Enhanced conversion reaction of Na-Cu-PO₃ via amorpholization and carbon-coating for large Na storage

Conversion-type cathodes have a higher theoretical capacity compared to intercalation-type cathodes due to the use of more transition metal cations. However, their sluggish kinetics and low operation voltage hinder their practical application in the industry, resulting in low specific capacity. To address these issues, we prepare an amorphous carbon-coated Cu(PO₃)₂ nanocomposite, and evaluate its electrochemical performance under rechargeable Na-ion battery system. At a current density of 24 mA/g, it achieves a large specific capacity of ∼232 mAh/g with an average operation voltage of ∼2.0 V (vs. Na⁺/Na). Furthermore, the amorphous carbon-coated Cu(PO₃)₂ nanocomposite exhibits a cycle retention of ∼90% compared to the initial capacity after 100 cycles. In contrast, bare Cu(PO₃)₂ shows poor electrochemical performance under the same conditions. Various experimental measurements have demonstrated that the amorphous carbon-coated Cu(PO₃)₂ nanocomposite exhibits a reversible and smooth conversion reaction of Cu(PO₃)₂ phase in the rechargeable Na-ion battery system.