LiFePO4150种合成方法汇编及正极结构图

1、 LiFePO4 150种合成方法汇编 大力李 2009-12-61LiFePO4 and C-LiFePO4 were prepared using stoichiometricLi2CO3 (99.95%), FeC2O4H2O (99%), NH4H2PO4 (98%), and glucose(99%). The starting materials were first precalcined at 400 C for6 h in flowing ultra-pure Ar in order to decompose the carbonate,oxalate, and ammoni

2、um. After cooling down, the decomposedmixtures were pressed into pellets ( 20mm, L 10mm, 10 kN) andtransferred to quartz tubes, which were then sealed in vacuum.The vacuum-sealed sampleswere then calcined in amuffle furnace.The quartz tubes with the samples were removed fromthe furnaceand immediatel

3、y put intowater. The product LiFePO4 was obtainedby removal from a broken quartz tube. In this paper, the notationsNC and WQ represent samples prepared by natural cooling and bywater quenching treatment, respectively.参考略2A LiFePO4/carbon compositewas synthesized from stoichiometricquantities of FePO

4、44H2O, LiOHH2O and a proper amount of citric acid. The mixture underwent the following three processes: (i)high-energy ball milling taken by two steps, by primary ball milling(coarse grinding) for 3 h and secondary ball milling (fine grinding)for 6 h with zirconia balls; (ii) spray-drying, and (iii)

5、 thermal treatment under flowing nitrogen at 450 C for 1 h and then at 675 C for 8h.3The FePO4 precursor was prepared as follows. The stoichiometricamounts of H3PO4 and FeNO39H2O were dissolved in distilled water. To obtain the FePO4 colloid, the dissolved aqueous solution was recipitated by adding

6、an NH3 solution of 5 mol L1, under an argon atmosphere, with continuous stirring at 50 C and a pH of 1.02.0. The co-precipitation mixture was then pressure-filtrated at 20MPa, dried under vacuum at 80 C for 6 h, washed, dried again under vacuum at 80 C for 6 h, and ground, yielding the final product

7、.4LiFePO4 was prepared by the solid-state reaction of Li2CO3 (99.9%, Fluka), Fe(II)C2O4 . H2O (99%, Aldrich) and (NH4)2HPO4 (99%, Fluka). To prevent oxidation of the iron, the synthesis was performed under a flow of nitrogen gas. The starting materials were weighed in stoichiometric amounts and homo

8、genized using a mixer. To decompose the oxalate and the phosphate,the mixture was placed in a tubular furnace and heated at 300 C for 20 h. The powder was cooled at room temperature and mixed with high-surface area carbonblack (Ketlen Jack Blak, Akzo Nobel, surface area 1250 m2 g1). After grinding a

9、nd homogenization, the mixture was transferred to the furnace and annealed at 800 C for 16 h under nitrogen flow. After this time,the powder was allowed to cool at room temperature.5LiFePO4 samples were prepared by mixing stoichiometric amounts of(NH4)2HPO4, FeC2O42H2O, and LiF as starting materials

10、; the precursors were dispersed into acetone and then ball milled for 7 h in a planetary mill. The rotatingspeed was 250rpm and the ball to charge weight ratio was 20:1. After evaporating acetone, the mixture was first decomposed at 350 C in a N2 atmosphere for 10 h to allow H2O and NH3 to evolve. T

11、he reagents were then re-ground prior to heating in a sealed tube furnace. The samples were heated at a rate of 2 Cmin1 to the temperatures ranging from 650 C to 800C, respectively, under a stream of a mixtureof 95% Ar + 5% H2. The materials were held for 10 h at the upper temperature and slowly coo

12、led down to room temperature prior to removal from the furnace. The gray powders (bare LiFePO4) were obtained. For the carbon-coated LiFePO4, carbon gel (with the total amount of 10 wt% for the final product LiFePO4) was added to the mixture of the starting materials. After the same mechanochemical

13、treatment, the carbon-coated LiFePO4 powders were synthesized with the same heat-treatment conditions as was adopted for bare LiFePO4.6Materials Chemistry and Physics 115 (2009) 2452501. Solid-state reactionSolid-state synthesis is a conventional method for preparingceramics and includes several suc

14、cessive steps of intimate grindingand annealing of the stoichiometric mixture of starting materials.In general, in the case of LiFePO4, the starting mixture consists ofa stoichiometric amount of iron salt (Fe(II)-acetate, Fe(II)-oxalate),a lithium compound (lithium carbonate or lithium hydroxide), a

