Synthesis characterization and improved electrochemical performance of Li2FeSiO4/C as cathode for lithium-ion battery by metal doping

In this paper, Li2FeSi0.98M0.02O4/C(M= Mg, Zn, Co, Mn, Ni) was synthesized as cathode material for lithium ion battery by solid-state method. The results show that the materials doped with Mg and Zn at the Si-sites have good initial discharge capacity. Then Li2FeSi1-xMxO4/C(M= Mg, Zn; x= 0.01, 0.02, 0.03, 0.05) were also synthesized via solid-state method. It is concluded that Li2FeSi0.99Mg0.01O4/C and Li2FeSi0.98Zn0.02O4/C have better initial discharge capacity which is 125 mAh/g and 166.2 mAh/g, respectively. The capacity of Li2Fe0.98Zn0.02SiO4/C is 157.3 mAh/g after 10 cycles at 0.1C, and the capacity retention rate is 94.6%. The Li+ diffusion coefficient of Li2FeSi0.98Zn0.02O4/C is higher than that of pure phase materials by one order of magnitude. The Li2FeSi0.99Mg0.01O4/C and Li2FeSi0.98Zn0.02O4/C were tested by XRD and SEM. XRD patterns indicate that the crystal structure of Li2FeSiO4 is not changed after being doped with metal ion at the Si-site. The SEM image indicates that no obvious agglomeration is detected in these materials. Li2FeSi0.98Zn0.02O4/C processes better electrochemical performance analyzed by EDS. XPS and FT-IR spectra. The data prove that Si4+ is successfully replaced by Zn2+ in the crystal structure of Li2FeSiO4.