The Research On Iron Phosphates Materials As Cathode For Lithium Batteries

Much attention has been devoted to the iron phosphates materials due to its low cost, superior safety, environmental benignity, rich source of raw materials, excellent electrochemical properties and other important advantages. There is no doubt that the iron phosphates materials are appealing cathode materials for lithium-ion batteries, however, there still exist several drawbacks, for example, the low electronic conductivity, the poor diffusion of Li+ intercalation-extraction process and careful synthetic procedures, which confined the application of iron phosphates materials. In this paper, several modification methods were conducted, such as the introduction of pores, carbon-coated and electrospinning, systematic studies on iron phosphates materials were conducted by TQ XRD, SEM, TEM, CV, EIS, etc.1 The morphology and electrochemical properties of six practical LiFePO4 samples were studied, compared with others crystal forms (sheet-shaped, layer-shaped, rod-shaped), the LiFePO4 with spherical crystal has more excellent electrochemical properties; the smaller particle size of LiFePO4, the better specific discharge capacity of low rate; when the primary particles of LiFePO4 distribute from tens of nanometers to a few hundred nanometers, the secondary LiFePO4 particles have a average size of about 3um, the specific discharge capacity of high rate is better; the carbon content, the existing forms and packing state of carbon layer has a remarkable influence to the electrochemical properties of active materials.2 Effects of LiFePO4 and activated carbon content on the electrochemical performance of the cathode were investigated by experiments of impedance spectrum, cyclic voltammetry and galvanostatic charge/discharge. The synergy effects of pseudo-capacitance and the electrochemical double layer capacitance reached the greatest benefits when the content of activated carbon was 25%, the electrochemical performance was better than pure activated carbon or LiFePO4, when cycled at 2-4 V with 0.2 C and 30 C, the initial specific discharge capacity spectively reached 163 mAh/g and 60 mAh/g.3 The LiFePO4 was prepared by a two-step high temperature solid-state-reaction synthesis route. The pre-curing temperature of 450℃, the second-curing temperature of 680℃and the second-curing time of 20h were identified as the most appropriate synthesis conditions. The modification research of LiFePO4 was conducted using PAS, the obtained mesoporous structured LiFePO4/C composite material has higher electrochemical properties than the unmodified LiFePO4. When the carbon content is 0.5%, the LiFePO4/C composite material has a good electrochemical property at low discharge rate, which delivered a specific discharge capacity of near 150 mAh·g-1 at 0.25 C; when the carbon content is 10%, the LiFePO4/C composite material has a good electrochemical property at high discharge rate, which delivered a specific discharge capacity of 70 mAh·g-1 at 15 C.4 A pomegranate-structured FePO4/C reunion clusters was synthesized via a combination of electrospinning and high temperature solid-state reaction. The systematic studies on testing and characterization of FePO4/C composites were conducted. The three-dimensional net-like structure covered with porous carbon layers could highly enhance the electrochemical performance of FePO4/C, which delivered a excellent specific discharge capacity of 109 mAh·g-1 at 0.2 C and 39 mAh·g-1 at 10C, and are comparable with the reported nano-level FePO4.