Interfacial behavior of polymer electrolytes

Abstract

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.

DMA and Conductivity Studies in PVA:NH4SCN:DMSO:MWNT Nanocomposite Polymer Dried Gel Electrolytes

“…This can be assigned to complexation caused by interaction among components and therefore referred to as composite of NCPE system. Kerr et al [21] have reported that when the fillers are of nanodimension and the concentration of filler particles is optimum, a composite or second may be observed in dynamic mechanical behaviour at higher temperatures. The composite is attributed to relaxation.…”

“…Thus conductivity drops significantly. At intermediate concentrations the decrease in conductivity may be due to pairing effect/re-association of free ions [1,5,21]. The second conductivity maxima is related to formation of highly conducting interfacial layer between MWNT and gel electrolyte caused by filler salt interaction which dominates over ion pairing effect [6,11,14,24].…”

On Two Nanocomposite Models: Differences, Similarities and Interpretational Possibilities Regarding Tsagaropoulos' Model and Tanaka's Model

“…Further support for this model was given in [6], where faster processes correspond to bulk polymer whereas slower processes are interpreted in terms of tightly bound polymer chains, whose segmental dynamics are slowed down wrt bulk dynamics as a consequence of the interaction with the silica nanoparticle surface. Further support is offered in [13], where Dynamic Mechanical Thermal Analysis suggests that polymer chain motion in polymer electrolytes is affected by the presence of nanoparticle surfaces, ie glass transition temperature increases by increasing the percentage of nanoparticles.…”

Influence of Pinning Effects on the Electrochemical Formation of Silver Patterns in Agarose-Containing Sols and Gels

“…This implies the possible existence of pinning/depinning transitions related to the dynamics of the interface. 7 This type of phenomenon, among others, has been observed in the crystallization of proteins, mass transfer processes in natural and synthetic porous media [8][9][10][11][12][13][14] and polymer electrolytes, [8][9] paper wetting experiments, 15 propagation of the burning front, 16 growth of bacterial colonies, 17,18 rupture of lines in paper sheets, 19 solid growth fronts, 20 electrochemical formation of solid phases, 21 tumoral growth mechanisms, 22 and their growth and spreading. [23][24][25] The diversity of processes involved in the above phenomena suggests the possibility to investigate time-dependent pinning effects that may occur, for instance, for front propagation in colloidal media.…”