CN100443400C - Method for preparing olivine structure lithium iron phosphate - Google Patents
Method for preparing olivine structure lithium iron phosphate Download PDFInfo
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- CN100443400C CN100443400C CNB2005100311162A CN200510031116A CN100443400C CN 100443400 C CN100443400 C CN 100443400C CN B2005100311162 A CNB2005100311162 A CN B2005100311162A CN 200510031116 A CN200510031116 A CN 200510031116A CN 100443400 C CN100443400 C CN 100443400C
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- lithium
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- phosphate
- ferrous
- source compound
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Abstract
The present invention relates to a method for preparing iron lithium phosphate with olivine structure. Divalent Fe source compounds, phosphorus source compounds and oxidants are mixed according to the stoichiometric ratio of LiFePO4, the PH value is controlled to be from 1 to 8, after the reaction, a FePo4 precursor of about 100 nm is obtained through filtration, washing and drying; then, the FePO4 precursor, lithium source compounds and reducers are mixed in a stove and are calcined at a constant temperature in non-oxidizing atmosphere to obtain the LiFePO4. Compared with the existing method, the present invention solves the problem that ferrous ions are easy to oxygenize, trivalent iron is directly used as the precursor to prepare the LiFePO4, and the problem that the raw materials are difficult to mix uniformly is solved. The grain size of the precursor FePO4 prepared by the present invention is small, which is beneficial to material synthesis and performance improvement, and superfluous reduction carbon is directly coated on LiFePO4 grains so that a later coating process is unnecessary. The present invention has the advantages of short preparation process, easy control, low calcination temperature and low energy consumption.
Description
Technical field
The invention belongs to the preparation of the lithium ion anode material in the field of material preparation.
Background technology
The LiFePO of olivine structural
4Can embed and the removal lithium embedded ion by reversible, take off the FePO that lithium obtains
4The original volume of volume ratio only lacked 6.81%, so have good cycle performance.While LiFePO
4Advantages such as that material has is nontoxic, environmentally friendly, the starting material source is abundant, specific storage high (theoretical capacity is 170mAh/g, and energy density is 550Wh/Kg), high temperature stability performance are good.But following shortcoming has hindered its practical application: Fe during (1) is synthetic
2+Easily be oxidized to Fe
3+, be difficult to obtain monophasic LiFePO
4(2) lithium ion is at LiFePO
4(spread coefficient is 8.1 * 10 for middle diffusion difficulty
-18With 2.7 * 10
-17), cause the utilization ratio of active material low; (3) LiFePO
4Specific conductivity itself is also very low, and causing its heavy-current discharge performance, poor (perveance is 10
-19Scm
-1).Existing research improves LiFePO by following several respects
4Performance: (1) adopts inert atmosphere to protect Fe
2+(2) LiFePO of synthetic small particle size
4Improve the diffusibility of lithium ion; (3) power up and lead agent and improve specific conductivity.Present several synthetic method:
Solid phase method: Li such as Goodenough
2CO
3, FeC
2O
42H
2O and NH
4H
2PO
4Mix by stoichiometric ratio, under inert atmosphere protection, in about 300 ℃, compound is tentatively decomposed, be warmed up to then about 700 ℃ and calcined tens hours.This method synthetic material particle size skewness, conductivity are low, and shortcoming such as long energy consumption of cycle is big.
Hydrothermal method: human FeSO such as Shuofeng Yang
4, H
3PO
4And LiH
2PO
4As parent material, be 6.91 at the control pH value, temperature is 120 ℃ of down synthetic LiFePO
4And its impulse electricity poor performance of this kind method synthetic material (the Rietveld analytical results is: the Fe that 7%-8% is wherein arranged approximately
2+Occupied Li
+The position, this is the reason that makes its impulse electricity degradation most probably), and synthetic materials contains water-soluble impurity and moisture content is more, is unfavorable for the making of lithium ion battery.
Sol-gel method: Huang etc. adopt the CH of solubility
3COOLi, (CH
3COO)
2Fe and NH
4H
2PO
4Make reactant, be blended in the carbon gel,, obtain LiFePO through aging, washing, thermal treatment by stoichiometric ratio
4People such as Yaoqin Hu are Fe (NO
3) 9H
2O and CH
3COOLi adds H
3PO
4In, add glycol acid again.Regulate pH value with ammoniacal liquor, be controlled between the 8-9.The gel that obtains is calcined down and insulation 10h at 500 ℃, just obtains LiFePO
4This method can make raw material uniform mixing on molecular level, and batch stability of product is easy to control, but the process complexity of preparation, the condition harshness, the cost height is so be difficult to industrialization.