15、ndmost commonly ammonium phosphate as a phosphorous source5,1824. The starting mixture firstly decomposes at the temperatureof 300400 C to expel the gases, and, after being reground,calcines at a temperatures ranging from 400 to 800 C for 1024 h.Before the second grinding step, some carbon-containin

16、g compound,for example carboxylic acid 25, can be added to theprecursor and can be employed as a carbon source in the LiFePO4/Ccomposite formation.2.Hydrothermal synthesis is quick, easy to perform, low-cost,energy-saving and easily scalable method to prepare fine particles.Yang et al. 53 originally

17、 showed that lithium iron phosphatecould be synthesized hydrothermally, starting from FeSO4, H3PO4and LiOH mixed in molar ratio 1:1:3. FeSO4 and H3PO4 solutionwere mixed first to avoid the formation of Fe(OH)2 because it easily oxidizes to FeO(OH), then LiOH solution was added to the mixture,which w

18、as then hydrothermally processed at 120 C for up to5 h. However, the capacity of the resulting lithium iron phosphatephase was not high, which was due to some lithium/iron disorderwith around 7% iron on the lithium sites, as later shown by thesame group of authors 54. As the structure has one-dimens

19、ionaltunnels, any iron in lithium tunnels would severely limit lithiuminsertion and removal. It is therefore essential to ensure completeordering of lithium and iron atoms. The firing of the hydrothermalmaterial at 700 C with carbonaceous materials resolved the disorder3. For the purposes of solgel

20、synthesisof LiFePO4 various solvents were used: N,N-dimethylformamide16,66,67,water with ascorbic acid 67, or citric acid 22,6871 aschelating agent, ethylene glycol 72,73, and ethanol 74. Lithiumacetate and iron (II) acetate 66,67,72, lithium phosphate and iron(III) citrate with phosphoric acid 22,6

21、9,75, lithium oxalate andiron (II) oxalate 73, lithium carbonate and iron (II) oxalate 71 areexamples of some combination of lithium and iron sources, respectively.Thus obtained sols were dried until the solvent evaporated,which was followed by calcination at temperatures from 500 to700 C in inert (

22、argon or nitrogen) 72,73,75, or slightly reductiveatmosphere (argon/nitrogen containing 510% of hydrogen)66,74,76. Apart from homogeneous mixing of precursors at themolecular level, another significant advantage of solgel methodis that surface carbon can be generated in situ when organic solvent72,7

23、6 or some carbon included compound (acetates, citrates,oxalates, etc.) 71 are used. Along with the in situ formed carboncoating, iron phosphides can be generated, for instance when gelprecursor made of iron(III) nitrate, 2-methoxyethanol, and sucrose followed by carbothermal reduction reaction of xe

24、rogel precursorwith Li, P resources is used 77. Composites with carbon and ironphosphides can also be generated from an aqueous solgel methodby using ethylene glycol as carbon source in a calcination atmosphereof N2 + 5 vol.% H2 76. The use of citrate in the preparationof the gel enables the formati

25、on of hierarchically organized poresin the meso and macro range, Fig. 4 69,75.4. lithium iron phosphate was synthesized by aqueous co-precipitation of an Fe(II) precursor material and subsequent heat treatment in nitrogen 78. Heating the solutioncontaining Li+, Fe2+, and P5+ ions above 105 C with th

26、e pH valueadjusted between 6 and 10 facilitates the formation of LiFePO4rather than the formation of Li3PO4 and Fe3(PO4)2. The solutionshould also contain water-miscible boiling point elevation additivesuch as: ethylene glycol, diethylene glycol, N-methyl formamide,dimethyl formamide, particularly d

27、imethyl sulfoxide 79. After thetemperature of the solution is increased to the solvents boilingpoint, LiFePO4 begins to precipitate. Afterward, the obtained precipitate is calcined at 500 C at a slightly reducing atmosphere 79.As the crystalline LiFePO4 phase is already formed during the precipitati

28、on step, the temperature and the dwell time of the thermaltreatment are significantly reduced compared to ceramic synthesisprocess. LiFePO4 was also prepared by aqueous precipitation ofFePO4H2O from FeSO47H2O and NH4H2PO4 with hydrogen peroxideas the oxidizing agent, followed by carbothermal reducti

29、onof a mixture made of precipitator iron(III) phosphate and lithiumcarbonate with carbon as the reducer 39. Modifying the latterapproach in the second stage of the synthesis where amorphousLiFePO4 was firstly obtained at room temperature through lithiationof FePO4xH2O using oxalic acid as a novel re

