New Generation of Ordered Polymer Electrolytes for Lithium Batteries

Abstract

In poly͑ethylene oxide͒-based solid electrolytes, ionic conduction can occur by cations moving inside the helix ͑along the helix axis͒ and by anions moving on its envelope. This particular mode of ion transport can be enhanced by alignment of the polymeric structural units. We describe a procedure for orienting the helices in the perpendicular direction, the result of which is a oneorder-of-magnitude increase in polymer electrolyte ͑PE͒ conductivity and a similar decrease in PE/electrode interphase resistance. This procedure could also be of importance in the orientation of polymers in the nanoscale for various applications. Manipulation of large molecules like polymers and the ability to position them in the desired orientation is of great importance in various fields, including thin-film-based devices, microelectromechanical systems, and nanotechnology. Thin-layer technology includes liquid crystal displays ͑LCDs͒, sensors, electrochromic displays, advanced high-energy-density batteries, and fuel cells. In these devices, a thin ͑0.02-0.1 mm͒ polymer electrolyte ͑PE͒ is sandwiched between two electrodes. PE, are generally semicrystalline materials, most commonly derived from the archetypal helical poly͑ethylene oxide͒ ͑PEO͒. The common preparation process for the PEO-based PEs is that of casting from solution. This leads to a preferential planar orientation of helices in the parallel-to-thecasting plane, denoted as XY. As a result, the longitudinal conductivity is much higher than that in the perpendicular Z direction. However, in most practical applications, especially in solid thin-film batteries, the conductivity of PE films in the Z direction is crucial. Another factor contributing to high internal resistance ͑and thus to low power͒ in lithium-PE batteries is the too-high electrode/PE interphase resistance. To complete the conduction path, ions must at some time jump from helix to helix through the helix ''envelope.'' This is a slow process that adds yet another resistance to the system. We denote this resistor as R inter or R GB ͑grain boundaries͒.Until now, to get maximum conductivity, the strategy has been to reach the maximum amorphicity of the polymer and the lowest glass-transition temperature (T g ). 1-3 Molecular-level approaches employed to effectively suppress crystallinity in PEO have included architectural modifications such as branched polyethoxy systems, 4,5 linear random copolyethers, 6 and comb copolymers. 7-9 Despite strenuous efforts over some 20 years involving the preparation of highly amorphous polymer electrolytes with low T g , the maximum conductivity of such electrolytes remains around 10 Ϫ5 S/cm at room temperature.10 Theoretical models [11][12][13] have been proposed to explain the mechanism responsible for ionic conductivity in these systems, and molecular dynamic ͑MD͒ and Monte Carlo ͑MC͒ simulations have been carried out for PEO:salt complexes. 14-18Recently, we found a way [19][20][21][22][23][24] to increase the ionic conduction of PEs in one direction by a longitudinal align...

Electrolytes and Interphases in Sodium‐Based Rechargeable Batteries: Recent Advances and Perspectives

“…The approach is well known since the first report by Scrosati and co‐workers [ 169 ] in 1998, lately intensively studied for application in polymeric lithium batteries. [ 170–174 ] The same group [ 167 ] investigated the effect of nanometric SiO 2 to a PEO/NaTFSI mixture. They demonstrated best performances with an EO/Na ratio of 20, and using the 5% wt SiO 2 , giving an ionic conductivity of 10 −5 S cm −1 and a Na transference number (t Na+ ) of 0.51.…”

Polyethylene oxide electrolyte added by silane-functionalized TiO2 filler for lithium battery

“…[2][3][4] So far, the polymer electrolyte application in lithium cells has been hindered by several issues, such as the limited conductivity at the room temperature, the low stability of the Li-electrolyte interface, the low lithium transference number and the poor mechanical properties. A great enhancement of the PEO electrolyte characteristics in terms of stability against the lithium metal, Li-ion transport ability and mechanical properties, has been obtained by adding ceramic powders to the membrane, such as titanium oxide, TiO 2 [5][6][7][8][9][10], aluminum oxide, Al 2 O 3 [11][12][13][14][15][16], silicon oxide, SiO 2 [17][18][19][20], and zirconium oxide, ZrO 2 [21][22][23][24][25][26]. Indeed, it has been reported that the interactions between the metal oxide surface, the polymer and the lithium salt may efficiently improve the electrolyte characteristics [24][25][26].…”

Crystallinity and order of poly(ethylene oxide)/lithium triflate complex confined in nanoporous membranes

“…For instance, alignment of the polymer backbones and crystalline units by stretching [22][23][24] and by magnetic fields [25] have been found to increase ionic conduction by an increased factor of 4-40-fold. Dang et al [26] have seen anisotropic ionic conduction in rigidrod, liquid-crystalline polymers while Hubbard et al [27] aligned liquid-crystalline polymer electrolytes by use of a magnetic field.…”