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1、Bio-synthesis participated mechanism of mesoporous LiFePO4/Cnanocomposite microspheres for lithium ion batteryXudong Zhang,aWen He,*aYuanzheng Yue,abRuiming Wang,cJianxing Shen,aShujiang Liu,aJingyun Ma,aMei Liaand Fengxiu XuaReceived 28th May 2012,Accepted 4th August 2012DOI:10.1039/c2jm33425aIn th
2、is paper we report a bio-synthesis route towards controllable mesoporous LiFePO4/Cnanocomposite microspheres(MP-LFP/C-NC-MS).During the synthesis bakers yeast cells were usedas both structure templates and a carbon source.Then we clarify the bio-deposited and biomolecularself-assembly mechanisms of
3、iron phosphate by means of the Langmuir biosorption isotherms of theyeast biomass in iron ion solution and by applying the model of heterogeneous nucleation of ironphosphate in a yeast cell.The MP-LFP/C-NC-MS show a uniform size distribution(4.76 mm),high tapdensity(1.74 g cm?3)and a large specific
4、surface area(203 m2g?1).The microsphere is composed ofdensely aggregatednanoparticles andinterconnectednanopores.The openmesoporous structureallowslithium ions to easily penetrate into the spheres,while a thorough coating of the biocarbon networkon the surface of the LiFePO4nanoparticles facilitates
5、 lithium ion and electron diffusion.The MP-LFP/C-NC-MS have a high discharge capacity of about 158.5 mA h g?1at a current density of 0.1 C,discharge capacity of 122 mA h g?1at 10 C,and high capacity retention rate.Therefore the mesoporousmicrospheres are an ideal type of cathode-active materials for
6、 making high-power Li-ion batteries.IntroductionNanobiotechnology is one of the most powerful routes fororganizing a nanoscale system with the highest possible accuracyand control.Such control will lead to programmable chemicalsynthesis.1,2Biological systems can produce extraordinary inor-ganic stru
7、ctures and morphologies.Both amorphous and crys-talline materials can be synthesized via biomineralization inbiologicalsystems.35Comparedwithotherfabricationprocesses,the advantages of the biomineralization processes arethat molecular control of the structure,size,aggregation,morphologyandcrystallog
8、raphicorientationofinorganicmaterials can be conducted and materials can be synthesized inan environmentally benign system.Bakers yeast Saccharomycescerevisiae is a ubiquitous unicellular eukaryotic microorganism.It has spherical or elliptical morphology,large surface area andabundant surface charge
9、 within a broad range of pH and ionicstrength.It provides nucleation centers and immobilizes theparticles,and hence establishes a mesoporous microspherestructure.The nucleation and growth of inorganic crystals aremostly controlled by gene and biomolecule in biomineralizationprocesses.6Both the biomi
10、neralization mechanism and thepotential application of bacterial magnetosomes in biotech-nology have been studied through molecular and geneticapproaches.7However,there are still a number of open questionsregarding the mechanism of formation of minerals in biologicalsystems.As a major advantage over
11、 other structural templates,yeast cell is non-toxic,easy to degrade and does not causepollution.Very recently,we have established an approach,bywhich we are able to prepare advanced mesoporous materialsusing yeast cells as biotemplates under ambient conditions.8Lithium iron phosphate(LiFePO4)is a pr
12、omising candidate ofcathode materials for making next generation lithium ionbatteries.In recent years,the mesoporous LiFePO4/C nano-composite microspheres(MP-LFP/C-NC-MS)for high powerapplications have attracted extensive interest from researchers.Note that MP-LFP/C-NC-MS is a kind of nanocomposite
