In-situ construction of porous carbon substrate from sodium carboxymethyl cellulose boosting ultra-long lifespan for Na3V2(PO4)3 cathode material

Abstract

Na3V2(PO4)3 (trisodium divanadium (III) tris (orthophosphate [NVP]), the cathode material for sodium ion batteries, faces several challenges, such as lower intrinsic electronic and ionic conductivities, which hinder its commercial viability. In this work, NVP system is modified by introducing sodium carboxymethyl cellulose (Na CMC) to achieve triple modification effects: sodium-rich, cross-linked carbon coating network, and carbon layer surface modification. Meanwhile, CMC, as a porous carbon substrate with large pores, provides a fast migration channel for Na+. Similarly, carbon nanotubes (CNTs) grown from the active particles become the connecting carriers between the active particles, thus effectively improving the electron transport. Notably, the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images after cycling verify the stabilized porous structure of the Na3V2(PO4)3/C@0.7wt.%CMC@CNTs (0.7wt.%CMC@CNTs) composite. Distinctively, the modified 0.7wt.%CMC@CNTs reveals a capacity of 111.4 mAh/g at 0.1 C. It submits a high value of 105.0 mAh/g at 1 C with a capacity retention rate of 84.10% after 1,000 cycles. Even at 15 C, it still releases 86.6 mAh/g with a low capacity decay rate of 0.0230% per cycle after 3,600 cycles. Notably, its capacity retention reaches an astonishing 96.09% after 13,000 cycles at an ultra-high rate of 80 C.