30、ducing agent, andthen amorphous LiFePO4 was calcined at 500 C, nanocrystallineLiFePO4 with enhanced electrochemical performance was formed5. Emulsion-drying method was also used for the preparation ofLiFePO4/C composite powder 8284. Stochiometric amounts ofLiNO3, Fe(NO3)39H2O, and (NH4)2HPO4 were di

31、ssolved in water,and the obtained solution was vigorouslymixed with an oily phaseto prepare a homogeneous water-in-oil emulsion 82,83. The oilyphase was a mixture made of emulsifying agent named Tween85 (Polyoxyethylene Sorbitan Trioleate) and kerosene 82,83. Theprecursor powders were obtained by dr

32、opping the emulsion into hot kerosene (170180 C). Water and kerosene contained in theemulsion were distilled through a spiral-type condenser and theresultant powder sank to the bottom of the reaction vessel. Thelatter powder contained kerosene and Tween 85 and was heatedat 300 C or 400C for a specif

33、ic time in an air-limited box furnace.The dried emulsion precursor was calcined at differenttemperatures, and 750 C was found to be the optimal calcinationtemperature 82. LiFePO4/C composite with nanometricdimensions and uniform size distribution was also prepared by noctane/n-butyl/cetyltrimethyl a

34、mmoniumbromide microemulsionsystem 84. The main advantage of this synthesis route is that thereactants are mixed onmore homogeneous level and that grains areeffectively inhibited fromcoalescence during the synthetic process.6. the synthesis of olivine typeLiFePO4 and LiFePO4/C powders is spray pyrol

35、ysis, an effective techniquefor obtaining cathode powders with fine size and regularmorphology. The starting solutions can be sprayed ultrasonically8587 or peristaltically 88 into the high-temperature reactorat temperatures from 450 to 650 C by a carrier gas. The precursorsolution can be made by dis

36、solving stoichiometric amountsof lithium carbonate, iron(II) oxalate and ammonium dihydrogenphosphate in nitric acid with the addition of sucrose. In that casesucrose serves as a carbon source and enables the formation ofreductive atmosphere so that air can act as a carrier gas 88.LiFePO4/carbon com

37、posite powder was also synthesized startingfromFe3+ precursor, for example by dissolvingmetal nitrates, phosphoricacid, ascorbic acid and table sugar in water 85,89, or by acombination of spray pyrolysis with a planetary high-energy ballmillingfollowed by heat treatment 90. In addition, ultrasonicsp

38、ray pyrolysis can be a suitable method for obtaining metal-dopedsamples of LiFePO4/carboncomposite powders 89. The as-sprayedfine powders are spherical in shape but with low crystallinity, sopost-annealing process at temperatures ranging from 600 to 900 Cin inert or slightly reductive atmosphere is

39、necessary. However,during calcination spherical morphology was changed 86.7LiFePO4PAS was synthesized using lithium dihydrogen phosphate(LiH2PO4) and ferric oxide (Fe2O3) in a stoichiometric molar ratio (1:0.5). The precursors were mixed with an 8 wt% of phenolformaldehyde resin dissolved in a small

40、 quantity of ethanol, and its pyrolyzate is polyacence (PAS). The mixture was ball-milled in water for 5 h and then spray-dried at 180 C with air as the carrier gas, and calcined under N2 gas for 2, 4, 6 and 8 h at the heating rate of 3 Cmin1 at various temperature 600, 700, 750 and 800 C, respectiv

41、ely.8LiFePO4 was first prepared by a solid-state reaction involvinga mixture of iron(II) oxalate (Sigma, 99%), ammonium dihydrogenphosphate (Sigma, 99%), and lithium carbonate (Sigma, 99%) in a stoichiometric molar ratio (1:1:1). The precursors were mixed byball milling in acetone for 3 h. The resul

42、ting gelwas dried at 333K ina furnace, thoroughly reground, and heated in purified Ar/H2 (95:5,v/v) gas for 10 h at 593 K. The decomposed mixture was pressedinto pellets and sintered at 873K in Ar/H2 (95:5, v/v) gas for 12 h. Agrayish black powder of LiFePO4 was obtained. To coat LiFePO4 withcarbon,

43、 various wt.% (compared to the LiFePO4 to be coated) of highsurface area carbon precursors were prepared. LiFePO4 was addedto the carbon precursor and was ground by ball milling to makesure that the LiFePO4 powder was totally covered by the carbonprecursor. The mixture was finally heated at 873K in

44、Ar/H2 (95:5,v/v) for 1 h. Carbon precursors for this work were synthesized as describedbelow. Good quality dry peanuts (from a local source) were priedopen to obtain the shells. The shells were ground into a fine powder.Twenty grams of the powder was mixed with 100 g of a ZnCl2porogenic agent and st

