Understanding the role of Na-doping on Ni-rich layered oxide LiNi0.5Co0.2Mn0.3O2

Na-doped Ni-rich layered oxide LiNi0.5Co0.2Mn0.3O2 cathode materials are synthesized via co-precipitation method in this work. The crystal structure, thermal stability as well as electrochemical performance are studied. Results show that when the Na-doping amount is less than and equal to 2%, the samples can exhibit better electrochemical performance than the parent compound. One reason is that the Na doping can reduce the cationic mixing in the compound, as confirmed by X-Ray powder diffraction (XRD). Beside, results from X-ray photoelectron spectroscopy (XPS) and galvanostatic intermittent titration technique (GITT) show that the introduced sodium can also impact the chemical environment of lithium, making the latter become more easily de-intercalated from the bulk material. However, as the Na-doping amount increases, the electrochemical properties of the samples were deteriorated. Furthermore, results from differential scanning calorimetry (DSC) measurement indicate that the added Na+ is also beneficial for improving the thermal stability of the layered oxide.