Probing the degradation of LiCoO 2 in batteries subjected to high-voltage cycling with 17 O solid-state NMR spectroscopy.

The long-term cycling stability of LiCoO 2 under high-voltage operation in lithium-ion batteries is still not satisfactory and the mechanism of capacity decay is not well understood. Here we mainly apply 17 O MAS NMR spectroscopy to probe the phase transformation of cycled LiCoO 2 cathodes in both liquid cells and solid cells. It turns out that deterioration into the spinel phase is the main cause.