Titanium dioxide and preparation method and application thereof

Abstract

The invention discloses titanium dioxide as well as a preparation method and application thereof. The preparation method of the titanium dioxide comprises the following steps: reacting a mixed solution in a micro coil pipe to obtain the titanium dioxide, the mixed solution comprises titanium tetrachloride and ammonia water, and the mass ratio of the titanium tetrachloride to the ammonia water is 1: (0.5-3); the reaction temperature is 140 to 200 DEG C; the titanium dioxide has the advantages of large specific surface area and small secondary particle size, and the lithium iron phosphate material doped with the titanium dioxide is applied to the lithium ion battery, so that the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The invention relates to titanium dioxide and a preparation method and application thereof. Background Art

[0002] As a new generation of material for lithium-ion batteries, lithium iron phosphate can make lithium-ion batteries have good cycle performance and high safety. However, lithium iron phosphate itself has low electrical conductivity and slow ion and electron transmission speed. Currently, coating and metal element doping are often used to solve the ion and electron transmission problems. Common doping functional additives include vanadium, titanium, strontium and niobium. Titanium dioxide can improve the electrical conductivity of lithium iron phosphate electrode materials, thereby accelerating the transmission speed of electrons and ions, and improving the discharge performance and cycle life of the battery. In addition, doping with titanium dioxide can also improve the crystallinity of the electrode material and enhance its stability. In lithium iron phosphate electrode materials, titanium dioxide doping can inhibit the dissolution of cobalt, nickel and other ions and slow down the capacity decay of the battery. At the same time, titanium dioxide can also improve the battery's resistance to overcharge and over-discharge, thereby extending the battery's service life. However, most of the titanium dioxide currently sold on the market is at the micron level, and a few are at the nano level. The specific surface area of conventional titanium dioxide products is 10-30m 2 / g, the specific surface area of some products can reach 60m 2 / g, the use of commercially available titanium dioxide cannot effectively improve the cycle performance of the battery. Summary of the Invention

[0003] To address the poor cycling performance of lithium-ion batteries using lithium iron phosphate as the active material in existing technologies, a titanium dioxide (TiO2) and its preparation method and application are provided. The TiO2 of the present invention has the advantages of a large specific surface area and a small secondary particle size. The application of a lithium iron phosphate material doped with TiO2 in a lithium-ion battery can improve the cycling performance of the battery.

[0004] The present invention solves the above technical problems through the following technical solutions.

[0005] The present invention provides a method for preparing titanium dioxide, which comprises the following steps:

[0006] The mixed solution is reacted in a micro coil to obtain titanium dioxide;

[0007] The mixed solution comprises titanium tetrachloride and ammonia water, and the mass ratio of the titanium tetrachloride to the ammonia water is 1:(0.5-3);

[0008] The reaction temperature is 140-200°C.

[0009] The present invention reacts a mixed solution containing titanium tetrachloride and ammonia water in a microcoil, which can improve heat transfer efficiency, enhance heat transfer, and accelerate the reaction. The secondary flow generated at the bend can enhance mass transfer, allowing for rapid and continuous synthesis of titanium dioxide. Simultaneously, the titanium tetrachloride in the mixed solution can be rapidly hydrolyzed into a titanium dioxide precursor at the aforementioned temperature. The rapid hydrolysis of ammonia water at the aforementioned temperature can further increase the supersaturation of the system. The combination of titanium tetrachloride, ammonia water, and the microcoil can effectively reduce the particle size of titanium dioxide. Furthermore, the microcoil can be used to directly obtain metal oxides without the need for calcination. If the reaction temperature is too high, the growth of titanium dioxide particles will be accelerated, resulting in an increase in particle size and a decrease in specific surface area. Furthermore, if the reaction temperature is too low, titanium dioxide cannot be obtained.

[0010] In the present invention, the mass ratio of titanium tetrachloride to ammonia water in the mixed solution is preferably 1:(0.5-2.55), for example, 1:1.05, 1:1.55 or 1:2.05.

[0011] In the present invention, preferably, the reaction temperature is 140-180°C, for example 160°C.

[0012] In the present invention, preferably, the mixed solution is prepared by introducing the titanium tetrachloride solution and the ammonia solution into a mixer respectively and mixing them.

[0013] The introduction is performed, for example, by using a pump.

[0014] Preferably, the concentration of the titanium tetrachloride solution is 20-40 g / L, for example, 22 g / L.

[0015] Preferably, the concentration of the ammonia solution is 10-140 g / L, more preferably 10-60 g / L, for example, 11 g / L, 23 g / L, 34 g / L, 45 g / L or 56 g / L.

[0016] Preferably, the flow rate ratio of the titanium tetrachloride solution and the ammonia solution into the mixer is 1:1.

[0017] Preferably, the flow rate of the titanium tetrachloride solution into the mixer is 5-25 mL / min, for example, 10 mL / min.

[0018] Preferably, the flow rate of the ammonia solution into the mixer is 5-25 mL / min, for example, 10 mL / min.

