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 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 O MAS NMR spectroscopy to probe the phase transformation of cycled LiCoO cathodes in both liquid cells and solid cells. It turns out that deterioration into the spinel phase is the main cause.