Method for preparing carbon-nitrogen co-doped lithium iron phosphate positive electrode material from titanium waste liquid and lithium ion battery

Abstract

The invention discloses a preparation method for preparing a carbon-nitrogen co-doped lithium iron phosphate positive electrode material from titanium waste liquid and a lithium ion battery, and the preparation method comprises the following steps: S1, mixing an iron source, a phosphorus source and deionized water, then adding the titanium-containing waste liquid, uniformly stirring, then adjusting the pH value to 2-7, heating, stirring and drying to obtain powder, roasting the powder to obtain a titanium modified FePO4 precursor material; and S2, mixing the titanium-modified FePO4 precursor material, a lithium source, an organic carbon-nitrogen source and a dispersing agent, performing ball milling to obtain slurry, and drying and roasting the slurry to obtain the positive electrode material. The method can solve the problem of treatment of the titanium tetrachloride waste liquid generated in the catalyst preparation process.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid and a lithium-ion battery. Background Technology

[0002] LiFePO4, a lithium metal phosphate with an olivine-type structure, has attracted widespread attention from researchers worldwide as a cathode material for lithium-ion batteries (LIBs). Among numerous lithium-ion battery cathode materials, it has become the preferred choice due to its low production cost, high discharge potential (a very stable voltage curve around 3.4V), abundant raw material sources, large theoretical capacity (170mAh / g), good thermal stability, excellent cycle performance, and environmentally friendly and safe properties. It is widely used in large-scale energy storage and lithium-ion batteries for new energy electric vehicles and hybrid vehicles. Meanwhile, in the production of polyolefin industrial catalysts, a large amount of titanium tetrachloride is required, often in excess. Therefore, after separating and precipitating the catalyst solid during polyolefin catalyst production, a large amount of titanium-containing mother liquor is generated, with titanium tetrachloride being the main component. This mother liquor readily reacts with water to generate corrosive hydrochloric acid gas, posing a certain degree of environmental harm. In addition to unreacted titanium tetrachloride, this mother liquor may also contain hydrocarbon organic solvents, haloalkoxy titanium, or alkoxy titanium components. If the waste liquid is discarded directly, it will inevitably cause environmental pollution and waste of resources. Therefore, using it for lithium iron phosphate modification and making harmless and effective use and treatment is a good choice.

[0003] There are currently no reports on the application of titanium tetrachloride waste liquid generated during the preparation of polypropylene catalysts to the modification of lithium iron phosphate.

[0004] Chinese patent CN116692801A discloses a method for preparing iron phosphate, a precursor for battery cathode materials, using waste acid from titanium dioxide. The method includes the following steps:

[0005] Step one involves preparing primary iron phosphate using waste acid from titanium dioxide, achieving comprehensive utilization of the waste acid. Step two involves modifying the primary iron phosphate by adding 10-15% bentonite compounding agent, 10% lithium carbonate, and 5% composite carbon source (a 1:1 mixture of glucose and citric acid) to the product from step two. The mixture is then ball-milled for modification. After ball milling, the product is washed with water. This invention regulates the raw materials in the liquid, enhancing the activity and dispersibility of bentonite. Combined with fluorinated carbon, silane coupling agent KH560, and lignin solution as a coordinating agent, the improvement effect of the bentonite compounding agent on the primary iron phosphate is optimized. This results in a product with excellent capacity retention, as well as improved acid and temperature resistance.

[0006] Existing technologies do not address the use of titanium tetrachloride waste liquid generated during the preparation of polypropylene catalysts for the synthesis of various industrial catalyst binders or for their green and rational utilization. Furthermore, they do not cover the application of environmentally friendly and green titanium-modified carbon and nitrogen co-doped lithium iron phosphate in improving charge and discharge capacity, coulombic efficiency, long cycle life, and reducing costs. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, which can solve the problem of treating titanium tetrachloride waste liquid generated during catalyst preparation.

[0008] Another objective of this invention is to provide a lithium-ion battery.

