Nanowormlike Li₂FeSiO₄–C Composites as Lithium-Ion Battery Cathodes with Superior High-Rate Capability

Nanoworm-like Li2FeSiO4-C composites are synthesized using triblock copolymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), EO20PO70EO20) as the structure directing agent (SDA) and under the effects of ethanol. As a polar nonaqueous cosolvent, ethanol has effects on the self-organization behavior of Pluronic P123 in water, which determines the final morphologies of the Li2FeSiO4-C composites synthesized. Li2FeSiO4-C composite nanoparticles are obtained if no ethanol is added into the system during the synthesis process. When tested as lithium-ion battery cathodes, the Li2FeSiO4-C nanoworms show superior electrochemical performances. At the rate of 1 C (1 C=166 mA g(-1)) the discharge capacity of the Li2FeSiO4-C nanoworms can reach 166 mAh g(-1) in the voltage window of 1.5-4.8 V at room temperature. At the rates of 5, 10, and 20 C, the discharge capacities of the Li2FeSiO4-C nanoworms can stabilize at 120, 110, and 90 mAh g(-1), respectively, and do not show obvious declines after hundreds of cycles. This performance of the Li2FeSiO4-C nanoworms at high rates is better than that of the Li2FeSiO4-C nanoparticles synthesized and many other Li2FeSiO4/C composites reported in the literature. The excellent electrochemical performances of the Li2FeSiO4-C nanoworms are believed to be related to the small sizes of the Li2FeSiO4 nanocrystals inside the nanoworms and the carbon that coats and embeds the nanocrystals.