An electron energy loss spectroscopy and electron diffraction study of the Pmnb polymorph of Li2MnSiO4

[Display omitted] ► EELS spectroscopy and electron diffraction of Pmnb polymorph of Li2MnSiO4. ► SAED showed a non-uniform loss of crystallinity in delithiated material. ► Evidence for non-uniform lithium extraction in the cathode from EELS data. ► O K-edge changes possibly linked to O charge compensation for lithium loss. The Mn valency and the crystallinity of Li2MnSiO4 cathodes (Pmnb form) were examined with electron energy-loss spectroscopy (EELS) and selected area electron diffraction (SAED) both before and after electrochemical lithium extraction. A decrease in the crystallinity of the delithiated charged cathode particles compared to the as-prepared material was observed. The decrease in crystallinity varied from particle to particle. EELS analysis showed that the non-uniform decrease in crystallinity was due to a non-uniform extraction of lithium from the particles. The observed decrease in discharge capacity of the Pmnb polymorph of Li2MnSiO4 with cycling was attributed to the progressive loss of crystallinity and the structural collapse of Li diffusion pathways.