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⁺, PO₄^3-, 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.