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Séminaire de Steve Greenbaum

Nuclear Magnetic Resonance Studies of Battery and Fuel Cell Materials : 1st part


Steeve Greenbaum

Hunter College, The City University of New York

 
Nuclear Magnetic Resonance Studies of Battery and Fuel Cell Materials

 

Fundamental materials research is needed to move present-day energy storage technologies to the scale needed to develop all-electric vehicles and to manage intermittent sources such as wind and solar. Structural studies of materials utilized in lithium battery and fuel cell technology are often hampered by the lack of long-range order found only in well-defined crystalline phases. Powder x-ray diffraction, while being an indispensable technique in the characterization of electrode materials, yields only structural parameters that have been averaged over hundreds of lattice sites, and is unable to provide structural information about amorphous compounds. Our laboratory utilizes solid state nuclear magnetic resonance (NMR) methods to investigate structural and chemical aspects of lithium ion cathodes, anodes, electrolytes, interfaces and interphases. NMR is element- (nuclear-) specific and sensitive to small variations in the immediate environment of the ions being probed, for example Li+. NMR is also a powerful tool for probing ion and molecular motion in polymer electrolytes for lithium batteries and fuel cells (both hydrogen and direct methanol), with a dynamic range spanning some ten orders of magnitude through spin-lattice relaxation and both pulsed and static field gradient echo self-diffusion measurements. Solid state NMR has also been productively employed in identifying the composition of the passivating layers (i.e. the solid electrolyte interphase - SEI) which both enable and limit Li+ ion transport in batteries, in ways that other spectroscopic methods such as XPS or FTIR cannot, due to the uniquely quantitative aspect of NMR spectroscopy. On the other hand, because of the low inherent sensitivity of NMR (which is a radiofrequency method) compared to other probes in the optical or x-ray region of the electromagnetic method, larger sample amounts are typically required, or in some cases other enhancements such as isotopic enrichment are necessary.

 

This series of two lectures will begin with a description of some of the standard NMR methods used to study structure and dynamics and some relatively non-standard techniques such as high pressure NMR. A survey of several recent NMR investigations in our lab will be presented as well as some related work reported by other groups, including water and proton transport in nanocomposite PEM fuel cells membranes, single crystal studies of the commercially important cathode material LiMPO4 (M = Fe, Co, Ni) cathodes, SEI formation in lithium batteries and asymmetric hybrid supercapacitors, charge storage mechanism in carbon/MnO2 nanofoam electrodes, structural aspects of CFx primary lithium battery cathodes, and ion transport in solvent-free polymer electrolytes and in ionic liquid based membranes for lithium batteries.