AVS 62nd International Symposium & Exhibition
    Atom Probe Tomography Focus Topic Tuesday Sessions
       Session AP+AS-TuM

Paper AP+AS-TuM11
Investigating the Alternating Cation/Anion Compositions in a High-Voltage Li-Mn-Rich Oxide Electrode during First Charge-Discharge Cycle using Atom Probe tomography

Tuesday, October 20, 2015, 11:20 am, Room 211D

Session: New Applications of Atom Probe Tomography
Presenter: Baishakhi Mazumder, Oak Ridge National Laboratory
Authors: B. Mazumder, Oak Ridge National Laboratory
D. Mohanty, Oak Ridge National Laboratory
C. Daniel, Oak Ridge National Laboratory
D. Wood III, Oak Ridge National Laboratory
Correspondent: Click to Email
High-voltage layered lithium and manganese-rich (LMR) oxides are potential cathodes for high-energy-density lithium-ion batteries for electric vehicles1. Unfortunately, structural transformation during charging and discharging in these oxides2 leads to undesired phenomena, such as voltage fade during subsequent cycles and lower columbic efficiency in the first cycle, that remain stumbling blocks for practical usage. Understanding the micro-structural changes during the first cycle is critical to obtaining fundamental insight regarding the activation mechanism(s) related to the first cycle capacity loss. In this work, Atom Probe Tomography (APT) has been employed to obtain the 3D microstructural and sub-nm-level compositional information of LMR oxides during the first cycle to resolve the activation mechanism(s) that lead to structural transformation.

The greatest challenge for APT analysis from the actual electrode materials is the complexity in creating needle-shaped specimens. Owing to the discontinuous geometry of the electrode, which is characterized by non-uniform interconnected channels, it is extremely difficult to make a structurally stable needle for controlled field evaporation. Micro-fractures and irregular evaporation due to differences in evaporation fields between the composite elements during APT analysis is also challenging. Additionally, experimental parameters, including tip temperature, laser energy, and detection rate, all strongly impact the field-evaporation and subsequent data analysis. By overcoming these challenges, reliable and reproducible data has been obtained after optimizing the experimental parameters and developing a reliable procedure to prepare stable samples. Mass spectra reveal molecular complexes MxOy for M=Ni,Mn,Co, while the Li appears predominantly as elemental ions. The 3D distributions as well as the compositions of each element were obtained for each sample at different states of charge during the first cycle. These data provides insight towards understanding the structural rearrangements during the first charge-discharge cycle that correlates with the first cycle irreversible capacity loss.

1) M.M. Thackeray, et al., J. Mat. Chem.17 3112 (2007)

2) D. Mohanty, et al., Chem. Mat. 26 6272 (2014)

Research supported by CNMS, which is a DOE Office of Science User Facility.LMR material was obtained from Argonne National Laboratory. The electrodes/cell fabrication, and cell testing were carried out at the DOE’s Battery Manufacturing R&D Facility at Oak Ridge National Laboratory, which is supported by VTO within the core funding of the ABR subprogram. Authors thank Dr. Jianlin Li at ORNL for fabricating electrodes.