The Na₃V₂(PO₄)₂F₃/Carbon Na-Ion Battery: Its Performance Understanding as Deduced from Differential Voltage Analysis

The Na 3 V 2 (PO 4 ) 2 F 3 /Carbon Na-ion battery technology is appealing because of its high energy and power density, hence the need to assess its viability under practical operation. Here we provide a comprehensive understanding of its storage and cycling performances in various electrolytes and at different temperatures via a through differential voltage ( dV/dQ ) analysis of the data obtained from coin and pouch cells. The cells show excellent long-term cycling performance (capacity decay less than 0.020 mAh g −1 per cycle at 1C rate whatever the electrolytes), but suffer at 55°C from copious self-discharge stemming from either reduction or oxidization of electrolytes. We could deduce, from monitoring side reactions rate as a function of temperature, the activation energies of 34 and 29 kJ mol −1 for the parasitic reactions proceeding at the anode and cathode side, respectively. We hope our analysis protocol to be widely implemented for the fundamental investigation of side reactions between electrode and electrolyte interface in Na-ion battery; a must for optimizing battery performances via the screening of various electrolyte formulations.