Understanding Doping and Coating for Improvement of Electrochemical Performance in High Voltage Lithium Ion Cathode Materials
EMSL Project ID
49095
Abstract
Lithium ion batteries are the top candidates for on-board energy storage in plug-in hybrid electric vehicles as well as fully electric vehicles due to their high energy and power density. One group of materials that have been the workhorse is nickel rich layered oxides. They have several advantages including high theoretical capacity, low cost, low toxicity, and high volumetric tap density. However, there is still a gap between the theoretical and practical energy densities. For instance, the cycle life deteriorates significantly if the operating cut-off voltage exceeds 4.5V, as a consequence the energy density achievable in practice is only 60% of the theoretical one. During the high voltage, our group has found that cation migration and oxygen layer shifting are possible causes for capacity decay, besides the electrolyte/electrode interface instability. Some doping and coating methods significantly circumvent this problem, though the exact mechanism is not well understood. The main challenge to understand these mechanisms has been identification of minor doping elements distribution, such as Al, Mg etc, with high spatial resolution. Atom probe tomography (APT) is an ideal technique to precisely identify phase distribution since it can map the type and 3-D location of each atom to within less than a nanometer. A detailed knowledge of the phase distribution and reaction mechanism can help researchers design better layered materials for high voltage operation (>4.5V). APT is a powerful technique for studying phase boundaries and distribution of light elements, especially when combined with high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS).Despite the advances in recent years on the APT analysis of a wide variety of materials, very little work has been done on the family of materials used in Li-ion batteries. We intend to establish standards in this technique for the identification of doping elements, coating phase distribution, an integral factor in electrode performance. The use of XPS and nano-SIMS would also be complimentary in confirming the oxidation state of elements and phase-distribution respectively observed by APT and STEM/EELS studies.
Project Details
Project type
Exploratory Research
Start Date
2015-10-15
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
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