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CBE Seminar: Dr. Steve Greenbaum

Friday, April 13, 2018 @ 11:00 AM

Event Location:
AME 106

Liquid and Solid State NMR Investigations of Electrolytes for Beyond Lithium Ion Applications
Nuclear magnetic resonance (NMR) has been productively employed to investigate ion transport and solvation in Li ion battery electrolytes. NMR is a unique method of probing local structure and dynamics in a wide variety of materials owing to the short range nature of the interactions that produce spectral features and govern relaxation behavior. Among its advantages are elemental (nuclear) specificity and its reliably quantitative nature in that the integrated intensity of a particular spectral component is directly proportional to the number of nuclei in the corresponding material phase. Modern day NMR has grown into an enormously diverse array of sophisticated experimental techniques in studies ranging from complex biochemical systems in the solution phase to a wide selection of solid-state compounds, with often negligible overlap in methodology. As a counterexample of the increasing divergence between the liquids and solids NMR communities, we present here several recent or ongoing NMR investigations of lithium battery materials, utilizing both liquid state and solid state NMR. Future electrochemical power sources require new electrolytes to adapt to disruptive changes in the basic working chemistry, such as moving from Li ion to Na ion, or to Li metal electrodes. We highlight three recent collaborative activities on electrolytes in our group (i) glyme-based electrolytes for Li-S and Na ion batteries; (ii) Li3PS4 solid electrolyte (iii) non-polyether polymer electrolyte for Li-metal batteries.

A series of Li electrolytes made with glymes of variable length (mono, di, tri, tetra, and higher) has been synthesized by collaborators (Jusef Hassoun, Lorenzo Carbone) at the University of Ferrara, Italy. Natural abundance 17O NMR is found to be an exquisitely sensitive probe of the total charge on the solvent as well as anion oxygens, and thus provides useful information on solvent-ion and ion-ion association. Though these electrolytes show promise for use in Li metal and Li-S batteries, NMR measurements reveal a significant degree of ion association. Results are also presented for the corresponding Na electrolytes, as well as for (time permitting) binary carbonate solvent mixtures for Na ion batteries in collaboration with the U.S. Army Research Lab (Kang Xu, et.al.)

In the solid electrolyte realm, in collaboration with Chengdu Liang, et.al., (formerly of Oak Ridge National Lab), we investigated the phase evolution of nanoporous β-Li3PS4 prepared by wet chemical synthesis and subsequent thermal treatment by 7Li and 31P magic angle spinning NMR. The β phase exhibits ionic conductivity over two orders of magnitude higher than that of the corresponding bulk crystalline compound, γ -Li3PS4.

Ionic Materials, Inc. (Mike Zimmerman, Randy Leising, et.al.) has invented a novel polymer electrolyte with extremely high ionic conductivity over a range of temperatures, even surpassing that of a commercial porous separator containing the standard liquid carbonate-based electrolyte at room temperature. This solid polymer can be reliably extruded into very thin films, is non-flammable, has attractive mechanical properties for lithium dendrite suppression, is electrochemically stable against Li, and is compatible with a variety of different anodes and cathodes. The polymer electrolyte is based on an inexpensive semicrystalline commercially available polymer such as polyether ether ketone or polyphenylene sulfide and Li salts familiar to the battery and polymer electrolyte communities. The ionic transport mechanism is unlike that which characterizes the PEO salt complexes that is ion mobility is completely decoupled from polymer host motion, as verified by differential scanning calorimetry and NMR. In fact NMR pulsed gradient measurements reveal Li self-diffusion coefficients at room temperature that the highest in any known solid.

Kimber Ann Spann
Contact Phone Number
(850) 410-6149