Advanced Concentration Gradient Cathode Material for Next-Generation Electric Vehicles

Abstract

With the prevalence of electric vehicles (EVs), the use of Li-ion batteries (LIBs) in EVs presents a new set of challenges such as cost, charging behavior, driving range per charge, risk of thermal runaway, and battery life. As the performance of LIBs is largely determined by the cathode material, the development of high-performance LIBs for EVs has focused on increasing the capacity of the cathode by using Ni-rich Li[NixCoyAl1−x−y]O2 (NCA) and Li[NixCoyMn1−x−y]O2 (NCM) cathodes.1 Ni-rich core encapsulated by a shell with concentration gradients (CSG) is the only field-proven strategy that is able to tap the potential capacity of Ni-rich cathodes while providing long cycle life.2 Despite the success of CSG cathodes, concentration gradients in the hydroxide precursor are intrinsically unstable and susceptible to flattening through interdiffusion during lithiation process.3 Furthermore, excessive coarsening during lithiation destroys the aligned microstructure, which undermines the mechanical stability of the cathode against microcrack formation.3 Therefore, CSG cathodes require a narrow processing temperature window; however, this increases their manufacturing cost. Herein, it was demonstrated that the doping of a CSG cathode with an average composition of Li[Ni0.9Co0.5Mn0.5]O2 with 0.5 mol% Sb substantially improved its cycling stability while providing manufacturing flexibility. Sb doping allowed precise tailoring of the cathode microstructure through the retardation of cation migration and the inhibition of coarsening by pinning particle boundaries. The Sb-doped CSG cathode retained ~80% of its initial capacity for 2500 cycles, while the pristine CSG90 cathode showed similar capacitive deterioration over only 1500 cycles. The proposed Sb-doped CSG90 cathode for use in electric vehicles represents an ideal high-energy-density cathode with a composition engineered to maximize capacity; its modified microstructure ensures a long battery life and ease of manufacturing, enabling cost reduction. Reference s : [1] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121. [2] U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mucke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2019, 9, 1803902. [3] G.-T. Park, H.-H Ryu, T.-C. Noh, G.-C. Kang, Y.-K. Sun, Mater. Today, 2022, 52, 9.