Optimization of lithium content in LiFePO₄ for superior electrochemical performance: the role of impurities.

ABSTRACT: Carbon coated Li _x FePO₄ samples with systematically varying Li-content (x = 1, 1.02, 1.05, 1.10) have been synthesized via a sol-gel route. The Li : Fe ratios for the as-synthesized samples is found to vary from ∼0.96 : 1 to 1.16 : 1 as determined by the proton induced gamma emission (PIGE) technique (for Li) and ICP-OES (for Fe). According to Mössbauer spectroscopy, sample Li_1.05FePO₄ has the highest content (i.e., ∼91.5%) of the actual electroactive phase (viz., crystalline LiFePO₄), followed by samples Li_1.02FePO₄, Li_1.1FePO₄ and LiFePO₄; with the remaining content being primarily Fe-containing impurities, including a conducting FeP phase in samples Li_1.02FePO₄ and Li_1.05FePO₄. Electrodes based on sample Li_1.05FePO₄ show the best electrochemical performance in all aspects, retaining ∼150 mA h g^-1 after 100 charge/discharge cycles at C/2, followed by sample Li_1.02FePO₄ (∼140 mA h g^-1), LiFePO₄ (∼120 mA h g^-1) and Li_1.10FePO₄ (∼115 mA h g^-1). Furthermore, the electrodes based on sample Li_1.05FePO₄ retain ∼107 mA h g^-1 even at a high current density of 5C. Impedance spectra indicate that electrodes based on sample Li_1.05FePO₄ possess the least charge transfer resistance, plausibly having influence from the compositional aspects. This low charge transfer resistance is partially responsible for the superior electrochemical behavior of that specific composition.

SUBMITTER: Halankar KK 

PROVIDER: S-EPMC9076985 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature