Lithium-ion batteries (LIBs) are considered to be the most promising power sources for electric vehicles (EVs) because of their high energy densities and long cycle lives. However, major impediments for general public acceptance of EVs are their cost, durability, and driving range.¹ Therefore, significant improvements in the energy density, cycle life, and safety of the current state-of-the-art LIBs are necessary. Compared to the anode, cathode design is more challenging because the cathode performance is typically limited by low capacity, poor cycle life, safety problems, high cost, and the degradation of the active material resulting from parasitic reactions with the electrolyte, especially hydrogen fluoride (HF). These limitations have provided the impetus for the development of new cathodes that could reduce the weight, volume, and cost of next-generation LIBs while increasing the driving range of EVs by increasing the capacity.

In this study, we have revisited the core–shell structure that we proposed previously to develop a multi-compositional NCM cathode material (CSG90) in which LiNiO₂ is placed at the particle core and encapsulated by the well-tested Ni-rich NCM cathode material Li[Ni_0.8Co_0.1Mn_0.1]O₂.^2,3,4 After lithiation, the final composition of the core is Li[Ni_0.94Co_0.038Mn_0.022] O₂, providing a high capacity, while this core is surrounded by a 1.5 μm thick concentration gradient shell with an outermost surface composition of Li[Ni_0.841Co_0.077Mn_0.082]O₂. In order to benchmark the effectiveness of the micrometer-scale compositional partitioning of the CSG90 cathode against a conventional single-composition cathode, the structural stability and electrochemical properties of the CSG90 cathode were intensively studied and compared with those of a conventional cathode with a similar average chemical composition.

References

1. S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.
2. Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak, K. Amine, Nat. Mater. 2009, 8, 320.
3. D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, Chem. Mater. 2017, 29, 5048.
4. U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv, Energy Mater. 2019, 1803902.