Nanoporous hybrid electrolytes

Abstract

Oligomer-suspended SiO 2 -polyethylene glycol nanoparticles are studied as porous media electrolytes. At SiO 2 volume fractions, φ, bracketing a critical value φ y ≈ 0.29, the suspensions jam and their mechanical modulus increase by more than seven orders.For φ > φ y , the mean pore diameter is close to the anion size, yet the ionic conductivity remains surprisingly high and can be understood, at all φ, using a simple effective medium model proposed by Maxwell. SiO 2 -polyethylene glycol hybrid electrolytes are also reported to manifest attractive electrochemical stability windows (0.3-6.3V) and to reach a steady-state interfacial impedance when in contact with metallic lithium. IntroductionLithium ions are the active charge carrying species in the most energy dense secondary batteries of today, those used in electronics and hybrid electric transportation. Currently commercialized lithiated anode materials such as LiC 6 and Li 4 Ti 5 O 12 have relatively low theoretical energy capacities (360 mAh/g and 175 mAh/g, respectively). Advanced secondary battery systems employing electrodes such as LiCoPO 4 , 1 lithium, 2-5 or sulfur 6 require electrolytes with specific properties such as wide electrochemical stability windows, high mechanical strength, and/or inertness or non-solvency towards the electrode materials and their intercalation products.Next-generation lithium ion batteries should also employ electrolytes that are nonflammable, non-volatile, non-leakable, and non-toxic, making them safer both in use and after disposal. In pursuit of such materials, several classes of electrolytes have been studied as replacements for conventional liquid electrolytes: polymers, [7][8][9][10][11] polymer composites, [12][13][14][15] hybrids, 16-18 gels, 19,20 ionic liquids, 21 and ceramics. 22In many cases, mechanical integrity of the electrolyte comes at a cost: namely, a large loss in ionic conductivity, which places undesirable limits on the charge/discharge rate of the cell. Liquid and particulate plasticizers have been used with some success in circumventing this constraint in composite and gel polymer electrolytes. 4,15,19,23 With a mechanically strong framework in place such as a polymer or ceramic, the liquid plasticizer serves as a freely diffusing ionic conduction medium that provides ionic conductivities near that of a pure liquid electrolyte. If a liquid plasticizer with good thermal and electrochemical properties is utilized, safety concerns are reduced. In the case of particulate plasticizers, of either nano-or micron-scale, the particles have been shown to decrease crystallization of the surrounding matrix, thereby enhancing segmental motion of the host polymer and increasing conduction. While nanoparticles have been shown most successful in this area, in typical polymer composites particle aggregation occurs; this reduces the effectiveness of the individual particles in inhibiting crystallization but allows for formation of a percolated particulate network that aids in bulk mechanical strength.Recently, we r...

Diffusivities, viscosities, and conductivities of solvent-free ionically grafted nanoparticles

“…Due to the strong electrostatic forces, ionically graed nanoparticles are also expected to behave differently from neutral systems of graed nanoparticles in free chains. 7,12,13 NIMs share features with charged colloids, 14 and have been characterized as ionic liquids with large, nanoscale ions, 15,16 or as nanoparticles covalently tethered to ionic liquids.…”

Ionic liquid-nanoparticle hybrid electrolytes

“…The figure further shows that both G 0 and G 00 become larger as the SiO 2 -IL-TFSI content is increased, which is consistent with normal expectations for polymer-particle hybrids and with results reported in our previous studies of nanoparticle-hybrid electrolytes. 36,38,39 Finally, Fig. 3(a) shows that both moduli are at most weak functions of the strain frequency (deformation rate) and that the dependence becomes weaker as the SiO 2 -IL-TFSI content is increased.…”

Enabling the Li-ion conductivity of Li-metal fluorosulphates by ionic liquid grafting

“…Sixteen transients were recorded for 7 Li with a 1.1-μs long π/12 excitation pulse. The chemical shifts were referenced with 4-acetophenone at δ=−107 ppm for 19 F, TMS at 0 ppm for 1 H and 1 M LiCl at 0 ppm for 7 Li. The variable temperature NMR spectra were realized on a 9.4-T Bruker Avance NMR spectrometer operating at 400 MHz for 1 H, 155 MHz for 7 Li and 376 MHz for 19 F, respectively, using a 4-mm Bruker WVT probe with liquid nitrogen cooling and using a 5-kHz and 10-kHz MAS rate at low temperatures and high temperatures, respectively.…”

“…Sixteen transients were recorded for 7 Li with a 3.9-μs long π/12 excitation pulse. The RF excitation field for 19 F was set at 93 kHz, and in both cases, the recovery delay was 10 s. The temperature was calibrated using the 207 Pb chemical shift of PbNO 3 [15].…”