Method for doping iron phosphate with titanium

Abstract

The invention relates to the technical field of preparation of iron phosphate materials, in particular to a method for doping iron phosphate with titanium, which comprises the following steps: 1, dissolving a titanium dioxide by-product ferrous sulfate powder in water to prepare a titanium-containing iron source solution; 2, adding water into the reaction kettle, and stirring; 3, adding the titanium-containing iron source solution, the phosphorus source solution, ammonia water and an oxidizing agent into a reaction kettle to prepare primary slurry; 4, carrying out filter pressing on the primary slurry, washing until the conductivity is less than or equal to 2000us / cm, and then adding water to prepare secondary slurry; 5, phosphoric acid is added into the reaction kettle for bottoming, and the temperature is increased to 60-70 DEG C; 6, adding the secondary slurry into the reaction kettle, and carrying out heat preservation reaction on the secondary slurry and phosphoric acid; and 7, filtering the reaction product obtained in the step 6, washing until the conductivity is less than or equal to 500us / cm, and then drying and sintering. According to the method, the titanium doping technological process is simplified, and meanwhile the titanium element utilization rate in the titanium dioxide by-product and the purity of the titanium-doped iron phosphate product are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing iron phosphate materials, and particularly relates to a method for doping titanium in iron phosphate. Background Art

[0002] A lithium-ion battery is a secondary battery (rechargeable battery), which mainly works by the movement of lithium ions between the positive electrode and the negative electrode. During the charge and discharge process, Li + intercalates and deintercalates between the two electrodes: during charging, Li + deintercalates from the positive electrode, passes through the electrolyte and intercalates into the negative electrode, and the negative electrode is in a lithium-rich state; during discharging, the opposite occurs. The structure of a lithium-ion battery mainly includes a positive electrode material, a negative electrode material, a separator, and an electrolyte. As a key component of a lithium-ion battery, the performance of the positive electrode material directly affects core indicators such as the energy density, charge and discharge performance, and cycle life of the battery. Currently, common positive electrode materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), lithium iron phosphate (LiFePO4), and lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2). Lithium cobalt oxide (LiCoO2), as the positive electrode material of the first-generation commercial lithium-ion battery, is well-known for its high working voltage and excellent cycle stability. However, lithium cobalt oxide has limited resources, high price, and insufficient thermal stability, and thus cannot be widely used; lithium manganese oxide has a lower cost and higher safety, but has a lower energy density; lithium nickel oxide has a higher energy density, but has a shorter cycle life; the ternary positive electrode material of lithium nickel cobalt manganese oxide has the advantages of both high energy density and long cycle life. The ternary positive electrode material of lithium nickel cobalt manganese oxide mainly uses a lithium source, a nickel source, a cobalt source, and a manganese source. Except for the lithium source, the prices of the cobalt source and the nickel source are both relatively high; compared with the ternary material of lithium nickel cobalt manganese oxide, lithium iron phosphate has more cost advantages, better safety performance, and longer cycle life, but both its ionic conductivity and electronic conductivity are relatively poor.

