Demonstrating Oxygen Loss and Associated Structural Reorganization in the Lithium Battery Cathode Li[Ni 0.2 Li 0.2 Mn 0.6 ]O 2

The cathode in rechargeable lithium-ion batteries operates by conventional intercalation; Li+ is extracted from LiCoO2 on charging accompanied by oxidation of Co3+ to Co4+; the process is reversed on discharge. In contrast, Li+ may be extracted from Mn4+-based solids, e.g., Li2MnO3, without oxidation of Mn4+. A mechanism involving simultaneous Li and O removal is often proposed. Here, we demonstrate directly, by in situ differential electrochemical mass spectrometry (DEMS), that O2 is evolved from such Mn4+ -containing compounds, Li[Ni(0.2)Li(0.2)Mn(0.6)]O2, on charging and using powder neutron diffraction show that O loss from the surface is accompanied by diffusion of transition metal ions from surface to…