Synthesis and properties of single-crystal Ni-rich cathode materials in Li-ion batteries

Single-crystal Ni-rich cathode material LiNi0.88Co0.09Al0.03O2(SC) was synthesized by a high-temperature solid-state calcination method. Physicochemical properties of primary and delithiated SC samples were investigated by X-ray diffractometry, X-ray photoelectron spectroscopy, and transmission electron microscopy. Electrochemical performance was characterized by long-term cycling, cyclic voltammetry, and in-situ impedance spectroscopy. The results indicated that high temperature rendered layered oxides to lose lithium/oxygen in the interior and exterior, and induced cationic disordering. Besides, the solid-phase synthesis process promoted phase transformation for electrode materials, causing the coexisting multi-phase in a single particle. High temperature can foster the growth of single particles, but it caused unstable structure of layered phase.

Single-Crystal Nickel-Based Cathodes:Fundamentals and Recent Advances

Lithium-ion batteries(LIBs)represent the most promising choice for meeting the ever-growing demand of society for various electric applications,such as electric transportation,portable electronics,and grid storage.Nickel-rich layered oxides have largely replaced LiCoO_(2)in commercial batteries because of their low cost,high energy density,and good reliability.Traditional nickel-based oxide particles,usually called polycrystal materials,are composed of microsized primary particles.However,polycrystal particles tend to suffer from pulverization and severe side reactions along grain boundaries during cycling.These phenomena accelerate cell degradation.Single-crystal materials,which exhibit robust mechanical strength and a high surface area,have great potential to address the challenges that hinder their polycrystal counterparts.A comprehensive understanding of the growing body of research related to single-crystal materials is imperative to improve the performance of cathodes in LIBs.This review highlights origins,recent developments,challenges,and opportunities for single-crystal layered oxide cathodes.The synthesis science behind single-crystal materials and comparative studies between single-crystal and polycrystal materials are discussed in detail.Industrial techniques and facilities are also reviewed in combination with our group’s experiences in single-crystal research.Future development should focus on facile production with strong control of the particle size and distribution,structural defects,and impurities to fully reap the benefits of single-crystal materials.