Organophosphonic acid as precursor to prepare LiFePO4/carbon nanocomposites for high-power lithium ion batteries

• Amino tris(methylene phosphonic acid) is served as a novel precursor for LiFePO4/C.
• Nano-sized and high-purity LiFePO4/C composites are obtained by a quasi-sol–gel route.
• Core-shell structured LiFePO4/C nanocomposites are fabricated by further introducing sucrose.
• Superior electrochemical performance is observed in the organophosphorus-synthesized LiFePO4/C.

Amino tris(methylene phosphonic acid) (ATMP) is selected as phosphorus and carbon co-source for the synthesis of uniformly nano-sized LiFePO4/C by a quasi-sol–gel method. This strategy using ATMP instead of conventional NH4H2PO4 supplies two advantages: firstly, ATMP in situ chelates Li+ onto its framework and subsequently binds with FeC2O4 in aqueous solution, forming a molecule-scale homogeneous precursor which can obviously improve the purity of LiFePO4. Secondly, the organic carbon contained in ATMP can form uniformly distributed conductive carbon networks among LiFePO4 particles after calcination, which improves the electrical conductivity. The resultant LiFePO4/C with 1.1 wt.% carbon achieves a higher discharge capacity than those of LiFePO4 and LiFePO4/C prepared with inorganic NH4H2PO4. Moreover, core-shell structured LiFePO4/C nanocomposites are also fabricated by further introducing sucrose into the synthesis system. The high-quality carbon shell effectively hinders the LiFePO4 particle growth and aggregation under high-temperature treatment, which further enhances the electrical conductivity and lithium-ion diffusion, resulting in the improved electrochemical performance with excellent cycle stability (the optimum discharge capacity of 158.6 mAh g−1 at 0.1 C and 138.4 mAh g−1 at 2 C). The high purity, nanosize and core-shell structure of LiFePO4/C composites yielded by the novel synthesis strategy account for their outstanding electrochemical performance in high-power lithium-ion batteries.

LiFePO4/C nanocomposites were prepared by a quasi-sol–gel method with the use of organophosphonic acid, exhibiting improved electrochemical performance with excellent cycle stability.Figure optionsDownload as PowerPoint slide