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1. Polyvinylidene Fluoride-Based Gel Polymer Electrolytes for Calcium Ion Conduction: A Study of the Influence of Salt Concentration and Drying Temperature on Coordination Environment and Ionic Conductivity

   https://doi.org/10.1021/acs.jpcc.3c02342  

   Fluker, Edward C.; Pathreeker, S.; Hosein, Ian D. (August 2023, Journal of physical chemistry C)

   Calcium-ion batteries emerged as a potential sustainable alternative energy storage system; however, there remains the need to further develop electrolytes to improve their performance. We report a gel polymer electrolyte (GPE)-based on polyvinylidene fluoride (PVDF) for calcium ion conduction. The gel electrolyte was synthesized by combining a PVDF polymer host, Ca(TFSI)2 salt, and N-methyl-2-pyrrolidone (NMP) solvent. Using Fourier transform infrared spectroscopy, we analyze the effect of salt concentration and drying temperature on the degree of salt dissociation in the electrolyte. Our results show that the concentration of free cations in the electrolyte is primarily coordinated with NMP as well as PVDF, generating a suitable network for ion transport, i.e., a liquid electrolyte encompassed within a polymer matrix. We find that processing conditions such as drying temperature, which varies solvent content, play a critical role in developing polymer electrolytes that demonstrate optimal electrochemical performance. The GPEs are semicrystalline and stable up to 120 °C, which is critical for their use in applications such as in electric vehicles and renewable energy storage systems. The ionic conductivity of the GPEs exhibit Arrhenius-type behavior, and the total ionic conductivity at room temperature is suitable for applications, with values of 0.85 × 10–4 S/cm for 0.5 M and 3.56 × 10–4 S/cm for 1.0 M concentrations. The results indicate that the GPE exhibits high conductivity and good stability, making it a promising candidate for use in high-performance calcium ion batteries. 

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2. Task-Specific Phosphonium Iongels by Fast UV-Photopolymerization for Solid-State Sodium Metal Batteries

   https://doi.org/10.3390/gels8110725  

   Porcarelli, Luca; Olmedo-Martínez, Jorge L.; Sutton, Preston; Bocharova, Vera; Fdz De Anastro, Asier; Galceran, Montserrat; Sokolov, Alexei P.; Howlett, Patrick C.; Forsyth, Maria; Mecerreyes, David (November 2022, Gels)

   Sodium metal batteries are an emerging technology that shows promise in terms of materials availability with respect to lithium batteries. Solid electrolytes are needed to tackle the safety issues related to sodium metal. In this work, a simple method to prepare a mechanically robust and efficient soft solid electrolyte for sodium batteries is demonstrated. A task-specific iongel electrolyte was prepared by combining in a simple process the excellent performance of sodium metal electrodes of an ionic liquid electrolyte and the mechanical properties of polymers. The iongel was synthesized by fast (<1 min) UV photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of a saturated 42%mol solution of sodium bis(fluorosulfonyl)imide (NaFSI) in trimethyl iso-butyl phosphonium bis(fluorosulfonyl)imide (P111i4FSI). The resulting soft solid electrolytes showed high ionic conductivity at room temperature (≥10−3 S cm−1) and tunable storage modulus (104–107 Pa). Iongel with the best ionic conductivity and good mechanical properties (Iongel10) showed excellent battery performance: Na/iongel/NaFePO4 full cells delivered a high specific capacity of 140 mAh g−1 at 0.1 C and 120 mAh g−1 at 1 C with good capacity retention after 30 cycles. 

