Font Size: a A A

Preparation Of LiFePO4 Nanowires As Cathode Material Of Rechargeable Lithium-ion Battery

Posted on:2011-02-03Degree:MasterType:Thesis
Country:ChinaCandidate:Y TianFull Text:PDF
GTID:2121360305971374Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Olivine-structured LiFePO4, due to its advantages such as excellent electrochemical capability, high theoretical specific capacity(170 mAh/g) and voltage(about 3.4V versus Li/Li+), inexpensive, nontoxic, environmentally friendly, is considered as the best cathode material of lithium-ion battery. But low electronic conductivity, ionic conductivity and discharge capability in large rate of LiFePO4 limit its business application. Nanoparticles have good performance in charge and recharge of large rate because of large surface area and short ion-migration distance, but there is a problem that utilization rate of active materials is relatively low. Nanowires own these advantages too; this problem can be resolved by preparing nanowires. There are few reports about Preparation of LiFePO4 nanowires now. Preparation method is a key factor impacting its application. Therefore, sol-gel templates method was mention In this paper .Porous anodized aluminum oxide (AAO) template was prepared by using two-step anodization in oxalic acid under different conditions (oxidation voltage, oxidation time, oxidation temperature, Electrolyte concentration and pore-widening time etc). Formation mechanism of AAO templates was discussed too. It was found that AAO templates prepared in different electrolyte have different aperture, porosity and regularity. when oxidation voltage increase from 40 V to 100 V, Aperture increase from 30 nm to 90 nm, and thickness of AAO templates increase from 20μm to 120μm, pore density do not change; when oxidation time grow from 4 h to 10 h, Aperture increase from 56 nm to 78 nm, and thickness of AAO templates increase from 32μm to 82μm; when oxidation temperature raise from 5℃to 15℃, Aperture increase from 70 nm to 81 nm, and thickness increase from 63μm to 74μm, there was not apparent difference in thickness and regularity of AAO templates; there was not apparent impact on aperture, pore density and regularity of AAO templates prepared in electrolyte (0.3-0.5mol/L) of different concentration; the best pore-widening time is between 30 min and 60 min.template prepared in 0.3 mol/L oxalic acid, oxidation voltage at 40 V-60 V, under 0℃, have a good surface morphology after oxidation of 8 h and pore-widening of 1 h. Aperture is among 70-90 nm, thickness is 70μm. It can be used to prepare One-dimensional nanowries.Fe(NO3)3·9H2O,Li2CO3,NH4H2PO4,citric acid, ethylene glycol were used as raw material to prepare LiFePO4 by through sol-gel method. It was found that product was impact by sintered temputure and atmosphere. Product sintered at 700℃in (90%N2+10%H2) mixed atmosphere is pure LiFePO4.Two methods in filled AAO template were compared in preparing LiFePO4 nanowires, dipping method and vacuum adsorption. Concentration and fill-times impact mainly fillrate in diapping method. Fillrate increase when fill-times and concentration increase. Fillrate was 30% using dipping method in 0.8 mol/L sol(concentration of Fe3+), there are little of LiFePO4 in pores; Concentration, fill-times and vacuum impact mainly fillrate in vacuum adsorption, Fillrate can be improved by increasing fill-times, sol concentration and vacuum. Fillrate can be up to 90% by using vacuum adsorption, there are whole nanowires in pores. If concentration is too high or dilute, AAO templates will bend in sintering process and will affect the next filling. SEM indicated diameter of LiFePO4 nanowires depends on the diameter of micro-porous; the length of nanowires depends on the thickness of the AAO templates.
Keywords/Search Tags:lithium-ion batteries, cathode material, sol-gel-template method, LiFePO4, nanowires
PDF Full Text Request
Related items