![]() So far, cathode materials have received considerable attention because they are considered to be a primary determinant for increasing cell energy and power densities 1, 2, 3, 4. In a lithium ion cell, the energy and power delivery is achieved by shuttling lithium ions between positive and negative electrodes, where the active materials undergo redox reactions using electrons from an external circuit within certain voltage windows. The development of lithium ion battery technologies has spurred major breakthroughs in portable electronics, power tools, electric vehicles, and grid energy storage. The improved high-voltage cycling behaviour exhibited by cells containing these cathodes demonstrates the importance of controlling LiNi 1− x− yMn xCo yO 2 surface chemistry for successful development of high-energy lithium ion batteries. The tailored surfaces result in superior resistance to surface reconstruction compared with those of conventional LiNi 0.4Mn 0.4Co 0.2O 2, as shown by soft X-ray absorption spectroscopy experiments. Here, using advanced nano-tomography and transmission electron microscopy techniques, we show that hierarchically structured LiNi 0.4Mn 0.4Co 0.2O 2 spherical particles, made by a simple spray pyrolysis method, exhibit local elemental segregation such that surfaces are Ni-poor and Mn-rich. ![]() 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. In technologically important LiNi 1− x− yMn xCo yO 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. ![]()
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