[0019] In certain specific embodiments of the present invention, the flow rate of the titanium tetrachloride solution into the mixer is 10 mL / min, the flow rate of the ammonia solution into the mixer is 10 mL / min, the concentration of the titanium tetrachloride solution is 22 g / L, and the concentration of the ammonia solution is 10-60 g / L.

[0020] In certain preferred embodiments of the present invention, the method for preparing titanium dioxide further comprises the step of passing the mixed solution into the microcoil.

[0021] Preferably, during the introduction process, the flow rate of the mixed solution is 10-50 mL / min, for example, 20 mL / min.

[0022] In the present invention, preferably, the reaction time is 1-6 min, more preferably 2-4 min, for example, 2 min, 3 min, 3.5 min or 4 min.

[0023] In the present invention, preferably, the reaction pressure is 0.5-1.8 MPa, more preferably 1-1.4 MPa, for example, 1.07 MPa, 1.09 MPa, 1.1 MPa, 1.11 MPa, 1.15 MPa, 1.2 MPa, 1.21 MPa, 1.24 MPa, 1.27 MPa, 1.29 MPa, 1.31 MPa, 1.34 MPa or 1.35 MPa.

[0024] The microcoil in the present invention is defined as a chemical reactor that is manufactured with a solid matrix using a special micromachining technology and can be used for continuous operation. The microcoil is usually composed of multiple pipes that are spirally arranged to form a compact bed structure.

[0025] In the present invention, preferably, the micro coil comprises N interconnected coil units, where N is an integer greater than or equal to 1, and the coil unit is a cylindrical pipeline formed by spirally winding a pipe segment.

[0026] Preferably, when N is greater than 2, the axes of every two adjacent coil units are arranged at right angles.

[0027] Preferably, the ratio of the height to the diameter of the coil unit is (8-12):1, for example, 10:1.

[0028] Preferably, the length of the coil unit is 5-30 m, more preferably 5-20 m, for example 10 m or 15 m. The length refers to the length from the mixed solution entering the coil unit to the length of the mixed solution exiting the coil unit.

[0029] Preferably, the height of the coil unit is 24-36 mm, for example, 30 mm.

[0030] Preferably, the diameter of the coil unit is 2-4 mm, for example, 3 mm.

[0031] In the present invention, preferably, the reaction further includes a drying step.

[0032] The drying temperature is preferably 105-130°C.

[0033] The drying time is not particularly limited, as long as the solvent is completely removed.

[0034] The present invention also provides titanium dioxide prepared by the above-mentioned titanium dioxide preparation method.

[0035] In the present invention, the titanium dioxide exists in the form of secondary particles. It is generally understood by those skilled in the art that secondary particles are formed by the aggregation of primary particles.

[0036] In the present invention, the particle size of the titanium dioxide may satisfy one or more of the following conditions:

[0037] The particle size D10 of the secondary particles of titanium dioxide is 0.2-0.4 μm, for example, 0.234 μm, 0.237 μm, 0.246 μm, 0.247 μm, 0.25 μm, 0.251 μm, 0.252 μm, 0.254 μm, 0.259 μm or 0.271 μm;

[0038] The particle size D50 of the secondary particles of titanium dioxide is 0.3-0.6 μm, preferably 0.4-0.5 μm, more preferably 0.41-0.48 μm, for example, 0.413 μm, 0.414 μm, 0.417 μm, 0.420 μm, 0.427 μm, 0.434 μm, 0.435 μm, 0.447 μm, 0.451 μm, 0.464 μm, 0.467 μm, 0.471 μm or 0.473 μm;

[0039] The particle size D99 of the secondary particles of titanium dioxide is 0.7-4 μm, preferably 2-4 μm, for example, 2.769 μm, 2.841 μm, 2.894 μm, 2.912 μm, 2.945 μm, 3.014 μm, 3.016 μm, 3.124 μm, 3.134 μm, 3.467 μm or 3.791 μm;

[0040] The maximum particle size of the secondary particles of titanium dioxide is less than 10 μm, preferably less than 8 μm, more preferably 5-7 μm, and even more preferably 0.23-0.3 μm, for example, 5.146 μm, 5.247 μm, 5.476 μm, 5.479 μm, 5.592 μm, 5.764 μm, 5.811 μm, 5.812 μm, 5.827 μm, 5.841 μm, 5.946 μm, 6.124 μm, 6.157 μm or 6.271 μm;

[0041] In the present invention, the particle size D50 of the primary particles in the secondary particles of titanium dioxide is 4-6 nm, more preferably 4.1-5.8 nm, for example, 4.2 nm, 4.5 nm, 4.7 nm, 4.8 nm, 5.0 nm, 5.3 nm, 5.7 nm or 5.8 nm.

[0042] In the present invention, the specific surface area of the secondary particles of titanium dioxide can be 247-331m 2 / g, more preferably 300-330.3m 2 / g.

