CN105060266A - Hydro-thermal synthesis method for nano LiFePo4 - Google Patents
Hydro-thermal synthesis method for nano LiFePo4 Download PDFInfo
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- CN105060266A CN105060266A CN201510425066.XA CN201510425066A CN105060266A CN 105060266 A CN105060266 A CN 105060266A CN 201510425066 A CN201510425066 A CN 201510425066A CN 105060266 A CN105060266 A CN 105060266A
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Abstract
The invention provides a hydro-thermal synthesis method for nano LiFePo4. The method comprises the following steps: step 1, a lithium hydroxide solution and phosphoric acid are added to an autoclave, an iron source solution is then added, and a reaction system is heated to 150-170 DEG C from 40 DEG C at the speed of 4-8 DEG C/min; step 2, heat is preserved for 2 h at the temperature of 150-170 DEG C and reduced to 70-80 DEG C, a filter cake and mother liquor are obtained through filtering, the filter cake is washed and dried in vacuum, and grey white LiFePo4 powder is obtained; step 3, the LiFePo4 powder obtained in the step 2 and a carbon source are mixed uniformly in the mass ratio being 100: (15-20), the mixture is roasted for 4 h at 700 DEG C with inert gas shielding, and a carbon coated LiFePo4 product is obtained. The high-rate discharge ability of the product is improved, the capacity cycling retention rate of the product is increased, equipment investment is little, the process is simple and controllable, and the batch stability of the product is good.
Description
Technical field
The invention belongs to technical field of energy material preparation.In particular to the iron lithium phosphate with water heat transfer with nanostructure, this material can be used as anode material for lithium-ion batteries.
Technical background
The security that iron lithium phosphate has because of it, inexpensive property, environment friendly and receive very big concern.In recent years because this shortcoming of low electroconductibility of material is progressively modified, be that the battery of positive pole is just in popularization and application with iron lithium phosphate.But its high these performance index of charge and discharge high rate performance comparatively actual requirement still have certain gap.Reduce particle diameter and carbon coated be the most effective two kinds of methods.In reduction particle diameter, the particle diameter of material can be prepared into nano level, nano level level compound has been proved to be and it can have been made to reach be bordering on its theoretical capacity, we use water heat transfer iron lithium phosphate in ZL200710058353.7, and illustrate in ZL200710058352.2 and control granular size with tensio-active agent, prevent the method for reuniting between particle, and illustrate pH value to the impact of synthesizing iron lithium phosphate pattern at ZL202010031395.3 and obtain the optimal ph of its synthesis.Compared with solid phase method, Hydrothermal Synthesis have simple to operate, thing mutually evenly, advantage that particle diameter is little.The step mainly taked that current existing hydrothermal method prepares iron lithium phosphate is dissolved by a certain percentage soluble ferrite, phosphoric acid and lithium hydroxide, be warming up to 120 ~ 374 DEG C (critical temperatures of water) after mixing in reactor, all iron lithium phosphate crystal can be obtained in a wider temperature range, but the pattern of crystal is different with granular size, in general the particle of the crystal of the higher preparation of temperature of reaction is less, and chemical property is more excellent.In order to obtain tiny lithium iron phosphate particles, higher temperature of reaction need be adopted and be aided with tensio-active agent, organic solvent to reach the object of micronized particles, the shortcoming existed is reacted at relatively high temperatures, the autogenous pressure of reaction system is larger, bring that facility investment is large thus, operation control difficult and because of the pressure of reactor large, corresponding with it, the wall thickness of reactor will be thicker, cause heat transfer efficiency low, make process energy consumption large, the existence of tensio-active agent produces the problems such as a large amount of foam makes mother liquid evaporation process control difficult.
Summary of the invention
Technical problem to be solved by this invention is: a kind of method providing Synthesized by Hydrothermal Method level iron lithium phosphate, by on the control of important technical parameter-heat-up rate affecting iron lithium phosphate crystal growth, the problem of indirect heating by heat transfer area restriction is overcome by steam direct heating method, control the heat-up rate of reaction system within the scope of 4 ~ 8 DEG C/min, shorten crystal at the nucleation of low-temperature zone and growth time, make it nucleation and growth at relatively high temperatures, reach crystal grain tiny, the object that sphericity is high, realize the control to product morphology and particle diameter, to improve the chemical property of product, high rate performance and tap density.
