Carbon-coated LiTi₂(PO₄)₃: An ideal insertion host for lithium-ion and sodium-ion batteries

We report the extraordinary performance of carbon-coated sodium super ion conductor (NASICON)-type LiTi₂(PO₄)₃ as an ideal host matrix for reversible insertion of both Li and Na ions. The NASICON-type compound was prepared by means of a Pechini-type polymerizable complex method and was subsequently carbon coated. Several characterization techniques such as XRD, thermogravimetric analysis (TGA), field-emission (FE) SEM, TEM, and Raman analysis were used to study the physicochemical properties. Both guest species underwent a two-phase insertion mechanism during the charge/discharge process that was clearly evidenced from galvanostatic and cyclic voltammetric studies. Unlike that of Li (≈1.5 moles of Li), Na insertion exhibits better reversibility (≈1.59 moles of Na) while experiencing a slightly higher capacity fade (≈8 % higher than Li) and polarization (780 mV) than Li. However, excellent rate capability profiles were noted for Na insertion relative to its counterpart Li. Overall, the Na insertion properties were found to be superior relative to Li insertion, which makes carbon-coated NASICON-type LiTi₂(PO₄)₃ hosts attractive for the development of next-generation batteries. A good host: A high-performance insertion-type electrode material, sodium super ion conductor (NASICON)-type carbon-coated LiTi₂(PO₄)₃, is proposed as a prospective host for the reversible accommodation of both Li ⁺ and Na⁺ ions with excellent cyclability and high power capability (see figure).