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Towards Understanding Atomic and Electronic Structure of Battery Materials

This is an exciting time in the history of vehicular transportation. The recent commercial introduction of hybrid electric vehicles coupled with the huge international effort to develop batteries and fuel cells for automotive use has made the dream of widespread electric vehicle use a real possibility. The last decade has seen the introduction of a variety of promising new materials for lithium rechargeable batteries. Application of these materials to electric vehicle batteries requires that they be inexpensive, lightweight, environmentally compatible, and able to withstand years of electrochemical use. The research groups of Jeff Reimer and Elton Cairns have focused on the application of nuclear magnetic resonance (NMR) spectroscopy to the study of up-and-coming lithium battery electrode materials.

The local atomic structure for LiFePO4.

The local atomic structure for LiFePO4.

NMR allows direct observation of lithium in the bulk of a battery electrode, providing insight into the local atomic and electronic environment surrounding the lithium ion. Studying the changes in this local environment and their relationship to electrochemical cycling and abuse of the material elucidates the critical connection between the atomic-scale structure of the electrode and the resulting electrochemical performance. Our recent research in this area has ranged from fundamental to applied and focuses on both novel and well-studied materials.

One type of electrode material we have explored is the lithium-manganese-oxide spinel (LiMn2O4) system. It is well known that these materials show a greatly increased number of charge-discharge cycles before failure when chromium (Cr), aluminum (Al), or other metal ions substitute for some of the manganese in the spinel crystal. The mechanism of failure and the role of metal substitution are still subjects of debate. We have used NMR and other techniques to study the evolution of the atomic-scale structure of spinel materials on charge-discharge cycling and after failure. Our results suggest that the dominant mode of failure is dissolution of manganese via a lithium-for-manganese ion-exchange process. We furthermore surmise that substitution of the manganese promotes covalence in the Li-O-Mn bond, producing a more robust material that can withstand the rigors of long-term electrochemical cycling.

7Li MAS NMR isotropic peaks for (a) LiMn2O4 and (b) LiCr0.1Mn1.9O4

7Li MAS NMR isotropic peaks for (a) LiMn2O4 and (b) LiCr0.1Mn1.9O4: fresh (solid orange line), charge/discharge cycled once (dashed black line), and cycled 100 4V times (green line). Notice that the spectrum changes much more for LiMn2O4, which showed rapid failure.

Our most recent research is in collaboration with Marca Doeff of the Materials Sciences Division and includes study of a novel electrode material, LiFePO4-type olivines. We have just published a new model for understanding the NMR properties of the pristine material (as a communication in the Journal of the American Chemical Society). We expect this work to lay the foundation for future applied studies of the effects of synthesis technique and electrochemical history on the performance of this promising material.

— Jeffrey Reimer

For more information, contact:

  • Jeffrey Reimer
  • (510) 642-8011; fax (510) 642-4778

The early portions of this research were supported by the Director, Office of Basic Energy Sciences, Chemical Sciences Division of the U.S. Department of Energy. The more recent work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy.

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