CN108448113B - Preparation method of doped modified lithium iron phosphate positive-grade material - Google Patents

Preparation method of doped modified lithium iron phosphate positive-grade material Download PDF

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CN108448113B
CN108448113B CN201810271437.7A CN201810271437A CN108448113B CN 108448113 B CN108448113 B CN 108448113B CN 201810271437 A CN201810271437 A CN 201810271437A CN 108448113 B CN108448113 B CN 108448113B
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lithium
iron phosphate
solution
rare earth
source
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CN108448113A (en
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刘述平
李超
廖祥文
张贻
周雄
冯雪茹
唐湘平
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Institute of Multipurpose Utilization of Mineral Resources Chinese Academy of Geological Sciences
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a preparation method of lithium iron phosphate as a lithium ion battery anode material, which comprises the steps of taking battery-grade lithium carbonate doped with magnesium or magnesium and rare earth as a lithium source, mixing the lithium source with an iron source, a phosphorus source and a carbon source, grinding, drying to obtain a doped and modified lithium iron phosphate precursor, and roasting the precursor to obtain a lithium iron phosphate anode material product; the Mg content of the battery-grade lithium carbonate is 0.06-1.75%. The preparation method has short grinding time and is energy-saving, is beneficial to realizing the uniform doping of magnesium, cerium or lanthanum to the lithium iron phosphate, and is particularly convenient to realize the doping of magnesium, cerium or lanthanum to the lithium position of the lithium iron phosphate. According to the invention, rare earth and/or magnesium are compounded in the battery-grade lithium carbonate for preparing the lithium iron phosphate, so that the grinding time is reduced, the cost is lower, and the lithium iron phosphate anode material prepared by the method has superior discharge capacity, cycle performance and rate capability, and better meets the application requirements.

Description

Preparation method of doped modified lithium iron phosphate positive-grade material
Technical Field
The invention relates to a preparation method of lithium iron phosphate serving as a lithium ion battery anode material, in particular to a doping modification method of a lithium iron phosphate anode material, and belongs to the technical field of lithium ion battery anode materials.
Background
Lithium iron phosphate is widely used as an important lithium ion battery positive-grade material in electric automobiles, energy storage devices and the like. Because the electronic conductivity and the ionic conductivity of the lithium iron phosphate are low, in order to improve the electrical property of the lithium iron phosphate, the following methods are generally adopted: reducing the granularity of the material, coating the conductive layer and doping ions. The ion doping method mainly means that a plurality of metal ions with good conductivity are doped at the position of positive ions in a lithium iron phosphate crystal lattice, the size of crystal grains is changed, and the crystal lattice defect of the material is caused, so that the conductivity of electrons in the crystal grains and the diffusion rate of lithium ions are improved, and further the purpose of improving the LiFePO is achieved4 The purpose of the electrical property of the material. At present, the doped metal ions are mainly Ti4+、Zn2+、Mn2+、La3+、Ce3+、V3+、Mg2+And the like.
And doping positive ions in lithium iron phosphate crystal lattices, and performing lithium position doping and iron position doping. Wherein, the common doping element for lithium doping is Mg2+、La3+、Ce3+And the like. The existing research shows that the multi-element composite doping of 2-3 impurities is better than the single-element doping of 1 impurity.
In the preparation of lithium ion battery positive-grade materials (lithium iron phosphate, ternary materials and the like), impurities of magnesium and rare earth are doped more. Currently, magnesium ion doping of lithium iron phosphate usually employs co-precipitation of trace magnesium in an iron source when synthesizing a precursor iron source (ferrous oxalate, iron phosphate, etc.), or uses organic acid salts (magnesium oxalate, etc.) and inorganic acid salts (magnesium nitrate, for example) of magnesium as a dopant when blending. But the magnesium doping in ferrous oxalate by a coprecipitation method is difficult to be controlled quantitatively; if a small amount of magnesium compound or a small amount of rare earth compound is doped during burdening and mixing, uniform mixing is difficult, and the requirements on burdening, mixing and grinding are high.