[0043] In the present invention, the specific surface area of the secondary particles of titanium dioxide can be 247-320m 2 / g, for example, 247.5m 2 / g, 251.7m 2 / g, 254.6m 2 / g, 257.3m 2 / g, 257.5m 2 / g, 272.7m 2 / g, 287.6m 2 / g, 296.3m 2 / g, 297.4m 2 / g、310.4m 2 / g or 313.0m 2 / g.

[0044] In the present invention, the purity of the titanium dioxide can reach above 98%, for example, 99% or 99.5%. Other impurities in the titanium dioxide in the present invention mainly include water.

[0045] In the present invention, the crystal form of the titanium dioxide may be anatase crystal form and / or rutile crystal form.

[0046] In the present invention, the relative crystallinity of the titanium dioxide may be 40%-130%, preferably 50%-130%, for example, 53.9%, 54.1%, 62.4%, 66.9%, 69.8%, 75.8%, 75.9%, 77.3%, 90.7%, 100%, 119% or 129%. The relative crystallinity refers to the ratio of the crystallinity of the titanium dioxide to the crystallinity of a 100% crystalline or amorphous standard sample.

[0047] The present invention also provides a method for preparing a lithium iron phosphate material, which comprises the following steps:

[0048] The mixture is dried and sintered in sequence to obtain lithium iron phosphate material;

[0049] The mixture includes iron phosphate, a lithium source, a carbon source, titanium dioxide and a solvent; the particle size D50 of the secondary particles of the titanium dioxide is 0.3-0.6 μm; and the titanium dioxide is prepared by the above-mentioned titanium dioxide preparation method.

[0050] The present invention avoids the agglomeration problem occurring during the mixing process by controlling the particle size D50 of the secondary particles of titanium dioxide, and can make the titanium dioxide evenly distributed in the lithium iron phosphate material.

[0051] In the present invention, the particle size D50 of the secondary particles of titanium dioxide is preferably 0.4-0.5 μm, more preferably 0.41-0.48 μm, for example, 0.413 μm, 0.414 μm, 0.417 μm, 0.420 μm, 0.427 μm, 0.434 μm, 0.435 μm, 0.447 μm, 0.451 μm, 0.464 μm, 0.467 μm, 0.471 μm or 0.473 μm.

[0052] In the present invention, preferably, the particle size D10 of the secondary particles of titanium dioxide is 0.2-0.4 μm, more preferably 0.23-0.3 μm, for example, 0.234 μm, 0.237 μm, 0.246 μm, 0.247 μm, 0.25 μm, 0.251 μm, 0.252 μm, 0.254 μm, 0.259 μm or 0.271 μm.

[0053] In the present invention, preferably, the particle size D99 of the secondary particles of titanium dioxide is 0.7-4 μm, more preferably 2-4 μm, for example, 2.769 μm, 2.841 μm, 2.894 μm, 2.912 μm, 2.945 μm, 3.014 μm, 3.016 μm, 3.124 μm, 3.134 μm, 3.467 μm or 3.791 μm.

[0054] In the present invention, preferably, the specific surface area of the secondary particles of titanium dioxide is 247-331m 2 / g, more preferably 300-330.3m 2 / g.

[0055] In the present invention, the specific surface area of the secondary particles of titanium dioxide is preferably 247-320 m 2 / g, for example, 247.5m 2 / g, 251.7m 2 / g, 254.6m 2 / g, 257.3m 2 / g, 257.5m 2 / g, 272.7m 2 / g, 287.6m 2 / g, 296.3m 2 / g, 297.4m 2 / g、310.4m 2 / g or 313.0m 2 / g.

[0056] In the present invention, preferably, the purity of the titanium dioxide is greater than 98%, for example, 99% or 99.5%. In the present invention, titanium dioxide includes pure titanium dioxide and impurities, wherein purity refers to the percentage of the mass of pure titanium dioxide to the mass of titanium dioxide. The impurities mainly include water.

[0057] In the present invention, preferably, the particle size D50 of the primary particles in the secondary particles of titanium dioxide is 4-6 nm, more preferably 4.1-5.8 nm, for example, 4.2 nm, 4.5 nm, 4.7 nm, 4.8 nm, 5.0 nm, 5.3 nm, 5.7 nm or 5.8 nm.

[0058] In the present invention, preferably, the maximum particle size of the secondary particles of titanium dioxide is less than 10 μm, more preferably less than 8 μm, and further more preferably 5-7 μm, for example, 5.146 μm, 5.247 μm, 5.476 μm, 5.479 μm, 5.592 μm, 5.764 μm, 5.811 μm, 5.812 μm, 5.827 μm, 5.841 μm, 5.946 μm, 6.124 μm, 6.157 μm or 6.271 μm.

[0059] In the present invention, preferably, the crystal form of the titanium dioxide is anatase crystal form and / or rutile crystal form.

[0060] In the present invention, preferably, the relative crystallinity of the titanium dioxide is 40%-130%, more preferably 50%-130%, for example, 53.9%, 54.1%, 66.9%, 69.8%, 75.8%, 75.9%, 77.3%, 90.7%, 100%, 119% or 129%.

