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.