[0009] To achieve the above objectives, this invention provides a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, comprising the following steps:

[0010] S1, mix iron source, phosphorus source and deionized water, then add titanium-containing waste liquid, stir evenly and adjust pH to 2-7, heat and stir, dry to obtain powder, calcine the powder to obtain titanium-modified FePO4 precursor material;

[0011] S2, the titanium-modified FePO4 precursor material, lithium source, organic carbon and nitrogen source and dispersant are mixed and ball-milled to obtain a slurry, and the slurry is dried and calcined to obtain the cathode material.

[0012] The method described in this invention uses titanium-containing waste liquid, such as titanium tetrachloride waste liquid generated during the preparation of polypropylene catalysts, as a titanium source for titanium modification. Due to the charge compensation effect, it can also induce defect generation, thereby reducing the activation energy required for lithium-ion diffusion, enhancing the diffusion kinetics of lithium-ions, improving the ionic and electronic conductivity of lithium iron phosphate, and thus improving the rate performance of the material. In environmentally friendly organic carbon and nitrogen sources, nitrogen atoms can contribute additional electrons, providing electron carriers for the conduction band, further improving the electronic conductivity of the material.

[0013] In this invention, during ball milling, a mixed dispersant is used for grinding. The agate balls account for 4 to 8 times the total mass of the precursor material, lithium source, organic carbon and nitrogen source and dispersant. The mass ratio of the total amount of precursor material, lithium source and organic carbon and nitrogen source to the mass of dispersant is 1:2. The ball mill speed is controlled at 400 r / min and the ball milling time is 5 to 18 h.

[0014] The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium-containing waste liquid according to the present invention, wherein the iron source is calculated as iron atoms, the phosphorus source is calculated as phosphorus atoms, and the molar ratio of the iron source to the phosphorus source is 0.9-1.1:0.9-1.2.

[0015] The present invention relates to a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, wherein the titanium compound in the titanium-containing waste liquid is 0.5 wt% to 20 wt% of the total mass of phosphorus source and iron source.

[0016] The present invention relates to a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, wherein the titanium compound in the titanium-containing waste liquid is titanium tetrachloride.

[0017] The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to the present invention includes a calcination condition of 500-700℃ for 4-7 hours in step S1.

[0018] The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to the present invention, in step S1, the heating and stirring conditions are stirring at 60-80°C for 10-18 hours.

[0019] The present invention discloses a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, wherein the titanium-modified FePO4 precursor material is calculated on the basis of iron atoms, the lithium source is calculated on the basis of lithium atoms, and the molar ratio of titanium-modified FePO4 precursor material to lithium source is 1:1 to 1.1.

[0020] The present invention describes a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid, wherein the organic carbon-nitrogen source is 5 wt% to 30 wt% of the total mass of titanium-modified FePO4 precursor material and lithium source.

[0021] The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to the present invention includes a calcination condition in step S2 of calcination at 600-800°C for 9-24 hours under inert gas protection, wherein the inert gas is nitrogen and / or argon.

[0022] The present invention discloses a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid. The organic carbon-nitrogen source includes one or more of gelatin, L-lysine, melamine, carbamide, glutamic acid, and polyaniline, preferably gelatin and / or L-lysine. Using carbamide as the organic carbon-nitrogen source results in better carbon-nitrogen stability after calcination, leading to a more stable carbon-coated lithium iron phosphate structure. Using lysine and glutamic acid as organic carbon-nitrogen sources results in a more uniform distribution of the carbon-nitrogen source, which is more conducive to the uniform distribution of carbon-nitrogen coating and lithium iron phosphate after calcination and to lithium-ion conduction. Gelatin and lysine both have a thickening effect during ball milling modification, preventing agglomeration or uneven dispersion during the milling process.

[0023] The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to the present invention includes one or more of deionized water, anhydrous ethanol, anhydrous methanol, polyethylene glycol aqueous solution and benzyl alcohol, preferably anhydrous ethanol and / or anhydrous methanol.

