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An unresolved question for the layered oxides is: what is the optimum value of y in the formula LiNi y Mn y Co 1-2y O 2 for energy storage at moderate reaction rates? Here we report a systematic study of the specific capacity, rate capability and cycle life of Li x-Ni y Mn y Co 1-2y O 2 (y ¼ 0.5, 0.45, 0.4, and 0.333). The voltage of the Li/y ¼ 0.333 couple crosses over those of lower cobalt content for x < 0.55, as the Co redox begins to get involved. This early involvement of cobalt, rather than just Ni, leads to a slightly smaller specific capacity for y ¼ 0.333 than for LiNi y Mn y Co 1-2y O 2 with y > 0.333 when charging above 4 V. Overall the y ¼ 0.4 material has the optimum properties, having the highest theoretical capacity, less of the expensive cobalt and yet rate capabilities and capacity retention comparable to the y ¼ 0.333 material.

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In situ near edge x-ray absorption fine structure spectroscopy (NEXAFS) is performed on LiNbO2 analog memristors to identify the underlying analog resistance modulation mechanism. Empty electronic state gradients in the NEXAFS difference spectra are observed in biased devices indicating a gradual movement of lithium. This movement of lithium supports the assertion that simple ion dopant drift and diffusion dominate the analog memristor’s resistance response. By identifying the physical memristance mechanism in analog LiNbO2 memristors, suggestions are made for additions to the memristor to modify device performance for both neuromorphic computing and memory applications.

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