Chitosan Derived Carbon Matrix Encapsulated CuP₂ Nanoparticles for Sodium-Ion Storage

Sodium-ion batteries (SIBs) are more feasible for grid-scale applications than their lithium-ion counterparts when abundant sodium resources with an even geographic distribution are taken into consideration. However, developing an anode presents a major challenge since the standard graphite anode shows a limited Na-ion storage capacity. Here we report a CuCl₂/chitosan monolith derived CuP₂/C composite where CuP₂ nanoparticles are uniformly embedded in the carbon matrix. The strong chemical bonding between electron rich groups in chitosan and the heavy metal ion (Cu²⁺) plays a key role for the synthesis of the homogeneous monolithic composite, and chitosan derived carbon prevents Cu and CuP₂ particles from aggregation upon the following thermal reduction and phosphorization. Benefiting from the synergistic effect of small particle size and conductive carbon matrix, the CuP₂/C composite, as an anode for SIBs, delivers a high reversible capacity of 630 mAh/g at a current density of 100 mA/g and a capacity retention ratio of 91% after 200 cycles, while bare CuP₂ shows a rapid capacity decay within 50 cycles.