[0024] The present invention discloses a method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid. The iron source comprises one or more of ferric nitrate nonahydrate, ferrous sulfate, ferric citrate, ferrous oxalate, ferric oxide, ferric chloride, and ferrous chloride, preferably one or more of ferrous oxalate, ferric nitrate nonahydrate, and ferric citrate; the phosphorus source comprises one or more of phosphoric acid, phosphorus oxychloride, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and monoammonium phosphate, preferably ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate; the lithium source comprises one or more of lithium oxide, lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate, and lithium citrate, preferably lithium hydroxide and / or lithium carbonate.

[0025] To achieve the above objectives, the present invention also provides a lithium-ion battery comprising a carbon-nitrogen co-doped lithium iron phosphate cathode material prepared by the preparation method described above.

[0026] Beneficial effects of this invention:

[0027] (1) The titanium-modified lithium iron phosphate provided by the present invention has high discharge capacity, coulombic efficiency and long cycle life, and the preparation process is highly tunable, which can provide a method for the preparation of industrial lithium iron phosphate cathode materials.

[0028] (2) The addition of titanium to lithium iron phosphate introduces more defects due to the charge compensation effect, which lowers the energy barrier for lithium ion transport and improves the electrochemical performance of lithium iron phosphate.

[0029] (3) The titanium source used in this invention mainly comes from titanium tetrachloride-containing waste liquid generated during the preparation of industrial polypropylene catalysts. This source is widely available and can not only introduce titanium ions for modification but also adjust the pH. Furthermore, the titanium-containing waste liquid contains a small amount of organic matter, which, after thorough mixing, drying, and calcination, acts as an organic template agent, resulting in more contact mesopores within the material. This not only improves the electrochemical performance of carbon-nitrogen co-doped lithium iron phosphate but also effectively utilizes the titanium tetrachloride waste liquid generated during the preparation of industrial polypropylene catalysts in a harmless manner.

[0030] (4) The titanium-modified carbon and nitrogen co-doped lithium iron phosphate of the present invention has carbon and nitrogen sources that are both environmentally friendly materials. Its preparation process is simple, green and environmentally friendly, highly reproducible, and low in cost, making it suitable for industrial production applications. Attached Figure Description

[0031] Figure 1 The XRD pattern of the lithium iron phosphate sample prepared in Example 1;

[0032] Figure 2 The XRD pattern of the lithium iron phosphate sample prepared in Example 2;

[0033] Figure 3 SEM image of the lithium iron phosphate sample prepared in Example 1;

[0034] Figure 4 The image shows a SEM image of the lithium iron phosphate sample prepared in Example 2. Detailed Implementation

[0035] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0036] The phase structure of LFP / C was characterized using a Rigaku D / Max-3C X-ray diffractometer; the surface morphology of the samples was characterized using a Zeiss Ultra-Plus field emission scanning electron microscope. The corresponding electrochemical performance was characterized using a Blue Electric electrochemical workstation CHI660D and a LAND battery testing system. The modified lithium iron phosphate and its preparation method provided by this invention, in several preferred embodiments, include the following raw materials:

[0037] (1) Waste liquid containing titanium tetrachloride generated during the preparation of polypropylene catalyst (hereinafter referred to as: waste liquid containing titanium tetrachloride): titanium content 70wt%~95wt% (calculated as TiCl4), provided by Lanzhou Chemical Research Center of Petroleum and Chemical Research Institute of China Petroleum;

[0038] (2) Diammonium phosphate, phosphoric acid, diammonium hydrogen phosphate, lithium carbonate, lithium hydroxide, lysine, gelatin, anhydrous ethanol, polyethylene glycol, anhydrous methanol, ferric nitrate nonahydrate, melamine, carbamide, polyaniline, benzyl alcohol;

[0039] Example 1

[0040] (1) Under normal temperature and pressure conditions, 181.8 g of ferric nitrate nonahydrate and 57.52 g of ammonium dihydrogen phosphate were weighed according to the stoichiometric molar ratio Fe:P = 0.9:1 and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 1.56 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and stirring was continued until the solution was homogeneous. The pH was adjusted to 2.9 using 18 wt% ammonia water. The solution was heated in an 80℃ water bath and stirred for 10 h until it was fully mixed. The resulting slurry was dried overnight at 90℃ to obtain powder, which was then calcined at 500℃ for 6 h to obtain ferric phosphate powder samples.

