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8789628 
Journal Article 
YYYY Modifying Li+ and Anion Diffusivities in Polyacetal Electrolytes: A Pulsed-Field-Gradient NMR Study of Ion Self-Diffusion 
Halat, DM; Snyder, RL; Sundararaman, S; Choo, Y; Gao, KW; Hoffman, ZJ; Abel, BA; Grundy, LS; Galluzzo, MD; Gordon, MP; Celik, H; Urban, JJ; Prendergast, D; Coates, GW; Balsara, NP; Reimer, JA 
2021 
Yes 
Chemistry of Materials
ISSN: 0897-4756
EISSN: 1520-5002 
33 
13 
4915-4926 
WOS:000674266000008 
Polyacetal electrolytes have been demonstrated as promising alternatives to liquid electrolytes and poly(ethylene oxide) (PEO) for rechargeable lithium-ion batteries; however, the relationship between polymer structure and ion motion is difficult to characterize. Here, we study structure-property trends in ion diffusion with respect to polymer composition for a systematic series of five polyacetals with varying ratios of ethylene oxide (EO) to methylene oxide (MO) units, denoted as P(xEO-yMO), and PEO. We first use Li-7 and F-19 pulsed-field-gradient NMR spectroscopy to measure cation and anion self-diffusion, respectively, in polymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixtures. At 90 degrees C, we observe modest changes in Li+ diffusivity across all polymer compositions, while anion (TFSI-) self-diffusion coefficients decrease significantly with increasing MO content. At a given reduced temperature (T - T-g), all polyacetal electrolytes exhibit faster Li+ self-diffusion than PEO. Intriguingly, P(EO-MO) and P(EO-2MO) also show slower TFSI-anion self-diffusion than PEO at a given reduced temperature. Molecular dynamics simulations reveal that shorter distances between acetal oxygen atoms (O-CH2-O) compared to ether oxygens (O-CH2-CH2-O) promote more diverse, often asymmetric, Li+ coordination environments. Raman spectra reveal that anion-rich ion clusters in P(EO-MO) and P(EO-2MO) lead to decreased anion diffusivity, which along with increased cation diffusivity, support the viability of polyacetals as high-performance polymer electrolytes.