13、sincecarbon is attached to the surface of the LiFePO4nanoparticles.Mesoporous microspheres synthesized by a number of methodsincluding traditional solid state,hydrothermal and solgelmethods,have been found to possess good electrochemicalperformance.9Here we report a bio-synthesis participatedapproac
14、h of high-performance MP-LFP/C-NC-MS.A crucialaShandongProvincialKeyLaboratoryofProcessingandTestingTechnology of Glass and Functional Ceramics,Key Laboratory ofAmorphous and Polycrystalline Materials,Department of MaterialsScience and Engineering,Shandong Polytechnic University,Jinan,China.E-mail:;
15、Fax:+86 531 89631518;Tel:+86 531 89631018bSection of Chemistry,Aalborg University,Aalborg,Denmark.E-mail:yybio.auu.dk;Fax:+45 96350558;Tel:+45 96358522cShandong Key Laboratory of Fermentation Engineering,ShandongPolytechnic University,Jinan,China.E-mail:;Tel:+86 531 89631076 Electronic supplementary
16、 information(ESI)available:Particle sizedistribution analysis,performance analysis of synthesized materials,cycle stability at high current ratio and cyclic voltammogram analysesof the MP-LFP/C-NC-MS cathode.See DOI:10.1039/c2jm33425a19948|J.Mater.Chem.,2012,22,1994819956This journal is The Royal So
17、ciety of Chemistry 2012Dynamic Article LinksCJournal ofMaterials ChemistryCite this:J.Mater.Chem.,2012,22,19948www.rsc.org/materialsPAPERDownloaded by Aalborg Universitetsbibliotek on 29 August 2012Published on 07 August 2012 on http:/pubs.rsc.org|doi:10.1039/C2JM33425AView Online/Journal Homepage/T
18、able of Contents for this issuestep of this approach is to use low cost microbe yeast cells astemplates and a carbon source.Our goal is to obtain a funda-mental understanding of the bio-deposited and biomolecularself-assembly mechanism during synthesis.We find that the ironphosphate replicates the o
19、rdered hierarchical structures of bak-ers yeast cells.In addition,the bakers yeast cell provides anelectric carbon network that forms due to heat treatment andself-doping into iron phosphate.These microspheres can bedensely packed together,giving a relatively high tap density.Simultaneously,both the
20、 primary nanoparticles and the meso-porous structure provide a huge surface that enhances the ratecapability of the lithium insertion/deinsertion reaction.ExperimentalSynthesis methodThe reagents used in this work include Fe(NO3)39H2O(99%,Aldrich,Sinopharm Chemical Reagent Co.,Ltd.),C2H2O4andLi2CO3(
21、99%,Aldrich,Sinopharm Chemical Reagent Co.,Ltd.),NH4H2PO4(99%,Tianjin Bodi Chemical Co.,Ltd.),glucosemonohydrate(C6H12O6$H2O)(Tianjin Bodi Chemical Co.,Ltd.)and bakers yeast cells(instant dry yeast,Angel Yeast Co.,Ltd.).The MP-LFP/C-NC-MS materials were prepared by a bio-synthesis method.The general
22、 procedure of this experiment isdescribed as follows.Instant dry yeast(10,20,30,40 and 50 g)wascultivated in1000mL glucoseaqueoussolution for 30 min at37?C,respectively,resulting in a uniform bio-emulsion.The purified yeastcellswereobtainedbycentrifugingandwashingwithdistilledwater.The Fe(NO3)39H2O
23、was dissolved in deionized water(0.5 molL?1),and added to the purified yeast cell solution with magneticstirring at room temperature for 2 h.Then 0.5 mol L?1NH4H2PO4was added to the Feyeast cell mixture solution in a stoichiometricratio of Fe:P 1:1.A yellow colored solution with depositedFePO4wasobt
24、ained.Themixturesolutionwascontinuouslystirredfor 3 h and mineralized for 24 h at room temperature.Finally,thedeposited FePO4was centrifuged and washed several times withdistilledwater,andthendriedinanovenat120?Cfor24h.ThedryFePO4/yeast products were mixed with Li2CO3and C2H2O4on thebasis of the sto
25、ichiometric ratios(Fe:Li:C2H2O4 1:1:2)for3 h through a dry ball-milling process.Then,the mixtures weredried in ambient conditions overnight and heat-treated at varioustemperatures in N2atmosphere for 6 h.The heating rates were keptrelatively low,at 5?C min?1,to avoid structural collapse from fastcry
