Challenges and Strategies towards Single‐Crystalline Ni‐Rich Layered Cathodes

Abstract

The ever‐increasing energy density requirements in electric vehicles (EVs) have boosted the development of Ni‐rich layered oxide cathodes for state‐of‐the‐art lithium‐ion batteries. Nevertheless, the commercialization of polycrystalline Ni‐rich cathodes (PCNCs) is hindered by the severe performance degradation and safety concerns that are tightly related to its particle cracking during cycling. Single‐crystalline Ni‐rich cathodes (SCNCs) with eliminated grain boundaries and high mechanical strength have recently attracted extensive attention owing to their superior structural and cycling stability, which present high crack resistance during electrochemical operation. Various articles have focused on the trial‐and‐error synthesis and modifications of SCNCs, as well as the comparison of performances and mechanisms with PCNCs. However, there has been much less effort in systematic analysis and summary to reveal their key challenges, controversies, and the corresponding primary causes. In this review, the advantages and debates in structural and electrochemical properties of SCNCs over PCNCs are summarized to provide fundamental understanding of SCNCs. Then the current practical issues and challenges are comprehensively discussed from the viewpoints of both academia and industry, as well as the proposed modification strategies and underlying mechanisms for SCNCs. The outlook and perspectives are further given to facilitate the commercial applications of SCNCs in high‐performance EVs.

Single‐Crystalline Ni‐Rich LiNixMnyCo1−x−yO2 Cathode Materials: A Perspective

“…[ 17 ] Both traditional high‐temperature sintering and preparation in alkali chloride flux were utilized in the early days. [ 18 ] However, the particle size of SC‐NMC obtained at the early stage was typically less than 1 µm, which would greatly lose the merits when compared to PC‐NMC [ 19 ] . [ 20 ] Dahn et al.…”

“…[17] Both traditional high-temperature sintering and preparation in alkali chloride flux were utilized in the early days. [18] However, the particle size of SC-NMC obtained at the early stage was typically less than 1 µm, which would greatly lose the merits when compared to PC-NMC [19] . [20] Dahn et al [21] systematically studied the influence of several key parameters, such as precursor grain size, molar ratio, [7c,22] sintering duration, and temperature on the morphology and particle size of the SC products.…”

Recent achievements of free‐standing material and interface optimization in high‐energy‐density flexible lithium batteries

“…[72][73][74] It is worth noting that the goal of achieving the high energy density of FLBs requires employing high-voltage Ni-rich or Li-rich cathode materials. [75,76] Therefore, the optimization of the interface between FSEs and active materials is extremely critical. For instance, Guo's group [56] (c) and (d) Schematic illustration for the fabrication of the flexible free-standing C/Si/CNTs anode and electrochemical stability.…”

“…[ 72–74 ] It is worth noting that the goal of achieving the high energy density of FLBs requires employing high‐voltage Ni‐rich or Li‐rich cathode materials. [ 75,76 ] Therefore, the optimization of the interface between FSEs and active materials is extremely critical. For instance, Guo's group constructed a soft polymer nanolayer onto the surface of high voltage Ni‐rich cathode materials (LiNi 0.6 Mn 0.2 Co 0.2 O 2 , Figure 6a).…”

Controlled Synthesis of Single–Crystalline Ni–Rich Cathodes for High-Performance Lithium–Ion Batteries

“…The reported conventional preparation method for well-studied single–crystalline lower-Ni–content NCM includes a coprecipitation process to synthesize spherical precursors with a diameter of 3–5 μm aggregated by nanosized primary particles and subsequent high-temperature calcination (≥900 °C) for the growth of single crystals. ,,,− ,, However, this preparation method does not work for single–crystalline Ni–rich NCM owing to the weak structure stability of higher-Ni–content cathodes at high temperatures. − It is hard to convert a polycrystalline precursor to single–crystalline NCM particles by high–temperature calcination without structural damages.…”