The related patent applications are as follows: 1. CN 101070149a discloses a lithium iron phosphate material prepared by vacuum carbon reduction and a method thereof, comprising the following steps: first, the iron source compound, the lithium source compound and the doped metal compound are mixed according to a molar ratio of P: Fe: Li: M of 1: (0.001-0.05), wherein M represents doped metal; secondly, placing the mixture obtained by mixing in the first step into a vacuum high-energy ball milling tank, vacuumizing and ball milling; thirdly, adding a carbon reducing agent into the mixture subjected to ball milling in the second step according to the molar ratio of Fe to C of 1 to 0.8-1.6, vacuumizing, and continuing ball milling to obtain a reaction precursor; transferring the reaction precursor into a vacuum reaction furnace, introducing nitrogen, vacuumizing, heating, introducing nitrogen again at a constant temperature, sealing and cooling to room temperature to obtain the carbon-coated metal-doped lithium iron phosphate cathode material; the doped metal compound comprises one or more of aluminum dihydrogen phosphate, zinc oxide, magnesium oxide and cobalt oxide. 2. CN 103137966A discloses a preparation method of a doped modified lithium iron phosphate anode material, which comprises the steps of placing lithium source, iron source, phosphorus source, doping source, dispersant, binder and other substances in a stirring ball mill for uniform mixing, then adopting a rotary gravity reduction composite granulation technology, adopting one-step vacuum drying and forming, preparing a pre-sintered material into a spherical particle shape, enabling all components of the pre-sintered material to achieve the effects of uniform mixing and densification, placing the spherical particle pre-sintered material in an inert atmosphere sintering furnace, calcining for a plurality of hours at 600-800 ℃, furnace cooling, crushing and screening to obtain the lithium iron phosphate anode material; the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium oxalate, the iron source is one or more of ferrous oxalate or ferric oxide, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide, and the doping source substance is one or more of acetylene black, conductive carbon black, glucose, epoxy resin, phenolic resin, polyethylene glycol and metal oxide. The above patent applications all have the problems that the grinding time is long, and trace doping source substances are difficult to be uniformly mixed with iron sources, lithium sources and carbon sources with large mass ratio.
As is known, battery grade lithium carbonate (Li)2CO3) Is an important inorganic chemical product and is mainly used as a lithium source for preparing anode materials (lithium cobaltate, ternary materials, lithium iron phosphate and the like) of lithium ion batteries. Currently, battery grade lithium carbonate requires its Li2CO3The content is more than or equal to 99.5 percent, and the content of impurity Pb is<0.0003%，Ca<0.005 percent. In ChinaLithium ion sourceThe Mg content of battery grade lithium carbonate with ore as raw material is required<0.008% of the Mg content of battery-grade lithium carbonate prepared from brine<0.015%。
In order to uniformly dope a trace amount of doping components into lithium iron phosphate particles during preparation of lithium iron phosphate, rare earth and/or magnesium is compounded into battery-grade lithium carbonate for preparing the lithium iron phosphate, so that the content of Mg in the lithium carbonate is 0.02-1.73%, the content of rare earth is 0.00-3.2%, and uniform doping of lithium sites and iron sites or uniform doping of multiple components of the lithium iron phosphate can be realized, thereby obtaining the lithium iron phosphate anode material with excellent electrical property. The technical method is not reported at home and abroad.
Disclosure of Invention
The invention aims to provide a preparation method of a doped modified lithium iron phosphate cathode material, which aims to solve the problems that the quantitative control is difficult when magnesium is doped in ferric oxalate by the existing coprecipitation method, a small amount of magnesium-doped compound or a small amount of rare earth-doped compound is difficult to mix uniformly when the materials are mixed, the requirements on the mixing, the material mixing and the grinding are high, and the like. According to the invention, rare earth and/or magnesium are compounded in the battery-grade lithium carbonate for preparing the lithium iron phosphate, so that the grinding time is reduced, the production cost is reduced, and the lithium iron phosphate anode material prepared by the method has superior discharge capacity, cycle performance and rate capability, and can better meet the application requirements.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a doped and modified lithium iron phosphate positive electrode material is characterized in that battery-grade lithium carbonate doped with magnesium or magnesium and rare earth is used as a lithium source, the lithium source is mixed with an iron source, a phosphorus source and a carbon source, the mixture is ground and dried to obtain a doped and modified lithium iron phosphate precursor, and the precursor is roasted to obtain a lithium iron phosphate positive electrode material product.
The battery grade lithium carbonate has the Mg content of 0.06-1.75%, and preferably has the Mg content of 0.5-1.3%.
The battery-grade lithium carbonate contains 0.00-3.2% of rare earth, and the rare earth element is selected from light rare earth elements Ce and La or a combination of the light rare earth elements Ce and La.