[0061] In the present invention, preferably, in the mixture, the atomic percentage of the titanium element in the titanium dioxide to the phosphorus element in the ferric phosphate is 0.25%-1.5%, more preferably 1%-1.5%, for example 1.25%.

[0062] In the present invention, preferably, the molar ratio of the iron element to the phosphorus element in the ferric phosphate is (0.95-1.01):1, more preferably (0.97-1):1, for example, 0.98:1 or 0.985:1.

[0063] In certain specific embodiments of the present invention, the molar ratio of the iron element of the iron phosphate, the phosphorus element of the iron phosphate, and the titanium element of the titanium dioxide in the mixture is (95-101):100:(0.25-1.5), for example, 98:100:1.25. By controlling the contents of these three elements in the mixture, the present invention can significantly improve the lithium ion diffusion coefficient of the lithium iron phosphate material while also preventing the formation of impurity phases.

[0064] In the present invention, preferably, the specific surface area of the iron phosphate is 5-30m 2 / g, more preferably 10-30m 2 / g, for example, 13m 2 / g、15m 2 / g or 25m 2 / g.

[0065] In the present invention, preferably, the purity of the ferric phosphate is greater than 80%, for example, 85%, 99%, 99.5% or 99.8%.

[0066] In the present invention, the lithium source is a conventional lithium-containing compound in the art, wherein, preferably, the lithium source is a lithium-containing compound that does not contain phosphorus and iron elements, more preferably one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium oxide, for example, lithium carbonate.

[0067] In the present invention, the carbon source is a conventional carbon-containing compound in the art, wherein preferably, the carbon source is one or more of glucose, sucrose and polyethylene glycol.

[0068] In the present invention, preferably, the mixture further comprises a non-titanium source, wherein the non-titanium source is one or more of a vanadium source, a niobium source, a strontium source, a copper source, an aluminum source, and a zirconium source. The vanadium source is a conventional vanadium-containing compound in the art, the niobium source is a conventional niobium-containing compound in the art, the strontium source is a conventional strontium-containing compound in the art, the copper source is a conventional copper-containing compound in the art, the aluminum source is a conventional aluminum-containing compound in the art, and the zirconium source is a conventional zirconium-containing compound in the art.

[0069] In the present invention, preferably, the solvent is water.

[0070] In the present invention, preferably, the mixture further comprises an auxiliary agent, such as vanadium pentoxide and / or strontium carbonate.

[0071] In the present invention, preferably, a sanding step is further included before the drying.

[0072] Preferably, the sanding device is a sand grinder.

[0073] Preferably, the particle size D50 after sand grinding is 200-1000 nm, for example 800 nm. The use of the above particle size after sand grinding in the present invention can further promote the dispersion of titanium dioxide, making the titanium dioxide dispersed evenly, thereby further improving the overcharge and over-discharge resistance of the lithium iron phosphate material and reducing the degree of capacity decay.

[0074] In the present invention, preferably, the mixture is a suspension.

[0075] Preferably, the solid content of the suspension is 30%-70%.

[0076] Preferably, the pH value of the suspension is 3-8.

[0077] Preferably, the viscosity of the suspension is 1000-20000 mPa.S.

[0078] In the present invention, preferably, the drying method is spray drying.

[0079] The air inlet temperature of the spray drying is, for example, 280°C.

[0080] The outlet temperature of the spray drying is, for example, 130°C.

[0081] Preferably, the average particle size of the particles obtained after the spray drying is 10-150 μm.

[0082] In the present invention, the sintering includes, for example, a temperature rising stage and a constant temperature stage.

[0083] The heating rate in the heating stage is, for example, 5° C. / min.

[0084] The temperature in the constant temperature stage is preferably 600-760°C, for example 720°C.

[0085] The constant temperature stage preferably lasts for 5-20 hours, for example, 13 hours.

[0086] In the present invention, the sintering is preferably performed under an inert gas atmosphere.

[0087] The inert gas is, for example, nitrogen, and the purity of the nitrogen is, for example, 99.999%.

[0088] In the present invention, the above sintering temperature is adopted to facilitate the fusion of primary particles and thus destroy the structure of secondary particles.

[0089] In the present invention, preferably, a crushing step is further included after the sintering.

[0090] Preferably, the crushing is air flow crushing.

[0091] Preferably, the particle size D50 after crushing is 1.5-3 μm.

[0092] In the present invention, the titanium dioxide is preferably subjected to a surface hydrophilic modification treatment. After the surface modification treatment, the hydrophilicity of the titanium dioxide can be further improved, and the titanium dioxide can be more evenly distributed in the lithium iron phosphate material.

[0093] Wherein, the surface hydrophilic modification treatment preferably adopts a silane coupling agent.

[0094] The silane coupling agent is, for example, γ-(methacryloyloxy)propyltrimethoxysilane (KH570).

[0095] The present invention also provides a lithium iron phosphate material prepared by the above-mentioned preparation method of the lithium iron phosphate material.