[0041] (2) Weigh 75.41g of iron phosphate powder, 20.35g of lithium carbonate, 4.5g of lysine, 200g of 15wt% polyethylene glycol solution, and 400g of agate balls from step (1) at a stoichiometric ratio of Fe:Li = 1:1.1. Mix and grind in a planetary ball mill (Hefei Kejing SFM-1) for 5 hours. Dry the resulting slurry in a vacuum drying oven (Tianjin Zhonghuan Electric Furnace) at 70℃. When the sample is dried into powder, put it into a tube furnace, introduce nitrogen gas, and calcine at 600℃ for 9 hours in a tube furnace (Hefei Kejing OTC-1200X) to obtain the final LFP / CN-T-1 sample. Figure 1 The XRD pattern of the sample shows that the synthesized lithium iron phosphate has high purity and is free of impurities. Figure 3 The SEM image of the sample shows that it has reached the nanoparticle level.

[0042] Example 2

[0043] (1) Under normal temperature and pressure conditions, 71.93 g of ferrous oxalate and 49 g of phosphoric acid were weighed according to the stoichiometric molar ratio Fe:P = 1:1 and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 4.37 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and stirring was continued until the solution was homogeneous. The pH was adjusted to 3.3 using 18 wt% ammonia water. The solution was heated in an 80℃ water bath and stirred for 15 h until it was fully mixed. The resulting slurry was dried overnight at 90℃ to obtain powder, which was then calcined at 600℃ for 6 h to obtain ferric phosphate powder samples.

[0044] (2) Weigh 75.41g of iron phosphate powder, 12g of lithium hydroxide, 7g of gelatin, 200g of anhydrous ethanol, and 400g of agate balls from step (1) at a stoichiometric ratio of Fe:Li = 1:1. Mix them and grind them in a planetary ball mill for 14 hours. Dry the resulting slurry in a vacuum drying oven at 70°C. When the sample is dried into powder, put it into a tube furnace, introduce argon gas, and calcine it at 700°C for 14 hours to obtain the final LFP / CN-T-2 sample. Figure 2 The XRD pattern of the sample shows that the synthesized lithium iron phosphate has high purity and is free of impurities. Figure 4 The SEM image of the sample shows that it has reached the nanoparticle level.

[0045] Example 3

[0046] (1) Under normal temperature and pressure conditions, 122.47 g of ferric citrate and 66.03 g of diammonium hydrogen phosphate were weighed according to the stoichiometric molar ratio Fe:P = 1:1 and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 34 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and stirring was continued until the solution was homogeneous. The pH was adjusted to 4.9 using 18 wt% ammonia water. The solution was heated in an 80℃ water bath and stirred for 18 h until it was fully mixed. The resulting slurry was dried overnight at 90℃ to obtain powder, which was then calcined at 700℃ for 5 h to obtain ferric phosphate powder samples.

[0047] (2) Weigh 75.41g of iron phosphate powder, 12g of lithium hydroxide, 12.59g of carbamide, 200g of anhydrous methanol, and 400g of agate balls from step (1) at a stoichiometric ratio of Fe:Li = 1:1. Mix them and grind them in a planetary ball mill for 18 hours. Dry the resulting slurry in a vacuum drying oven at 70°C. When the sample is dried into powder, put it into a tube furnace and calcine it at 700°C for 24 hours with argon gas to obtain the final LFP / CN-T-3 sample.

[0048] Example 4

[0049] (1) Under normal temperature and pressure conditions, 61.23 g of ferric citrate, 80.8 g of ferric nitrate nonahydrate, 28.8 g of ammonium dihydrogen phosphate, and 24.5 g of phosphoric acid were weighed according to a stoichiometric molar ratio of Fe:P = 0.9:1 and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 38.9 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and the mixture was stirred until homogeneous. The pH was adjusted to 3.1 using 18 wt% ammonia water. The solution was heated in an 80°C water bath and stirred for 12 h until it was fully mixed. The resulting slurry was dried overnight at 90°C to obtain powder, which was then calcined at 700°C for 4 h to obtain ferric phosphate powder samples.

