Study on Preparation of Cathode Material of Lithium Iron Phosphate Battery by Self-Craning Thermal Method

The cathode material of carbon-coated lithium iron phosphate(LiFePO4/C)lithium-ion battery was synthesized by a self-winding thermal method.The material was characterized by X-ray diffraction(XRD)and scanning electron microscope(SEM).The electrochemical properties of LiFePO4/C materials were measured by the constant current charge-discharge method and cyclic voltammetry.The results showed that the LiFePO4/C material prepared by the self-propagating heat method has a typical olivine crystal structure,and the product had fine grains and good electrochemical properties.The optimal sintering temperature is 700℃,the sintering time is 24 h,the particle size of the lithium iron phosphate material is about 300 nm,and the maximum discharge capacity is 121 mAh/g at 0.1 C rate.

Enhancing the Activity of N/C Catalyst for Oxygen Reduction Reaction by Fluorination

The synthesis of non-metal carbon catalysts with high catalytic activity for ORR(oxygen reduction reaction)in acidic media is a great challenge in the field of PEMFC(proton exchange membrane fuel cells).In this research,N-and F-codoped carbon catalyst with high performance was synthesized from ZIF-8 and NH4F,which are easily prepared structure and common chemical,respectively.The as-prepared catalyst has a high surface area of 789 m2/g and micro-porosity of~2 nm,facilitating more active sites to the ORR and O2 mass transfer in the diffusion of the catalyst matrix,respectively.The prepared N/C(NH4F)catalyst exhibited an onset potential of 0.94 V(vs.RHE)and a half-wave potential of 0.65 V in 0.1 M HClO4 solution.It also showed excellent durability in the cycling test of 10,000 times and a degradation shift of half-wave potential 70 mV was observed.Its diffusion-limiting current reached 5.85 mA/cm2 next to the theoretic value of 6 mA/cm2,suggesting that it has plenty of active sites for ORR,which could be attributed to fluorine introduction into the N/C catalyst.It proved that the introduction of fluorine into the structure of the N/C catalyst fine-tunes the Lewis basic sites of the carbon atoms adjacent to pyridinic and graphitic nitrogen species,facilitating the adsorption of oxygen molecules in the initial step of the ORR.The correlation between the N/C catalyst activity and the fluorination provides new insight into the ORR catalyst design.