Research Of The New LiFePO₄/C Composite Cathode Materials

By using ATP as a phosphorous source, a nucleating agent, a structural template anda biocarbon source, we successfully synthesized the lithium iron phosphate cathodematerial (LiFePO4/C): the mesoporous biocarbon nanowire coating LiFePO4withHEQDs (MBCNW-LFP-HEQDs), cage-like LiFePO4shell@biocarbon coremicrospheres.The metabolic energy systems power your work—and your day. Adenosinetriphosphate (ATP) is considered by biologists to be the energy currency of life. It isthe high-energy biomolecule, which takes the role of an energy carrier of essentially alllife forms.By using a multifunctional high-energy biomolecule—adenosine triphosphate(ATP)we fabricated high-energy quantum dots (HEQDs) with a feature size of less than10nm， then use high-energy phosphate bonds in crystal structure of LiFePO4nanoparticles and synthesized the mesoporous biocarbon nanowire coated LiFePO4with HEQDs synthesized the mesoporous biocarbon nanowire coated LiFePO4withHEQDs(MBCNW-LFP-HEQDs).The analysis results of HRTEM, AFM, BET and XPS clearly demonstrated thatHEGDs were homogeneously formed inside ultra-thin LiFePO4nanosheet (<10nm)and mesoporous (14nm) biocarbon nanowire network structure was coated on thesurface of nanosheet. The XRD results indicat that the crystal growth of LiFePO4nanosheet is preferential in the [010] direction, resulting in increase of theircrystallinity and distance of crystal faces, decrease of their strain and latticeexpansion than that of a usual LiFePO4nanoparticle (10～100nm)(ULFPNP, theULFPNP sample is from Peking University leading science and technology industryco., LTD). In LiFePO4nanoparticle, HEQDs result in more storage sites of Li+ions andeasier transfer kinetics of electrons and lithium ions, where the kinetic transformationpath between LiFePO4and FePO4is fundamentally different from the path deducedfrom its equilibrium phase diagram of bulk materials. Unlike the ULFPNP cathode, theMBCNW-LFP-HEQDs cathode shows a best high first discharge capacity of197mAh/g at the0.1C rate, which is higher than the theoretical capacity of LiFePO4(170mAh g-1). After56cycles at varied current rates:0.1C,0.5C,1C,5C and10C, thiscathode still delivered a high discharge capacity of180mAh/g (at the0.1C rate) andthe ultra-high coulombic efficiency with an average efficiency of almost100%. It should be noticed that as long as the current rate reverses back low current rate, the cellcapacity can still be higher than the theoretical capacity of LiFePO4.This is attributedto the quanlum tunneling of HEGDs in LiFePO4nanoparticle and better percolation ofmesoporous biocarbon nanowire coating network structure.The LFP@BC/SCMs were prepared by using hydrothermal and carbon thermalreduction method with ATP as biotemplate. The synthesis of the electrochemicalperformance is close to the theoretical specific capacity of the sample. Importantly,after the75cycles at different rate, its discharge energy density was able to recover to95%of the initial reversible values, implying their good reversibility.