[0050] (2) Weigh 75.41g of iron phosphate powder, 6g of lithium hydroxide, 9.62g of lithium carbonate, 11.3g of gelatin, 8.6g of glutamic acid, 5.48g of lysine, 200g of anhydrous ethanol, and 400g of agate balls from step (1) with a stoichiometric ratio of Fe:Li = 1:1.02. Mix them and grind them in a planetary ball mill for 16 hours. Dry the resulting slurry in a vacuum drying oven at 70°C. When the sample is dried into powder, put it into a tube furnace, introduce nitrogen gas, and calcine it at 700°C for 20 hours to obtain the final LFP / CN-T-4 sample.

[0051] Example 5

[0052] (1) Under normal temperature and pressure conditions, according to the stoichiometric molar ratio Fe:P = 1:1.1, 28.8 g of ferrous oxalate, 40.4 g of ferric nitrate nonahydrate, 49 g of ferric citrate, 33.015 g of diammonium hydrogen phosphate, and 34.5 g of ammonium dihydrogen phosphate were weighed and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 43.4 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and the mixture was stirred until homogeneous. The pH was adjusted to 2.7 using 18 wt% ammonia water. The solution was heated in an 80°C water bath and stirred for 17 h until it was fully mixed. The resulting slurry was dried overnight at 90°C to obtain powder, which was then calcined at 600°C for 7 h to obtain ferric phosphate powder samples.

[0053] (2) Weigh 75.41g of iron phosphate powder, 6g of lithium hydroxide, 9.24g of lithium carbonate, 7.51g of melamine, 8.3g of carbamide, 7.76g of polyaniline, 200g of benzyl alcohol, and 400g of agate balls from step (1) at a stoichiometric ratio of Fe:Li = 1:1. Mix them and grind them in a planetary ball mill for 10 hours. Dry the resulting slurry in a vacuum drying oven at 70°C. When the sample is dried into powder, put it into a tube furnace, introduce nitrogen gas, and calcine it at 700°C for 18 hours to obtain the final LFP / CN-T-5 sample.

[0054] Comparative Example 1

[0055] A carbonitrided lithium iron phosphate material is prepared according to the scheme provided in patent CN 104051738 A. The preparation method is as follows:

[0056] (1) Weigh out ferrous chloride tetrahydrate, phosphoric acid, and lithium acetate dihydrate in a molar ratio of 1:1:3 and dissolve them separately. The total mass of solids is 10% of the mass of the solvent water.

[0057] (2) Add phosphoric acid and ferrous chloride tetrahydrate solution to an autoclave and mix them with vigorous high-speed stirring, maintaining the temperature inside the autoclave at 70°C. Introduce a protective gas, then slowly add lithium acetate solution to the autoclave. Seal the autoclave and begin heating at a rate of approximately 3°C / min until reaching 220°C. Maintain the reaction system temperature at 220°C and control the system pressure at 1.6 MPa. The isothermal time is controlled at 6 hours. After the reaction is complete, separate the solid and liquid phases by centrifugation or filtration. The separated solid is washed to obtain the lithium iron phosphate crystal precursor.

[0058] (3) The prepared lithium iron phosphate crystal precursor is added to a high-temperature vacuum carbonitriding furnace.

[0059] (4) When the temperature rises to about 550°C at a rate of about 10°C / min, start to introduce a mixture of methane and ammonia gas to make the carbonitriding agent generate active carbon and nitrogen atoms. Maintain a constant temperature of 570°C for 4 hours.

[0060] (5) After carbonitriding, continue to raise the furnace temperature to 680℃, hold it at that temperature for 4 hours, and then allow it to cool naturally to below 60℃ to complete the SP2 hybridization and annealing process of carbon. The target product can then be obtained. The lithium iron phosphate material after carbonitriding has a specific capacity of 152 mAH / g, and the sample is designated as D-1.

