Investigating the Structure of an Active Material–Carbon Interface in the Monoclinic Li₃V₂(PO₄)₃/C Composite Cathode

A widely adopted strategy to enhance the electronic conductivity of lithium transition metal phosphates is to form a phosphate/C composite by introducing reagents (carbon sources) that can transform to carbon during calcination. In the present work, a systematic study combining X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, solid-state nuclear magnetic resonance, and electrochemical measurements was conducted to investigate how the electrostatic interaction between the functional groups (carboxyl, hydroxyl, etc.) of a carbon source and the building units of Li3V2(PO4)3 (Li+, VO2+, PO43–, etc.) in the original precursor affects the structure of a Li3V2(PO4)3–carbon interface in the final composite. It was demonstrated that the types and concentrations of electronegative functional groups in a carbon source play an important role in controlling not only the morphology of the product but also the composition, crystallinity and microstructure of the Li3V2(PO4)3–carbon interface and, in turn, the electrochemical behavior of the Li3V2(PO4)3/C composite. This study provides guidance on carbon–lithium transition metal phosphate interface design and control.