Carbonyl-Containing Solid Polymer Electrolyte Host Materials: Conduction and Coordination in Polyketone, Polyester, and Polycarbonate Systems

Abstract

Research on solid polymer electrolytes (SPEs) is now moving beyond the realm of polyethers that have dominated the field for several decades. A promising alternative group of candidates for SPE host materials is carbonyl-containing polymers. In this work, SPE properties of three different types of carbonyl-coordinating polymers are compared: polycarbonates, polyesters, and polyketones. The investigated polymers were chosen to be as structurally similar as possible, with only the functional group being different, thereby giving direct insights into the role of the noncoordinating main-chain oxygens. As revealed by experimental measurements as well as molecular dynamics simulations, the polyketone possesses the lowest glass transition temperature, but the ion transport is limited by a high degree of crystallinity. The polycarbonate, on the other hand, displays a relatively low coordination strength but is instead limited by its low molecular flexibility. The polyester performs generally as an intermediate between the other two, which is reasonable when considering its structural relation to the alternatives. This work demonstrates that local changes in the coordinating environment of carbonyl-containing polymers can have a large effect on the overall ion conduction, thereby also showing that desired transport properties can be achieved by fine-tuning the polymer chemistry of carbonyl-containing systems.

Water-Assisted Ion Conduction in Solid-State Charge-Transfer Complex Electrolytes for Lithium Batteries

“…The operating temperature of batteries with solid polymer electrolytes is usually elevated to improve conductivity. Efforts to decouple ion conduction from polymer segmental motion have met limited success, and there are few examples of solid-state polymer electrolytes with ionic conductivity above 10 –3 S/cm at room temperature. , Research of decoupled ion conduction in polymer electrolytes is currently focused on carbonyl-containing polymers and polymerized ionic liquids. − …”

Chain-Length-Dependent Hydrogen-Bonded Self-Assembly of Terminally Functionalized Discrete Polyketones

“…We have recently developed discrete aliphatic polyketones , made from 3,3-dimethylpentane-2,4-dione as shapable molecular ropes for derivatization into π-conjugated chromophores, − metal ion conductors, , and macrocyclic hosts for ions. , Owing to the structural flexibility derived from their hydrocarbon chains and the inter/intramolecular interactions of their carbonyl groups, these polyketones show chain-length-dependent conformations in the solid state: dimer, trimer, and tetramer adopt curved, linear, and figure-S conformations, respectively, whereas longer analogues (≥5-mer) commonly take a helical conformation . These unique conformational features of polyketones prompted us to explore their chain-length-dependent self-assembling behaviors as terminally functionalized forms.…”

Binding of Li+ to Negatively Charged and Neutral Ligands in Polymer Electrolytes

“…The neutral ligands studied all have a carbonyl group with two heavy atoms on each side of the carbonyl C atom. These ligands correspond to the binding groups of the polymers studied by Eriksson et al 12 They are 3-pentanone (also known as diethyl ketone), methyl propionate, and dimethyl carbonate. We will label these ligands as ketone (K), ester (E), and carbonate (C).…”

“…The ΔΔG for the ketone and ester are also sufficiently small that there is a transport mechanism for Li + to diffuse more readily and achieve higher conductivity that is experimentally found, especially at high temperatures where the chain flexibility enables movement of the ligand group. 12 We note that, since these are neutral systems, a lithium salt must be part of the system and, in this case, the salt includes TFSI. Interactions with the TFSI will also influence the Li + cluster structure and energetics.…”

“…These neutral polymers show much better conductivities than single ion conductors. 12 They studied three ligand binding groups, a polyketone, polyester, and polycarbonate, to examine the effect of O atoms in the polymer backbone on the interactions of Li + with the carbonyl O. Presumably, these neutral coordinating ligands have smaller binding free energies than the anionic ligands, and this trend would yield better Li + conductivity.…”