26、stallization.The final product obtained was in the form of blackpowder.The pure LiFePO4sample was synthesized by using theabove-described method,but without using bakers yeast celltemplate at 650?C for 6 h.Biosorption experimentsBiosorption experiments were carried out by using flameabsorption spect
27、roscopy to obtain residual Fe3+concentrations.Standard synthetic solutions were prepared in our laboratoriesusing iron nitrate nonahydrate with concentrations of 1,2 and3 g L?1Fe3+ions in solution.The factors that affect the bio-sorption rate were examined in a batch system.Three parame-ters,i.e.,bi
28、omass concentration(yeast cell),Fe3+concentration,and contact time,were examined regarding their effect on thebiosorption of Fe3+ions from solutions.All experiments werecarried out with purified yeast cell suspension in flasks in anincubator at 37?0.5?C with constant shaking to createoptimum conditi
29、ons(contact time,pH,initial Fe3+concentra-tion and yeast dose).The content of the flasks was thereafterfiltered and the filtrates were diluted(10 mL was pipetted into100 mL volumetric flask and filled to the mark with distilledwater).The flame absorption spectroscopy was used to analyzethe residual
30、Fe3+concentration.The Fe3+adsorbed by yeast cellbiomass was calculated as follows:Fe3mass%adsorbed by yeast biomassCi?CfCi?100%(1)where Ciand Cfare the initial and final Fe3+concentration,respectively.Material characterizationX-Ray diffraction(XRD)measurements were performed at aPANalytical XPert PR
31、O X-ray diffractometer with Cu Ka(l 0.15418 nm)incident radiation.The diffraction patterns werecollected at room temperature in the 2q ranges of 1.1 to 8?,and 10to 60?,respectively.X-Ray photoelectron spectroscopy(XPS)measurements were conducted on a Kratos Axis Ultra DLD(delayline detector)spectrom
32、eter equipped with a monochromatic Al KaX-ray source(1486.6 eV).All binding energies were referenced totheC1speakat284.8eVofthesurfaceadventitiouscarbon.TheN2adsorptiondesorptionisotherms(NADI)weretaken at77K usinga computer controlled sorption analyzer(Micromeritics,Gemini V2.0)operating in the con
33、tinuous mode.The samples were degassedat 200?C for 10 h prior to the measurement.BrunauerEmmettTeller(BET)surface area was calculated using experimental pointsatarelativepressureofP/P0 0.050.25.Theporesizedistributionwas calculated from the desorption branch of the isothermby usingthe BarretJoynerHa
34、lenda(BJH)model.The particle size distri-bution was measured by a laser diffraction particle size analyzer(Beckman Coulter LS 13320).The morphology and porous struc-tures of the products were characterized by scanning electronmicroscopy(SEM),transmission electron microscopy(TEM)andhigh-resolutiontra
35、nsmissionelectronmicroscopy(HRTEM).SEMimages of the samples were collected by a Quanta 200 scanningelectron microscope with an accelerating voltage of 20 kV.TEM(JEM-100X,Japan)operating at 100 kV was employed to char-acterize the morphologies of the samples.HRTEM was carried outon a Philips Tecnai 2
36、0U-TWIN microscope,working at 300 kV.Preparation of electrodes and electrochemical testingCathodeelectrodeswereconstructedusingamixtureofthepreparedpowders(85 wt%),Carbon Black(5 wt%),and polyvinylidenefluoride(PVDF 10 wt%Aldrich)in N-methyl-2-pyrrolidone(NMP)to form a slurry.After the ethanol evapo
37、rated,the mixture wasrolled into a sheet of 0.1 mm thickness.The obtained sheet waspressed into a piece of Al foil and dried in an oven at 120?Covernight under vacuum.The dried tape was then punched tomake round plates with a diameter of 10.0 mm and a filmthickness of 50 mm as the cathode electrodes
