CN111498825A - Preparation method of titanium-doped lithium iron phosphate - Google Patents
Preparation method of titanium-doped lithium iron phosphate Download PDFInfo
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Abstract
The invention discloses a preparation method of titanium-doped lithium iron phosphate. Introducing titanium tetrachloride into a phosphoric acid solution, then putting the reaction slurry into a sealed reaction kettle, and evaporating under reduced pressure until water is completely evaporated to dryness; pouring out the evaporated and dried powder, mixing lithium carbonate through airflow crushing, mixing materials, slurrying, grinding, spraying and calcining to obtain a primary calcined material; adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture; mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate. The invention can obtain lithium iron phosphate with uniformly doped titanium, and has high discharge voltage platform, high compaction density and high energy density.
Description
Technical Field
The invention relates to a preparation method of titanium-doped lithium iron phosphate, belonging to the technical field of lithium batteries.
Background
As the current mainstream battery cathode material, the lithium iron phosphate gradually shrinks the market share in the early period due to the guidance of the subsidy policy, but the cost advantage of the lithium iron phosphate battery gradually becomes prominent after subsidy is taken off the slope. Meanwhile, a new energy bus as one of the main application scenes of the lithium iron phosphate battery or a policy will further support, thereby benefiting the lithium iron phosphate battery industry; for consumers in three-four-wire cities and even villages and towns, the lithium iron phosphate battery with low price and long service life has higher competitiveness. In addition, overall, compared with foreign manufacturers, the lithium iron phosphate battery in China has obvious relevant technical advantages, high product cost performance and industrial maturity, and complete supporting measures related to power management.
As the main force of power batteries, lithium iron phosphate batteries and ternary batteries have occupied about 95% of the market share of the whole industry in recent years, and the comparison between the two has never stopped. In 2015-2016, the market occupancy of lithium iron phosphate batteries reaches about 70%. However, as the subsidies of the national new energy vehicles gradually incline to products with high energy density and high endurance mileage, the market proportion of the lithium iron phosphate batteries gradually slides down. In two years of 2017 and 2018, the market share of the lithium iron phosphate is respectively reduced to 45% and 39%.
But the lithium iron phosphate battery market has been showing signs of warmth again since this year. According to the latest data published by the society of automotive industry of China, in 2019, 1-2 months, the cumulative output of the power battery in China reaches 11.6GWh, wherein the cumulative output of the ternary battery is 6.6GWh, which accounts for 57.2 percent of the total output; the cumulative production of the lithium iron phosphate battery is 4.6GWh, which accounts for 39.6 percent of the total output and is slightly increased compared with 36.03 percent of the total output in the same period in the last year.
In the existing preparation method of lithium iron phosphate, ion conductivity is improved by carbon coating, and electron conductivity is improved by metal ion doping, but a conventional doping mode is generally realized by adopting metal oxide or metal salt, so that doped metal ions may enter an iron position and a lithium position, and uncertainty is caused.
Disclosure of Invention
In view of the above, the invention provides a preparation method of titanium-doped lithium iron phosphate, which can obtain titanium-doped uniformly lithium iron phosphate, realizes directional doping of titanium to an iron site, has a high discharge voltage platform, a high compaction density and a high energy density, and is suitable for a lithium iron phosphate material for a power battery.
The invention solves the technical problems by the following technical means:
the invention relates to a preparation method of titanium-doped lithium iron phosphate, which comprises the following steps:
1) introducing titanium tetrachloride into a phosphoric acid solution of 1-2 mol/L, stirring while introducing titanium tetrachloride, introducing for 30-60min, maintaining the temperature at 50-70 ℃ in the introduction process, then stirring for 10-20min, then putting the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 30-60min, the pH value is maintained to be 2-2.5 in the process, the temperature is 50-70 ℃, then continuing stirring for 15-30min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
The mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.03-1.05, the pressure is reduced and the evaporation process is carried out, the pressure is maintained to be 0.01-0.2 atmospheric pressure, the temperature is 50-100 ℃, and the spray absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
The mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the air flow is pulverized to the particle size of the material of 0.5-1.5 mu m, a 50-150 mesh sieve is adopted for sieving, and the mole ratio of the titanium in the pulverized powder to the mixed lithium carbonate is 1:1.01 to 1.02, grinding to the particle size of 500-800nm, spray drying to obtain the dried material with the particle size of 1 to 10 mu m, calcining at the temperature of 600-700 ℃ for 5 to 8h, air-jet pulverizing to the particle size of 1 to 2 mu m to obtain the primary calcined material with the BET of 25 to 50m2/g。
In the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3-4, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.5-1%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.05-1.1, and the wastewater obtained by filtering and washing is subjected to membrane separation, concentration and crystallization to obtain the nitrogen-phosphorus compound fertilizer.
The molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.2-0.3.
The molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.01-1.05, the solid content of the slurry obtained by slurrying after mixing the iron-titanium mixture, lithium carbonate and a carbon source is 35-45%, the slurry is ground until the particle size of the slurry is 300-500nm, the particle size of the dried material obtained after spray drying is 1-20 mu m, and the carbon content is 3-5%.
The calcination process in the step (4) is divided into a temperature rising section, a heat preservation section and a temperature reduction section, wherein the temperature rising speed is 110-.
And (4) after the calcined material is pulverized into particles with the particle size of 2-2.5 microns by air flow, sieving the particles by an ultrasonic vibration sieve, removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
The invention prepares titanium phosphate first, then sinters with lithium carbonate to obtain sintered material, then stirs with dispersant solution to make slurry, makes it disperse in solution, then uses it as crystal nucleus, precipitates iron phosphate by coprecipitation, obtains the structure that uses sintered material as core and iron phosphate as shell, the structure is characterized in that titanium can be distributed in iron phosphate more evenly, at the same time, through first sintering, synthesizes titanium phosphate, then sinters with lithium carbonate, avoids titanium entering lithium position, but mainly enters iron position, then sinters after mixing with lithium source and carbon source, can obtain lithium iron phosphate with titanium doping evenly, at the same time, because the conventional doped titanium adopts nanometer titanium dioxide to dope, the compaction density of the obtained lithium iron phosphate with titanium doping will be reduced, because titanium dioxide adopts physical mixing with iron phosphate and lithium source, titanium will be on the surface of phosphoric acid, the invention adopts a titanium iron source with a core-shell structure, so that most of titanium can be positioned in the iron phosphate, so that the titanium can be positioned at the core of the lithium iron phosphate, and the influence of the titanium on the interface on the compaction density is avoided.
The invention has the beneficial effects that: the lithium iron phosphate with uniformly doped titanium can be obtained, has a high discharge voltage platform, high compaction density and high energy density, and is suitable for lithium iron phosphate materials for power batteries.
Drawings
FIG. 1 is a normal temperature cycle curve of the material of example 1 of the present invention;
FIG. 2 is a graph of the rate capability of the material of example 1 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and accompanying drawings, where the method for preparing titanium-doped lithium iron phosphate of the present embodiment includes the following steps:
1) introducing titanium tetrachloride into a phosphoric acid solution of 1-2 mol/L, stirring while introducing titanium tetrachloride, introducing for 30-60min, maintaining the temperature at 50-70 ℃ in the introduction process, then stirring for 10-20min, then putting the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 30-60min, the pH value is maintained to be 2-2.5 in the process, the temperature is 50-70 ℃, then continuing stirring for 15-30min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
The mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.03-1.05, the pressure is reduced and the evaporation process is carried out, the pressure is maintained to be 0.01-0.2 atmospheric pressure, the temperature is 50-100 ℃, and the spray absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
The mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the air flow is pulverized to the particle size of the material of 0.5-1.5 mu m, a 50-150 mesh sieve is adopted for sieving, and the mole ratio of the titanium in the pulverized powder to the mixed lithium carbonate is 1:1.01 to 1.02, grinding to the particle size of 500-800nm, spray drying to obtain the dried material with the particle size of 1 to 10 mu m, calcining at the temperature of 600-700 ℃ for 5 to 8h, air-jet pulverizing to the particle size of 1 to 2 mu m to obtain the primary calcined material with the BET of 25 to 50m2/g。
In the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3-4, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.5-1%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.05-1.1, and the wastewater obtained by filtering and washing is subjected to membrane separation, concentration and crystallization to obtain the nitrogen-phosphorus compound fertilizer.
The molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.2-0.3.
The molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.01-1.05, the solid content of the slurry obtained by slurrying after mixing the iron-titanium mixture, lithium carbonate and a carbon source is 35-45%, the slurry is ground until the particle size of the slurry is 300-500nm, the particle size of the dried material obtained after spray drying is 1-20 mu m, and the carbon content is 3-5%.
The calcination process in the step (4) is divided into a temperature rising section, a heat preservation section and a temperature reduction section, wherein the temperature rising speed is 110-.
And (4) after the calcined material is pulverized into particles with the particle size of 2-2.5 microns by air flow, sieving the particles by an ultrasonic vibration sieve, removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
Example 1
A preparation method of titanium-doped lithium iron phosphate comprises the following steps:
1) introducing titanium tetrachloride into a 1.5 mol/L phosphoric acid solution, stirring while introducing titanium tetrachloride, introducing for 50min, maintaining the temperature at 60 ℃ in the introduction process, then stirring for 15min, then putting the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 50min, the pH value in the process is maintained to be 2.3, the temperature is 60 ℃, then continuously stirring for 20min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
The mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.04, the pressure is maintained at 0.1 atmosphere in the process of reduced pressure evaporation, the temperature is 65 ℃, and the sprayed absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
The mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the powder is subjected to air flow crushing until the particle size of the material is 0.9 mu m, a 60-mesh sieve is adopted for sieving, and the molar ratio of the titanium in the crushed powder to the mixed lithium carbonate is 1: 1.015, grinding to the particle size of the material of 600nm, spray drying to obtain the dried material of 6.5 μm, calcining at 680 deg.C for 7h in air atmosphere, airflow pulverizing to 1.5 μm to obtain the primary calcined material with BET of 42.5m2/g。
In the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3.5, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.8%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.07, and the wastewater obtained by filtering and washing is subjected to membrane separation and then concentrated and crystallized to obtain the nitrogen-phosphorus compound fertilizer.
The molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.25.
the molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.035, the solid content of the slurried material obtained by slurrying the iron-titanium mixture mixed with lithium carbonate and a carbon source is 39%, the slurry is ground until the particle size of the slurry is 430nm, the particle size of the dried material obtained by spray drying is 12.5 μm, and the carbon content is 4.3%.
And (4) the calcining process in the step (4) is divided into a heating section, a heat preservation section and a cooling section, wherein the heating speed is 120 ℃/h, the heating temperature is 770 ℃, the heat preservation time is 11h, the material is discharged after being cooled to the material temperature of less than or equal to 100 ℃, and nitrogen is introduced in the calcining process, so that the oxygen content in the sintering furnace is lower than 5ppm, and the humidity of the heat preservation section is less than 1.5%.
And (4) after the calcined material is pulverized into particles with the particle size of 2.3 microns by air flow, sieving the particles by an ultrasonic vibration sieve, and removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
The indexes of the obtained lithium iron phosphate are as follows:
the method for measuring the compaction density comprises the steps of putting lithium iron phosphate powder into a die of powder compaction measuring equipment, pressing the powder under the pressure of 3 tons until the thickness of the powder is not changed any more, and dividing the powder by the volume to obtain powder compaction data.
