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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.

Abstract.Evidence is presented concerning the effect of surfaces on the segmental motion of PEO-based polymer electrolytes in lithium batteries. For dry systems with no moisture the effect of surfaces of nano-particle fillers is to inhibit the segmental motion and to reduce the lithium ion transport. These effects also occur at the surfaces in composite electrodes that contain considerable quantities of carbon black nano-particles for electronic connection. The problem of reduced polymer mobility is compounded by the generation of salt concentration gradients within the composite electrode. Highly concentrated polymer electrolytes have reduced transport properties due to the increased ionic cross-linking. Combined with the interfacial interactions this leads to the generation of low mobility electrolyte layers within the electrode and to loss of capacity and power capability. It is shown that even with planar lithium metal electrodes the concentration gradients can significantly impact the interfacial impedance. The interfacial impedance of lithium/PEO-LiTFSI cells varies depending upon the time elapsed since current was turned off after polarization. The behavior is consistent with relaxation of the salt concentration gradients and indicates that a portion of the interfacial impedance usually attributed to the SEI layer is due to concentrated salt solutions next to the electrode surfaces that are very resistive. These resistive layers may undergo actual phase changes in a non-uniform manner and the possible role of the reduced mobility polymer layers in dendrite initiation and growth is also explored. It is concluded that PEO and ethylene oxide-based polymers are less than ideal with respect to this interfacial behavior.Introduction.

Self-dopable poly(aniline) derivatives gave reversible color change in an all solid state electrochromic window assembled from an electrochromic poly(aniline-Nbutylsulfonate) and an ion conducting polymer electrolyte membrane. Ion conducting polymer electrolyte membranes were prepared by radiation curing of unsaturated PEG acrylates or a sol-gel process using PEG modified triethoxysilane. The solid polymer electrolyte membrane showed high ionic conductivities (4 x 10-4S/cm) at 30°C. The all solid state electrochromic window responded to a potential step from +2.3-1.5V to -1.5 -0.5V by turning its color from green-blue to transparent yellow within 60 s. Color contrast and optical reponse of poly(aniline-N-butylsulfonate)s in contact to different polymer electrolyte systems were a function of electrolyte composition.