The battery grade lithium carbonate is prepared by the following method (I) or method (II):
the method (I): carrying out lithium-rich magnesium reduction treatment on old brine with the Li content of 300-6000 mg/L to obtain a lithium chloride salt lithium-rich solution with the Li content of 6.0-38 g/L, Mg and the Li content of 8-1740 mg/L, Ca and the Li content of 1.2-50 mg/L, heating the lithium chloride salt lithium-rich solution to 70-95 ℃, adding Na under the stirring condition2CO3Solution, Na added after completion of the addition2CO3Continuously stirring the solution for reaction for 60-130 min, and finally synthesizing, filtering, washing and drying to obtain Li2CO3The battery grade lithium carbonate product with the content of 93.9-99.4% and the Mg content of 0.04-1.3%.
In the method (one), when the synthesis temperature of the lithium carbonate is relatively high, that is, the temperature of the lithium chloride salt rich solution reaches 85 to 95 ℃, in order to effectively control the particle size of the lithium carbonate product, polyethylene glycol is usually added into the sodium carbonate solution or the lithium chloride salt rich solution before the synthesis reaction, and the addition amount of the polyethylene glycol is 0.2 to 0.4 percent of the weight of the lithium carbonate product.
In the above process (I), the Na is2CO3Solution of Na in2CO3The content of the sodium-containing lithium chloride is 200-310 g/L, Mg, the content of the sodium-containing lithium chloride is 20-30 mg/L, and each liter of the lithium-rich solution of the lithium chloride contains Na2CO3The addition amount of the solution is 1.07-1.17 times of the stoichiometric amount.
In the above method (one), Na may be further added for better use performance of the lithium carbonate product2CO3Slowly dripping solution containing beneficial component rare earth into lithium chloride salt lithium-rich solution while the solution is dissolved; the rare earth solution is an inorganic compound solution of one or more of rare earth elements Ce, La and Nd, or an organic compound solution of one or more of rare earth elements Ce, La and Nd; the content of rare earth in the rare earth solution is 5.0-80 g/L, and the content of the rare earth in a brine battery grade lithium carbonate product is as follows: 0.05 to 3.2 percent.
In the method (one), when the Li/Ca mass ratio of the lithium chloride salt lithium-rich solution is less than 4300, Ca impurities in the solution are selectively removed, and then Na is added2CO3The solution is prepared by the following specific method: adding 75-120 g/L sodium hydroxide solution into lithium chloride lithium-rich solution to adjust the pH value to 6.5-7.0, heating to 30-60 ℃, and then adding 1.7-2.2 times of stoichiometric Na2CO3Reacting for 40-60 min, and filtering to remove 70-94% of Ca impurities in the lithium-rich solution.
The method (II): removing impurities from a lithium sulfate solution produced by using lithium ore as a raw material to obtain a lithium sulfate purified solution with the Li content of 16-30 g/L, Mg of 20-100 mg/L, Ca of 2-4 mg/LThen, adding Na dissolved with EDTA and polyethylene glycol at the temperature of 80-90 ℃ into the purified lithium sulfate solution at the temperature of 20-60 ℃ under stirring2CO3Adding the purified lithium sulfate solution into the solution, continuously stirring and reacting at 85-97 ℃ for 30-60 min, and then filtering, washing and drying to obtain Li2CO3A battery grade lithium carbonate product with a content of 93.1-99.4% and a Mg content of 0.02-1.75%; or after obtaining the lithium sulfate purifying solution, dissolving Na in EDTA and polyethylene glycol at the temperature of 20-60 DEG C2CO3Adding the solution into purified lithium sulfate solution at the temperature of 70-90 ℃, and adding Na after the solution is completely added2CO3Continuously stirring the solution at 85-97 ℃ for reaction for 30-60 min, and then filtering, washing and drying to obtain Li2CO3The battery grade lithium carbonate product with the content of 93.1-99.4% and the content of Mg of 0.02-1.75%.
In the above process (II), the Na salt is2CO3Solution of Na in2CO3The content of the Na is 280-300 g/L, Mg, the content of the Na is 10-30 mg/L, and each liter of the Na in the lithium sulfate purifying solution2CO3The addition amount of the solution is 1.1-1.2 times of the stoichiometric amount.
In the second method, Na is used to obtain the lithium carbonate product with low Ca content2CO3The solution was added with a suitable amount of EDTA. The EDTA and Na2CO3The molar ratio of calcium in the solution is 1.5: 1-2.5: 1.
In the second method, in order to make the lithium carbonate product have better service performance, the lithium sulfate purified solution or Na can be added2CO3Dripping rare earth solution containing beneficial component light rare earth into the solution; the rare earth solution is an inorganic compound solution of one or more of rare earth elements Ce and La or an organic compound solution of one or more of rare earth elements Ce and La; the content of rare earth in the rare earth solution is 5.0-80 g/L, and the content of the rare earth in a battery-grade lithium carbonate product is as follows: 0.05 to 3.2 wt%.
