Ni-rich Li­[Ni1–x–y Co x Al y ]­O2 (NCA) cathodes (1 – x – y = 0.8, 0.88, and 0.95) are synthesized to investigate the capacity fading mechanism of Ni-rich NCA cathodes. The capacity retention and thermal property of the cathodes deteriorate as their discharge capacity increases when the Ni fraction is increased. The capacity fading correlates well with the anisotropic volume variations caused by the H2–H3 phase transition and the resulting extent of microcracking. Although all three cathodes start to develop microcracks after being charged to 3.9 V, the potential at which microcracks propagated to the outer surface of the particle decreases with increasing Ni content. These microcracks undermine the mechanical integrity of the cathode and facilitate electrolyte penetration into the particle core, which accelerates surface degradation of the internal primary particles. Therefore, mitigating or delaying the H2–H3 phase transition is key to improving the cycling performance of Ni-rich NCA cathodes.

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A hybrid-structured Li­[Ni0.9Co0.045­Mn0.045Al0.01] (HS-NCMA90) cathode is proposed, in which Li­[Ni0.92Co0.04­Mn0.03Al0.01]­O2 forms the interior of the cathode particle enclosed in a buffer layer of Li­[Ni0.845Co0.067­Mn0.078Al0.01]­O2. The hybrid structure is compositionally partitioned into interior and outer regions and develops radially aligned, size-refined primary particles with a high aspect ratio. This optimized microstructure enables the primary particles to contract uniformly and produces differential states of stress that apply compressive stress to the particle interior, thereby effectively suppressing the propagation of microcracks toward the outer surface. The unique microstructure of the HS-NCMA90 cathode markedly improves its cycling stability, which retains 84.7% of its initial capacity after 1500 cycles. The proposed microstructurally engineered cathode, with high mechanical stability and fracture toughness, prolongs the service life of batteries with high energy densities.

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The electrochemical and structural stabilities of a conventional Li[Ni0.90Co0.045Mn0.045Al0.01]O2 (NCMA90) cathode and a core–shell with concentration gradient cathode (CSG‐NCMA90) are evaluated by cycling the cathodes at different depths of discharge (DoDs). The CSG‐NCMA90 cathode consists of fine, elongated primary particles that are radially aligned from the center of a spherical secondary particle. This unique microstructure effectively suppresses microcrack formation and propagation in the highly charged state. Moreover, microstructural analysis through transmission electron microscopy reveals that the thin elongated primary particles, largely featuring (001) facets on their lateral sides, are tolerant of electrolyte attack, thus suppressing surface degradation. In a full cell, these microstructural features enable the CSG‐NCMA90 cathode to retain 90.7% of its initial capacity after 1000 cycles at 100% DoD. Unlike conventional Ni‐rich layered cathodes whose capacity should be restricted to ≈60–80% to ensure their long service life, the proposed CSG‐NCMA90 cathode can be cycled at full capacity, thus facilitating higher electrochemical performance and realizing the development of economical Li‐ion batteries.

A new class of layered cathodes, Li[NixCoyB1−x−y]O2 (NCB), is synthesized. The proposed NCB cathodes have a unique microstructure in which elongated primary particles are tightly packed into spherical secondary particles. The cathodes also exhibit a strong crystallographic texture in which the a–b layer planes are aligned along the radial direction, facilitating Li migration. The microstructure, which effectively suppresses the formation of microcracks, improves the cycling stability of the NCB cathodes. The NCB cathode with 1.5 mol% B delivers a discharge capacity of 234 mAh g−1 at 0.1 C and retains 91.2% of its initial capacity after 100 cycles (compared to values of 229 mAh g−1 at 0.1 C and 78.8% for pristine Li[Ni0.9Co0.1]O2). This study shows the importance of controlling the microstructure to obtain the required cycling stability, especially for Ni‐rich layered cathodes, where the main cause of capacity fading is related to mechanical strain in their charged state.

Recharging capability of Ni-rich layered cathodes deteriorates rapidly upon cycling mainly from mechanical instability caused by removing a large amount of Li ions from the host structure. Through multi-stage microstructural...