In technologically important LiNi 1−x−y Mn x Co y O 2 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 0.4 Mn 0.4 Co 0.2 O 2 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 0.4 Mn 0.4 Co 0.2 O 2 , as shown by soft X-ray absorption spectroscopy experiments. The improved high-voltage cycling behaviour exhibited by cells containing these cathodes demonstrates the importance of controlling LiNi 1−x−y Mn x Co y O 2 surface chemistry for successful development of highenergy lithium ion batteries.

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