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3. Non-solvating, side-chain polymer electrolytes as lithium single-ion conductors: synthesis and ion transport characterization

   https://doi.org/10.1039/c9py01035a  

   Liu, Jiacheng; Pickett, Phillip D.; Park, Bumjun; Upadhyay, Sunil P.; Orski, Sara V.; Schaefer, Jennifer L. (January 2020, Polymer Chemistry)

   Solid-state single-ion conducting polymer electrolytes have drawn considerable interest for secondary lithium batteries due to their potential for high electrochemical stability and safety, but applications are limited by their low ionic conductivities. Specifically, poly(ethylene oxide) (PEO) based electrolytes have the highest reported Li + conductivities for these materials; however, their potential is limited due to the ion transport mechanism being coupled to segmental relaxations of the cation solvating polymer chain. To investigate the potential of single-ion conducting polymer electrolytes lacking polar matrices, we synthesized three para -polyphenylene-based, side-chain polymer electrolytes with various pendent anion chemistries (–SO 3 − , –PSI − , and –TFSI − ) with differing binding affinities to Li + . Compared with the previously reported lithium poly(4-styrenesulfonyl(trifluoromethylsulfonyl)imide) (LiPSTFSI), the side-chain polymers showed at least 3 orders of magnitude higher conductivity with the same –TFSI − anion (6.7 × 10 −6 S cm −1 compared with 1.2 × 10 −10 S cm −1 at 150 °C). We found that the side-chain electrolyte showed a dielectric relaxation dominated transport mechanism through use of dielectric spectroscopy analysis. The conductivity is highly dependent on the charge delocalization and size of the pendent anion, which provides a pathway forward for the engineering of polymeric ion conductors for electrochemical applications. 

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4. Porous Polymer Gel Electrolytes Influence Lithium Transference Number and Cycling in Lithium-Ion Batteries

   https://doi.org/10.3390/electronicmat2020013  

   Boz, Buket; Ford, Hunter O.; Salvadori, Alberto; Schaefer, Jennifer L. (June 2021, Electronic Materials)

   null (Ed.)

   To improve the energy density of lithium-ion batteries, the development of advanced electrolytes with enhanced transport properties is highly important. Here, we show that by confining the conventional electrolyte (1 M LiPF6 in EC-DEC) in a microporous polymer network, the cation transference number increases to 0.79 while maintaining an ionic conductivity on the order of 10−3 S cm−1. By comparison, a non-porous, condensed polymer electrolyte of the same chemistry has a lower transference number and conductivity, of 0.65 and 7.6 × 10−4 S cm−1, respectively. Within Li-metal/LiFePO4 cells, the improved transport properties of the porous polymer electrolyte enable substantial performance enhancements compared to a commercial separator in terms of rate capability, capacity retention, active material utilization, and efficiency. These results highlight the importance of polymer electrolyte structure–performance property relationships and help guide the future engineering of better materials. 

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5. Polymer Precursor Derived LixPON Electrolytes: Toward Li−S Batteries

   https://doi.org/https://dx.doi.org/10.1021/acsami.0c03341  

   Temeche, E.; Zhang, X.; Laine, R. M. (April 2020, ACS applied materials interfaces)

   Efforts to develop polymer precursor electrolytes that offer properties anticipated to be similar or superior to (lithium phosphorus oxynitride, LiPON) glasses are reported. Such precursors offer the potential to be used to process LiPON-like thin glass/ceramic coatings for use in all solid state batteries, ASBs. Here, LiPON glasses provide a design basis for the synthesis of sets of oligomers/polymers by lithiation of OP(NH2)3−x(NH)x [from OP(NH)3],OP-(NH2)3‑x(NHSiMe3)x and [PN]3(NHSiMe3)6−x(NH)x. The resulting systems have degrees of polymerization of 5−20. Treatment with selected amounts of LiNH2 provides varying degrees of lithiation and Li+ conducting properties commensurate with Li+ content. Polymer electrolytes impregnated in/on Celgard exhibit Li+ conductivities up to ∼1 × 10−5S cm−1 at room temperature and are thermally stable to ∼150 °C. A Li−S battery assembled using a Li6SiPON composition polymer electrolyte exhibits an initial reversible capacity of 1500 mAhgsulfur −1 and excellent cycle performance at 0.25 and 0.5 C rate over 120 cycles at room temperature. 

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