Enhanced Electrochemical and Thermal Stabilities of Li[Ni 0.88 Co 0.09 Al 0.03 ]O 2 Cathode Material by La 4 NiLiO 8 Coating for Li–Ion Batteries

Organo-Soluble Decanoic Acid-Modified Ni-Rich Cathode Material LiNi0.90Co0.07Mn0.03O2 for Lithium-Ion Batteries

Ni-rich layered oxides as cathode materials deliver a higher capacity than those used currently, in hopes of improving the energy density of Li-ion batteries. However, the surface residual alkali and the interfacial parasitic reactions caused by the rich nickel bring a series of problems such as surface slurrying, structure deterioration, mechanical fracture, and capacity decay. Herein, different from the common surface coating strategies with inorganics, an organo-soluble acid modification approach is proposed to meet the challenges. For LiNi_0.90Co_0.07Mn_0.03O₂ (NCM90), decanoic acid can react with the residual lithium salts on the surface to form an organic lithium salt-dominant modification layer. During cycling, an organic lithium-involved cathode/electrolyte interface (CEI) layer is rapidly formed. Specially, the solubility of decanoic acid in the organic electrolyte makes the CEI layer keep strong interaction with NCM90, thin but effective. Consequently, the modified NCM90 exhibits notable performances in terms of structural stability, mechanical integrity, and capacity retention.

Elucidating the Effect of the Dopant Ionic Radius on the Structure and Electrochemical Performance of Ni-Rich Layered Oxides for Lithium-Ion Batteries

The merits of Ni-rich layered oxide cathodes in specific capacity and material cost accelerate their practical applications in electric vehicles and grid energy storage. However, detrimental structural deterioration occurs inevitably during long-term cycling, leading to potential instability and capacity decay of the cathodes. In this work, we investigate the effect of the doped cation radius on the electrochemical performance and structural stability of Ni-rich cathode materials by doping with Mg and Ca ions in LiNi_0.8Co_0.1Mn_0.1O₂. The results reveal that an increase in the doping ion radius can enlarge the interlayer spacing but lead to the collapse of the layered structure if the ion radius is too large, which undermines the cycling stability of the cathode material. Compared with the Ca-doped sample and the pristine material, Mg-doped LiNi_0.8Co_0.1Mn_0.1O₂ presents improved structural stability and superior thermal stability due to the pillar and glue roles of medium-sized Mg ions in the lithium layer. The results of this study suggest that a suitable ionic radius of the dopant is critical for stabilizing the structure and improving the electrochemical properties of Ni-rich layered oxide cathode materials.