Comparison of Ni-Rich Li[Ni1 −x−YCoxAly]O2(NCA) Cathodes for Lithium-Ion Batteries Depending on Extent of Microcracks

Abstract

Ni-rich layered cathode materials Li[Ni1 − x − yCoxMy]O2 (M = Al and Mn are denoted as NCA and NCM, respectively) are typical cathodes for the batteries of electric vehicles (EVs). In particular, Tesla, one of the most promising EVs producers, uses the Panasonic NCA cathode in its Model S. For the wide adoption of EVs, driving range need to be raised by the increase in energy density of lithium ion batteries (LIBs). However, developing LIBs which have high energy density with stable cycle life is mainly hampered by the cathode materials.The general strategy for increasing the reversible capacity of NCM and NCA cathodes is to increase the relative Ni fraction in their composition. However, it is well acknowledged that increasing the Ni composition in NCM cathodes leads to the deterioration in both cycling performance and thermal stability.1 The fast capacity fading of Ni-rich NCM cathode is mostly attributed to the H2–H3 phase transition at the charged state, inducing an anisotropic lattice volume change generating internal microcracks in the particles.2 The extent of microcrack, which is a crucial factor dictating a performance of cathode material, increases as Ni fraction increases. Similar to NCM cathodes, Ni-rich NCA cathodes are also supposed to suffer from capacity fading and thermal instability problems owing to microcracks. To apply Ni-rich NCA cathodes in high-energy batteries for EVs, it is important to establish the capacity-cycling stability-thermal stability relationship depending on the extent of microcracks.Based on the results in NCM cathodes, we investigated the comparative study of NCA cathodes whose Ni fraction are 80%, 88%, and 95% to assess their cycling stability and to determine the capacity limit that can be attained by Ni-rich NCA cathodes without substantial sacrifice of the cycling stability. In addition, The extent of microcracks during charging and discharging was focused to identify the capacity-fading mechanism of these Ni-rich NCA cathodes. The results can provide the technical and scientific basis for further material development of these cathodes. Reference s 1. H.-J. Noh, S. Youn, C. S. Yoon and Y.-K. Sun, J. Power Sources, 2013, 233, 121.2. H.-H. Ryu, K.-J. Park, C. S. Yoon and Y.-K. Sun, Chem. Mater. 2018, 30, 1155.