From molecular models to system analysis for lithium battery electrolytes

Abstract

The behavior of polymer electrolytes in lithium batteries is reviewed in the context of molecular scale models as well as on the system scale. It is shown how the molecular structure of the electrolyte strongly influences ion transport through the polymer as well as across the interfaces and determines the values of a number of parameters needed for system models that can predict the performance of the battery (e.g. κ, D, t+ o and i o ). The interaction of the electrolyte with the electrodes not only leads to transfer of the lithium ion across the interface but also to side reactions that profoundly influence the calendar and cycle life of the battery. Typically these electrochemically induced side reactions generate the SEI layer but also inherent instability of the bulk electrolyte may also play a role in the formation of surface layers. These various reactions can lead to changes in the mechanical properties of the separator and electrode structure that promote life-limiting phenomena such as dendrite growth, passivation and morphology changes. The rheological model of Eisenberg is drawn upon to show how the interactions of the electrolyte with surfaces can lead to distinct changes in mechanical and transport properties that may limit the battery performance and lead to diminished performance with time. The molecular level models may be combined with the rheological models to provide workable models of the interfaces and bulk electrolyte dynamics that in turn can be used to provide a more accurate level of performance prediction from the system models. This connects molecular structure with battery performance and guides the design and synthesis of new and better materials.

Ionic liquid-nanoparticle hybrid electrolytes

“…And the motion of the ions themselves from one electrolyte site to another is of minor importance. 37 Although perhaps expected for systems such as ours, where the chain length of the tethered ionic liquid is small compared with the diameter of particle core, the VFT dependence implies that the ionic conductivity of the SiO 2 -IL-TFSI/LiTFSI mixtures can be understood in terms of local segmental and breathing motions of molecules in the materials. Fig.…”

Steric effect on Li+ coordination and transport properties in polyoxetane-based polymer electrolytes bearing nitrile groups

“…6 Polyoxetanes are polyethers that contain trimethylene oxide units and can also be used as a polymer matrix for PEs. [10][11][12] PEs based on polyoxetanes with polar side chains, such as nitrile groups and phosphate ester groups, were reported. [13][14][15] The increase in glass transition temperature (T g ) associated with complexation with Li + ions, which is a typical behavior for PEs, does not occur in poly(3-(2cyanoethoxymethyl)-3-ethyloxetane) (PCEO); rather, T g decreases with increasing salt concentration.…”

Graft copolymer-based lithium-ion battery for high-temperature operation

“…Although recent work by Zhang et al and Gadjourova at el. demonstrated that ion conduction is possible in crystalline polymers [33,34], the majority of the previous studies focused on the amorphous phase, where ion transport is dependent on the segmental motion of the polymer chains [35][36][37][38][39][40]. When lithium salts are introduced to the polymer matrix forming PEO/LiX complexes, the oxygen atoms from both the PEO chains and the anions coordinate the lithium ions [41].…”