Preparation And Performance Research Of Biocarbon Coated LiFePO₄ Cathode Materials

Lithium iron phosphate?LiFePO₄?is regared as a kind of prospective cathode material,which is used in electronic devices and hybrid electric vehicles.H owever,the material has low electronic conductivity an d Li-ion conductivity because of the structure of LiFePO₄.Some researches show that this problem can be solved to synthesize a carbon coating on LiFePO₄ particles.Currently,the process of carbon coating is complex that need to sinter again,and the coating effect is not well.According to the biomineralization assembly concept,good carbon coating LiFePO₄/C composites are successfully obtained using common and inexperience yeast cells as biocarbon source.And this thesis systematically researched the effect of density of yeast and p H value of precursor solution on electrochemical performance of the electrode materials.The mainly contents and results are as follows:1.LiFePO₄/C composites are successfully obtained via an biomimetic sol-gel method.Then,we research the effect of density of yeast for prepared samples.The results show that the LiFePO₄/C composites can be prepared under four ki nds density of yeast conditions,and the morphology of samples have some changes,which have a great effect on electrochemical performance.When the density of yeast cells is 20 g/L,the LiFePO₄ particles are microspheres that have a good distribution,the size of LiFePO₄ particles are about 100-300 nm.A carbon layer is formed on the surface and the layer is about 20.37 nm.The electrochemical tests show that electrochemical performance of LiFePO₄/C prepared with yeast cells is better than LiFePO₄/C prepared without yeast cells.2.LiFePO₄/C composites are successfully obtained via an effective and controllable biomimetic hydrothermal method using yeast cells as biocarbon.Comparing with four samples prepared by different density of yeast cells,it finds that the LiFePO₄/C materials are successfully synthesized.The results show when the density of yeast cells is 20 g/L,most of particles are microspheres and a minority partiicles are blockages,the blockages are filling in pore space between two microspheres that can effectively reduce electronic transmission path and enhance electrochemical performance.The discharge capacity maintains 158.7 m Ah/g at 0.1C that is the best one,which is obviously higher than the di scharge capacity?124.7m Ah/g?of LiFePO₄ prepared without yeast cells and the stability of battery is wonderful.3.The LiFePO4/C composites are prepared under the condition of p H=3,5,7,8,9.We research the effect of p H value on morphology and electrochemical performance.It finds that LiFePO4/C is successfully prepared under different p H values,and the morphology and electrochemical performance of different samples have obvious changes.When the p H is 8,the electrochemical performance is best and the stability of battery is good.