Example 2
A preparation method of titanium-doped lithium iron phosphate comprises the following steps:
1) introducing titanium tetrachloride into a 1.2 mol/L phosphoric acid solution, stirring while introducing titanium tetrachloride, introducing for 50min, maintaining the temperature at 65 ℃ in the introduction process, then stirring for 15min, then putting the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 60min, the pH value in the process is maintained to be 2.2, the temperature is 70 ℃, then continuously stirring for 25min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
The mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.04, the pressure is maintained at 0.1 atmosphere in the process of reduced pressure evaporation, the temperature is 65 ℃, and the sprayed absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
The mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the powder is subjected to air flow crushing until the particle size of the material is 0.9 mu m, a 60-mesh sieve is adopted for sieving, and the molar ratio of the titanium in the crushed powder to the mixed lithium carbonate is 1: 1.015, grinding to the particle size of the material of 600nm, spray drying to obtain the dried material of 6.5 μm, calcining at 680 deg.C for 7h in air atmosphere, airflow pulverizing to 1.5 μm to obtain the primary calcined material with BET of 42.2m2/g。
In the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3.5, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.8%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.07, and the wastewater obtained by filtering and washing is subjected to membrane separation and then concentrated and crystallized to obtain the nitrogen-phosphorus compound fertilizer.
The molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.25.
the molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.03, the solid content of the slurried material obtained by slurrying the iron-titanium mixture after mixing with lithium carbonate and a carbon source is 39%, the slurry is ground until the particle size of the slurry is 430nm, the particle size of the dried material obtained after spray drying is 12.5 μm, and the carbon content is 4.3%.
And (4) the calcining process in the step (4) is divided into a heating section, a heat preservation section and a cooling section, wherein the heating speed is 120 ℃/h, the heating temperature is 770 ℃, the heat preservation time is 11h, the material is discharged after being cooled to the material temperature of less than or equal to 100 ℃, and nitrogen is introduced in the calcining process, so that the oxygen content in the sintering furnace is lower than 5ppm, and the humidity of the heat preservation section is less than 1.5%.
And (4) after the calcined material is pulverized into particles with the particle size of 2.2 microns by air flow, sieving the particles by an ultrasonic vibration sieve, and removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
The indexes of the obtained lithium iron phosphate are as follows:
| index (I) | Fe | P | Li | C |
| Numerical value | 34.11％ | 19.18％ | 4.43％ | 1.85％ |
| Index (I) | BET | Loose-pack | Tap density | Ti |
| Numerical value | 15.3m2/g | 0.65g/mL | 1.15g/mL | 623.6ppm |
| Index (I) | Ni | Ca | Mn | Zn |
| Numerical value | 2.5ppm | 18.5ppm | 21.9ppm | 10.1ppm |
| Index (I) | Na | Cd | Mg | Moisture content |
| Numerical value | 15.4ppm | 1.5ppm | 16.5ppm | 431ppm |
| Index (I) | K | pH | Sulfur | Magnetic substance |
| Numerical value | 16.6ppm | 9.18 | 89ppm | 0.34ppm |
| Index (I) | D10 | D50 | D90 | Density of compaction |
| Numerical value | 0.58μm | 2.2μm | 7.5μm | 2.50g/mL |
Example 3
A preparation method of titanium-doped lithium iron phosphate comprises the following steps:
1) introducing titanium tetrachloride into a 2 mol/L phosphoric acid solution, stirring while introducing titanium tetrachloride, introducing for 50min, maintaining the temperature at 55 ℃ in the introduction process, then stirring for 20min, then placing the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 50min, the pH value in the process is maintained to be 2, the temperature is 55 ℃, then continuously stirring for 20min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
The mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.04, the pressure is maintained at 0.08 atmospheric pressure in the process of reduced pressure evaporation, the temperature is 88 ℃, and the sprayed absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
The mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the powder is subjected to airflow pulverization until the particle size of the material is 1.2 mu m, an 80-mesh sieve is adopted for sieving, and the molar ratio of the titanium in the pulverized powder to the mixed lithium carbonate is 1: 1.015, grinding to the particle size of the material of 620nm, spray drying to obtain the dried material of 5.8 μm, calcining at 665 deg.C for 7.5h in air atmosphere, airflow pulverizing to 1.6 μm, and obtaining the primary calcined material with BET of 40.8m2/g。
In the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3.7, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.8%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.07, and the wastewater obtained by filtering and washing is subjected to membrane separation and then concentrated and crystallized to obtain the nitrogen-phosphorus compound fertilizer.
The molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.23.
the molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.02, the solid content of the slurried material obtained by slurrying the iron-titanium mixture after mixing with lithium carbonate and a carbon source is 40.5%, the slurry is ground until the particle size of the slurry is 380nm, the particle size of the dried material obtained after spray drying is 14.7 mu m, and the carbon content is 4.2%.
And (4) the calcining process in the step (4) is divided into a heating section, a heat preservation section and a cooling section, wherein the heating speed is 120 ℃/h, the temperature is increased to 765 ℃, the heat preservation time is 12h, the material is discharged after being cooled to the temperature of less than or equal to 100 ℃, nitrogen is introduced in the calcining process, so that the oxygen content in the sintering furnace is lower than 5ppm, and the humidity of the heat preservation section is less than 1.5%.
And (4) after the calcined material is pulverized into the particle size of 2.1 microns by air flow, sieving the pulverized material by an ultrasonic vibration sieve, and removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
The indexes of the obtained lithium iron phosphate are as follows:
| index (I) | Fe | P | Li | C |
| Numerical value | 34.19％ | 19.16％ | 4.40％ | 1.52％ |
| Index (I) | BET | Loose-pack | Tap density | Co |
| Numerical value | 15.8m2/g | 0.67g/mL | 1.41g/mL | 1.2ppm |
| Index (I) | Ni | Ca | Mn | Zn |
| Numerical value | 0.6ppm | 4.6ppm | 13.2ppm | 1.6ppm |
| Index (I) | Na | Cd | Mg | Moisture content |
| Numerical value | 12.5ppm | 1.1ppm | 13.1ppm | 323ppm |
| Index (I) | K | pH | Sulfur | Magnetic substance |
| Numerical value | 7.1ppm | 9.15 | 42ppm | 0.52ppm |
| Index (I) | D10 | D50 | D90 | Density of compaction |
| Numerical value | 0.46μm | 1.3μm | 5.6μm | 2.69g/mL |
Performing a power-on test on the lithium iron phosphate material obtained in the embodiments 1 to 3, mixing nano titanium dioxide with iron phosphate, lithium carbonate and glucose, then grinding, spraying, sintering and crushing to obtain titanium-doped lithium iron phosphate, wherein the sintering process is the same as that of the embodiment 1, the finally obtained lithium iron phosphate is prepared into the power-on test, and the detection result is as follows:
| example 1 | Example 2 | Example 3 | Comparative example | |
| 0.1C first charge capacity | 162.2mAh/g | 162.4mAh/g | 162.4mAh/g | 162.4mAh/g |
| First discharge capacity at 0.1C | 159.9mAh/g | 159.9mAh/g | 158.7mAh/g | 157.7mAh/g |
| First discharge capacity at 0.5C | 154.7mAh/g | 154.3mAh/g | 154.3mAh/g | 153.1mAh/ |
| 1C first discharge capacity | 147.7mAh/g | 147.8mAh/g | 147.1mAh/g | 145.4mAh/g |
| Voltage platform | 3.311V | 3.322V | 3.301V | 3.126V |
The electricity deduction test method comprises the following steps: SP: the mass ratio of PVDF is 90: 5: and 5, assembling to obtain a power-on test, wherein the cut-off voltage is 2.0V.
The material of example 1 was prepared into a 25Ah square pouch battery, and the normal temperature cycle performance was measured, and the result is shown in fig. 1, wherein the capacity retention rate is close to 90% after 1000 times of normal temperature cycles, and the discharge curve is shown in fig. 2 when the battery is discharged at different rates at normal temperature.
