Synthesis and electrochemical characterization of Cr-doped lithium-rich Li_1.2Ni_0.16Mn_0.56Co_0.08-xCr_xO₂ cathodes

Lithium-rich layer oxide, Li_1.2Ni_0.16Mn_0.56Co_0.08O₂ (NMC), is a potential cathode candidate for high-energy density batteries. Issues such as cycling stability, rate performance, and cost are yet to be overcome before successful commercialization of the material. Here, we report on the synthesis of Cr-doped lithium-rich phases Li_1.2Ni_0.16Mn_0.56Co_0.08-xCr_xO₂ (where x = 0.00, 0.01, and 0.02) (NMC-Cr) by the sol-gel technique. Cr is homogeneously distributed in the crystal structure evidence by elemental mapping measurements. The Cr-doped materials exhibit much better cycling stability with 100% capacity retention versus 44% for the undoped sample after 50 cycles. The Cr-doped samples show excellent electrochemical performance at higher C-rate in comparison with the undoped NMC. The latter shows rapid capacity fading from 220 to 50 mAh g⁻¹ at the 0.1 to 1C rates, respectively. Moreover, the Cr-containing materials do not show significant signs of voltage fading during cycling owing to the stabilization of the crystal lattice by Cr. The electrochemical impedance spectroscopy measurements also indicate the stable cell resistance on cycling for the Cr-doped phases compared to the undoped phase. [Figure not available: see fulltext.]