[0096] In the present invention, preferably, the atomic percentage of titanium element in the lithium iron phosphate material to phosphorus element is 0.25%-1.5%, more preferably 1%-1.5%, for example 1.25%.

[0097] The use of the titanium dioxide content in the above atomic percentage can significantly improve the electrical properties of the lithium iron phosphate material, especially its cycle performance.

[0098] In the present invention, preferably, the particle size D10 of the lithium iron phosphate material is greater than 0.35 μm, more preferably 0.4-0.5 μm, for example 0.45 μm, 0.46 μm or 0.47 μm.

[0099] In the present invention, preferably, the particle size D50 of the lithium iron phosphate material is 1-2.2 μm, more preferably 1.1-2 μm, for example, 1.16 μm, 1.2 μm, 1.21 μm, 1.32 μm, 1.33 μm, 1.34 μm, 1.35 μm, 1.36 μm, 1.37 μm, 1.38 μm, 1.39 μm, 1.43 μm or 1.44 μm.

[0100] In the present invention, preferably, the particle size D99 of the lithium iron phosphate material is less than 12.5 μm, more preferably 5-6 μm, for example, 5.28 μm, 5.44 μm, 5.56 μm, 5.66 μm, 5.68 μm, 5.71 μm, 5.74 μm, 5.79 μm, 5.83 μm, 5.85 μm, 5.92 μm, and 5.97 μm.

[0101] In the present invention, preferably, the maximum particle size of the lithium iron phosphate material is less than 15 μm, more preferably 6-8 μm, for example, 6.33 μm, 7.12 μm, 7.26 μm, 7.27 μm, 7.28 μm, 7.3 μm, 7.31 μm, 7.32 μm or 7.33 μm.

[0102] The present invention also provides a pole piece, which includes the above-mentioned lithium iron phosphate material.

[0103] The present invention also provides a lithium-ion battery comprising the above-mentioned pole piece.

[0104] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0105] The reagents and raw materials used in the present invention are commercially available.

[0106] The positive progress effect of the present invention is:

[0107] The present invention provides a method for preparing titanium dioxide, which uses titanium tetrachloride and ammonia as raw materials and cooperates with micro-coils. The titanium tetrachloride can be rapidly hydrolyzed to form a titanium dioxide precursor, and the ammonia can further increase the supersaturation of the system. The high heat and mass transfer efficiency of the micro-coils combined with the two raw materials can effectively reduce the particle size of the titanium dioxide.

[0108] The present invention provides a method for preparing a lithium iron phosphate material. Titanium dioxide having a secondary particle size D50 of 0.3-0.6 μm is used to uniformly distribute the titanium dioxide within the lithium iron phosphate material, resulting in a lithium iron phosphate material with excellent performance. The pole pieces and lithium-ion batteries prepared using this material exhibit excellent electrical properties, including low resistivity, high capacity, and, in particular, excellent long-term cycling performance. The present invention dopes the titanium dioxide obtained by the titanium dioxide preparation method into lithium iron phosphate to obtain a lithium iron phosphate material with even lower resistivity and higher capacity, thereby improving the long-term cycling performance of pole pieces and lithium-ion batteries containing this lithium iron phosphate material. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] Figure 1 This is a TEM image of titanium dioxide in Example 1.

[0110] Figure 2 for Figure 1 TEM image at 25x magnification.

[0111] Figure 3 This is the XRD pattern of titanium dioxide prepared in Example 1.

[0112] Figure 4 This is the diffraction spot pattern of titanium dioxide prepared in Example 1.

[0113] Figure 5 Schematic diagram of the structure of the micro coil used in Examples 1-14 and Comparative Example 1. DETAILED DESCRIPTION

[0114] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0115] Examples 1-14 and Comparative Example 1: Preparation of Titanium Dioxide

[0116] The preparation method of titanium dioxide of Examples 1-14 and Comparative Example 1 comprises the following steps:

[0117] A titanium tetrachloride solution and an ammonia solution are respectively introduced into a mixer through pumps for mixing to obtain a mixed solution, and the mixed solution is introduced into a microcoil through a pump for reaction to obtain titanium dioxide; after the reaction, the mixture is dried at a temperature of 110° C. The flow rate of the titanium tetrachloride solution into the mixer is 10 mL / min, and the flow rate of the ammonia solution into the mixer is 10 mL / min.

[0118] Parameters such as the reaction temperature, the mass ratio of titanium tetrachloride to ammonia water in the mixed solution, etc. are listed in Table 1 below.

[0119] The schematic diagram of the micro coil structure is as follows Figure 5 As shown, it includes a coil unit, which is a cylindrical pipe formed by spirally winding a pipe segment. The ratio of the height to diameter of the coil unit is 10:1; the height of the coil unit is 30mm; and the diameter of the coil unit is 3mm.