38、(58 mg loading).The electrodes were dried again at 120?C for 5 h in a vacuumprior to use.The electrochemical performance was tested afterassembling coin-type half-cells(2016R-type)with a Li electrodeThis journal is The Royal Society of Chemistry 2012J.Mater.Chem.,2012,22,1994819956|19949Downloaded b
39、y Aalborg Universitetsbibliotek on 29 August 2012Published on 07 August 2012 on http:/pubs.rsc.org|doi:10.1039/C2JM33425AView Onlineand ethyl carbonate/dimethyl carbonate(EC/DMC)(1:1 vol%)with 1 M LiPF6salt in an Ar-filled glove box(H2O and O2 1),linear(RL 1),favorable(0 RL 1)or irreversible(RL 0).1
40、0The RLwas found to be 0.75 to 0.17 for the initialconcentrations of 1 to 3 g L?1Fe3+,indicating that the adsorp-tion of Fe3+by yeast cells was favorable.The sorption of iron byyeast biomass was very rapid for 1 g L?1solutions and equilib-rium was achieved within 23 min and the percentage adsorbed i
41、s86%(Fig.1b).It is clear from the results that the time requiredfor maximum uptake of Fe3+by yeast was dependent on theinitial Fe3+concentrations.The amount of yeast biomassrequired to attain the maximum sorption capacity for 1 g L?1Fe3+solutions was 9 g L?1(Fig.1c).The Langmuir adsorptionisotherm s
42、tudy has revealed that yeast biomass tends to adsorbmore Fe3+ions at high concentrations and for shorter contactperiods.Hydrophilic anion groups on the cell surface can improve themineralization ability of yeast cells and regulate crystal nucle-ation and growth.11When iron nitrate(Fe(NO3)39H2O)aqueo
43、ussolution was added into the yeast solution,the ferric ions werecombined with the negatively charged COO?and OPO32?groups on biomolecules in yeast cells,and were self-assembled tothe yeast cells surface by electrostatic interaction.This self-assembly induced the formation of an iron phosphate layer
44、 onthe surface of the yeast cell wall.Evidence of Fe3+adsorptioninteractions of the yeast cells was obtained by using S94Hmicroelectrophoresis and Meiji ML9420 binocular polarizingmicroscopy.Yeast cells move towards the anode,and its zetapotential is?30.5,indicating that yeast cells themselves arene
45、gatively charged(Fig.1d).The superfluous negative chargesare propitious to bond Fe3+to protein macromolecules.12Whenyeast cells adsorb Fe3+,the surface of yeast cells is positivelycharged as shown in Fig.1f and its zeta potential is 17.6.Fromthe surface charge change of the samples,we can infer that
46、 theyeast cells interact with Fe3+ions.Observing the considerablelevel change(an optical parameter under plane polarized light)ofyeast cell wall surface before(Fig.1e)and after(Fig.1g)theFig.1(a)Langmuir adsorption isotherm for Fe3+biosorption atoptimum conditions(pH 3,37?C,120 min at 100 rpm).(b)Bi
47、o-sorptions of Fe3+from solution at different Fe3+concentrations(inpercentage),pH 3,by 30 g L?1yeast biomass as related to the time ofcontact at 100 rpm.(c)Effect of the quantity of yeast biomass on thebiosorption of Fe3+from solutions at different iron ion concentrations,pH 3 for contact time of 12
48、0 min at 100 rpm.(d)Micro electrophoresisimage and(e)polarizing microscopy image of purified yeast cells.(f)Micro electrophoresis image,(g)polarizing microscopy image and(h),(i)TEM images after contact interaction equilibrium of yeast cell(12 g L?1)with Fe3+ions(the initial concentrations of 1 g L?1
49、)at optimumconditions(pH 3,37?C).19950|J.Mater.Chem.,2012,22,1994819956This journal is The Royal Society of Chemistry 2012Downloaded by Aalborg Universitetsbibliotek on 29 August 2012Published on 07 August 2012 on http:/pubs.rsc.org|doi:10.1039/C2JM33425AView Onlineinteraction equilibrium with Fe3+b
50、y polarizing microscopy,weconfirm that ferric ions are accumulated on the yeast cell wall.Biodeposition of Fe3+occurs on the yeast cell wall surface andinside the cell,and this is seen from the contrast change in theTEM image of the yeast cell structure(Fig.1h and i).This meansthat yeast cells accum