In the second method, Na is used to obtain the lithium carbonate product with smaller particle size2CO3Polyethylene glycol is added into the solution. Addition of the polyethylene glycolThe input amount is 0.2-0.4% of the weight of the lithium carbonate product.
The iron source is selected from ferrous oxalate or iron phosphate, preferably iron phosphate.
When the iron phosphate is selected as the iron source, the iron phosphate is also a phosphorus source; when ferrous oxalate is used as the iron source, ammonium dihydrogen phosphate is selected as the phosphorus source.
In order to further improve the electrical property of the lithium iron phosphate, the binary doping of magnesium and titanium is usually required; magnesium is doped into lithium iron phosphate through lithium carbonate, titanium is doped into iron phosphate in advance through a conventional coprecipitation method, and the content of Ti in the iron phosphate is 0.15-0.32%.
The carbon source is selected from glucose or sucrose.
The preparation method of the lithium iron phosphate precursor comprises the following steps: and weighing and mixing the lithium source, the iron source, the phosphorus source, the carbon source and the doped metal compound, adding the mixture into a high-energy ball mill, grinding for 3-8 hours, and drying at 70-80 ℃ to obtain the lithium iron phosphate precursor.
Mixing the lithium source, the iron source, the phosphorus source and the doped metal compounds at a molar ratio of Li to Fe to P to M of 1.00 to 1.05 to 1.1 to 1.03 to 0.001 to 0.04, wherein M is the doped metal; the carbon source is added according to the weight ratio of 6-17% of the solid phase material. And anhydrous ethanol accounting for 82-92% of the weight of the solid phase materials can be added in the ball milling process.
The doped metal M is one or more of Mg, Ce, La and Ti.
The roasting treatment of the precursor comprises the following steps: and (3) placing the lithium iron phosphate precursor in a box type roasting furnace, roasting at 660-750 ℃ for 7-15 hours under the protection of nitrogen, cooling to 25-50 ℃ along with the furnace, discharging, crushing, sieving and packaging to obtain the lithium iron phosphate anode material product.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. doping lithium iron phosphate, in the prior art, a compound of an element to be doped is added into an iron source (ferrous oxalate or ferric phosphate) and a lithium source (lithium carbonate or lithium hydroxide), or a doping element (such as magnesium) is compounded in the iron source (such as ferrous oxalate) in advance, or a report that titanium is coprecipitated in the ferric phosphate to be singly doped is also reported; however, when two or more kinds of multi-element composite doping are performed, it is difficult to uniformly mix a trace amount of doping component with the main raw materials such as an iron source and a lithium source. The invention compounds magnesium or magnesium and rare earth in lithium carbonate as lithium source in advance, which is beneficial to doping magnesium and rare earth or uniformly doping magnesium and rare earth when preparing lithium iron phosphate, and is especially beneficial to doping Mg, Ce and La at the lithium position of the lithium iron phosphate.
2. In order to uniformly mix the doped components and the main raw materials, in the prior art, the mixture of doped components (such as magnesium acetate) such as an iron source, a lithium source (such as lithium carbonate), Mg and the like is subjected to grinding and mixing, the required time is long, and is usually 5-16 h; in the invention, the doped component is compounded in the lithium source (lithium carbonate) and the iron source (iron phosphate) in advance, so the required grinding time is short, only 3-5 h, and energy is saved.
3. According to the invention, beneficial components of magnesium or magnesium and rare earth are compounded with lithium carbonate, so that not only is uniform doping of lithium iron phosphate easily realized, but also the prepared lithium iron phosphate anode material has higher first discharge capacity, better cycle performance and rate capability, and better meets the application requirements.
Detailed Description
The following examples are provided for the purpose of illustrating the technical contents of the present invention and the technical effects achieved, but the examples themselves do not constitute a limitation of the present invention.
First, an iron source according to the present invention, which is referred to in the following embodiments, includes: iron phosphate, iron phosphate containing titanium and ferrous oxalate, and the main chemical components (weight percentage) are detailed in the table I.
