Unmodified α-LiFe5O8 as potential anode material of lithium ion battery and the revelation of conversion mechanism.

Spinel structured α-LiFe 5 O 8 were prepared via ball milling combined with a straightforward solid-phase method, using Fe 2 O 3 and Li 2 CO 3 as the raw materials. The material maintained a stable capacity of 440 mAh g−1 after 200 cycles at 900 mA g−1 with Coulomb efficiency more than 95 % and also showed facile lithium ion diffusion dynamics. The calculated diffusion coefficient of α-LiFe5O8 ranged around 10−10-10−12 cm2 s−1. Diffusion controlled contribution was dominant over capacitive contribution in the sweeping range 0.1–1.5 mV s−1. A new intercalation-decomposition-conversion mechanism was proposed on the basis that there existed a small pit at the initial stage of the discharge plateau and a significantly low initial discharge plateau voltage was observed compared with the followed discharge cycles. Based on the DFT calculations and the phase diagram of the Li–Fe–O system, we supposed that for the initial discharge of the material, after 1 mol of lithium ion intercalation per unit formula, α-LiFe 5 O 8 decomposed to LiFeO 2 and Fe 3 O 4. The followed discharge was the conversion of both LiFeO 2 and Fe 3 O 4 to metal Fe and Li 2 O. Thereafter, the system cycled between Fe 2 O 3 at the fully charged state and metal Fe and Li 2 O at the fully discharged state. Li–Fe–O phase diagram used to disclose the conversion mechanism. [Display omitted] • Unmodified α-LiFe 5 O 8 show good electro-chemical performance. • Li+ transportation kinetics reveals the features of fast ion conductor. • A new intercalation-decomposition-conversion mechanism was proposed. [ABSTRACT FROM AUTHOR]