The effects of sodium additive on Li_1.17Ni_0.10Co_0.10Mn_0.63O₂ for lithium ion batteries

Highlights: • High manganese content cathode material with a new ratio of transition metal ions. • Sodium ions are successfully introduced into Li_1.17Ni_0.01Co_0.01Mn_0.63O₂. • Sodium additive induces a secondary phase with the structure of Na_0.7MnO_2.05. • The secondary phase improves the cycling stability and rate capability. - Abstract: Li_1.17−xNa_xNi_0.01Co_0.01Mn_0.63O₂ (x = 0, 0.02, 0.04, 0.06 and 0.08) cathode materials have been synthesized via carbonate co-precipitation method followed by a solid state reaction. The elementary composition, crystal structure features and electrochemical properties of the powders are studied in detail using inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), galvanostatic charge–discharge test and electrochemical impedance spectra (EIS). XRD patterns show that the additive sodium causes the formation of the secondary phase with the structure of Na_0.7MnO_2.05 and does not enter into the Li_1.17Ni_0.10Co_0.10Mn_0.63O₂ lattice. Electrochemical results show that sodium additive samples demonstrate an improved rate performance in comparison with the bare sample, which can be attributed to the enhanced electron conductivity and lithium ion diffusion. In contrast, the material with x = 0.06 has the best electrochemical property, in terms of large reversible capacity, prolonged cycling stability and excellent rate capability