As shown in fig. 1 and 2, the room temperature cycle and rate performance of example 1 are very good.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
Claims (8)
1. A preparation method of titanium-doped lithium iron phosphate is characterized by comprising the following steps:
1) introducing titanium tetrachloride into a phosphoric acid solution of 1-2 mol/L, stirring while introducing titanium tetrachloride, introducing for 30-60min, maintaining the temperature at 50-70 ℃ in the introduction process, then stirring for 10-20min, then putting the reaction slurry into a sealed reaction kettle, evaporating under reduced pressure until water is completely evaporated to dryness, condensing and recovering the evaporated steam, and spraying and absorbing the tail gas;
2) pouring out the evaporated and dried powder, performing jet milling, screening and iron removal, mixing lithium carbonate, mixing materials, slurrying, grinding, spraying and calcining to obtain a material, and performing jet milling, screening and iron removal to obtain a primary calcined material;
3) adding the primary calcined material into a polyethylene glycol solution, stirring and slurrying to obtain a slurried material, then adding a ferrous sulfate solution, a phosphoric acid solution and an ammonia water solution into the slurried material together, wherein the adding time is 30-60min, the pH value is maintained to be 2-2.5 in the process, the temperature is 50-70 ℃, then continuing stirring for 15-30min, and filtering, washing and drying the reaction material to obtain an iron-titanium mixture;
4) mixing the iron-titanium mixture with lithium carbonate and a carbon source, pulping, grinding, spraying and calcining to obtain a material, and performing air flow crushing, screening and iron removal on the obtained material to obtain the titanium-doped lithium iron phosphate.
2. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: the mole number of the titanium tetrachloride and the phosphoric acid added in the step (1) is 1:1.03-1.05, the pressure is reduced and the evaporation process is carried out, the pressure is maintained to be 0.01-0.2 atmospheric pressure, the temperature is 50-100 ℃, and the spray absorption liquid and the condensate are mixed to obtain the hydrochloric acid solution.
3. A method as claimed in claim 1The preparation method of the titanium-doped lithium iron phosphate is characterized by comprising the following steps: the mass fraction of the water content of the evaporated and dried powder in the step (2) is less than or equal to 1%, the air flow is pulverized to the particle size of the material of 0.5-1.5 mu m, a 50-150 mesh sieve is adopted for sieving, and the mole ratio of the titanium in the pulverized powder to the mixed lithium carbonate is 1:1.01 to 1.02, grinding to the particle size of 500-800nm, spray drying to obtain the dried material with the particle size of 1 to 10 mu m, calcining at the temperature of 600-700 ℃ for 5 to 8h, air-jet pulverizing to the particle size of 1 to 2 mu m to obtain the primary calcined material with the BET of 25 to 50m2/g。
4. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: in the step (3), the mass ratio of the primary calcined material to the polyethylene glycol solution is 1:3-4, the mass fraction of the polyethylene glycol in the polyethylene glycol solution is 0.5-1%, the molar ratio of the ferrous sulfate to the phosphoric acid added into the slurry is 1:1.05-1.1, and the wastewater obtained by filtering and washing is subjected to membrane separation, concentration and crystallization to obtain the nitrogen-phosphorus compound fertilizer.
5. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: the molar ratio of iron to titanium in the iron-titanium mixture obtained in the step (3) is 100: 0.2-0.3.
6. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: the molar ratio of iron to lithium carbonate in the iron-titanium mixture added in the step (4) is 1:1.01-1.05, the solid content of the slurry obtained by slurrying after mixing the iron-titanium mixture, lithium carbonate and a carbon source is 35-45%, the slurry is ground until the particle size of the slurry is 300-500nm, the particle size of the dried material obtained after spray drying is 1-20 mu m, and the carbon content is 3-5%.
7. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: the calcination process in the step (4) is divided into a temperature rising section, a heat preservation section and a temperature reduction section, wherein the temperature rising speed is 110-.
8. The method for preparing titanium-doped lithium iron phosphate according to claim 1, wherein the method comprises the following steps: and (4) after the calcined material is pulverized into particles with the particle size of 2-2.5 microns by air flow, sieving the particles by an ultrasonic vibration sieve, removing iron by using a battery iron remover until the magnetic substance is less than 0.5ppm, and stopping removing iron to obtain the titanium-doped lithium iron phosphate.
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| WO2023124574A1 (en) | 2021-12-29 | 2023-07-06 | 湖北万润新能源科技股份有限公司 | Titanium and zirconium co-doped, carbon-coated lithium iron phosphate material, preparation method therefor and use thereof |
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