Electrochemical Characterization of Li1.07V0.83Fe0.1O2 ANODE Material for Li-ION Batteries

INTRODUCTION
Recently a novel compounds based on layered LiV_1-yM_yO₂ (M = Li, Fe, Cr) were found to be promising anode materials for Li-ion technology [1-3], as they exhibit long low-voltage plateau vs. metallic lithium, and higher volumetric capacity than commonly used graphite-based anode materials.
This work presents synthesis and evaluation of electrochemical properties of Li_1.07V_0.83Fe_0.1O₂, in particular open circuit voltage (OCV) and XRD analysis at different discharge (lithium content) stages.

EXPERIMENTAL
Li_1.07V_0.83Fe_0.1O₂ was synthesized using a high-temperature solid-state reaction method with Li₂CO₃, V₂O₃ and Fe₂O₃ taken as substrates. Stoichiometric amounts of reactants were milled in a high efficiency mill. Obtained powder was pressed into pellets and sintered in two steps: 1) at 800 °C for 10 h in Ar and 2) at 1050 °C for 12 h in 5 vol.% of H₂ in Ar, followed by quenching.
Structural studies were performed in 10-110° range with CuKα radiation using Panalytical Empyrean diffractometer, followed by Rietveld refinement of identified structures.
Electrical conductivity was measured using 4-probe AC technique in -60°C to 70°C temperature range.
Electrochemical studies were done in Li/Li⁺/ Li_1.07V_0.83Fe_0.1O₂ cells constructed using CR2032-type containers. 1M solution of LiPF₆in EC/DEC (in 1:1 ratio) was used as the electrolyte. For the positive electrode powder of active material was used (mass ≈ 50mg). OCV values were assumed as voltages of batteries after discharging to designated compositions followed by at least 24 h of relaxation.

RESULTS AND DISCUSSION
XRD analysis shown that the material is single phase and exhibits layered R-3m α-NaFeO₂ type structure.
Electrical conductivity values are almost two order of magnitude higher than for materials with no iron substitution.
Discharge characteristics upon load shown step-like character, distinctly different than in Li_1.07V_0.93O₂with shorter and right-shifted low voltage plateau.

ACKNOWLEDGMENT
This work was supported by NCN grant no. NCN 2011/02/A/ST5/00447.

REFERENCES

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[3] X. Ma, G. Hautier, A. Jain, R. Doe, G. Ceder, J. Electrochem. Soc., 160 (2013) A279-A284.