1) Oxidizing Fe in ferrous sulfate solution with hydrogen peroxide2+Is Fe3+Adding ammonium dihydrogen phosphate into the solution for reaction, filtering, washing and drying to obtain hydrated iron phosphate (FePO)4·2H2O); calcining hydrated ferric phosphate at 600-650 ℃ for 2h to obtain ferric phosphate (FePO)4）。
2) Adding titanium into the iron phosphate by adopting a coprecipitation method to obtain the iron phosphate with the titanium content of 0.15-0.32%. The preparation method of the titanium-containing iron phosphate comprises the following steps: adding iron phosphate containing crystal water prepared by a conventional method into an aqueous solution with the concentration of phosphoric acid being 0.5mol/L, slowly dropwise adding a theoretical amount of titanium-containing solution (a solution obtained by dissolving titanyl sulfate in a small amount of distilled water) into the iron phosphate slurry under the conditions of the temperature being 70-75 ℃, the liquid-solid ratio being 3 and stirring, stirring for reaction for 2 hours, and then filtering and drying. And calcining the prepared titanium-doped iron phosphate in a muffle furnace at 600-650 ℃ for 2h to obtain the titanium-doped anhydrous iron phosphate.
3) The battery grade ferrous oxalate is a commercial product.
TABLE (A) main chemical composition of iron source/%)
Figure 52807DEST_PATH_IMAGE002
Secondly, the method for testing the electrical property of the lithium iron phosphate in the embodiment comprises the following steps:
and (3) mixing the components in a mass ratio of 90: 5: 5 LiFePO4Dissolving powder, a conductive agent SP and a binder PVDF in NMP to prepare positive electrode slurry with the solid content of 42%, coating the positive electrode slurry on an aluminum foil, drying the positive electrode slurry at the high temperature of 90-115 ℃ to prepare a positive electrode belt with the thickness of 200 mu m, drying the positive electrode belt at the temperature of 80 ℃ in vacuum for 8 hours, and rolling and punching to prepare a positive electrode sheet with the diameter of 14 mm. Taking the prepared pole piece as a positive electrode, a metal lithium piece as a negative electrode and Celgard 2400 as a diaphragm; at 1mol.L-1LiPF of6The electrolyte solution of/EC + DMC + DEC (1:1:1) was assembled into half-cells in an argon glove box. The cycling and rate capability were then tested on a wuhan blue electricity (model LANDCT 2001A) test system.
Example 1
Lithium iron phosphate with magnesium uniformly doped is prepared by taking lithium carbonate with magnesium as a lithium source and taking iron phosphate as an iron source.
Examples 1 to 1
Lithium carbonate containing 0.06% of magnesium is taken as a lithium source, and ferric phosphate is taken as an iron source to prepare lithium iron phosphate (LiMg) uniformly doped with magnesium0.001Fe0.999PO4/C）。
And adding 48.00g of iron phosphate, 11.85g of lithium carbonate with the magnesium content of 0.06%, 8.00g of glucose and 72mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 3h, drying at 70 ℃, heating to 670 ℃ under the protection of nitrogen, sintering for 13h, cooling to 25 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium-doped lithium iron phosphate product, wherein the product is numbered L-1-1 a.
Examples 1 to 2
Lithium carbonate containing 0.65% of magnesium is taken as a lithium source, and ferric phosphate is taken as an iron source to prepare lithium iron phosphate (LiMg) uniformly doped with magnesium0.01Fe0.99PO4/C）。
And (2) adding 48.00g of iron phosphate, 12.27g of lithium carbonate with the magnesium content of 0.65%, 8.00g of glucose and 80mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 3h, drying at 80 ℃, heating to 700 ℃ under the protection of nitrogen, sintering for 10h, cooling to 40 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium-doped lithium iron phosphate product, wherein the product is numbered L-1-1 b.
Examples 1 to 3
Lithium iron phosphate (LiMg) with magnesium uniformly doped is prepared by taking lithium carbonate containing 1.74% of magnesium as a lithium source and taking ferric phosphate as an iron source0.03Fe0.97PO4/C）。
And adding 48.00g of iron phosphate, 13.04g of lithium carbonate with the magnesium content of 1.74%, 8.00g of glucose and 80mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 4 hours, drying at 80 ℃, heating to 720 ℃ under the protection of nitrogen, sintering for 8 hours, cooling to 50 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium-doped lithium iron phosphate product, wherein the product is numbered L-1-1 c.
In contrast, a lithium iron phosphate product, which was numbered L-1-2, was synthesized under the same conditions as in example 1-2, using battery grade lithium carbonate having a magnesium content of 0.005% as a lithium source, adding magnesium acetate to dope the same amount of magnesium, and grinding for 6 hours. Under the same conditions as in example 1-2, a lithium iron phosphate product, numbered L-1-3, was prepared without doping magnesium using battery grade lithium carbonate having a magnesium content of 0.005% as a lithium source. The results of the electrical property tests of the products are shown in Table 1.