Technical scheme of the present invention is:
A hydrothermal synthesis method for nano-grade lithium iron phosphate, comprises the following steps:
The first step, hydrothermal synthesis reaction
Lithium hydroxide is water-soluble, add in autoclave, then add phosphoric acid, after the air in dead volume in inert gas purge still, sealing autoclave, be heated to 40 DEG C from room temperature under stirring, open feed valve and vent valve, then add pure source of iron solution, the reinforced used time is 20 ~ 40 minutes, stir after 10 ~ 30 minutes, pass into the steam of 200 DEG C, with the speed of 4 ~ 8 DEG C/min, reaction system is heated to 150 ~ 170 DEG C; The mol ratio adding material is: Li:Fe:P=3.0:1.0:1.0; After reinforced, in solution, the concentration of ferro element is 0.3 ~ 0.6mol/L;
Second step, the filtration of resultant, washing and drying
150 ~ 170 DEG C of insulations are after 2 hours, stop heating, water coolant is led to autoclave by spiral coil cooling tube, make temperature be reduced to 70 ~ 80 DEG C, open bleeder valve, resultant is filtered, obtain filter cake and mother liquor, then washing leaching cake is to sulfate radical-free ion, and filter cake, in 110 DEG C ~ 120 DEG C vacuum-dryings 12 hours, obtains canescence LiFePO4 powder; Reclaim(ed) sulfuric acid lithium after mother liquid evaporation is concentrated.
3rd step, the coated process of carbon
By the LiFePO of second step gained
4powder and carbon source in mass ratio 100:15 ~ 20 mix, and under protection of inert gas, in 700 DEG C of roastings 4 hours, obtain the iron lithium phosphate product that carbon is coated.
Above-mentioned source of iron is the liquid before ferrous sulfate crystal or its crystallization, or the clear liquor of byproduct ferrous sulfate of titanium dioxide after purification and impurity removal.
Described carbon source is specially glucose.
The invention has the beneficial effects as follows:
(1) high-rate discharge ability of product and capacity circulating conservation rate improve.
(2) the present invention adopts steam direct heating, fast relative to indirect heating heat transfer, the uniform particles of obtained material, pattern turns to bar-shaped or near-spherical by sheet, smallest dimension can reach Nano grade, be conducive to the shortening of lithium ion the evolving path, be conducive to the intergranular contact of positive active material after electrode materials addition pole piece, be fundamentally conducive to the prolongation of the electroconductibility of material and the raising of high rate performance and cycle life.
(3) controlling nucleus formation speed by controlling heat-up rate, realizing controlling granular size, instead of adopt tensio-active agent to control granular size, greatly simplify the control difficulty of the evaporation technology of mother liquor.
(4) facility investment is little, and technique is simply controlled, and the lot stability of product is good.
The above-mentioned beneficial effect of the inventive method is proved in the examples below that.
Accompanying drawing explanation
The stereoscan photograph of Fig. 1 product, wherein, Fig. 1 a is embodiment 1, Fig. 1 b be embodiment 2, Fig. 1 c be comparative example 1, Fig. 1 d is comparative example 2.
Specific implementation method
Below in conjunction with embodiment and accompanying drawing, the present invention is further described.
Embodiment 1
The first step, hydrothermal synthesis reaction
Will containing 223.4gFe
2+pure copperas solution dilution 3.5L (pH value of this solution is about 1) of (i.e. 4mol); The 461.2g85% phosphoric acid containing pure phosphoric acid being 4mol is diluted to 1L; By the LiOHH of 503.3g and 12mol
2o is soluble in water and be diluted to 3L.
Above-mentioned whole lithium hydroxide solution and phosphoric acid solution are added in the autoclave of 10L band sealing filling tube and heat exchange coil, after the air in dead volume in inert gas purge still, sealing autoclave, start stirring, rotating speed 200rpm, be heated to 40 DEG C from room temperature, open feed valve and vent valve, add all above-mentioned copperas solution, feeding in raw material is 30 minutes, closes feed valve sealing autoclave and continue stirring 20 minutes after reinforced.
The water vapor of 200 DEG C is passed in reactor, the temperature in reactor is made to be 30min (heat-up rate is 4 DEG C/min) from 40 DEG C of times risen to needed for 160 DEG C after reinforced, in 160 DEG C of reactions 2 hours, the autogenous pressure now corresponding to system was 0.62Mpa.
Second step, the filtration of resultant, washing and drying
After above-mentioned reaction completes, autoclave, by coil pipe water quench to 80 DEG C, opens blow-off valve and bleeder valve, and filtered by resultant, obtain filter cake and mother liquor, then washing leaching cake is to using BaCl
2solution inspection is without SO
4 2-till.Filter cake, in 120 DEG C of vacuum dryings to constant weight, obtains 625.1gLiFePO
4canescence powder.Mother liquor enters withdrawing can and goes out Lithium Sulphate for evaporative crystallization.