45、irred well for 24 h. The water in the mixturewas allowed to evaporate at 383K over a period of 4 days.The dry sample was heated at a heating ramp of 10Kmin1 in anargon atmosphere and maintained at 423K for 1 h. Subsequently,the temperature of the sample was raised at a rate of 5Kmin1 upto 873K, at w

46、hich point itwas held again for 1 h. After natural coolingto room temperature, the residue of the ZnCl2 porogenic agentwas removed by the treatment in 3N HCl, followed by a 1 h dryingat 463 K.9The LiFePO4 powder (Phostech Lithium Inc.) employed hasan average particle size of 5.0_m and a carbon conte

47、nt of1.9% by weight. Surface coating of TiO2 on the LiFePO4 powderwas conducted as follows. Firstly, Ti(C3H7O)4 (Aldrich, 97%) inethanol was mixed with the LiFePO4 powder in a molar ratio ofTi(C3H7O)4:LiFePO4 = 0.03:1, and the slurry was heated to 70 Cin ambient until totally dried. The as-prepared

48、powder was thenfired in a horizontal oven at 750 C for 0.5 h under 1% H2/N2 atmosphere.101. Solgel synthesis: LiFePO4 was prepared by a solgelmethod using Li3PO4, phosphoric acid (0.85H3PO4 0.15H2O) and ferric citrate n-hydrate (FeC6H8O7nH2O) as starting materials. Lithium phosphate (0.03 M) and pho

49、sphoric acid (0.06 M) were dissolved in 200 ml of water. Ferric citrate n-hydrate (0.09 M) was dissolved in 500 ml of boiling water, and the two solutions were combined and concentratedon a hot plate until a wet gel with high viscosity was formed. The wet gel was placed in an oven and heated at140 C

50、 for 12 h. The dried gel was ground before firing ata heating rate of 10 Cmin1 under Ar up to 600 C, heldfor 24 h, and the samples were then air quenched to obtaincrystallized LiFePO4. The final product contains 5% carbonand 4% iron phosphide. Carbon content was determined bychemical analysis, and t

51、he iron phosphide contribution wasestimated by Mossbauer analysis 23.2. Solid-state synthesis: The reaction mixture comprisedFeC2O42H2O, NH4H2PO4, and 0.5Li2CO3 that were combinedin stoichiometric molar amounts. The reaction mixturewas ball milled in silicon nitride media for 2 h, then fired at600 C

52、 under nitrogen, followed by heating at 700 C under7% H2/N2 during 30 min. The final product contains 1%carbon and 2% Fe2P.3. Hydrothermal synthesis: The reagents H3PO4, (NH4)2Fe(SO4)6H2O, 3LiOHH2O, and ascorbic acid were placed in an 45 ml Parr autoclave, and the containerwas filled to 67%with dist

53、illed water. The autoclave was heated to 190 C for5 h, and then cooled. The product was isolated by filtration,and fired at 600 C for 6 h under Ar. The final product contains1.8% carbon. None of the pristine powders containedany Fe3+ compound. The only contamination in the as synthesizedmaterials in

54、cludes carbon and/or iron phosphide, 11LiFePO4 was prepared by the solid-state reaction of Li2CO3 (99.9%, Fluka), Fe(II)C2O4 . H2O (99%, Aldrich) and (NH4)2HPO4 (99%, Fluka). To prevent oxidation of the iron, the synthesis was performed under a flow of nitrogen gas. The starting materials were weigh

55、ed instoichiometric amounts and homogenized using amixer. To decompose the oxalate and the phosphate,the mixture was placed in a tubular furnace and heatedat 300 C for 20 h. The powder was cooled at roomtemperature and mixed with high-surface area carbonblack(Ketlen Jack Blak, Akzo Nobel, surface ar

56、ea1250 m2 g1). After grinding and homogenization, themixture was transferred to the furnace and annealed at800 C for 16 h under nitrogen flow. After this time,the powder was allowed to cool at room temperature.12LiOHH2O (Aldrich, 98%), Fe2O3 (Aldrich, 99%),(NH4)2HPO4 (Aldrich, 99%), and acetylene bl

57、ack powderswere used as starting materials. The MA process wascarried out for 4 h under argon atmosphere using a shakertype ball miller (SPEX 8000 M) rotating at around 1000 rpm.Detailed MA conditions were described in a previous study The mechanical-alloyed powders were then fired from500 to 900 C for 30 min in a tube-type vacuum furnace at apressure 106 Torr. For comparison, another LiFePO4 samplewas prepared by the solid-state reaction under differentfiring condition. The mixture, which the same