A vanadium-based oxide-phosphate-pyrophosphate framework as a 4 V electrode material for K-ion batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Potassium-ion batteries (KIBs) are attractive for grid-scale energy storage due to potassium's abundance and unique electrochemical properties.
• Vanadium-based polyanionic compounds offer high working voltages and structural stability, crucial for long cycle life in KIB cathodes.

Purpose of the Study:

• To investigate K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇) as a 4V-class positive electrode material for non-aqueous KIBs.
• To explore the synthesis, electrochemical performance, and structural evolution of this novel cathode material.

Main Methods:

• Synthesis of K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇) via pyrolysis of a metal-organic precursor at 500 °C.
• Electrochemical evaluation including charge/discharge cycling in a highly concentrated electrolyte.
• Operando and ex situ powder X-ray diffraction (PXRD) for structural analysis during cycling.

Main Results:

• The material reversibly stores 2.7 mol of potassium at a discharge voltage of ~4.03 V vs. K.
• PXRD studies confirmed a reversible two-phase reaction mechanism for potassium ion extraction/insertion.
• Exceptional cycling stability was observed over 100 cycles with minimal capacity degradation and only ~1.2% volume change.

Conclusions:

• K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇) is a promising 4V-class cathode for KIBs, demonstrating high voltage and excellent structural stability.
• The robust polyanionic framework ensures long-term cycling performance, making it suitable for energy storage.
• The material's ability to accommodate large potassium ions with minimal volume change is key to its stability.