(Invited) High-Capacity Cathode for Next-Generation Electric Vehicles
Authors: Sun Yang-Kook 
Published: December 2020

The ability of Li-ion batteries (LIBs) to provide portable high-density energy sources with outstanding cycle life has led to their deployment in recent electric vehicles (EVs). For wider consumer acceptance of EVs, however, the current state-of-the-art LIBs face formidable technological challenges, including concerns related to the battery cost, durability, and driving range. Resolving these hurdles requires substantial improvements in energy density, cycle life, and safety of current LIBs. Compared to the most widely accepted anode, graphite, cathodes suffer from inferior capacity, poor cycle life, thermal characteristics, and high cost. As a result, high-energy cathodes enabling a long cycle life and reliable safety need to be developed. Among the available cathode materials for LIBs, layered LiMO2 (M = Ni, Co, Mn, or Al) is the material of choice owing to its high theoretical capacity of 275 mAh g-1. To increase the capacity of the current LiMO2 cathodes, the fraction of Ni in the cathodes has been progressively increased (Co fraction decreased); however, this approach is limited by the deterioration of the cycling performance and thermal stability due to the anisotropic volume change.
To overcome the tradeoff relationship between reversible capacity and cycling stability, I propose two approaches. One approach is to control the primary particle microstructure by adjusting the columnar grains that have a long rod-shaped morphology and that are elongated along the radial direction toward the particle center. One example, concentration gradient Li[Ni0.9Co0.05Mn0.05]O2 cathode delivers a discharge capacity of 229 mAh g-1 and exhibits capacity retention of 88% after 1000 cycles in a pouch-type full cell (compared to 68% for the conventional NCM cathode). Another approach is to engineer the microstructure via doping, such as using B and W. B and W doping substantially changed the microstructure of a conventional LiMO2 cathode by generating long rod-shaped grains with a highly crystalline texture, which alleviated the internal strain that resulted from the phase transition (H2−H3) in the deeply charged state. Therefore, the B-doped Li[Ni0.878Co0.097Al0.015B0.01]O2 and W-doped Li[Ni0.9Co0.09W0.01]O2 cathodes exhibited outstanding capacity retention of 83% and 92% after 1000 cycles even when they are cycled at 100% depth of discharge, respectively. Furthermore, I will discuss the improved cycling stability mechanism in terms of microstructure and crystal structure. the [ð Eng
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