Summary of the invention
At above-mentioned deficiency, the present invention proposes a kind of method for preparing olivine structure lithium iron phosphate, and this method synthetic material can well be protected ferrous iron, the LiFePO that obtains
4The purity height, and its size distribution is even and tiny, specific conductivity also is improved significantly, reduces the cost of material simultaneously, simplifies technology, is easy to industrialization.
Concrete implementation step of the present invention is: the solution or the solid of ferrous iron source compound, P source compound and oxygenant are mixed, press LiFePO
4Stoichiometric ratio mix, the concentration of ferrous iron source compound, P source compound, oxygenant is 0.01-3mol/L, control PH=1-8, reaction is 0.5-24 hour in 20-100 ℃ stirred reactor, filters, washing, oven dry obtain the FePO about 100nm
4Presoma, bake out temperature is at 30-160 ℃.Then with FePO
4Presoma is placed in the stove with Li source compound and reductive agent mixing, heat-up rate with 1-40 ℃/min in non-oxidizing atmosphere heats, in 400-800 ℃ of calcining at constant temperature 2-35 hour, the cooling rate with 1-20 ℃/min descended or furnace cooling simultaneously, makes LiFePO
4
The optional iron protochloride of described divalence source of iron, Iron nitrate, ferrous sulfate, sulfuric acid two ammoniums are ferrous, ammonium sulfate is ferrous, a kind of in the Iron diacetate.A kind of in the optional phosphoric acid of P source compound, triammonium phosphate, primary ammonium phosphate, Secondary ammonium phosphate, potassiumphosphate, dipotassium hydrogen phosphate, potassium primary phosphate, sodium phosphate, SODIUM PHOSPHATE, MONOBASIC, the Sodium phosphate dibasic.A kind of in the optional sodium peroxide of oxygenant, hydrogen peroxide, potassium permanganate, the Potcrate.Regulate: the reagent of pH value can be selected a kind of in lithium hydroxide, sodium hydroxide, potassium hydroxide, the ammoniacal liquor for use.A kind of in the optional lithium hydroxide in lithium source, Lithium Acetate, lithium chloride, Lithium Sulphate, lithium nitrate, the Quilonum Retard.A kind of in the optional carbon black of reductive agent, acetylene black, graphite, charcoal gel, the sucrose.The source of the gas of non-air atmosphere selects a kind of in nitrogen, argon gas, the hydrogen.
The present invention compares with existing method, has solved the easy problem of oxidation of ferrous ion, directly prepares LiFePO with tervalent iron as presoma
4With FePO
4Solved the problem that raw material is difficult to mix as presoma; The presoma FePO of the present invention's preparation
4Granularity is little, about about 100nm, helps the raising of the synthetic and performance of material; Unnecessary reduction carbon directly is coated on LiFePO
4Particle on, handle the electron conduction can improve material so must not carry out the coating in later stage; Preparation process time is short and be easy to control, and firing temperature is low, and energy consumption is low; The LiFePO of preparation
4It is tiny, even to have particle, adjustable between synthesis temperature 400-800 ℃, can obtain varigrained material.
Description of drawings
Fig. 1: presoma FePO
4Scanning electron microscope;
The LiFePO of Fig. 2: embodiment 1 preparation
4XRD figure spectrum;
The LiFePO of Fig. 3: embodiment 1 preparation
4The SEM collection of illustrative plates;
The LiFePO of Fig. 4: embodiment 1 preparation
4The impulse electricity curve.
Embodiment
Further specify method provided by the present invention below by embodiment.
After embodiment 1 fully mixes the iron protochloride of 0.01mol/L and 0.01mol/L phosphoric acid, adding lithium hydroxide control pH value is 3.5, adds sodium peroxide again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, carbon gel and Lithium Acetate mix (the carbon gel is calculated by carbon content) by stoichiometry; guarantee carbon gel excessive 5% simultaneously; through ball milling 30min; then compound is put into reduction furnace; feed Ar gas as protective atmosphere, with the heat-up rate of 2 ℃/min be heated to respectively 500 ℃, 600 ℃, 700 ℃, 800 ℃ temperature and be incubated 20 hours.The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.With resulting product be assembled into the experiment button cell survey its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, carry out impulse electricity, first loading capacity and the circulation 30 times after loading capacity see Table 1.