TABLE 1 comparison of electrical performance indexes of lithium iron phosphate cathode materials
Figure 376472DEST_PATH_IMAGE004
Example 2
Lithium carbonate containing rare earth is taken as a lithium source, and ferric phosphate is taken as an iron source to prepare the lithium iron phosphate uniformly doped with the light rare earth.
Example 2-1
Lithium carbonate with the lanthanum content of 0.36 percent is taken as a lithium source, iron phosphate is taken as an iron source, and lithium iron phosphate (Li) with uniformly doped lanthanum is prepared0.997La0.001FePO4/C）。
And (2) taking 48.00g of iron phosphate, 11.92g of lithium carbonate with the lanthanum content of 0.36%, 12.00g of glucose and 80mL of absolute ethyl alcohol, adding the materials into a high-energy ball mill, grinding for 4h, drying at 80 ℃, heating to 680 ℃ under the protection of nitrogen, sintering for 13h, cooling to 30 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a lanthanum-doped lithium iron phosphate product, wherein the product is numbered L-2-1.
Examples 2 to 2
Lithium carbonate containing 1.75% of lanthanum is taken as a lithium source, iron phosphate is taken as an iron source, and lithium iron phosphate (Li) with uniformly doped magnesium is prepared0.985La0.005FePO4/C）。
And adding 48.00g of iron phosphate, 11.97g of lithium carbonate with the lanthanum content of 1.75%, 8.00g of glucose and 80mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 3h, drying at 80 ℃, heating to 700 ℃ under the protection of nitrogen, sintering for 10h, cooling to 40 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a lanthanum-doped lithium iron phosphate product, wherein the product is numbered L-2-2.
Examples 2 to 3
Lithium carbonate containing 0.08% of cerium is taken as a lithium source, iron phosphate is taken as an iron source, and lithium iron phosphate (Li) with uniformly doped cerium is prepared0.9994Ce0.0002FePO4/C）。
And (2) adding 48.00g of iron phosphate, 12.10g of lithium carbonate with the cerium content of 0.08%, 8.00g of glucose and 80mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 3h, drying at 80 ℃, heating to 750 ℃ under the protection of nitrogen, sintering for 7h, cooling to 25 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a cerium-doped lithium iron phosphate product, wherein the product is numbered L-2-3.
In contrast, a lithium iron phosphate product, which was numbered L-2-4, was synthesized under the same conditions as in example 2-1, using battery grade lithium carbonate having a magnesium content of 0.005% as a lithium source, adding lanthanum oxalate to dope the same amount of lanthanum, and milling for 6 hours. The results of the electrical property tests of the product are shown in Table 2.
TABLE 2 comparison of electrical performance indexes of rare earth-doped lithium iron phosphate cathode materials
Figure 687368DEST_PATH_IMAGE006
Example 3
Lithium carbonate containing 0.63% of magnesium is taken as a lithium source, iron phosphate containing 0.32% of titanium is taken as an iron source, and the magnesium-titanium composite doped lithium iron phosphate cathode material (Li)0.98Mg0.01Fe0.98Ti0.01PO4/C）。
And (2) adding 48.00g of iron phosphate, 12.17g of lithium carbonate with the magnesium content of 0.63%, 8.50g of glucose and 80mL of absolute ethyl alcohol into a high-energy ball mill, grinding for 4h, drying at 80 ℃, heating to 680 ℃ under the protection of nitrogen, sintering for 12h, cooling to 35 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium and titanium doped lithium iron phosphate product, wherein the product is numbered L-3-1.
And compared with the magnesium acetate doped magnesium, and the butyl titanate doped titanium are added to prepare the magnesium and titanium composite doped lithium iron phosphate cathode material (the contents of Mg and Ti are the same as the previous sample). The product number is L-3-2. The electrical performance test results of the product are shown in table 3.
TABLE 3 comparison of electrical performance indexes of lithium iron phosphate cathode materials
Figure DEST_PATH_IMAGE008
Example 4
Lithium carbonate containing 0.55 percent of magnesium and 0.37 percent of cerium is taken as a lithium source, and ferric phosphate containing 0.32 percent of titanium is taken as an iron source, so as to prepare the magnesium, cerium and titanium composite doped lithium iron phosphate cathode material.
