Improved Cycling Stability of Na-Doped Cathode Materials Li1.2Ni0.2Mn0.6O2 via a Facile Synthesis

Lithium-ion battery cathode materials Li1.2‑xNaxNi0.2Mn0.6O2 (x = 0, 0.03, 0.05, 0.08, 0.10) were synthesized by introducing Na ions into the Li layer through a facile ball-milling method. XRD results reveal that the cathode materials Li1.2‑xNaxNi0.2Mn0.6O2 display a typical layered structure. The enlarged Li layer spacing was confirmed by the characterization of morphology and structure. The Li1.12Na0.08Ni0.2Mn0.6O2 electrode shows excellent electrochemical performance including high reversible discharge capacity (257 mAh g–1), enhanced rate capability (112 mAh g–1 at 5 C), and superior cycling stability (100% capacity retention after 50 cycles, 96% capacity retention after 100 cycles). The improved electrochemical performance of the Na-LNMO sample compared to the pristine LNMO sample mainly stems from Na doping, which stabilizes the host layered structure by suppressing the phase transformation from a layered to spinel structure during cycling. Moreover, the EIS results also confirm that Na doping effectively decreases the charge transfer resistance and facilitates the Li diffusion of the as-prepared cathode material. This method provides novel insights into enhancing the electrochemical performance and preventing the high-performance layered electrode materials from structural degradation.