| AVS 60th International Symposium and Exhibition | |
| In Situ Spectroscopy and Microscopy Focus Topic | Thursday Sessions |
| Session IS+EN+SP+SS-ThA |
| Session: | In Situ Studies of Electrochemical Interfaces and Processes |
| Presenter: | E. Stach, Brookhaven National Laboratory |
| Authors: | E. Stach, Brookhaven National Laboratory S. Hwang, Brookhaven National Laboratory S.-M. Bak, Brookhaven National Laboratory K.-W. Nam, Brookhaven National Laboratory W. Chang, Korean Institute of Science and Technology X. Yu, Brookhaven National Laboratory E. Hu, Brookhaven National Laboratory K.-B. Kim, Brookhaven National Laboratory K.-Y. Chung, Korean Institute for Science and Technology X.-Q. Yang, Brookhaven National Laboratory |
| Correspondent: | Click to Email |
Li-ion batteries have seen widespread application as secondary batteries in numerous applications in consumer electronics, and have attracted recent attention for various forms of electric vehicles. One particularly attractive material for the cathode is the Ni-rich system of LiNi0.8Co0.15Al0.05O2. These materials are being explored as a replacement to LiCoO2, as they offer several performance improvements, including higher energy density and lower cost. However, these materials have demonstrated a significant increase in impedance and capacity fade during aging, or upon cycling at elevated temperatures. Additionally, when in highly delithiated states, the reduction of Ni ions during thermal cycling releases oxygen from the crystal structure, which can lead to both thermal runaway and violent reactions with the flammable electrolyte.
We have utilized a variety of in-situ characterization methods to understand the mechanisms associated with the thermal degradation of LiNi0.8Co0.15Al0.05O2materials, as a function of their delithiation / charge state. By combining time-resolved synchrotron x-ray diffraction and mass spectrometry, we have directly shown that these materials undergo a specific sequence of phase transformations - from layered to disordered spinel to rock salt - as a function of temperature, and directly correlate these phase transformations with the evolution of oxygen from the microstructure. In-situ observations in an environmental transmission electron microscope confirm these global average measurements on the nanoscale, and allow us to kinetically track the evolution of oxygen from the surfaces of the nanoparticles into their bulk. In-situ spectroscopic results - from XAS and EELS - allow correlation between electronic structure changes and the resulting phase transformations. Finally by performing these same thermal treatments in-situ to the TEM and in the presence of excess oxygen, we show that it is possible to suppress these phase transformations to significantly higher temperatures, thereby suggesting that methods to protect the surfaces from oxygen evolution could lead to significant enhancements in the safety performance of these materials. Throughout the presentation, the insights gained from complementary in-situ techniques will be highlighted.