Systematic investigation on Cadmium-incorporation in Li2FeSiO4/C cathode material for lithium-ion batteries.

Cadmium-incorporated Li2FeSiO4/C composites have been successfully synthesized by a solid-state reaction assisted with refluxing. The effect and mechanism of Cd-modification on the electrochemical performance of Li2FeSiO4/C were investigated in detail by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectra, transmission electron microscopy, positron annihilation lifetime spectroscopy and Doppler broadening spectrum, and electrochemical measurements. The results show that Cd not only exists in an amorphous state of CdO on the surface of LFS particles, but also enters into the crystal lattice of LFS. Positron annihilation lifetime spectroscopy and Doppler broadening spectrum analyses verify that Cd-incorporation increases the defect concentration and the electronic conductivity of LFS, thus improve the Li(+)-ion diffusion process. Furthermore, our electrochemical measurements verify that an appropriate amount of Cd-incorporation can achieve a satisfied electrochemical performance for LFS/C cathode material.

Reduced graphene oxide modified Li2FeSiO4/C composite with enhanced electrochemical performance as cathode material for lithium ion batteries.

Reduced graphene oxide modified Li2FeSiO4/C (LFS/(C+rGO)) composite is successfully synthesized by a citric-acid-based sol-gel method and evaluated as cathode material for lithium ion batteries. The LFS/(C+rGO) shows an improved electronic conductivity due to the conductive network formed by reduced graphene oxide nanosheets and amorphous carbon in particles. Electrochemical impedance spectroscopy results indicate an increased diffusion coefficient of lithium ions (2.4 × 10(-11) cm(2) s(-1)) for LFS/(C+rGO) electrode. Compared with LFS with only amorphous carbon, the LFS/(C+rGO) electrode exhibits higher capacity and better cycling stability. It delivers a reversible capacity of 178 mAh g(-1) with a capacity retention ratio of 94.5% after 40 cycles at 0.1 C, and an average capacity of 119 mAh g(-1) at 2 C. The improved performance can be contributed to the reduced crystal size, good particle dispersion, and the improved conductive network between LFS particles.