3rd step, the coated process of carbon
By the canescence powder of second step gained and glucose in mass ratio 100:15 mix, 700 DEG C, calcining 4 hours under nitrogen protection, obtain the iron lithium phosphate (LiFePO that carbon is coated
4/ C) product.
Fig. 1 a is the electron scanning micrograph of the present embodiment sample, and the granule-morphology of product is bar-shaped small-particle, and the smallest dimension of particle is about 90 ~ 100 nanometers, basic soilless sticking phenomenon between particle.
The charge-discharge performance test of the present embodiment product: by iron lithium phosphate LiFePO coated for carbon obtained above
4/ C, acetylene black, 60% ptfe emulsion in mass ratio 7: 2: 1 ratio mixing, be rolled into the sheet that thickness is 0.10 ~ 0.15 ㎜, and press together with aluminium foil, in 120 DEG C of vacuum-dryings 12 hours, obtained anode.With the LiPF of metal lithium sheet negative pole, 1M
6solution is electrolytic solution, cellgard2300 is barrier film, is assembled into button cell with above-mentioned positive pole, carries out discharge and recharge with 0.2C, 1C, 3C multiplying power, and the voltage range of discharge and recharge is 4.2 ~ 2.3V.0.2C, 1C, 3C specific storage of material is respectively 163.6,155.3 and 140.1mAh/g.
Embodiment 2
Reactant in embodiment 1 is become 15min (heat-up rate is 8 DEG C/min), the other the same as in Example 1 from 40 DEG C of times risen to needed for 160 DEG C of mixed temperature.
After having synthesized, filter, washing, filter cake, in 120 DEG C of vacuum dryings to constant weight, obtains 624gLiFePO
4canescence powder.
The granule-morphology of product is the spherical particle of the bar-shaped of corner angle fuzzy and class, and the smallest dimension size of particle is about 100 nanometers, basic soilless sticking between particle.Electrochemical property test the results are shown in Table 1.Fig. 1 b is the electron scanning micrograph of the present embodiment gained sample.Comparison diagram 1a and Fig. 1 b is known, and after heat-up rate is greater than 4 DEG C/min, pattern and the particle size of sample substantially no longer change.
Comparative example 1
Reactant in embodiment 1 is become 40min (heat-up rate is 3 DEG C/min), the other the same as in Example 1 from 40 DEG C of times risen to needed for 160 DEG C of mixed temperature.
After having synthesized, filter, washing, filter cake, in 120 DEG C of vacuum dryings to constant weight, obtains 625gLiFePO
4canescence powder.
The granule-morphology of product is the hexagon sheet of corner angle fuzzy, and thick about 90 ~ 100 nanometers of sheet, have the agglomeration of less degree between particle.Electrochemical property test the results are shown in Table 1.
Comparative example 2
Reactant in embodiment 1 is become 240 minutes, the other the same as in Example 1 from the temperature time risen to needed for 160 DEG C of latter 40 DEG C of mixing.
The granule-morphology of product is sharp-featured diamond platy particle, and have and be mingled with small-particle in platy shaped particle, on direction perpendicular to maximum crystal face, the thick of sheet is about 150 nanometers, this direction is unique dispersal direction of lithium ion in LiFePO 4 material, obviously, the thickness increase of sheet is unfavorable for the diffusion of lithium ion and the performance of chemical property.And granular size is uneven, reduce the processing characteristicies such as the tap density of material, electroconductibility, homogenate dispersiveness.Electrochemical property test the results are shown in Table 1.
The chemical property of table 1 product
As can be seen from above data and SEM figure, the pattern of heat-up rate remarkably influenced crystal and chemical property.Thus the dissolution rate that heat-up rate affects presoma affects the degree of saturation of lithium in reaction system, iron, phosphate anion, affects the growth conditions of iron lithium phosphate crystal thus and finally affects the selecting to growth characteristics of crystal.Heat-up rate is lower, and the precursor Trilithium phosphate of reaction and eight water ferrous phosphate dissolution raties are slow, and in system, the degree of supersaturation of configurational ion is low, is deposited on the high crystal face of energy and the crystal face that makes energy low reveals ion selectivity.The crystal of the large grain size as comparative example 2 and less crystal face is caused to generate.When heat-up rate is greater than 4 DEG C, the time of reaction system residing for low-temperature zone is shorter, precursor dissolves rapidly at relatively high temperatures, in system, the degree of supersaturation of various ion is large, configurational ion must precipitate rapidly the free energy that could reduce system, therefore, heat up and low-temperature growth phase relative to low speed, crystal growth select to trend replace by rapid growth of crystal, a large amount of nucleus grows fast, the particle of final product is tiny, and sphericity is high, is conducive to the raising of electrode compacted density and the performance of electrochemistry capacitance.But too fast heat-up rate is except the difficulty of the operation strengthened, the pattern of product and chemical property are not effectively improved.Direct steam heating is utilized to control the method for heat-up rate, simply, effectively can controlling the growth of iron lithium phosphate crystal, the problem of the mother liquid disposal difficulty produced because using tensio-active agent or make organic solvent go to control crystal morphology in reaction system can being avoided.Under optimal conditions of the present invention, LiFePO 4 material shows splendid chemical property.Therefore, adopting the art of this patent scheme, is that under most economical condition, (as far as possible low temperature of reaction) prepares the technical scheme of nano-grade lithium iron phosphate by most economical means (control heat-up rate).
