

et al. 2022

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Poly(ethylene oxide) (PEO)-based polymer electrolytes are often mixed with rigid, nonconductive polymers to improve mechanical strength. The suppressed conductivity of the mixture typically arises from a reduced segmental mobility and a diminished connectivity between conductive PEO sites. To decouple these two mechanisms, we compare transport in symmetric miscible blends and disordered block copolymers (BCP) of PEO and poly(methyl methacrylate) (PMMA). Because the two systems have identical physicochemical properties, differences in their conductivity directly reflect the underlying PEO network connectivity. We find that, at short distances (<5 Å), the Li+ solvation networks are identical for the two systems; however, a distinct variation in the network connectivity arises at length scales between 5 and 10 Å. Specifically, the BCP exhibits a lower connectivity, and therefore a lower conductivity than the blend. A quantitative model is proposed that associates long-range Li+ transport with local miscibility; the concept of network connectivity discussed here could be useful for designing polymer electrolyte systems.

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“…Specifically, recent calculations suggest that the relaxation time of different EOs in PEO graft polymers spans even three orders of magnitude from the backbone to side chain tails. [40,41] Such heterogeneous segmental dynamics cause that, within a certain scale, the longer side chains contain more proportion of highly mobile EOs, and therefore perform higher conductivity. One the other hand, the c in PEO-based electrolytes depends on the cation solvation by polymer chains, which commonly requires either one single chain with six contiguous EOs or two chains each with three contiguous EOs to coordinate with Li + .…”

Section: Resultsmentioning

confidence: 99%

Crosslinked Polymer‐Brush Electrolytes: An Approach to Safe All‐Solid‐State Lithium Metal Batteries at Room Temperature

Cao

et al. 2021

Batteries & Supercaps

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Electric vehicles, intelligent machines, and portable electronics in our daily lives are placing insatiable demand on safe and powerful battery materials that can function at room temperature. Herein, we report an ultrathin and robust solid-state electrolyte with crosslinked polymer-brush architecture. On one hand, the highly mobile polymer brushes with a moderate side chain length enable efficient cation solvation and fast ion transport, offering room-temperature ionic conductivity as high as 0.23 mS cm À 1 . On the other hand, incorporation of the inorganic core crosslinker endows the material with enhanced mechanical strength, thermal stability, and fire resistance. As a result, the crosslinked polymer-brush electrolyte films demonstrate stable lithium electrodeposition and great electrochemical performance in Li/LiFePO 4 cells at 30 °C, providing a promising pathway to next-generation safe and high-energy lithium metal batteries.

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Role of solvation site segmental dynamics on ion transport in ethylene-oxide based side-chain polymer electrolytes

Abstract: Ionic conductivity is governed primarily by the segmental mobility of the side-chain ethylene oxide units which form effective solvation sites, rather than system-wide dynamics.

Cited by 29 publications

References 73 publications

Enhancing the Ionic Conductivity of Poly(3,4-propylenedioxythiophenes) with Oligoether Side Chains for Use as Conductive Cathode Binders in Lithium-Ion Batteries

Enhancing the Ionic Conductivity of Poly(3,4-propylenedioxythiophenes) with Oligoether Side Chains for Use as Conductive Cathode Binders in Lithium-Ion Batteries

Critical Percolation Threshold for Solvation-Site Connectivity in Polymer Electrolyte Mixtures

Crosslinked Polymer‐Brush Electrolytes: An Approach to Safe All‐Solid‐State Lithium Metal Batteries at Room Temperature

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