Detrimental MnPOF and MnF formation on LiMnO in the 3 V region

In this work, we studied the electrochemistry of LMO using thin-film electrodes in LiClO 4 and LiPF 6 based electrolyte solutions. The thin-film system allows the removal of all passive components, leaving only the LMO with a single well-defined electrode/electrolyte interface, making it an ideal system to study interactions at this interface. We observed a peculiar decomposition reaction when using a LiPF 6 salt based electrolyte solution, as soon as the LMO electrode was discharged below 3 V. This decomposition reaction led to the formation of a highly ionically resistive interphase layer, greatly affecting the insertion kinetics into the active material. This was in stark contrast to the LiClO 4 based electrolyte solutions, which showed ideal insertion behaviour. Through the combination of elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS) we determined that the reaction stems from a direct interaction between the LiPF 6 salt and tetragonal Li 2 Mn 2 O 4 . The 3 V region of LMO is inhibited when using LiPF 6 based electrolytes, due to the formation of a LiF/MnF 2 decomposition layer. This layer is formed by direct interaction between LiPF 6 and Li 2 Mn 2 O 4 , as demonstrated using a thin-film model electrode.