Engineering topics

Zanelotti, Curt J.

Publications and source records attributed to Zanelotti, Curt J..

4 records

DOE OSTI2021

Solvent-Cast Solid Electrolyte Membranes Based on a Charged Rigid-Rod Polymer and Ionic Liquids

Solid-state electrolytes are attractive for use in electrochemical devices because they remove the need for a flammable liquid electrolyte while contributing to the structural integrity of the device. We have recently developed a class of solid electrolytes, termed molecular ionic composites (MICs), composed of ionic liquids (ILs) and a rigid-rod polyelectrolyte, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). MIC materials, originally obtained through an ion-exchange process between IL and PBDT aqueous solution, possess an unprecedented combination of high ionic conductivity, high thermal stability, low flammability and widely tunable tensile storage moduli. Here we present a facile solvent casting method for preparing MIC membranes. These membranes are uniform, flexible, and tough, with tunable composition and thickness (≥ 40 μm). Unlike the previous ion-exchange method, which only allowed incorporation of hydrophilic ILs, we can now incorporate hydrophobic ILs to prepare MIC membranes for, e.g. battery electrolytes. A sodium (Na) metal symmetric cell constructed with a PBDT-Pyr 14 TFSI membrane as the solid electrolyte shows long-term stable cycling (> 500 h.) at 60 °C. Furthermore, the ability to prepare MICs using both hydrophilic and hydrophobic ILs initiates a wider range of MIC materials and broadens the array of applications accessible by MIC membranes.

25 ENERGY STORAGE↗

DOE OSTI2021

Solid-state rigid-rod polymer composite electrolytes with nanocrystalline lithium ion pathways

A critical challenge for next-generation lithium-based batteries lies in development of electrolytes that enable thermal safety along with use of high-energy-density electrodes. We describe molecular ionic composite (MIC) electrolytes based on an aligned liquid crystalline polymer combined with ionic liquids and concentrated Li salt. This high strength (200 MPa) and non-flammable solid electrolyte possesses outstanding Li + conductivity (1 mS cm -1 at 25 °C) and electrochemical stability (5.6 V vs Li|Li + ) while suppressing dendrite growth and exhibiting low interfacial resistance (32 Ω cm 2 ) and overpotentials (≤ 120 mV @ 1 mA cm -2 ) during Li symmetric cell cycling. A heterogeneous salt doping process modifies a locally ordered polymer-ion assembly to incorporate an inter-grain network filled with defective LiFSI & LiBF 4 nanocrystals, strongly enhancing Li + conduction. Furthermore, this modular material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer electrolytes.

25 ENERGY STORAGE↗

DOE OSTI2021

Room Temperature to 150 °C Lithium Metal Batteries Enabled by a Rigid Molecular Ionic Composite Electrolyte

Molecular ionic composites (MICs), made from ionic liquids and a rigid-rod polymer poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), are a new type of rigid gel electrolyte that combine fast ion transport with high thermal stability and mechanical strength. In this work, a MIC electrolyte membrane is prepared that is composed of PBDT, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr 14 TFSI) in a mass ratio of 10:10:80. The ionic conductivity at 25 °C is 0.56 mS cm –1 with no added flammable/volatile components. Although the polymer content is only 10 wt%, this MIC membrane is rigid with a tensile modulus of 410 MPa at room temperature. The MIC membrane remains stable and rigid at 200 °C with the shear storage modulus (G') only slightly decreasing by 35%. Li/MIC/LiFePO 4 cells demonstrate stable cycling performance over a wide temperature range from 23 to 150 °C. The specific discharge capacity at 100 and 150 °C at 1 C rate exceeds 160 mAh g –1 . The discharge capacity retention is 99% after 50 cycles at 150 °C. Furthermore, this stable battery performance shows that this low polymer content MIC membrane qualifies for use as a solid electrolyte in lithium metal batteries operating over a wide temperature range.

25 ENERGY STORAGE↗

DOE OSTI2020

Ion Transport and Mechanical Properties of Non-Crystallizable Molecular Ionic Composite Electrolytes

Polymer electrolytes show promise as alternatives to conventional electrolytes in energy storage and conversion devices but have been limited due to their inverse correlation between ionic conductivity and modulus. In this study, we examine surface morphology, linear viscoelastic, dielectric and diffusive properties of molecular ionic composites (MICs), materials produced through the combination of a rigid and charged double helical polymer, known as poly(2,2’)-disulfonyl-4,4’benzidine terepthalamide (PBDT), with ionic liquids (ILs). To probe temperature extremes, we incorporate a non-crystallizable IL to allow measurements from to -90 to 200°C. As we increase PBDT weight percentage (wt%), shear moduli increase and do not decay up to 200°C while maintaining room temperature ionic conductivity within a factor of two of the neat IL. We connect diffusion coefficients of IL ions with ionic conductivity through the Haven ratio across a wide temperature range and analyze trends in ion transport based on a relatively high and composition-dependent static dielectric constant. This behavior may result from collective rearrangement of IL ions in these networks. We propose that these properties are driven by a two-phase system in MICs corresponding to IL-rich “puddles” and PBDT-IL associated “bundles” where IL ions form alternating sheaths of cations and anions around each PBDT rod. Furthermore, these polymer-based MIC electrolytes show great promise for use in electrochemical devices that require fast ion transport, high modulus, and a broad thermal window.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