[0120] The specific process parameters of Examples 1-14 and Comparative Example 1 are listed in Table 1:

[0121] Table 1

[0122]

[0123] Examples 15-39 and Comparative Examples 2-3: Preparation of Lithium Iron Phosphate Materials

[0124] The preparation method of the lithium iron phosphate material of Examples 15-39 and Comparative Examples 2-3 comprises the following steps:

[0125] The ferric phosphate, a lithium source, a carbon source, a non-titanium source, titanium dioxide, an additive, and a solvent are mixed to obtain a mixture, wherein the mixture is a suspension; wherein the relevant parameters of the ferric phosphate, the types of the lithium source, and the carbon source are listed in Table 2 below, the non-titanium source is a vanadium source, the solvent is water, and the additive is vanadium pentoxide;

[0126] The suspension is sequentially subjected to sand milling, spray drying, sintering and crushing to obtain lithium iron phosphate material.

[0127] The sand milling device is a sand mill. The solids content of the suspension is 50%. The pH value of the suspension is 7. The viscosity of the suspension is 10,000 mPa.s. The air inlet temperature of the spray dryer is 280°C. The air outlet temperature of the spray dryer is 130°C. The average particle size of the particles obtained after spray drying is 100 μm.

[0128] Sintering consisted of a heating phase and a constant temperature phase. The heating rate during the heating phase was 5°C / min, and the temperature and time during the constant temperature phase are listed in Table 2. Sintering was performed under an inert gas atmosphere. The inert gas was nitrogen with a purity of 99.999%.

[0129] The crushing is air flow crushing, and the particle size D50 after crushing is 1.5-3um.

[0130] Among them, Examples 15-28 respectively use the titanium dioxide prepared in Examples 1-14; Examples 29-39 respectively use commercially available titanium dioxide, wherein the specific surface area of the secondary particles is 75m 2 / g, the source of titanium dioxide with anatase crystal form is the product of Xuancheng Jingrui, model VK-TA30D; the specific surface area of the secondary particles is 33m 2 / g, the titanium dioxide with rutile crystal form comes from the product model VK-T30D of Xuancheng Jingrui.

[0131] Comparative Example 2 uses the titanium dioxide prepared in Comparative Example 1.

[0132] Comparative Example 3 uses commercially available titanium dioxide, the specific surface area of which is 19 m 2 / g, titanium dioxide with anatase crystal form, sourced from the product model Ti-R-230703 of Hubei Tianci.

[0133] Among them, the iron phosphate used in Examples 15-39 and Comparative Examples 2-3 was purchased from Tianci Materials.

[0134] Table 2

[0135]

[0136] Effect Example 1

[0137] 1. The particle sizes of the primary and secondary particles of titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 were tested:

[0138] Primary Particle Size Test: XRD testing of nanoparticles was performed using a Thermo Scientific ARL EQUINOX 3000 X-ray diffractometer. The test conditions were as follows: scanning between 20° and 80° 2θ, with a step size of 0.02° and a scanning speed of 1° / min. Cu Kα radiation was used as the X-ray source. XRD patterns were obtained, and K (Scherrer constant), λ (wavelength of X-rays), β (half-maximum width of the diffraction peak, i.e., the peak width at half the peak intensity), and θ (diffraction angle, in radians) were obtained from the XRD patterns. The particle size D50 of the titanium dioxide primary particles was calculated according to the following formula:

[0139]

[0140] Secondary particle size test: A laser particle size analyzer was used for testing. The equipment manufacturer is Zhuhai OMEC Instrument Co., Ltd., and the equipment model is TopSizer. The specific method is as follows: weigh 0.5g of titanium dioxide sample into a disposable cup, add 3mL of anhydrous ethanol, use a disposable dropper to disperse the titanium dioxide sample, and add it dropwise to the sample cell for testing. Set the refractive index of the laser particle size analyzer to 1.8 and the refractive ratio to 8-12 before starting the test.

[0141] 2. The purity of the titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 was tested: the test method was based on the national standard GB / T 37632-2019.

[0142] 3. The specific surface area of the titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 was tested: the test method was in accordance with the national standard GB / T 19587-2004.

[0143] 4. The crystal forms of titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 were tested: the test method was based on the national standard GB / T 37054-2018.

[0144] 5. The relative crystallinity of the titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 was tested: The crystallinity was calculated by comparing the diffraction intensity of the test sample with that of a 100% crystalline or amorphous standard sample. The standard sample was anatase titanium dioxide. The formula is: Xc = Ic / I0, where Xc is the crystallinity of the test sample, Ic is the integrated intensity of the diffraction peak of the test sample, and I0 is the integrated intensity of the standard sample.

[0145] 6. TEM images and diffraction spot patterns of the titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 were measured using a JEOL 2100f TEM instrument, manufactured by JOEL Ltd., Tokyo, Japan.

[0146] The parameters of titanium dioxide used in Examples 15-39 and Comparative Examples 2-3 are listed in Table 3:

[0147] Table 3

[0148]

[0149] Note: “ / ” represents the absence of titanium dioxide.

[0150] According to the data of Comparative Example 2, during the preparation of titanium dioxide, the reaction temperature was too low, 120° C., and titanium dioxide could not be obtained.

