Journal
ELECTROCHIMICA ACTA
Volume 170, Issue -, Pages 191-201Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2015.04.010
Keywords
solid polymer electrolytes; electrode binders; micro-phase separated blends; SiO1.5 nanoparticle reinforcement; nanostructured electrolytes
Categories
Funding
- NSF [DMR1207221]
- Office of Naval Research - College of Engineering, Temple University [N0014-12-1-0777]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1207221] Funding Source: National Science Foundation
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Solid polymer electrolytes (SPEs) were prepared by blending LiClO4, methyl cellulose (MC) and an oligometric dendritic polyethylene glycol (PEG), formed from polyoctahedralsilsesquioxane functionalized with similar to 8 PEG side chains (POSS-PEG) on the SiO1.5 core. Compositions with 80/20, 70/30 and 60/40 POSS-PEG/MC, and LiClO4 (O/Li = 16/1) were investigated for their electrochemical, mechanical and morphological properties, where O/Li indicates the molar ratio of ether oxygens from POSS-PEG to Li+ ions. Since compatible blends can be made over a range of compositions, ranging from tacky with low amounts of MC, to hard with high percentages of MC, this system is a paradigm for preparing batteries with continuous interfaces from the electrodes to the SPE. SEM and TEM images indicate that POSS-PEG/LiClO4(O/Li = 16/1)/MC form microporous structures in which the pore walls are microphase separated. In these microphase separated blends, the LiClO4 partitions into the POSS-PEG phase and is amorphous between -100 degrees C and its decomposition temperature, T-d similar to 300 degrees C, as evidenced by an increased glass transition temperature (T-g) for the POSS-PEG/LiClO4 phase, while the MC phase is semicrystalline, as evidenced by x-ray diffraction data, showing the persistance of crystalline regions of MC in the blends. At temperatures below the glass transition temperature (T-g) of POSS-PEG/LiClO4(O/Li = 16/1) the moduli of the blends increase with increasing POSS-PEG content, indicating that the POSS-PEG component behaves like high molar mass polyethylene oxide (PEO) reinforced with SiO1.5. At temperatures T > T-g (POSS-PEG/LiClO4), where POSS-PEG/LiClO4 is highly viscous (does not flow under its own weight) but not a true solid, the moduli of the blends increase with MC content, consistent with the high modulus MC forming cross-link sites to the dominant POSS-PEG/LiClO4 phase. It is proposed that these crosslink sites are due to residual primary OH groups from MC that form hydrogen bonds with ether oxygens of POSS-PEG/LiClO4 and result in a rubbery morphology (32 - 156 MPa) at room temperature, with the Li+ ions preferentially binding to the ether oxygens in the interior of the microphase separated regions. Conductivities of 1.6x10(-5) and 1.1x10(-6) S/cm were measured at 30 degrees C and 0 degrees C, respectively, for the 80/20 POSS-PEG/LiClO4 (O/Li = 16/1)/MC blend. Stability and reversibility of the blends at 50 degrees C were observed in the range 1.5 to 4.2 V. (C) 2015 Elsevier Ltd. All rights reserved.
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