To cope with global warming and ever-increasing energy demands, there has been a great effort to develop an efficient energy storage system (ESS) for electric vehicles (EVs) and grid-scale ESSs. Li-ion batteries (LIBs) have the greatest potential to be used such applications on their high energy and power densities, however, as the size of battery packs is getting larger, there is a growing concern on the battery safety issues.[1-2] Battery safety is closely related to the thermal stability of the cathode materials because the structural transition or decomposition of charged cathode generally involves O2 evolution, which increase the risk of thermal explosion of battery packs.[3-4] In this regards, in-situ monitoring the structural evolution of cathode materials at various conditions (i.e. temperature, state of charge, C-rates, etc.) is a critical issue to develop safer electrode materials.
Neutron diffraction techniques have been widely used to investigate the crystal structure of electrode materials for rechargeable batteries on the merit of the direct interaction of neutron with atomic nucleus, which enable us to investigate detailed structure of electrode materials containing light elements such as Li, Na and O. Furthermore, quantitative discussion on neighborhood elements in the periodic table such as Mn, Fe, Co, and Ni are comparably easy, which is difficult with X-ray. For this reason, neutron diffraction researches on electrode materials for rechargeable batteries have been significantly increased for several years.
In this presentation, we will demonstrate the effect of transition metal ions in Ni-Co-Mn-based oxide (NCM) electrode materials upon phase transition at high temperature using combined in-situ high temperature neutron diffraction and gas analyses. We believe that this research can provide a new insight into atomic migration and phase evolution in NCM materials and intuition for the design of cathode materials with high thermal stability.
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