Abstract
The worldwide development of electric vehicles as well as large-scale or grid-scale energy storage to compensate for the intermittent nature of renewable energy generation has led to a surge of interest in battery technology. Understanding the factors controlling battery capacity and, critically, their degradation mechanisms to ensure long-term, sustainable and safe operation requires detailed knowledge of their microstructure and chemistry, and their evolution under operating conditions, on the nanoscale. Atom probe tomography (APT) provides compositional mapping of materials in three dimensions with sub-nanometre resolution, and is poised to play a key role in battery research. However, APT is underpinned by an intense electric field that can drive lithium migration, and many battery materials are reactive oxides, requiring careful handling and sample transfer. Here, we report on the analysis of both anode and cathode materials and show that electric-field driven migration can be suppressed by using shielding by embedding powder particles in a metallic matrix or by using a thin conducting surface layer. We demonstrate that for a typical cathode material, cryogenic specimen preparation and transport under ultra-high vacuum leads to major delithiation of the specimen during the analysis. In contrast, the transport of specimens through air enables the analysis of the material. Finally, we discuss the possible physical underpinnings and discuss ways forward to enable shielding from the electric field, which helps address the challenges inherent to the APT analysis of battery materials.
Highlights
Batteries are at the core of many technologies that will have a significant impact on decarbonation of our society[1]
The highcapacity energy storage needed in electric vehicles or grid energy storage is currently largely achieved using Li-ion batteries (LIBs)[2], which appear one of the most viable and scalable energy storage technology to accommodate the variability of renewable energy sources[3,4], assuming sufficient Li can be extracted
We have shown that the analysis of Li-containing materials by Atom probe tomography (APT) is extremely challenging due to the influence of the electrostatic field applied during the experiment that drives in-situ delithiation
Summary
Batteries are at the core of many technologies that will have a significant impact on decarbonation of our society[1]. LIBs and their individual constituents have been subject to significant research and development efforts in the past decades[6], leading to the Nobel Prize in Chemistry in 2019 to Goodenough, Whittingham, and Yoshino for their work on Co-based oxides[7,8]. Extending the operation lifetime of LIBs would decrease the environmental footprint and cost, but requires understanding the microstructural origins of capacity-loss and the degradation during cycling to develop strategies to design new highperformance materials[9]. These degradation mechanisms occur across length scales ranging from subnanometres to microns or more[10,11], and precluding direct investigation by any single characterization technique. The Li distribution on the nanoscale remains elusive due to its low atomic weight, which limits its interactions with electrons in transmission electron microscopy (TEM), as well as its high mobility
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