Taking 48.00g of iron phosphate, 12.34g of lithium carbonate containing 0.55 percent of magnesium, 0.37 percent of cerium, 8.50g of glucose and 85mL of absolute ethyl alcohol, adding the materials into a high-energy ball mill, grinding for 3h, drying at 80 ℃, heating to 660 ℃ under the protection of nitrogen, sintering for 15h, cooling to 30 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium and titanium doped lithium iron phosphate product, wherein the product is numbered L-4-1.
Compared with the magnesium acetate and cerium oxalate and titanium titanate, the magnesium, cerium and titanium composite doped lithium iron phosphate (the product with the contents of Mg, Ce and Ti being the same as the product with the serial number of L-4-1) cathode material is prepared by adding magnesium acetate and cerium, and adding butyl titanate and titanium, and the product with the serial number of L-4-2. The electrical performance test results of the product are shown in table 4.
TABLE 4 comparison of electrical performance indexes of lithium iron phosphate cathode materials
Figure DEST_PATH_IMAGE010
Example 5
Lithium carbonate containing 0.63% of magnesium is used as a lithium source, ferric oxalate is used as an iron source, ammonium dihydrogen phosphate is used as a phosphorus source, and lithium iron phosphate (LiMg) uniformly doped with magnesium is prepared0.01Fe0.99PO4/C）。
Example 5-1
Taking 48.00g of ferric oxalate, 10.74g of lithium carbonate with the magnesium content of 0.63 percent, 31.21g of ammonium dihydrogen phosphate, 6.00g of glucose and 80mL of absolute ethyl alcohol, adding the materials into a high-energy ball mill, grinding for 4h, drying at 80 ℃, then heating to 400 ℃ under the protection of nitrogen, calcining for 6h, heating to 750 ℃ and sintering for 12h, cooling to 50 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium and titanium doped lithium iron phosphate product, wherein the product is numbered L-5-1.
Examples 5 and 2
Taking 48.00g of ferric oxalate, 10.74g of lithium carbonate with the magnesium content of 0.63 percent, 31.21g of ammonium dihydrogen phosphate, 6.00g of glucose and 80mL of absolute ethyl alcohol, adding the materials into a high-energy ball mill, grinding for 4h, drying at 75 ℃, heating to 450 ℃ under the protection of nitrogen, calcining for 3h, heating to 700 ℃ and sintering for 16h, cooling to 25 ℃ along with the furnace, discharging, grinding, sieving and packaging to obtain a magnesium and titanium doped lithium iron phosphate product, wherein the product is numbered L-5-2.
In contrast, a battery grade lithium carbonate with a magnesium content of 0.005% was used as a lithium source, magnesium acetate was added to dope the same amount of magnesium, the milling time was 6 hours, and then the product was synthesized under the same conditions as the product number L-5-2, yielding a magnesium-doped lithium iron phosphate product, which was designated as L-5-3. The electrical performance test results of the product are shown in table 5.
TABLE 5 comparison of Electrical Performance indices of lithium iron phosphate cathode materials
Figure DEST_PATH_IMAGE012
As can be seen from the electrical property test results in tables 1 to 5, the lithium iron phosphate cathode material prepared by using battery-grade lithium carbonate compounded with magnesium and/or rare earth in advance as a lithium source and mixing the lithium source with an iron source, a phosphorus source and a carbon source has better 0.1C discharge performance and 1C discharge performance, and better discharge performance in 10 cycles of 1C and 30 cycles of 1C than the lithium iron phosphate cathode material prepared by using conventional battery-grade lithium carbonate as a lithium source and using organic acid salts (magnesium oxalate and the like), inorganic acid salts (such as magnesium nitrate) or rare earth oxalate as a dopant during mixing.

