The origin of stability and high Co2+/3+ redox utilization for FePO4-coated LiCo0.90Ti0.05PO4/MWCNT nanocomposites for 5 V class lithium ion batteries

Abstract

Highly-dispersed 10 wt% FePO₄ (FP)-coated LiCo_0.90Ti_0.05PO₄ (LCTP) was successfully synthesized within a multiwalled carbon nanotube matrix via our original ultracentrifugation process. 10 wt% FP-coated LCTP sample showed a higher discharge capacity of 116 mA h g⁻¹ together with stable cycle performance over 99% of capacity retention at the 100^th cycle in high voltage. A combination of TEM, XRD, XPS, and XAFS analyses suggests that (i) Ti⁴⁺-substitution increases the utilization of Co redox (capacity increase) in LCP crystals by suppressing the Co₃O₄ formation and creating the vacancies in Co sites, and (ii) the FP-coating brought about the Fe enrichment of the surface of LCTP which prevents an irreversible crystal structure change and electrolyte decomposition during cycling, resulting in the stable cycle performance.