Ultrafast nano-spherical single-crystalline LiMn0.792Fe0.198Mg0.010PO4 solid-solution confined among unbundled interstices of SGCNTs

Abstract

Spherical LiMn_0.792Fe_0.198Mg_0.010PO₄ nanocrystals, which are highly dispersed and encapsulated within the interstices of supergrowth (single-walled) carbon nanotubes (SGCNTs), were successfully synthesized by in situ material processing technology called “ultra-centrifuging (UC) treatment”. TEM images of these LiMn_0.792Fe_0.198Mg_0.010PO₄/SGCNT composites suggest the direct attachment of the LiMn_0.792Fe_0.198Mg_0.010PO₄ nanocrystals (10–40 nm) onto the surface of highly conductive SGCNTs. Mg-doping brought out 10% increase of Li⁺ capacity in Mn sites with 200% increase of Li⁺ diffusivity and 50% decrease of electrical resistance owing to such peculiar “nano–nano LiMn_0.792Fe_0.198Mg_0.010PO₄/SGCNT composites”. The synthesized LiMn_0.792Fe_0.198Mg_0.010PO₄/SGCNT composites overcome the inherent restrictions of one-dimensional diffusion and deliver a high electrochemical capacity density of ca. 54 mA h g⁻¹ per composite (corresponding to 77 mA h g⁻¹ per pure LiMn_0.792Fe_0.198Mg_0.010PO₄) at a high rate of 50 C, while showing excellent cycle life, retaining 84% of the initial capacity over 3000 cycles.