Synthesis Of Cathode Materials LiFePO₄ And Its Electrochemical Properties For Rechargeable Lithium Battery

Olivine LiFePO₄ is considered as the most promising candidate for the nextgeneration cathode materials of lithium batteries after layer LiCoO₂ and spinelLiMn₂O₄, because it has a high theoretical capacity, low price, good cycle stabilityhigh security advantages and is environmentally friendly. The main problem ofLiFePO₄ is low electronic conductivity and low lithium ion diffusivity,which hindersits application in the high power rechargeable battery. It is particularly important touse the optimal means to synthesize well-performance LiFePO₄.In this paper, electrospinning, hydrothermal and adjusted precipitation were usedto synthesize LiFePO₄/C composite, LiFePO₄/C composite prepared byelectrospinning and adjusted precipitation has a high discharge capacity and good rateperformance in aqueous and non- aqueous lithum batteries, comparing to othermethods, hydrothermal method is more sutible for large-scale production consideringlow temperature, simplicity and low costs.We report on a one-dimensional LiFePO₄/C nanowire with fiber structure,LiFePO₄ nano-particles are embedded inside carbon fiber, uniform and continuouscarbon fiber has a high degree of graphite and mesporous structure, which not onlyhelp the penetration of electrolyte to improve lithium-ion diffusion, but also thetransmission of electron. In electrochemical performance test, LiFePO₄/C nanowireshowed good rate performance, The initial discharge capacity is 143 mAh/g at 1C rate,and even 45 mAh/g at 50C. but the poor circulation in aqueous lithum batteries. Over100 cycles at 1C, the electrode retain 74.3% discharge capacity. The main reason isthe improved lithium-ion diffusion coefficient and dissolved oxygen in aqueoussystem.The traditional hydrothermal method was used to synthesize LiFePO₄/Ccomposites, The effects of amounts of the reducer, heat treatment temperatures, in situand ex situ carbon coating on electrochemical properties were investigated. It focus on the effect of feeding sequence on the microstructure and electrochemical properties,and found that LiFePO₄/C composites prepared by the sequential precipitation hasmore smaller particle size and high discharge capacity than product prepared byco-precipitation. In order to reduce the cost of synthesis, we choose cheap ferric ironas raw material to prapare LiFePO₄/C composites. The phase, morphology and poredistribution were characterized by XRD, FESEM, EDS, BET, and thenelectrochemical performances were tested by charge-discharge, cyclic stability, andAC impedance through assembly button batteries.LiFePO₄/C composite is prepared by aqueous precipitation of FePO₄ in a reversemicroemulsion, following carbothermal reduction with glucose as the reducer. Thegood crystal phase were characterized by X-ray diffraction (XRD). SEM and TEMobservations show that prepared materials constituted by secondary agglomerateswith a 100– 800nm particle size and primary particles with the particle size in 100–200 nm range. To some degree, the synthesized LiFePO₄ could inherit themorphology of FePO₄ precursor. The Li/LiFePO₄ cell showed a high initial dischargecapacity of 168.7 mAh/g at C/10 rate, and even 70 mAh/g at 10C. Over 100 cycles at0.5C, the electrode shows excellent cycle performance with less 5% capacity loss. ACimpedance test showed the prepared LiFePO₄/C composite had the more smallercharge and mass transfer resistance.