Mechanochemical Upcycling of Zinc Recovered From Spent Zinc–Carbon Batteries Into ZnP 2 /Carbon Composite Anodes for Sodium‐Ion Batteries

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Abstract
Sodium‐ion batteries (SIBs) have attracted increasing attention as promising alternatives to lithium‐ion batteries for large‐scale energy storage owing to the natural abundance and low cost of sodium resources. However, the development of high‐capacity and durable anode materials still hindered by volume expansion and structural degradation of alloying‐ and conversion‐type materials during repeated sodiation/desodiation. Herein, a sustainable mechanochemical upcycling strategy is proposed to convert zinc recovered from spent zinc–carbon batteries into recycled zinc phosphide/carbon (rZnP 2 /C) composite anodes through a two‐step high‐energy ball‐milling process. In this approach, zinc recovered from waste zinc–carbon batteries was converted into zinc phosphide and subsequently composited with hard carbon and carbon nanotubes (CNTs). Hard carbon served as a buffering matrix to mitigate the volume expansion of zinc phosphide, while CNT formed continuous conductive networks that improved the electrical conductivity of the composite. By optimizing the hard carbon content, the rZnP 2 /C‐2 composite exhibited the best electrochemical performance, delivering an initial discharge capacity of 469.19 mAh g –1 at 100 mA g –1 , retaining 269.37 mAh g –1 at a high current density of 1500 mA g –1 , and maintaining a reversible capacity of 128.50 mAh g –1 after 1000 cycles at 500 mA g –1 . This work demonstrates an effective mechanochemical upcycling strategy for transforming spent zinc–carbon batteries into value‐added ZnP 2 ‐based composite anodes, providing a sustainable route toward high‐performance SIBs and battery waste valorization.

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