Claims (7)

1. A preparation method of a doped modified lithium iron phosphate anode material is characterized by comprising the following steps: taking lithium carbonate doped with magnesium and rare earth as a lithium source, weighing and mixing the lithium source, an iron source, a phosphorus source, a carbon source and a doped metal compound, adding the mixture into a high-energy ball mill, grinding for 3-8 h, drying at 70-80 ℃ to obtain a lithium iron phosphate precursor, mixing and grinding the lithium source, the iron source, the phosphorus source and the carbon source to obtain a doped and modified lithium iron phosphate precursor, and roasting the precursor to obtain a lithium iron phosphate positive electrode material product; the lithium carbonate doped with magnesium and rare earth is obtained by adopting the preparation method (I) or the preparation method (II):
the preparation method (I) comprises the following steps: carrying out lithium-rich magnesium reduction treatment on old brine with the Li content of 300-6000 mg/L to obtain a lithium chloride salt lithium-rich solution with the Li content of 6.0-38 g/L, Mg and the Li content of 8-1740 mg/L, Ca and the Li content of 1.2-50 mg/L, heating the lithium chloride salt lithium-rich solution to 70-95 ℃, adding Na under the stirring condition2CO3Solution, Na added after completion of the addition2CO3Continuously stirring the solution for reaction for 60-130 min, and finally filtering, washing and drying to obtain Li2CO3A lithium carbonate product with a content of 93.9-99.4% and a content of Mg of 0.04-1.3%;
the method for doping rare earth in the preparation method (I) comprises the following steps: after adding Na2CO3Slowly dripping a rare earth solution containing beneficial component rare earth into the lithium chloride salt lithium-rich solution while the solution is dissolved; the rare earth solution is an inorganic compound solution of one or more of rare earth elements Ce, La and Nd, or an organic compound solution of one or more of rare earth elements Ce, La and Nd; the content of rare earth in the rare earth solution is 5.0-80 g/L, and the content of the rare earth in a brine battery grade lithium carbonate product is as follows: 0.05-3.2%;
the preparation method (II) comprises the following steps: removing impurities from a lithium sulfate solution produced by taking lithium ore as a raw material to obtain a lithium sulfate purified solution with the Li content of 16-30 g/L, Mg of 20-100 mg/L, Ca of 2-4 mg/L, and adding Na dissolved with EDTA and polyethylene glycol at the temperature of 80-90 ℃ into the lithium sulfate purified solution with the temperature of 20-60 ℃ under the stirring condition2CO3Adding the purified lithium sulfate solution into the solution, continuously stirring and reacting at 85-97 ℃ for 30-60 min, and then filtering, washing and drying to obtain Li2CO3A lithium carbonate product with a content of 93.1-99.4% and a content of Mg of 0.02-1.75%; or after obtaining the lithium sulfate purifying solution, dissolving Na in EDTA and polyethylene glycol at the temperature of 20-60 DEG C2CO3Adding the solution into purified lithium sulfate solution at the temperature of 70-90 ℃, and adding Na after the solution is completely added2CO3Continuously stirring the solution at 85-97 ℃ for reaction for 30-60 min, and then filtering, washing and drying to obtain Li2CO3A lithium carbonate product with a content of 93.1-99.4% and a content of Mg of 0.02-1.75%;
the method for doping rare earth in the preparation method (II) comprises the following steps: to lithium sulfate purified solution or Na2CO3Dripping rare earth solution containing beneficial component light rare earth into the solution; the rare earth solution is an inorganic compound solution of one or more of rare earth elements Ce and La or an organic compound solution of one or more of rare earth elements Ce and La; the content of the rare earth in the rare earth solution is 5.0-80 g/L, and the content of the rare earth in a lithium carbonate product is as follows: 0.05 to 3.2 wt%.
2. The preparation method of the doped modified lithium iron phosphate positive electrode material according to claim 1, characterized by comprising the following steps: mixing the lithium source, the iron source, the phosphorus source and the doped metal compounds at a molar ratio of Li to Fe to P to M of 1.00 to 1.05 to 1.1 to 1.03 to 0.001 to 0.04, wherein M is the doped metal; the carbon source is added according to the weight ratio of 6-17% of the solid phase material.
3. The preparation method of the doped modified lithium iron phosphate positive electrode material according to claim 2, characterized by comprising the following steps: the doped metal M is one or more of Mg, Ce, La and Ti.
4. The preparation method of the doped modified lithium iron phosphate positive electrode material according to claim 1, characterized by comprising the following steps: the roasting treatment of the precursor comprises the following steps: and (3) placing the lithium iron phosphate precursor in a box type roasting furnace, sintering for 7-15 hours at 660-750 ℃ under the protection of nitrogen, cooling to 25-50 ℃ along with the furnace, discharging, crushing, sieving and packaging to obtain the lithium iron phosphate anode material product.
5. The preparation method of the doped modified lithium iron phosphate positive electrode material according to claim 1, characterized by comprising the following steps: the iron source is selected from iron phosphate or ferrous oxalate.
6. The preparation method of the doping modified lithium iron phosphate positive electrode material according to claim 1 or 5, characterized in that: when the iron source is ferrous oxalate, ammonium dihydrogen phosphate is selected as a phosphorus source.
7. The preparation method of the doped modified lithium iron phosphate positive electrode material according to claim 5, characterized by comprising the following steps: titanium is doped into the iron phosphate, and the content of Ti in the iron phosphate is 0.15-0.32%.
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