Biosynthesis Of LiFePO₄ Cathode Materials And Study Of Electrochemical Performance

Designing, fabricating, and integrating nanomaterials are key to transferring nanoscale science into applicable nanotechnology. Many nanomaterials including amorphous and crystal structures are synthesized via biomineralization in biological systems. Amongst various techniques, bionanotechnology is an effective strategy to manufacture a variety of sophisticated inorganic nanomaterials with precise control over their chemical composition, crystal structure, and shape by means of genetic engineering and natural bioassemblies. This provides opportunities to use renewable natural resources to develop high performance lithium-ion batteries (LIBs). For LIBs, reducing the sizes and dimensions of electrode materials can boost Li+ ion and electron transfer in nanostructured electrodes. Recently, bionanotechnology has attracted great interest as a novel tool and approach, and a number of renewable biotemplatebased nanomaterials have been fabricated and used in LIBs.Electrochemical performances of electrode materials were found to be greatly dependent on carbon sources used in synthesis. The carbon coating plays a key role in improving rate capability and cycling retention of electrode materials. Among the different carbon materials, a novel type of mesoporous biocarbon material has shown unique structures and surface chemistry properties and is especially attractive as electrode materials for LIBs from the economical and environmentally friendly points of view. Compared with other fabrication processes, the advantage of bionanotechnology is that it not only yields mesoporous biocarbon materials in environment benign system, produces various nanomaterials with complicated, elaborate, and efficient hierarchical morphologies and even multiple nanoscale assemblies, but also enables control of the structure, size, morphology and crystallographic orientation of inorganic crystals. More importantly, it provides a simple, cost-effective way to use abundant renewable source to develop high-performance lithium battery for alternative energy storage and conversion systems. This development would lead to a significant reduction in the cost of large-scale energy storage, thus accelerating its market penetration.In this paper, the biosynthesis of LiFePO4 cathode materials and its electrochemical performance were investigated. Respectively, by using cotton fibers, spinage chlorophyll and yeast cells as biotemplate, carbon source or nucleating agent, LiFePO4/C nano-compo sites cathode materials with special morphology and crystal structure are synthesized. Accordingly, cotton fibers templated LiFePO4/C nano-composites display the unique crystal structure of LiFePO4/C superlattice, showing the best first discharge capacity of 181 mA h g-1 at the 0.1 C rate, which is higher than the theoretical capacity of LiFePO4(170 mA h g-1). The stacking faulted dislocations of LiFePO4 crystal structure is synthesized by the biotemplating of spinage chlorophyll, boosting the discharge capacity of 101 mA h g-1 at the 10 C rate of the LiFePO4/C nano-composites cathode. By using yest cells as biotemplate, carbon source and nucleating agent, mesoporous microspherical LiFePO4/C composite cathode materials are synthesized. After 75 cycles at varied current rates, this cathode still keeps a high capacity retention of 98%. Finally, the electrochemical performance of Nb doped LiFePO4/C composite cathode materials are investigated, showing that the Nb doping process can relieve cathode polarization and reduce the electrical impedance of the LiFePO4/C composite cathode materials.