Chemomechanically Stable Ultrahigh-Ni Single-Crystalline Cathodes with Improved Oxygen Retention and Delayed Phase Degradations

Abstract

The pressing demand in electrical vehicle (EV) markets for high-energy-density lithium-ion batteries (LIBs) requires further increasing the Ni content in high-Ni and low-Co cathodes. However, the commercialization of high-Ni cathodes is hindered by their intrinsic chemomechanical instabilities and fast capacity fade. The emerging single-crystalline strategy offers a promising solution, yet the operation and degradation mechanism of single-crystalline cathodes remain elusive, especially in the extremely challenging ultrahigh-Ni (Ni > 90%) regime whereby the phase transformation, oxygen loss, and mechanical instability are exacerbated with increased Ni content. Herein, we decipher the atomic-scale stabilization mechanism controlling the enhanced cycling performance of an ultrahigh-Ni single-crystalline cathode. We find that the charge/discharge inhomogeneity, the intergranular cracking, and oxygen-loss-related phase degradations that are prominent in ultrahigh-Ni polycrystalline cathodes are considerably suppressed in their single-crystalline counterparts, leading to improved chemomechanical and cycling stabilities of the single-crystalline cathodes. Our work offers important guidance for designing next-generation single-crystalline cathodes for high-capacity, long-life LIBs.

Elucidating the charge-transfer and Li-ion-migration mechanisms in commercial lithium-ion batteries with advanced electron microscopy

“…This surface phase inhibited the H2-H3 phase However, direct evidence of the reaction mechanism could not be fully obtained with these characterization methods. to corroborate theories and results [137][138][139][140][141][142]. To date, advanced electron microscopy has been an indispensable part of investigations on charge-transfer mechanisms owing to its repeatability and reliability.…”

Correlating Electrochemical Kinetic Parameters of Single LiNi1/3Mn1/3Co1/3O2 Particles with the Performance of Corresponding Porous Electrodes

“…The nonuniform distribution of particles' SOC along with the thickness direction may cause internal strain of active particles. [30,31] ature, lifetime). Therefore, there is still plenty of room for technical development and scientific measurement.…”

“…As a result, the SOC inhomogeneity of particles, in turn, would be further increased along with the electrode thickness. The non‐uniform distribution of particles’ SOC along with the thickness direction may cause internal strain of active particles [30, 31] …”

Accelerated Degradation in a Quasi-Single-Crystalline Layered Oxide Cathode for Lithium-Ion Batteries Caused by Residual Grain Boundaries

“…Layered oxide cathodes with high nickel content (LiNi 1– x – y Mn x Co y O 2 , also noted as NMC), owing to the high specific capacity and high energy density, are considered the critical material in next-generation Li-ion batteries for electric vehicles. − Conventional layered oxide cathodes are generally in the form of near-spherical polycrystalline particles (3–10 μm in size) consisting of hundreds of tightly packed primary particles (100–500 nm in size) . However, a consensus regarding this primary–secondary architecture is that the massive interfaces between primary particles facilitate Li + diffusion and consequently improve the rate performance; the drawback is equally discouragingthe anisotropic strain during the repeated lithiation/delithiation process can easily detach the primary particles from each other, continuously cause the formation of cracks, and lead to severe side reactions. − Although secondary-particle-level coating or doping strategies can significantly enhance capacity retention, it has been proved unsatisfactory in suppressing the intergranular crack formation. , The single-crystallization strategy is considered a promising pathway to suppress the microcrack formation. Benefiting from the absence of an internal grain boundary, the lattice-expansion-induced anisotropic strain will release at the surface rather than accumulate in the interior. ,, As a result, the crack formation widely observed at the grain boundaries of conventional polycrystalline cathodes can be intrinsically prohibited, leading to improved capacity retention.…”

“…Benefiting from the absence of an internal grain boundary, the lattice-expansion-induced anisotropic strain will release at the surface rather than accumulate in the interior. 10,15,16 As a result, the crack formation widely observed at the grain boundaries of conventional polycrystalline cathodes can be intrinsically prohibited, leading to improved capacity retention.…”