A kind of preparation method of low form nano ferric phosphate lithium anode material
Technical field
The present invention relates to the technology of preparing of anode material for lithium-ion batteries, particularly a kind of preparation method of low form nano ferric phosphate lithium anode material.
Background technology
Have good security performance, excellent cycle performance and advantages of environment protection as the LiFePO4 of anode material for lithium-ion batteries, and abundant raw materials, specific capacity high (theoretical capacity 170mAh/g, energy density is 550Wg/Kg).But also there are following three problems in lithium iron phosphate positive material: the embedding migration models is taken off according to its lithium ion in (1) can know that the ionic conductance of pure ferric phosphate lithium and electronic conductivity are all on the low side, and wherein electronic conductivity Se is 10
-9The s/cm order of magnitude, and ion transmission efficiency Si is 10
-11The s/cm order of magnitude, the two directly causes the low (Sw=Se * Si/Se+Si) of electrode transfer rate Sw; (2) tap density is low; (3) poor performance at low temperatures.
If the problems referred to above can not effectively solve, LiFePO4 is difficult to be applied to electric automobile.Solving the low problem of conductivity can solve through the method for carbon coating, ion doping.LiFePO4 itself is a non-conductor, and conductivity is low directly to have influence on the high-power scope of application that has limited high-power lithium ion battery that discharges and recharges, in particular for electric automobile.For address this problem the current way that generally adopts be at the LiFePO4 coated with carbon to improve its conductivity, research simultaneously shows the cryogenic property that can also promote LiFePO4 through carbon coated.Thereby the feasible way of another one is to make through ion doping to occur free electron or hole lifting conductivity in the LiFePO4 lattice.The method that solves the lithium ion transmission performance is under the unalterable prerequisite of LiFePO4 olivine one dimension lithium ion channel design, can only realize that this will the realistic nanometerization of LiFePO 4 material at present through reducing particle diameter shortening ion transfer path.
(for example the doping of lithium position, iron position even phosphoric acid position improves ion and electronic conductivity to present people through the whole bag of tricks; Increase electron conduction etc. through adding extra conductive agent) improve the cryogenic property of LiFePO4; But the inherent characteristics of LiFePO 4 material is difficult to fundamentally solve the LiFePO4 cryogenic property.
Summary of the invention
The objective of the invention is the relatively poor problem of lithium iron phosphate positive material cryogenic property to technology preparation at present, a kind of preparation method of low form nano ferric phosphate lithium anode material is provided, the lithium iron phosphate positive material cryogenic property of this method preparation is superior.
In order to reach above-mentioned purpose, solution of the present invention is:
A kind of preparation method of low form nano ferric phosphate lithium anode material is characterized in that comprising the steps:
The first step adds the water wet-mixed with Li source compound, ferric iron source compound, P source compound by stoichiometric ratio, adds doped metal ion oxide and a carbon source again, mixes; The slurry that forms carries out the ultra-fine mill of high energy to be handled 2-3 hour, and the slurry D50 that obtains is less than 0.1 μ m, and spray drying obtains dry powder, sieves;
Second step; With the powder in the first step in inert atmosphere in 300-500 ℃ of temperature range preliminary treatment 2-10 hour, cooling back adds secondary carbon source and water, stirs the slurry that forms; After the ultra-fine mill processing of secondary high energy; The slurry D50 that obtains is less than 0.1 μ m, and spray drying obtains spherical powder, sieves;
The 3rd step; Spherical powder in second step is carried out comminution by gas stream; Powder after the pulverizing was handled 6-30 hour through 500-600 ℃ in inert atmosphere; Carried out 600-900 ℃ of high-temperature heat treatment 10-30 hour again, and obtained low form nano ferric phosphate lithium anode material after the cooling, this material grains is of a size of 60 ~ 70nm.
In the first step, described lithium salts is one or both mixtures in lithium carbonate or the lithium hydroxide; Described ferric iron source compound is Fe
2O
3, Fe
3O
4Or FePO
4Described microcosmic salt compound is (NH
4)
3PO
4, (NH
4)
2HPO
4, NH
4H
2PO
4Or FePO
4Described doped metal ion oxide is MnO
2, TiO
2, MgO and Nb
2O
5Described Li source compound, ferric iron source compound, P source compound and the metering of metal ion oxide chemistry are than being in element molal quantity Li:Fe:P: doping metals M=1.01:1:1: the ratio of (0.01 ~ 0.05) adds; A described carbon source is glucose, sucrose and fructose in the soluble sugar compounds.
In second step, described secondary carbon source is sucrose, modified starch and the shitosan in the macromolecular organic compound.
In second step and the 3rd step, described inert atmosphere is nitrogen or argon gas.
