Nano-Li2FeSiO4/C composites (LFS/C-325 and LFS/C-221) and nano-Li2FeSiO4 (LFS-325 and LFS-221) with controlled porosity were prepared from the nano-fumed silicas with similar particle size and different porosity. N2 adsorption/desorption analysis reveals that the porosity of nano-Li2FeSiO4/C composites and nano-Li2FeSiO4 can be tuned by the choosing nano -fumed silica and LFS/C-325 possess the highest specific surface area among the four samples. XRD indicates that both LFS/C-325 and LFS/C-221 are crystalline powders with monoclinic Li2FeSiO4 of P21. FTIR spectra show that Li-O and Si-O bonds are existed in the four samples. SEM images demonstrate that LFS/C-325 and LFS/C-221 have similar particle sizes in the range of 20 ~ 25 nm, which are distinctly smaller than those of LFS-325 and LFS-221. LFS/C-325 features the smallest particle size and largest specific area, which enables LFS/C-325 to exhibit the best electrochemical performance. The initial discharge capacity of LFS/C-325 is as high as 185.2 mAh g−1 at 0.1 C.
Improving the rate performance is still a major challenge for Li 2 FeSiO 4 cathode material for Li-ion battery. Herein, hollow spherical Li 2 FeSiO 4 /C microscale particles, consisting of carbon-coated primary nanoparticles (20–40 nm) have been fabricated by a spray drying-assisted method. The particle size of spherical Li 2 FeSiO 4 /C is 1–5 μm, which is suitable for commercial application. When used as a cathode material for Li-ion battery, the as-prepared Li 2 FeSiO 4 /C composite with 16.7 wt.% carbon exhibits a high discharge capacity of 165 mAh g − 1 at 0.2 C rate. At 0.5 C, 5 C and 10 C rates, the capacities of 151 mAh g − 1 , 111 mAh g − 1 , and 96 mAh g − 1 are observed, respectively, indicating superior rate performance. Meantime, good cycling stability is achieved with a capacity retention of 94.5% at a high current density of 2 C after 100 cycles. The excellent electrochemical performance is mainly ascribed to the improved ionic/electronic conductivity arising from the hollow spherical structure and carbon-coated primary nanoparticles . The spray drying process shows a great potential for the large scale production of high quality Li 2 FeSiO 4 /C composite.
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