Microstructure-Tailored Ni-Rich NCA Cathode for Next Electric Vehicles

Abstract

Li[NixCoyAl1-x-y]O2 (NCA) cathodes have been adapted for the current fleet of electric vehicles, which still have unsatisfactory performances. To further increase the driving range, the Ni content in NCA cathodes should be progressively increased so that the energy density of the lithium-ion batteries is increased. However, an inherent trade-off relation between delivered capacity and cycling stability is clearly observed in Ni-rich NCA cathodes: the capacity gain from Ni enrichment is negated by the rapid capacity fading. The most dominant mechanism for the rapid fading is the microcrack formation of the cathode particles.1,2 Microcracks undermine the mechanical integrity of the Ni-rich NCA cathodes and allow the electrolyte to penetrate the particle interior, thus leading to parasitic surface reactions. Although various attempts, such as optimizing transition metal composition, finding effective doping or coating agents, have been proposed to improve the cycling stability of Ni-rich cathodes, these approaches are not a fundamental solution to the formation of microcracks on the particle.Recent researches provided valuable insights into a way to suppress microcrack formation.3 Because microcracks nucleate from the abrupt lattice contraction caused by the multiple phase transition during the electrochemical reaction, it is necessary to minimize the local strain build-up for particle integrity. Although intrinsic lattice volume changes are unavoidable during electrochemical reactions, the structural integrity of Ni-rich cathodes can be preserved by engineering the microstructure of cathode particles such that the strain distribution is delocalized.4 In this presentation, we propose boron-doped Li[Ni0.878Co0.097Al0.015 B0.01]O2 (B-NCA88) which have obviously different morphologies compared to a typical NCA cathode. To highlight the dramatic microstructure change caused by boron doping, B-NCA88 and typical Li[Ni0.885Co0.1Al0.015]O2 cathodes are extensively investigated by comparing their electrochemical properties, microcracking behavior, and structural stability. References G. W. Nam, N.-Y. Park, K.-J. Park, J. Yang, J. Liu, C. S. Yoon and Y.-K. Sun, ACS Energy Lett. 2019, 4, 2995.K.-J. Park, J.-Y. Hwang, H.-H. Ryu, F. Maglia, S.-J. Kim, P. Lamp, C. S. Yoon and Y.-K. Sun, ACS Energy Lett. 2019, 4, 1394.H. H. Sun, H.-H Ryu, U.-H. Kim, J. A. Weeks, A. Heller, Y.-K. Sun and C. B. Mullins, ACS Energy Lett. 2020, 5, 1136.U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon and Y.-K. Sun, Adv. Energy Mater. 2017, 2, 1150.