After adopting such scheme, the invention has the advantages that: through twice ultra-fine mill of high energy, reduced once the granularity with second particle effectively, improved the effecting reaction area.Particularly pass through the ultra-fine mill of high energy for the first time, the granularity D50 of material has greatly increased the contact area between the various raw materials less than 0.1 μ m, and the cryogenic property that promotes LiFePO 4 material is played crucial effect.Through the ultra-fine mill of the high energy second time, the granularity D50 of material is less than 0.1 μ m, and cooperation wet method adding secondary carbon source, makes carbon source evenly be coated on the LiFePO4 particle surface, has increased substantially the conductivity of LiFePO 4 material.Through facts have proved that this preparation technology's method is feasible.Adopting the LiFePO 4 material of the method preparation is the nanoscale crystalline material, and crystallite dimension is in 60 ~ 70nm scope, phosphorus content 1.5%~5%.After this material made battery, cryogenic property was superior, and capacity was 55% of a normal temperature when capacity was 80% ,-40 ℃ of normal temperature in the time of-20 ℃.
Description of drawings
Fig. 1 is the XRD figure of embodiment 1 prepared LiFePO 4 material, and wherein abscissa is angle of diffraction 2 θ (degree), and ordinate is diffracted intensity (a.u);
Fig. 2 is the SEM figure of embodiment 1 prepared LiFePO 4 material;
Fig. 3 is the low temperature discharge curve of embodiment 1 prepared LiFePO 4 material.
Embodiment
Embodiment 1
With 2.55molLi
2CO
3, 2.5molFe
2O
3, 5.0mol NH
4H
2PO
4Add in the agitator tank, add the 2L deionized water, add 0.01molMnO while stirring
2, 0.01molTiO
2With 30g glucose, change in the ball mill after stirring, carried out high-energy ball milling 2 ~ 3 hours, the D50 that obtains slurry must be less than 0.1 μ m.Carry out spray drying then and form powder, sieve.With this powder at N
2In the atmosphere, with 350 ℃ of sintering of rotary furnace 5 hours.Cooling is sieved, and changes in the ball grinder, adds 150g shitosan and 900ml deionized water, stirs, and changes in the ball mill, carries out the high-energy ball milling second time, and less than 0.1 μ m, spray drying forms spherical powder, sieves until the D50 of slurry.This powder is carried out joining in the rotary furnace, at N after comminution by gas stream handles
2650 ℃ of sintering are 8 hours in the atmosphere, are warming up to 800 ℃ of sintering again after 20 hours, and cooling is sieved and obtained product.
The products obtained therefrom crystallite dimension is 64nm, and carbon content is 2.3%, and 1C normal temperature discharge capacity is 139.59 mAh/g, and capacity is 111.76mAh/g in the time of-20 ℃, and capacity is 76.77mAh/g when being 80% ,-40 ℃ of normal temperature, is 55% of normal temperature.
Embodiment 2
With 2.55molLi
2CO
3, 5.0molFePO
4Add in the agitator tank, add the 2L deionized water, add 0.01molMnO while stirring
2, 0.01molTiO
2, 0.02mol MgO and 30g glucose, change in the ball mill after stirring, carried out high-energy ball milling 2 ~ 3 hours, the D50 that obtains slurry must be less than 0.1 μ m.Carry out spray drying then and form powder, sieve.With this powder at N
2In the atmosphere, with 350 ℃ of sintering of rotary furnace 5 hours.Cooling is sieved, and changes in the ball grinder, adds 150g shitosan and 900ml deionized water, stirs, and changes in the ball mill, carries out the high-energy ball milling second time, and less than 0.1 μ m, spray drying forms spherical powder, sieves until the D50 of slurry.This powder is carried out joining in the rotary furnace, at N after comminution by gas stream handles
2650 ℃ of sintering are 8 hours in the atmosphere, are warming up to 800 ℃ of sintering again after 20 hours, and cooling is sieved and obtained product.
The products obtained therefrom crystallite dimension is 62nm, and carbon content is 2.8%, and 1C normal temperature discharge capacity is 135.32 mAh/g, and capacity is 107.19mAh/g in the time of-20 ℃, and capacity is 73.26mAh/g when being 79% ,-40 ℃ of normal temperature, is 54% of normal temperature.
Embodiment 3
With 2.55molLi
2CO
3, 2.5molFe
2O
3, 5.0mol NH
4H
2PO
4Add in the agitator tank, add the 2L deionized water, add 0.01molMnO while stirring
2, 0.01molTiO
2With 30g sucrose, change in the ball mill after stirring, carried out high-energy ball milling 2 ~ 3 hours, the D50 that obtains slurry must be less than 0.1 μ m.Carry out spray drying then and form powder, sieve.With this powder at N
2In the atmosphere, with 350 ℃ of sintering of rotary furnace 5 hours.Cooling is sieved, and changes in the ball grinder, adds 180g modified starch and 900ml deionized water, stirs, and changes in the ball mill, carries out the high-energy ball milling second time, and less than 0.1 μ m, spray drying forms spherical powder, sieves until the D50 of slurry.This powder is carried out joining in the rotary furnace, at N after comminution by gas stream handles
2650 ℃ of sintering are 8 hours in the atmosphere, are warming up to 800 ℃ of sintering again after 20 hours, and cooling is sieved and obtained product.
The products obtained therefrom crystallite dimension is 68nm, and carbon content is 2.1%, and 1C normal temperature discharge capacity is 137.91 mAh/g, and capacity is 109.86mAh/g in the time of-20 ℃, and capacity is 74.62 mAh/g when being 79.6% ,-40 ℃ of normal temperature, is 54.1% of normal temperature.