Unaccomplished matter of the present invention is known technology.
Claims (3)
1. a hydrothermal synthesis method for nano-grade lithium iron phosphate, is characterized by and comprise the following steps:
The first step, hydrothermal synthesis reaction
Lithium hydroxide is water-soluble, add in autoclave, then add phosphoric acid, after the air in dead volume in inert gas purge still, sealing autoclave, be heated to 40 ~ 50 DEG C from room temperature under stirring, open feed valve and vent valve, then add pure source of iron solution, the reinforced used time is 20 ~ 40 minutes, stir after 10 ~ 30 minutes, pass into the steam of 200 DEG C, with the speed of 4 ~ 8 ° of C/min, reaction system is heated to 150 ~ 170 DEG C; The mol ratio adding material is: Li:Fe:P=3.0:1.0:1.0; After reinforced, in solution, the concentration of ferro element is 0.3 ~ 0.6mol/L
Second step, the filtration of resultant, washing and drying
150 ~ 170 DEG C of insulations are after 2 hours, stop heating, water coolant is led to autoclave by spiral coil cooling tube, make temperature be reduced to 70 ~ 80 ° of C, open bleeder valve, resultant is filtered, obtain filter cake and mother liquor, then washing leaching cake is to sulfate radical-free ion, and filter cake, in 110 ~ 120 DEG C of vacuum-dryings 12 hours, obtains canescence LiFePO4 powder; Reclaim(ed) sulfuric acid lithium after mother liquid evaporation is concentrated;
3rd step, the coated process of carbon
By the LiFePO of second step gained
4powder and carbon source in mass ratio 100:15 ~ 20 mix, and under protection of inert gas, in 700 DEG C of roastings 4 hours, obtain the iron lithium phosphate product that carbon is coated.
2. the hydrothermal synthesis method of nano-grade lithium iron phosphate as claimed in claim 1, it is characterized by source of iron is liquid before ferrous sulfate crystal or its crystallization, or the clear liquor of byproduct ferrous sulfate of titanium dioxide after purification and impurity removal.
3. the hydrothermal synthesis method of nano-grade lithium iron phosphate as claimed in claim 1, is characterized by described carbon source and is specially glucose.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113582149A (en) * | 2021-05-31 | 2021-11-02 | 佛山市德方纳米科技有限公司 | Preparation method of flaky lithium iron phosphate material |
| WO2023173645A1 (en) * | 2022-03-15 | 2023-09-21 | 深圳沃伦特新能源科技有限公司 | Method for preparing lithium iron phosphate from titanium dioxide by-product of ferrous sulfate |
| WO2023197483A1 (en) * | 2022-04-12 | 2023-10-19 | 深圳沃伦特新能源科技有限公司 | Hydrothermal synthesis method for nano lithium manganese iron phosphate |
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| CN103633321A (en) * | 2012-08-21 | 2014-03-12 | 中国科学院上海硅酸盐研究所 | Preparation method for lithium iron phosphate material |
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| CN102651475A (en) * | 2012-05-28 | 2012-08-29 | 深圳市贝特瑞新能源材料股份有限公司 | Synthesizing method of anode material lithium iron phosphate of lithium ion battery |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113582149A (en) * | 2021-05-31 | 2021-11-02 | 佛山市德方纳米科技有限公司 | Preparation method of flaky lithium iron phosphate material |
| WO2023173645A1 (en) * | 2022-03-15 | 2023-09-21 | 深圳沃伦特新能源科技有限公司 | Method for preparing lithium iron phosphate from titanium dioxide by-product of ferrous sulfate |
| WO2023197483A1 (en) * | 2022-04-12 | 2023-10-19 | 深圳沃伦特新能源科技有限公司 | Hydrothermal synthesis method for nano lithium manganese iron phosphate |
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