Synthesis of strontium hexaferrite nanoplates and the enhancement of their electrochemical performance by Zn2+ doping for high-rate and long-life lithium-ion batteries

Abstract

Hexagonal structured strontium hexaferrite (SrFe₁₂O₁₉) nanoplates with diameters of ca. 0.6–2.5 μm and thicknesses of 40–60 nm have been successfully synthesized by adjusting the Fe/Sr ratios via a solvothermal process followed by annealing. Zn²⁺-Doped strontium hexaferrite nanoplates were fabricated as above, except that zinc was also added. The as-prepared Zn²⁺-doped SrFe₁₂O₁₉ and SrFe₁₂O₁₉ nanoplates were then evaluated as anode materials for lithium-ion batteries (LIBs) for the first time. The electrochemical measurements showed that both the Zn²⁺-doped SrFe₁₂O₁₉ and SrFe₁₂O₁₉ nanoplates had high reversible capacities of 1015.8 mA h g⁻¹ and 456.5 mA h g⁻¹, respectively, after 270 cycles at a current density of 100 mA g⁻¹. In addition, both samples exhibited good high-rate cycling performances; in particular, the Zn²⁺-doped SrFe₁₂O₁₉ nanoplates delivered 457.6 mA h g⁻¹ at a high current density of 500 mA g⁻¹ after 700 cycles. Therefore, strontium hexaferrites could be investigated as a candidate for long-life lithium-ion batteries. The superior cycling performances exhibited by Zn²⁺-doped SrFe₁₂O₁₉ are ascribed to the zinc-doping, which can efficiently enhance the electronic conductivity and improve the lithium ion diffusion of SrFe₁₂O₁₉; this was confirmed by impedance measurements.