Polymer bonded electrolytes are definitely the most apparent candidates for safe “all-solid” Li-ion batteries and some other electrochemical devices. However, they continue to have relatively poor ionic conductivities, which limits their wider adoption in commercial applications. It has earlier been the traditional wisdom that only amorphous phases of polymer electrolytes show usefully high ionic conduction, while crystalline styles are insulators. However, this has been stunted in the past decade by the discovery of highly organized, low-dimensional ion-conducting materials. Specifically, the crystalline phases of LiXF6.PEO6 exhibit higher ionic conductivities than their amorphous counterparts, with the Li-ion conduction dating back to along the PEO channels. Polymer chain-length and chain-end registry has emerged as potentially significant in determining ionic conduction during these materials.Molecular Dynamics simulations have therefore been created of short-chain, monodisperse (Mw~1000), methoxy end-capped LiPF6.PEO6 to analyze relationships between ion conduction and mode of chain-ordering. Studies of smectic and nematic arrangements of PEO chains have said that ion-transport mechanisms within the smectic planes formed by cooperative chain-end registry seem to be more suppressed by ion-pairing than in-channel conduction.
Contents: Ordering in Crystalline Short-Chain Polymer Electrolytes
Introduction
A weak link in energy storage technologies
Polymer electrolytes
Ordering in polymer electrolytes
Short-chain LiPF6PEO6 crystal structures
Computer simulation of the crystalline polymer electrolytes
Methodology
Molecular dynamics simulations
Force field
Starting structures
Non-equilibrium molecular dynamics
Ion transport
Simulation of XRD profiles
Results
Structural stability
Li-O coordination and ion-pairing
The channel structure
The smectic surface
Simulated XRD profiles
Effect of ordering on ion transport in PEO channels
Li-ion conduction mechanisms
Anion conduction mechanisms
Ion transport within the smectic interface
Li-ion conduction mechanism
Anion conduction mechanism
Doping effects
Conclusions and future work
Acknowledgements…
Ordering in Crystalline Short-Chain Polymer Electrolytes
Source: Uppsala University Library
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