科研之友
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摘要
Strontium-doped Li2FeSiO4/C is prepared by using the sol-gel method with soluble Li, Fe, Si, and Sr sources. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements are carried out to determine the crystal structures, morphologies, particle sizes, and chemical valence states of the resulting products. Rietveld refinement confirms that strontium-doped Li2FeSiO4 has a monoclinic P2(1)/n structure and that a strontium cation occupies the Fe site in the lattice. The grain size of strontium-doped Li2FeSiO4 is approximately 20 nm, and the nanoparticles are interconnected tightly with amorphous carbon layers. As the cathode material of a lithium-ion battery, strontium-doped Li2FeSiO4/C delivers a high discharge capacity of 181 mAh g(-1) at a rate of 0.5 C. The capacity retention after the 100th cycle reaches 76%, which increases by 7 percentage points compared with Li2FeSiO4/C. The cathode exhibits good rate performance, with corresponding discharge capacities of 165, 145, and 119 mAh g(-1) for 1, 2, and 5 C rates, respectively. By analyzing the electrochemical impedance spectra, it can be concluded that strontium cation doping helps to increase the Li+ diffusion capability and weakens side reactions between the electrode and electrolyte. In summary, the improvement of the electrochemical performance can be attributed to the strengthened crystal structure stability during charging and discharging after strontium cation doping.