[0151] According to the data of Examples 16-19, a reaction temperature of 140-180° C. can further increase the specific surface area of titanium dioxide and reduce the particle size of primary particles of titanium dioxide.

[0152] According to the data of Examples 20-24, the concentration of the ammonia solution is 40-60 g / L, which can make the ammonia solution have a more appropriate supersaturation, further increase the specific surface area of titanium dioxide and reduce the particle size of the primary particles of titanium dioxide.

[0153] According to the data of Examples 25-28, the length of the coil unit is 5-15 m, which can further increase the specific surface area of titanium dioxide and reduce the particle size of the primary particles of titanium dioxide. This may be because the nucleation step of titanium dioxide is completed within the first 5 m of the coil (about 1 min), and the subsequent process is mainly the growth process of the particles.

[0154] Figure 1 is a TEM image of titanium dioxide in Example 1, Figure 2 for Figure 1 TEM image magnified 25 times, by Figure 1 and Figure 2 It can be seen that the titanium dioxide prepared in Example 1 has a small particle size. Figure 3 The XRD pattern of titanium dioxide prepared in Example 1 is shown in FIG. Figure 4 The diffraction spot pattern of titanium dioxide prepared in Example 1 is Figure 3 and Figure 4 It can be seen that the titanium dioxide prepared in Example 1 is anatase.

[0155] Effect Example 2

[0156] 1. The particle size of the lithium iron phosphate materials obtained in Examples 15-39 and Comparative Examples 2-3 was tested using a laser particle size analyzer, the model of which is TopSizer, and the manufacturer is OMEC.

[0157] 2. The resistivity, carbon content and compacted density of the lithium iron phosphate materials prepared in Examples 15-39 and Comparative Examples 2-3 were tested according to the national standard GB / T 33822-2017.

[0158] 3. The powder compaction density of the lithium iron phosphate materials obtained in Examples 15-39 and Comparative Examples 2-3 was tested using a UTM7305Z09 test machine with a test pressure of 30 kN.

[0159] 4. The electrical properties of the lithium iron phosphate materials prepared in Examples 15-39 and Comparative Examples 2-3 were tested:

[0160] (1) Positive electrode production

[0161] The lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride were dissolved in an NMP solution at a mass ratio of 90:5:5 and stirred in a vacuum mixer for 3 hours, controlling the solid content of the slurry to 50%, to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on aluminum foil and then dried in a vacuum drying oven at 120°C for 12 hours. After drying, the slurry was punched into 12mm diameter discs to serve as positive electrode sheets.

[0162] (2) Production of button batteries

[0163] A lithium metal sheet was used as the negative electrode, a Celgard 2400 microporous membrane as the separator, and a 1.0 mol / L LiPF6 solution as the electrolyte. The solvent was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio. The positive electrode sheet, negative electrode sheet, separator, and electrolyte were assembled into a CR2016 button cell in an argon-filled glove box.

[0164] The electrical performance of the button cell produced using the above method was tested. During the test, the cutoff voltage during the charging process was 3.75V, and the cutoff voltage during the discharging process was 2.0V.

[0165] Charge at a constant current of 0.1C to a voltage of 3.75V, then switch to constant voltage charging to a current of 0.02C, and discharge at a constant current of 0.1C to a voltage of 2.0V. Take the 0.1C charging specific capacity as the test result.

[0166] The test temperature was controlled at 25°C, and the battery was charged at a constant current of 1C to a voltage of 3.75V. The battery was then switched to constant voltage charging to a current of 0.02C, and discharged at a constant current of 1C to a voltage of 2.0V. The cycle performance test was performed and the test was stopped when the capacity of the battery decayed to 80% of the initial capacity. The number of cycles was recorded and the cycle performance of the material was evaluated based on the number of cycles.

[0167] The above test results of Examples 15-39 and Comparative Examples 2-3 are listed in Table 4 below:

[0168] Table 4

[0169]

[0170] According to the results in Table 4, the resistivity of the lithium iron phosphate material of Example 15-39 is lower than 34.71Ω-cm, the capacity at 0.1C is higher than 157.6mAh / g, the capacity at 0.2C is higher than 156.1mAh / g, the capacity at 0.5C is higher than 150.1mAh / g, the capacity at 1C is higher than 143.9mAh / g, and the number of cycles is more than 244, indicating that the lithium iron phosphate material of Example 15-39 has excellent electrical properties.

[0171] Comparative Example 3 uses titanium dioxide with a secondary particle size D50 of 0.658 μm, and the resulting lithium iron phosphate material has poor cycle performance.

[0172] Examples 15-28 use the titanium dioxide prepared in Examples 1-14, and the resulting lithium iron phosphate material has a resistivity lower than 24.49 Ω-cm, a capacity higher than 158.8 mAh / g at 0.1C, a capacity higher than 157.1 mAh / g at 0.2C, a capacity higher than 150.2 mAh / g at 0.5C, a capacity higher than 144.5 mAh / g at 1C, and more than 381 cycles. Compared with Examples 29-39 using commercially available titanium dioxide, the lithium iron phosphate materials of Examples 15-28 have better electrical properties.

