One-step bulk and surface co-modification of LiNi0.8Co0.15Al0.05O2 cathode material towards excellent long-term cyclability

Abstract

In order to improve the cycling stability of nickel-rich LiNi0.8Co0.15Al0.05O2 (NCA) cathode material for lithium-ion battery applications, a sulfur-modified NCA cathode material with bulk and surface co-modification is prepared by sol−gel method through addition of a very small amount of lithium sulfide (Li2S) as the sulfur-containing additive, and characterized in comparison with the pristine NCA material. Physical characterizations reveal that during the calcination process, some of the introduced S2− enter the layered oxide lattice to replace oxygen, while some of the introduced S2− are oxidized into a thin layer of Li2SO4 coated on the surface of the primary nanoparticles of the layered oxide. Doping of sulfur anion in bulk phase obviously reduces the content of Ni2+ and the degree of cation mixing. The electrochemical results demonstrate that the co-modified material has excellent long-term cycling stability and obviously improved storage stability. For example, when it is repeatedly cycled at 1C rate for 1100 cycles, its specific capacity is decreased from 145.0 to 102.1 mAh g−1, with capacity retention of 70.4%. The significantly improved cyclability is attributed to the enhanced structural stability owing to the reduced cation mixing and the improved electrode/electrolyte interfacial stability due to the surface modification.