Surface yttrium-doping induced by element segregation to suppress oxygen release in Li-rich layered oxide cathodes

Abstract

Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity. Here, we use an element segregation principle to realize a uniform surface doping without capacity sacrifice. On the basis of Hume-Rothery rule, element yttrium is chosen as a candidate dopant to spontaneously segregate at particle surface due to mismatched ionic size. Combined with X-ray photoelectron spectroscopy and electron energy loss spectroscopy mapping, yttrium is demonstrated uniformly distributed on particle surface. More importantly, a significant alleviation of oxygen release after surface doping is detected by operando differential electrochemical mass spectrometry. As a result, the modified sample exhibits improved reversibility of oxygen redox with 82.1% coulombic efficiency and excellent cycle performances with 84.15% capacity retention after 140 cycles. Postmortem analysis by transmission electron microscopy, Raman spectroscopy and X-ray diffraction reveal that the modified sample maintains the layered structure without a significant structure transformation after long cycles. This work provides an effective strategy with a series of elements to meet the industrial application.