Top-down synthesis of muscle-inspired alluaudite Na2+2xFe2-x(SO4)3/SWNT spindle as a high-rate and high-potential cathode for sodium-ion batteries

The tailoring of materials into bio-inspired structures is triggering unprecedented innovations. Muscle tissue is composed of myofibrils and densely wired blood vessels; it is a perfect model for designing high-performance electrode materials that have the advantage of fast mass transport and superior durability. We design a top-down strategy as a facile approach to tailor the alluaudite Na2+2xFe2-x(SO4)(3) into a muscle-like spindle. A precipitation process is employed to prepare the hydrated "top" precursor, which is subjected to dehydration and phase transformation to obtain the "down" product. The alluaudite sulfate nanoparticles closely anchor on the single-wall carbon nanotubes (SWNT), and they together aggregate into microscale particles in the shape of spindles. The Na2+2xFe2-x(SO4)(3)/SWNT composite as a whole copies the morphology and function of muscle tissue. Taking advantage of its 3D conductive framework and porous structure, the composite achieves fast electron/ion transport and sodium intercalation. Moreover, the single-phase reaction mechanism during sodium intercalation is beneficial to its cycling property. It exhibits such desirable electrochemical performance as an operating potential as high as similar to 3.8 V and a high-rate capability, which achieves a capacity retention of 92% after 100 cycles at 5C. The muscle-inspired architecture makes electrode materials favorable for superior electrochemical performance.