[0061] Comparative Example 2

[0062] Lithium chloride, lithium hydroxide, and iron phosphate were weighed in a molar ratio of 0.63:0.37:1 to obtain a mixture. Sucrose, accounting for 10% of the total raw material weight, was then added to the mixture. The mixture was ball-milled for 3 hours using ethanol as a dispersant in a planetary ball mill, followed by spray drying to obtain a lithium iron phosphate precursor. The lithium iron phosphate precursor was then sintered at 800°C for 8 hours in a high-temperature furnace under a nitrogen atmosphere. After cooling, pulverizing, and grading, a lithium iron phosphate cathode (denoted as D-2) was obtained.

[0063] Comparative Example 3

[0064] According to the molar ratio of iron, phosphorus, and lithium of 0.95:1.00:1.04, ferric nitrate, ammonium dihydrogen phosphate, and lithium hydroxide are mixed, and deionized water is added, with the mass of water being 12% of the sum of the masses of ferric nitrate, ammonium dihydrogen phosphate, and lithium hydroxide. After stirring evenly, citric acid is added, with the mass of citric acid being 10% of the theoretical yield (by mass) of lithium iron phosphate cathode material. After stirring evenly, magnesium oxide is added as a high-valence metal oxide additive, with the mass of magnesium oxide being 0.5% of the theoretical yield (by mass) of lithium iron phosphate cathode material. After stirring evenly, surfactant EG (ethylene glycol) is added, with the mass of EG being 1% of the theoretical yield (by mass) of lithium iron phosphate cathode material. After stirring evenly, a mixture is obtained (denoted as D-3).

[0065] Comparative Example 4

[0066] (1) Under normal temperature and pressure conditions, 202 g of ferric nitrate nonahydrate and 57.52 g of ammonium dihydrogen phosphate were weighed according to a stoichiometric molar ratio of Fe:P = 1:1 and dissolved in 2.5 times their weight of deionized water. The solution was stirred thoroughly and completely dissolved. 1.56 g of titanium tetrachloride waste liquid (containing 83 wt% TiCl4) was slowly added dropwise to the mixed solution, and stirring was continued until the solution was homogeneous. The pH was adjusted to 2.9 using 18 wt% ammonia water. The solution was heated in an 80℃ water bath and stirred for 10 h until it was fully mixed. The resulting slurry was dried overnight at 90℃ to obtain the powder.

[0067] (2) Weigh 75.41g of powder, 14.78g of lithium carbonate, 4.5g of lysine, 200g of 15wt% polyethylene glycol solution, and 400g of agate balls from step (1) at a stoichiometric ratio of Fe:Li = 1:1. Mix them and grind them in a planetary ball mill (Hefei Kejing SFM-1) for 5 hours. Dry the resulting slurry in a vacuum drying oven (Tianjin Zhonghuan Electric Furnace) at 70°C. When the sample is dried into powder, put it into a tube furnace, introduce nitrogen gas, and calcine it at 600°C for 9 hours in a tube furnace (Hefei Kejing OTC-1200X). This result is recorded as D-4.

[0068] Preparation of lithium iron phosphate button batteries

[0069] Using LFP / C as the positive electrode active material, acetylene black (battery grade) as the conductive agent, and polyvinylidene fluoride (battery grade) as the binder, these materials were uniformly mixed in a mass ratio of 8:1:1 and then combined with N-methylpyrrolidone (battery grade) to form a slurry. This slurry was then uniformly coated onto a 16 μm thick carbon-coated aluminum foil (battery grade) at a concentration of approximately 7 mg / cm⁻². After drying in a vacuum at 120 °C for 12 h, the material was allowed to cool naturally and cut into 12 mm diameter discs. Using lithium metal sheet (battery grade) as the negative electrode, Celgard 2400 as the separator, and 1 mol / L LiPF₂ / (EC+DMC) (volume ratio 1:1 battery grade) as the electrolyte, CR2016 coin cells were assembled in an argon-filled dry glove box. Their electrochemical performance was then tested.

