Effect of Cationic (Na(+)) and Anionic (F(−)) Co-Doping on the Structural and Electrochemical Properties of LiNi(1/3)Mn(1/3)Co(1/3)O(2) Cathode Material for Lithium-Ion Batteries

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na(+)/F(−) co-doping on the structure and electrochemical performance of LiNi(1/3)Mn(1/3)Co(1/3)O(2). The co-doped Li(1-z)Na(z)Ni(1/3)Mn(1/3)Co(1/3)O(2-z)F(z) (z = 0.025) and pristine LiNi(1/3)Co(1/3)Mn(1/3)O(2) materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na(+) and F(−) dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi(1/3)Mn(1/3)Co(1/3)O(2) electrode delivered an initial specific capacity of 142 mAh g(−1) at a 1C rate (178 mAh g(−1) at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate.