The rapid development of technology has necessitated the innovation of new battery technologies in order to keep up with a growing demand for renewable energy storage systems. Lithium ion batteries are promising as they boast high gravimetric and volumetric energy densities. The positive electrode (or cathode material), is a widely studied component of the Li Ion battery and commercially available options can be toxic and expensive. Solid State Nuclear Magnetic Resonance (NMR) is a useful tool for studying lithium ion dynamics in these types of materials as we can probe the lithium ion mobility as well as the host framework. The research focuses on the study of Li ion dynamics in a variety of phosphate and sulfate based cathode materials using NMR techniques such as 2D Exchange Spectroscopy, one-dimensional selective inversion recovery and Rotational-Echo Double Resonance (REDOR) experiments.  These methods allow us to determine site-specific dynamics in lithium intercalation materials in order to assess their viability for implementation into a battery.

The use of solid-state electrolytes in lithium ion batteries promises to increase the power output for use in electric vehicles. We use solid-state NMR to analyze the lithium ion conductivity in the solid-state electrolytes Li₆BaLa₂M₂O₁₂ (M = Ta and Nb). The research has taken two different approaches to study lithium ion mobility in these materials. Firstly, the mobile ion species have been studied directly, using ⁶Li{⁷Li}-REDOR to study the effective dipolar coupling, D_eff, as a function of temperature. Changes in the slope of the resulting REDOR curve are correlated to ionic hopping rates of lithium ions, and variable temperature studies can be used to determine the affect of temperature on ion mobility. The second method used the stationary framework elements, such as ¹³⁹La, to observe ionic motion from a secondary standpoint. Changes in the quadrupolar lineshape are correlated to changes in the lithium ion hopping rate, and spectral simulations are used to extract these rates. This method is used to circumvent some of the challenges of studying diamagnetic lithium materials, such as the long T1 relaxation and poor site resolution of ^6,7Li. Together these methods give a variety of ways of answer questions about lithium ion conductivity in solid-state electrolytes.

 

The choice of electrolyte can have a substantial impact on overall lithium ion battery performance. The most commonly used electrolytes are those based on flammable organic carbonates.  There is a push however towards electrolytes that are both non-flammable and more electrolytically stable (e.g. ionic liquids). While there are a large number of alternatives, their performance is often limited by their diffusional properties including viscosity and lithium transport number. NMR has the capability of elucidating diffusional properties in complex electrolytes to an extent that is difficult to match via other methodologies. It is done by utilizing pulsed field gradients to encode for position in a process known as diffusion ordered spectroscopy (DOSY). Our research uses NMR in this fashion to screen candidate electrolytes and includes in-situ studies of electrolytes under the application of an applied potential.

Our research in the area of PEM-FC focuses on the proton dynamics in proton exchange membranes such as Nafion™, Sulfonated polyether ether ketones (S-PEEK) and their composites obtained by doping conductive inorganic fillers. Proton mobility on microscopic level is investigated by dipolar recoupling pulse (BABA). Electrochemical impedance spectroscopy is used to measure bulk ionic conductivity. Our goal is to understand conductivity difference of PEMs on molecular level by combining solid state NMR and conductivity measurements.

Polymers & model complexes based on imidazole compounds are also studied using similar proton NMR techniques that were applied to Nafion with the goal of understanding the proton mobility within these compounds. The focus of this research is to understand the mechanism of ion conduction in these polymers and improve upon it using various methods & model compounds.

Lithium-air batteries have the potential to transform energy storage for electric and hybrid vehicles, as the theoretical energy is equivalent to gasoline [1]. The high energy density comes for the electrochemical reaction of metallic lithium and molecular oxygen, resulting in lithium peroxide.  Electrolytes that have been studied to date have been shown to be consumed during the discharge process [1]. Our research focuses on finding a compatible electrolyte.  Solid state NMR is utilized to track the species that are formed during discharge. to determine if lithium peroxide is being formed.   

 

 

 

 

 

 

1. M. Leskes, N. E. Drewett, L. J. Hardwick, P. G. Bruce, G. R. Goward and C. P. Grey, Angewandte Chemie International Edition 2012, 51, 8560-8563.