Claims

1. A method for preparing titanium dioxide, characterized in that: It includes the following steps: The mixed solution is reacted in a micro coil to obtain titanium dioxide; The mixed solution comprises titanium tetrachloride and ammonia water, and the mass ratio of the titanium tetrachloride to the ammonia water is 1:(0.5-3); The reaction temperature is 140-200°C.

2. The method for preparing titanium dioxide according to claim 1, wherein The mass ratio of titanium tetrachloride to ammonia water in the mixed solution is 1:(0.5-2.55); And / or, the mixed solution is prepared by: introducing titanium tetrachloride solution and ammonia solution into a mixer respectively and mixing them; and / or, the reaction temperature is 140-180° C.; And / or, the reaction time is 1-6 min; And / or, the reaction pressure is 0.5-1.8 MPa; And / or, the reaction further includes a drying step; And / or, the method for preparing titanium dioxide further comprises the step of passing the mixed solution into the microcoil; And / or, the micro coil includes N interconnected coil units, where N is an integer greater than or equal to 1, and the coil unit is a cylindrical pipeline formed by spirally winding a pipe segment.

3. Titanium dioxide obtained by the method for preparing titanium dioxide according to claim 1 or 2.

4. A method for preparing lithium iron phosphate material, characterized in that: It includes the following steps: The mixture is dried and sintered in sequence to obtain lithium iron phosphate material; The mixture comprises iron phosphate, a lithium source, a carbon source, titanium dioxide and a solvent; the particle size D50 of the secondary particles of the titanium dioxide is 0.3-0.6 μm; and the titanium dioxide is the titanium dioxide as claimed in claim 3.

5. The method for preparing the lithium iron phosphate material according to claim 4, wherein: The particle size D50 of the secondary particles of titanium dioxide is 0.4-0.5 μm; and / or, the particle size D10 of the secondary particles of titanium dioxide is 0.2-0.4 μm; and / or, the particle size D99 of the secondary particles of titanium dioxide is 0.7-4 μm; And / or, the specific surface area of the secondary particles of titanium dioxide is 247-331m 2 / g; And / or, the purity of the titanium dioxide is above 98%; and / or, the particle size D50 of the primary particles in the secondary particles of titanium dioxide is 4-6 nm; and / or, the maximum particle size of the secondary particles of titanium dioxide is less than 10 μm; And / or, the crystal form of the titanium dioxide is anatase crystal form and / or rutile crystal form; And / or, the relative crystallinity of the titanium dioxide is 40%-130%.

6. The method for preparing the lithium iron phosphate material according to claim 4, wherein: In the mixture, the atomic percentage of titanium element in the titanium dioxide to phosphorus element in the iron phosphate is 0.25%-1.5%; And / or, the molar ratio of iron to phosphorus in the ferric phosphate is (0.95-1.01):1; and / or, in the mixture, the molar ratio of the iron element of the ferric phosphate, the phosphorus element of the ferric phosphate, and the titanium element of the titanium dioxide is (95-101):100:(0.25-1.5); And / or, the specific surface area of the iron phosphate is 5-30m 2 / g; And / or, the purity of the ferric phosphate is greater than 80%; And / or, the lithium source is a lithium-containing compound that does not contain phosphorus and iron; and / or, the carbon source is one or more of glucose, sucrose and polyethylene glycol; And / or, the mixture further comprises a non-titanium source, wherein the non-titanium source is one or more of a vanadium source, a niobium source, a strontium source, a copper source, an aluminum source and a zirconium source; and / or, the solvent is water; And / or, the mixture further comprises an auxiliary agent; And / or, further comprising a sanding step before the drying; and / or, the mixture is a suspension; And / or, the drying method is spray drying; And / or, the sintering includes a temperature rising stage and a constant temperature stage; and / or, the sintering is performed under an inert gas atmosphere; And / or, further comprising a crushing step after the sintering; And / or, the titanium dioxide is subjected to surface hydrophilic modification treatment.

7. A lithium iron phosphate material obtained by the method for preparing the lithium iron phosphate material according to any one of claims 4 to 6.

8. The lithium iron phosphate material according to claim 7, wherein: The atomic percentage of titanium element in the lithium iron phosphate material to phosphorus element is 0.25%-1.5%; and / or, the particle size D10 of the lithium iron phosphate material is greater than 0.35 μm; And / or, the particle size D50 of the lithium iron phosphate material is 1-2.2 μm; and / or, the particle size D99 of the lithium iron phosphate material is less than 12.5 μm; And / or, the maximum particle size of the lithium iron phosphate material is less than 15 μm.

9. A pole piece, characterized in that: It comprises the lithium iron phosphate material as claimed in claim 7 or 8.

10. A lithium ion battery, characterized in that: It comprises the pole piece as claimed in claim 9.

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