The origin of stability and high Co 2+/3+ redox utilization for FePO 4 -coated LiCo 0.90 Ti 0.05 PO 4 /MWCNT nanocomposites for 5 V class lithium ion batteries.

Highly-dispersed 10 wt% FePO 4 (FP)-coated LiCo 0.90 Ti 0.05 PO 4 (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) Ti 4+ -substitution increases the utilization of Co redox (capacity increase) in LCP crystals by suppressing the Co 3 O 4 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.