Synthesis And Electrochemical Performance Of Li₂FeSiO₄ Active Material For Lithium Ion Battery

Lithium-ion battery has been used widely in portable electronics because of the advantages of high energy density and environmentally friendliness. However, the most key factor limiting the further improvment of energy density is the lower capacity of anode materials, so the researches on anode materials become a hotpot. Nowadays a new material named Li2 Fe Si O4 have drawn researchers’ attention due to its low cost, environmental friendly and high theoretical capacity. Hower, its conductivity is low. In this work, we prepared the composites of Li2 Fe Si O4 and different carbon used different Si O2 with different morphology as raw materials, and research on its preparation process and electrochemical performance. The main content in this paper are as follows:(1) Li2 Fe Si O4/C and Li2-xFe Si1-xPxO4/C was successfully obtained using spherical nano-Si O2 as raw materials. The results show that there is impurity Fe2O3 in Li2 Fe Si O4/C, while Li2-xFe Si1-xPxO4/C shows different structure and performance, among which there is no impurity in the product when x=3%. And the discharge capacity of Li1.97 Fe Si0.97P0.03O4/C can reach 179 m Ah g-1 at the electric current density of 10 m A g-1, corresponding to more than one lithium insertion per formula unit. The discharge capacities 3LFS after five cycles were reduced by approximately 8.9%. After five cycles, the specific discharge capacitity reach stable. The discharge capacity retentions after 30 cycles is approximately 94.5% of the corresponding discharge capacities in the sixth cycle. In addition, through exploration it can be fould that there is an autocatalysis process in the reaction, the H2 produced by NH4H2PO4 can improve the reducibility of the system, which preventing the appearance of impurity containing Fe3+.(2) Li1.97 Fe Si0.97P0.03O4/C/G combining two kinds of carbon(G=Graphene) was successfully obtained. In these experiments the amounts of amorphous carbon(C) were decreased, in addition, the amounts and the ways of adding graphene were explored. The results show that the product adding 8 wt.% graphene in the process of ball milling shows the best electrochemical performance. The discharge capacity can reach 150 m Ah g-1 at 0.1C, which is higher than that of product without graphene.(3) Spherical hollow structure-Li2 Fe Si O4/C and hollow structureLi2 Fe Si O4/C/G was prepared using hollow spherical Si O2 as template and raw material. The result shows that there is no impurity in the products and the morphology can inherit that of the template totally. Sample hollow structureLi2 Fe Si O4/C/G shows better rate performance than hollow structure-Li2 Fe Si O4/C.