[0070] The electrochemical performance of the modified lithium iron phosphate cathode materials LFP / CN-T-1 to LFP / CN-T-5 and D-1 to D-4 prepared in Examples 1-5 and Comparative Examples 1-4 was tested, and the test results are shown in Table 1:

[0071] Table 1. Performance evaluation data of modified lithium iron phosphate cathodes in Examples 1-5 and Comparative Examples 1-4

[0072]

[0073]

[0074] As shown in Table 1, which contains performance test and evaluation data of modified lithium iron phosphate in Examples 1-5 and Comparative Examples 1-4, the modified lithium iron phosphate LFP / CN-T-1 to LFP / CN-T-5 prepared according to Examples 1-5 and the modified lithium iron phosphate D1-D4 prepared according to Comparative Examples 1-4 show that the titanium-modified carbon-nitrogen co-doped lithium iron phosphate prepared by the present invention can effectively improve the electrochemical performance of lithium iron phosphate.

[0075] The titanium-modified carbon-nitrogen co-doped lithium iron phosphate of this invention not only improves the specific capacity of lithium iron phosphate, enhances charge-discharge efficiency, increases cycle retention rate, and has a wide range of material sources, but also effectively utilizes the large amount of titanium tetrachloride waste liquid generated during the industrial production of polypropylene catalysts.

[0076] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium-containing waste liquid, characterized in that, Includes the following steps: S1, mix iron source, phosphorus source and deionized water, then add titanium-containing waste liquid, stir evenly and adjust pH to 2-7, heat and stir, dry to obtain powder, calcine the powder to obtain titanium-modified FePO4 precursor material; S2, the titanium-modified FePO4 precursor material, lithium source, organic carbon and nitrogen source and dispersant are mixed and ball-milled to obtain a slurry, and the slurry is dried and calcined to obtain the cathode material.

2. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium-containing waste liquid according to claim 1, characterized in that, The iron source is measured in terms of iron atoms, and the phosphorus source is measured in terms of phosphorus atoms. The molar ratio of the iron source to the phosphorus source is 0.9–1.1:0.9–1.

2.

3. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The titanium compounds in the titanium-containing wastewater account for 0.5 wt% to 20 wt% of the total mass of phosphorus and iron sources.

4. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The titanium compound in the titanium-containing waste liquid is titanium tetrachloride.

5. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, In step S1, the roasting conditions are 500–700℃ for 4–7 hours.

6. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, In step S1, the heating and stirring conditions are 60-80℃ for 10-18 hours.

7. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The titanium-modified FePO4 precursor material is calculated based on iron atoms, the lithium source is calculated based on lithium atoms, and the molar ratio of the titanium-modified FePO4 precursor material to the lithium source is 1:1 to 1.

1.

8. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The organic carbon and nitrogen source is 5 wt% to 30 wt% of the total mass of titanium-modified FePO4 precursor material and lithium source.

9. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, In step S2, the calcination conditions are: calcination at 600–800°C for 9–24 hours under inert gas protection, wherein the inert gas is nitrogen and / or argon.

10. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The organic carbon and nitrogen source includes one or more of gelatin, L-lysine, melamine, carbamide, glutamic acid, and polyaniline, preferably gelatin and / or L-lysine.

11. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The dispersant includes one or more of deionized water, anhydrous ethanol, anhydrous methanol, polyethylene glycol aqueous solution and benzyl alcohol, preferably anhydrous ethanol and / or anhydrous methanol.

12. The method for preparing carbon-nitrogen co-doped lithium iron phosphate cathode material from titanium waste liquid according to claim 1, characterized in that, The iron source includes one or more of ferric nitrate nonahydrate, ferrous sulfate, ferric citrate, ferrous oxalate, ferric oxide, ferric chloride, and ferrous chloride, preferably one or more of ferrous oxalate, ferric nitrate nonahydrate, and ferric citrate; the phosphorus source includes one or more of phosphoric acid, phosphorus oxychloride, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and monoammonium phosphate, preferably ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate; the lithium source includes one or more of lithium oxide, lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate, and lithium citrate, preferably lithium hydroxide and / or lithium carbonate.

13. A lithium-ion battery, characterized in that, The invention comprises the carbon-nitrogen co-doped lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1-12.

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