Regulation of MIL-88B(Fe) to design FeS2 core-shelled hollow sphere as high-rate anode for a full sodium-ion battery

Abstract

Rich reserves, lower price, and high theoretical capacity of FeS2 as a promising anode for SIBs can’t cover up its low Na+ diffusion kinetic and severe volume expansion. Herein, the core-shelled hollow sphere FeS2 (CHS-FeS2) was synthesized using modified MIL-88B(Fe) as templates to promote Na+ diffusion kinetic and release volume expansion. In the preparation process of MIL-88B(Fe), the citric acid participated in coordination with Fe3+ to adjust the concentration of Fe3+ and regulate MIL-88B(Fe) curvature, thus constructing MIL-88B(Fe) with different nanostructures. After calcination, the Fe2O3 with different nanostructures was achieved due to the different combustion rates of MIL-88B(Fe) catalyzed by Fe3+ and different diffusion amounts of Fe3+ to the surface of MIL-88B(Fe). The FeS2 with different nanostructures were formed after sulfuration. Especially, the uniform sphere-like MIL-88B(Fe) with suited Fe3+ concentration was achieved when the citric acid was 0.05 g, leading to the formation of CHS-FeS2 after calcination and sulfuration. Additionally, as the electrode for SIBs in a half-cell system, the CHS-FeS2 exhibited a high specific capacity of 617.5 mAh/g at 0.5 A/g, maintained 546.5 mAh/g after 100 cycles, and still 224 mAh/g was retained at a current density of 20 A/g. Furthermore, the full cell of CHS-FeS2//NVP@C achieved a high specific capacity of 279.3 mAh/g at 0.05 A/g, a specific capacity of 156.7 mAh/g at 1.0 A/g, and 87.8 % of initial capacity after 100 cycles at 0.1 A/g, reflecting the excellent cycling stability and rate capability. We believe this paper provides an inspiration for constructing hollow structural materials with rich reserves, lower prices, excellent cycling stability, and rate performance.