The experiment condition of table 1 embodiment 1 and result
After embodiment 2 fully mixes the ferrous and 0.01mol/L phosphoric acid of the ammonium sulfate of 0.01mol/L, adding sodium hydroxide control pH value is 3.5, adds sodium peroxide again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, carbon gel and Lithium Acetate mix (the carbon gel is calculated by carbon content) by stoichiometry; guarantee carbon gel excessive 5% simultaneously; through ball milling 30min; then compound is put into reduction furnace; feed Ar gas as protective atmosphere, be heated to 600 ℃ and be incubated 10h, 20h, 30h respectively with the heat-up rate of 2 ℃/min.The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.With resulting product be assembled into the experiment button cell survey its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, carry out impulse electricity, first loading capacity and the circulation 30 times after loading capacity see Table 2.
The experiment condition of table 2 embodiment 2 and result
After embodiment 3 fully mixes the iron protochloride of 2mol/L and 2mol/L SODIUM PHOSPHATE, MONOBASIC, adding ammoniacal liquor control pH value is 3.5, adds sodium peroxide again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, carbon black and lithium hydroxide mix (carbon black is calculated by carbon content) by stoichiometry; guarantee carbon black excessive 2%, 5%, 7%, 10% simultaneously; through ball milling 30min; then compound is put into reduction furnace; feed protection of nitrogen gas, be heated to 600 ℃ and be incubated 20 hours with the heat-up rate of 2 ℃/min.The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.With resulting product be assembled into the experiment button cell survey its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, carry out impulse electricity, first loading capacity and the circulation 30 times after loading capacity see Table 3.
The experiment condition of table 3 embodiment 3 and result
After embodiment 4 fully mixes the Iron diacetate of 0.01mol/L and 0.01mol/L phosphoric acid, adding lithium hydroxide control pH value is 3.5, adds hydrogen peroxide again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, acetylene black and Quilonum Retard mix (acetylene black is calculated by carbon content) by stoichiometry; guarantee acetylene black excessive 5% simultaneously; through ball milling or hand mill for some time; then compound is put into reduction furnace; feed Ar gas as protective atmosphere, with 600 ℃ of the heat-up rate heating of 2 ℃/min and be incubated 20 hours.The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.With resulting product be assembled into the experiment button cell survey its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, carry out impulse electricity, first loading capacity and the circulation 30 times after loading capacity see Table 4.
The experiment condition of table 4 embodiment 4 and result
After embodiment 5 fully mixes the ferrous sulfate of 0.5mol/L and 0.5mol/L phosphoric acid, adding lithium hydroxide control pH value is 3.5, adds potassium permanganate again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, graphite and lithium chloride mix by stoichiometry, guarantees that simultaneously graphite is excessive 5%, through ball milling or hand mill for some time, then compound put into reduction furnace, feeds H
2The protection of gas is with 600 ℃ of the heat-up rate of 2 ℃/min heating and be incubated 20 hours.
The experiment condition of table 5 embodiment 5 and result
The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.Resulting product is assembled into the experiment button cell surveys its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, dash and put a little, their loading capacity first and circulate that loading capacity sees Table 5 after 30 times.
After embodiment 6 fully mixes the iron protochloride of 1mol/L and 1mol/L phosphoric acid, adding lithium hydroxide control pH value is 3.5, adds sodium peroxide again and obtains suspension liquid, and suspension liquid stopped 6 hours in intensively stirred reactor, filter then, wash, the filter cake (FePO that obtains
4) dried by the fire 12 hours down at 120 ℃.Forerunner FePO with oven dry
4, carbon gel and Lithium Acetate mix (the carbon gel is calculated by carbon content) by stoichiometry, guarantees that simultaneously the carbon gel is excessive 5%, through ball milling 30min, then compound put into reduction furnace, feeds H
2The protection of gas is heated to 500 ℃, 600 ℃, 700 ℃ and 800 ℃ respectively and is incubated 20 hours with the heat-up rate of 2 ℃/min.The product of gained shows to be LiFePO through X-ray diffraction analysis
4, do not have any dephasign, can obtain the particle diameter of product about 500nm by SEM.Resulting product is assembled into the experiment button cell surveys its impulse electricity specific storage and cycle performance, under the multiplying power of 0.2C, dash and put a little, their loading capacity first and circulate that loading capacity sees Table 6 after 30 times.
