Correlating Morphological and Structural Evolution with the Electrochemical Performance of Nickel-Rich Cathode Materials: From Polycrystal to Single Crystal

Abstract

Nickel-rich layered oxides (Ni≥90%) have been recognized as promising cathode materials for Lithium-ion batteries (LIBs) owing to their high energy density and low cost. Here, we prepared 20 LiNi0.90Co0.06Mn0.04O2 (Ni90) samples with various morphologies by regulating sintering temperature and the lithium to transition metal ratio. The correlation between the synthesis conditions, structural properties, and electrochemical performance of Ni90 materials was thoroughly investigated during the evolution from polycrystal to single crystal. A positive and linear relationship was found between sintering temperature and primary particle size (PPS), which affect the electrochemical performance profoundly. Polycrystals with small PPS show a high discharge capacity and low polarization, while single crystals with large PPS have low discharge capacity but excellent cycling stability. Moreover, the sluggish kinetic properties of Ni90 materials at the end of discharge (a sharp drop in lithium-ion diffusion coefficient at the end of discharge) lead the morphology factors to a critical feature that dominates the total discharge capacity. Taking discharge capacity and cycling stability into consideration, the quasi-single crystal Ni90 materials with moderate PPS and the lowest cation disordering is the first choice. These findings contribute to a better understanding of polycrystalline and single-crystal Nickel-rich cathode materials for LIBs.

Regulating Single-Crystal LiNiO2 Size and Surface Coating toward a High-Capacity Cathode for Lithium-Ion Batteries

“…LNO easily decomposes at high temperature with formation of Li/Ni anti-site defects by lithium loss . Generally, an increase in synthesis temperature is accompanied by not only particle size growth but also phase decomposition and increase in cation mixing defects . Thus, large particles are usually formed with lots of defects, so it is hard to decouple the two factors, particle size growth and defects.…”

“…29 Generally, an increase in synthesis temperature is accompanied by not only particle size growth but also phase decomposition and increase in cation mixing defects. 15 Thus, large particles are usually formed with lots of defects, so it is hard to decouple the two factors, particle size growth and defects. In this work, owing to the molten salt synthesis method, a particle size increase was achieved without increasing crystal anti-site defects.…”

“…Generally, increasing the particle size accompanies high cation mixing defects in Ni-rich layered oxides. 15 However, here, we used a molten salt synthesis method to form single-crystal LNO so that the synthesis process can retain similar cation mixing defects at high temperatures. Different single-crystal-sized samples were synthesized with similar cation mixing (Li/Ni mixing) defects.…”

“…In this study, we regulated the crystal sizes of single crystal LNO and studied the impact on its electrochemical properties for the first time. Generally, increasing the particle size accompanies high cation mixing defects in Ni-rich layered oxides . However, here, we used a molten salt synthesis method to form single-crystal LNO so that the synthesis process can retain similar cation mixing defects at high temperatures.…”

Dual-functional boron-modification on a cobalt-free single-crystal layered cathode for high-voltage lithium-ion batteries

“…12,13 Several strategies have been employed to solve the above challenges such as increasing the charge cut-off voltage and Ni content. 14 Although increasing the charge cut-off voltage can promote the capacity, stress-induced anisotropic volume shrinkage at deep SOC contributes to severe inter-and intragranular micro-cracking. 15 On the other hand, increasing Ni content in the cathode can deliver higher specic capacity.…”