Sustainable Upcycling of Industrial By-Products Into High-Rate and Stable Sulfate-Based Cathode for Sodium-Ion Batteries.

Transforming industrial by-products into high-value materials is crucial for sustainable development. The high-value conversion of industrial sodium sulfate (Na₂SO₄) by-product into a high-performance Na2.56Fe1.72(SO₄)₃/carbon (NFSO/KB) composite cathode material for sodium-ion batteries (SIBs) is studied. The cathode with a robust skeleton composed of [Fe₂O₁₀] dimers and [SO₄] tetrahedra ensures excellent structural stability, and the unique three-dimensional (3D) framework facilitates rapid Na⁺ diffusion. Theoretical and structural analyses reveal that NFSO/KB possesses an ultralow Na⁺ migration barrier and a highly reversible reaction mechanism with minimal volume change (1.21%) during cycling. As a result, the cathode delivers a reversible capacity of 84.26 mAh g⁻¹ at 10 mA g⁻¹, with a high operating voltage of 3.8 V (vs. Na/Na⁺). Moreover, it demonstrates a remarkable rate capability of 55.77 mAh g⁻¹ at 1000 mA g⁻¹ and exceptionally long cycle life (89.13% capacity retention after 3000 cycles). This work establishes a new paradigm for industrial by-products upcycling and provides a promising design strategy for low-cost, high-rate, and long-lifespan cathodes for SIBs.