Sn-stabilized Li-rich layered Li(Li0.17Ni0.25Mn0.58) O2 oxide as a cathode for advanced lithium-ion batteries

Li-rich layered oxides have been intensively investigated as cathodes for high energy lithium-ion batteries. However, oxygen loss from the lattice during the initial charge and gradual structural transformation during cycling can lead to capacity degradation and potential decay of the cathode materials. In this work, Sn4+ is used to partially substitute Mn4+ to prepare a series of Li(Li0.17Ni0.25Mn0.58-xSnx)O-2 (x=0, 0.01, 0.03, and 0.05) samples through a spray-drying method. Structural characterization reveals that the Sn4+ substituted samples with a suitable amount show low cation mixing, indicating an enhanced ordered layer structure. Moreover, the metal-oxygen (M-O) covalency is gradually decreased with increasing Sn4+ amount. It is shown from the initial charge-discharge curves that Sn4+ substituted samples present a shorter charging potential plateau at 4.5 V (vs. Li/Li+), implying that oxidation of the O-2 ion to O-2 is suppressed by Sn4+ substitution and leads to a minor structural change. Among the Sn4+ substituted samples, the Li(Li0.17Ni0.25Mn0.55Sn0.03) O-2 sample exhibits a higher capacity retention of 86% after 400 cycles at 0.1C rate and 92% after 200 cycles at 1C rate, showing excellent cycle stability and high-rate capability as compared with the as-prepared sample. The electrochemical performance improvement can be attributed to the influences of Sn such as enlarging the Li ion diffusion channel due to the large ionic radius of Sn4+ substitution with respect to Mn4+, a higher bonding energy of Sn-O than Mn-O, and weakening the M-O covalency. All the influences are favorable for stabilization of the host lattice in Li-rich layered oxides.