In the development of Li-ion batteries for electric vehicles (EVs), Ni-rich layered oxides are anticipated to be promising cathode materials. However, the rapid capacity fading originating from microcracks has prevented practical applications of Ni-rich cathodes. Herein, we systematically perform post-mortem analyses of Li[Ni x Co y Mn 1-x-y ]O 2 (x = 0.8 and 0.9) cathodes after long-term cycling, focusing on the particle interior. The results demonstrate that microcracks and the resultant degradation of the secondary particle interior by exposure to the deleterious electrolyte are dominant factors in the deterioration of Ni-rich cathodes. Moreover, cathode degradation significantly decreases the ionic and electrical conductivities, leading to the partial electrochemical insulation inside the cathode particles. This insulation contributes to the kinetic loss of capacity at high C-rates and induces structural inhomogeneity in the cathode. A comprehensive understanding of the degradation mechanism of Ni-rich cathodes suggests guidelines for developing Ni-rich cathode materials that are appropriate for application in EVs.

With the prevalence of electric vehicles (EVs), Ni-rich layered cathodes have been extensively studied to increase their capacities. The use of a 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. Herein, it was demonstrated that doping a CSG cathode with an average composition of Li­[Ni0.9Co0.05Mn0.05]­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 EVs 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.

z ]O 2 (NCMA) cathodes have attracted public attention owing to their improved durability by leveraging the advantages of NCM and NCA cathodes. As the Ni content approaches 90%, however, it is challenging to realize high-energy Ni-rich NCMA cathodes without sacrificing durability. Herein, we improve the cycling stability of a Ni-rich Li[Ni 0.93 Co 0.03 Mn 0.03 Al 0.01 ]O 2 (NCMA93) cathode using a combination strategy involving microstructural refinement and surface modification. The F-coating-induced protective layer of the Fcoated, Sb-doped NCMA93 cathode combined with its engineered microstructure enables the formation of a robust cathode−electrolyte interphase (CEI) layer on the cathode surface, which suppresses surface degradation to afford a long battery life. However, the F coating alone does not significantly improve the cycling stability of cathode because it suffers severe microcracking during cycling owing to its suboptimal microstructure. To realize a cathode with a long lifespan, a robust CEI layer should be generated and maintained on the cathode without severe microcracking.

The continuous expansion of the electric vehicle (EV) market is driving the demand for high-energy-density batteries using Ni-rich cathodes. However, the operation of Ni-rich cathodes under extreme-fast-charging (XFC) conditions compromises their structural integrity, resulting in rapid capacity fading; realizing Ni-rich cathodes operable under XFC conditions while maximizing energy density and long-term cycling performance is challenging. This study introduces a Li[Ni0.92Co0.06Al0.01Nb0.01]O2 (Nb-NCA93) cathode with a high energy density of 869 Wh kg–1. The presence of Nb in the Nb-NCA93 cathode induces the grain refinement of its secondary particles, alleviating internal stress and preventing heterogeneity of Li concentration during cycling. A resulting full-cell reaches full charge within 12 min and retains 85.3% of its initial capacity after 1000 cycles (cycled at full depth of discharge). In addition, the Nb-NCA93 cathode generates limited heat under XFC conditions due to its refined microstructure.

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.