The experiment condition of table 6 embodiment 6 and result
Claims (1)
1. a method for preparing olivine structure lithium iron phosphate is characterized in that: ferrous iron source compound, P source compound and oxygenant are pressed LiFePO
4Stoichiometric ratio mix, the concentration of ferrous iron source compound, P source compound, oxygenant is 0.01-3mol/L, control pH=1-8, reaction is 0.5-24 hour in 20-100 ℃ stirred reactor, filters, washing, oven dry obtain the FePO about 100nm
4Presoma, bake out temperature is at 30-160 ℃; Then with FePO
4Presoma is placed in the stove with Li source compound and reductive agent mixing, heat-up rate with 1-40 ℃/min in non-oxidizing atmosphere heats, in 400-800 ℃ of calcining at constant temperature 2-35 hour, the cooling rate with 1-20 ℃/min descended or furnace cooling simultaneously, makes LiFePO
4
Described divalence source of iron is iron protochloride, Iron nitrate, ferrous sulfate, sulfuric acid two ammoniums are ferrous, ammonium sulfate is ferrous or Iron diacetate in a kind of;
P source compound is a kind of in phosphoric acid, triammonium phosphate, primary ammonium phosphate, Secondary ammonium phosphate, potassiumphosphate, dipotassium hydrogen phosphate, potassium primary phosphate, sodium phosphate, SODIUM PHOSPHATE, MONOBASIC or the Sodium phosphate dibasic;
Oxygenant is a kind of in sodium peroxide, hydrogen peroxide, potassium permanganate or the Potcrate;
The lithium source is a kind of in lithium hydroxide, Lithium Acetate, lithium chloride, Lithium Sulphate, lithium nitrate or the Quilonum Retard;
Reductive agent is a kind of in carbon black, acetylene black, graphite, charcoal gel or the sucrose.
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Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100480178C (en) * | 2007-01-16 | 2009-04-22 | 北大先行科技产业有限公司 | Particle appearance regulatory lithium iron phosphate preparation method |
| CN101293641B (en) * | 2008-06-13 | 2010-07-28 | 南开大学 | Method for preparing chlorine ion doped iron lithium phosphate powder body |
| CN102244245A (en) * | 2011-06-09 | 2011-11-16 | 上海大学 | Two-step carbothermic reduction preparation method of anode material LiFePO4/C of lithium ion battery |
| EP3554996B1 (en) * | 2016-12-15 | 2021-02-17 | Hydro-Québec | Delithiation of carbon free olivine by addition of carbon |
| CN108448105A (en) * | 2018-05-16 | 2018-08-24 | 苏州大学 | A kind of preparation method of lithium ion battery anode material lithium iron phosphate/redox graphene |
| CN110407186A (en) * | 2019-08-01 | 2019-11-05 | 湖北昊瑞新能源有限公司 | A kind of method that coprecipitation prepares ferric phosphate and LiFePO 4 material |
| CN111740113B (en) * | 2020-07-01 | 2021-07-16 | 中南大学 | Preparation method of lithium iron phosphate/carbon nanotube composite positive electrode material |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1431147A (en) * | 2003-02-17 | 2003-07-23 | 郑绵平 | Wet chemistry method for preparing lithium iron phosphate |
| CN1511352A (en) * | 2001-05-23 | 2004-07-07 | ƶ��� | Lithium transition-metal phosphate powder for rechargeable batteries |
-
2005
- 2005-01-07 CN CNB2005100311162A patent/CN100443400C/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1511352A (en) * | 2001-05-23 | 2004-07-07 | ƶ��� | Lithium transition-metal phosphate powder for rechargeable batteries |
| CN1431147A (en) * | 2003-02-17 | 2003-07-23 | 郑绵平 | Wet chemistry method for preparing lithium iron phosphate |
Non-Patent Citations (6)
| Title |
|---|
| Lithium iron(II) phospho-olivines prepared by a novelcarbothermal reduction method. J. Barker et al.Electrochemical and solid-state letters,Vol.6 No.3. 2003 |
| Lithium iron(II) phospho-olivines prepared by a novelcarbothermal reduction method. J. Barker et al.Electrochemical and solid-state letters,Vol.6 No.3. 2003 * |
| Low temperature preparation of optimized phosphates for Li-battery applications. Charles Delacourt et al.Solid-state ionics,No.173. 2004 * |
| Low temperature preparation of optimized phosphates forLi-battery applications. Charles Delacourt et al.Solid-state ionics,No.173. 2004 |
| Morphological investigation of sub-micron FePO4 and LiFePO4 particles for rechargable lithium batteries, Materialresearch bulletin. Silvera Scaccia et al.Material research bulletin,Vol.38. 2003 * |
| Morphological investigation of sub-micron FePO4 andLiFePO4 particles for rechargable lithium batteries, Materialresearch bulletin. Silvera Scaccia et al.Material research bulletin,Vol.38 . 2003 |
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