Metal segregation in hierarchically structured cathode materials for high-energy lithium batteries

DOI:

10.1038/nenergy.2015.4

Authors:

Feng Lin, Dennis Nordlund, Yuyi Li, Matthew K. Quan, Lei Cheng, Tsu‐Chien Weng, Yijin Liu, Huolin L. Xin, Marca M. Doeff

Abstract:

In technologically important LiNi_1-x-yMn_xCo_yO₂ cathode materials, surface reconstruction from a layered to a rock-salt structure is commonly observed under a variety of operating conditions, particularly in Ni-rich compositions. This phenomenon contributes to poor high-voltage cycling performance, impeding attempts to improve the energy density by widening the potential window at which these electrodes operate. Here, using advanced nano-tomography and transmission electron microscopy techniques, we show that hierarchically structured LiNi_0.4Mn_0.4Co_0.2O₂ spherical particles, made by a simple spray pyrolysis method, exhibit local elemental segregation such that surfaces are Ni-poor and Mn-rich. The tailored surfaces result in superior resistance to surface reconstruction compared with those of conventional LiNi_0.4Mn_0.4Co_0.2O₂, as shown by soft X-ray absorption spectroscopy experiments. In conclusion, the improved high-voltage cycling behaviour exhibited by cells containing these cathodes demonstrates the importance of controlling LiNi_1-x-yMn_xCo_yO₂ surface chemistry for successful development of high-energy lithium ion batteries.