[0003] The prior art mainly improves the conductivity of lithium iron phosphate through the following two methods: 1. The surface coating method, that is, improving the conductivity by coating a carbon layer or a metal oxide layer on the surface of the lithium iron phosphate particles; 2. The element doping method, that is, improving the conductivity by introducing metal ions such as magnesium (Mg), titanium (Ti), zirconium (Zr), vanadium (V), etc. or non-metal ions such as nitrogen (N), sulfur (S), etc. into the crystal lattice structure of lithium iron phosphate. The process of the surface coating method is relatively simple and can effectively improve the surface performance of lithium iron phosphate. However, since the coating layer mainly improves electron conduction, this method has a relatively small effect on improving the diffusion rate of Li ⁺ The element doping method can introduce defects into the internal structure of lithium iron phosphate or change the energy band structure, thereby optimizing the intrinsic properties of lithium iron phosphate. Titanium element and Fe in lithium iron phosphate2+ 、 Li + has a compatible ionic radius with good oxidation state stability and is commonly used for the modification of lithium iron phosphate. Chinese Patent CN119118092A uses titanium dioxide powder as the titanium source, and then prepares a lithium iron phosphate product doped with 500 - 3500 ppm of titanium through processes such as sand grinding, spray drying, sintering, and air flow pulverization. However, during the sintering process, due to the high melting point of titanium dioxide, the sintering temperature is also high, resulting in high energy consumption and costs. Also, because this patent uses solid-phase reaction for titanium doping, there are not only problems such as difficulty in incorporating titanium elements into the lithium iron phosphate lattice, but also uneven distribution of titanium elements. Chinese Patent CN117756076A discloses a titanium-doped anhydrous iron phosphate material, its preparation method and application. First, using the by-product of titanium white as the formulation raw material, a titanium-containing ferrous sulfate raw material solution and a titanium-free ferrous sulfate raw material solution are respectively prepared, and then the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution are mixed to obtain a mixed solution; then the mixed solution is mixed with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate; the slurry is aged, rinsed, dried, and sintered in sequence to obtain the titanium-doped anhydrous iron phosphate material. Although this patent dopes some titanium elements in the by-product of titanium white into iron phosphate, to a certain extent reducing energy consumption and costs, due to the need to divide the ferrous sulfate raw material solution into two parts, respectively for preparing the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution, the doping process is complex and the titanium elements in the by-product of titanium white cannot be fully utilized. Summary of the Invention

[0004] Aiming at the technical problems of complex process and low utilization rate of titanium elements in the prior art for titanium doping of iron phosphate using the by-product of titanium white, the present invention provides a method for doping titanium into iron phosphate. The by-product of titanium white, ferrous sulfate powder, is dissolved in water to prepare a titanium-containing iron source solution, which is then added to water simultaneously with a phosphorus source solution, ammonia water, and an oxidant to prepare a primary slurry, simplifying the titanium doping process flow while improving the utilization rate of titanium elements in the by-product of titanium white and the purity of the titanium-doped iron phosphate product.

[0005] The present invention provides a method for doping titanium into iron phosphate, including the following steps: Step 1: Dissolve the by-product of titanium white, ferrous sulfate powder, in water to prepare a titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2000 - 3000 ppm; Step 2: Add water to the reaction kettle and then stir; Step 3: Under the stirring state, add the titanium-containing iron source solution, phosphorus source solution, ammonia water, and oxidant to the reaction kettle for reaction to prepare a primary slurry. Control the addition speeds of the titanium-containing iron source solution, phosphorus source solution, ammonia water, and oxidant to be synchronous, and the starting time and ending time of the addition are the same; Step 4: Press-filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, then add water to make a secondary slurry with an iron concentration of 1.1 - 1.5 mol / L. Step 5: Add phosphoric acid to the reaction kettle and heat it up to 60 - 70 °C. The mass concentration of phosphoric acid is 85%. Step 6: Under stirring, add the secondary slurry to the reaction kettle and carry out a heat-preservation reaction with phosphoric acid. The temperature of the heat-preservation reaction is 80 - 95 °C, and the time of the heat-preservation reaction is 3 - 5 h. Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, then carry out drying and sintering to obtain a titanium-doped iron phosphate product.

[0006] Further, in Step 1, the ferrous concentration of the titanium-containing iron source solution is 1.1 - 1.5 mol / L, and the titanium content is 600 - 700 ppm.

[0007] Further, in Steps 2 and 6, the stirring speed is 50 - 150 rpm; in Step 2, the mass ratio of the water added to the reaction kettle to the mass of ferrous sulfate powder is 1 - 3:1, preferably 2:1. The stirring method is preferably mechanical stirring, and the stirring speed should be such that the water can be stirred up.

[0008] Further, in Step 3, the phosphorus source solution is an aqueous solution of a phosphorus source, and the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium phosphate, triammonium phosphate, sodium dihydrogen phosphate, disodium phosphate, and trisodium phosphate; in Step 3, the reaction temperature is 40 - 60 °C, preferably 50 °C.

[0009] Further, in Step 3, the molar ratio of iron, phosphorus, ammonia, and the oxidant in the titanium-containing iron source solution, phosphorus source solution, ammonia water, and oxidant is 1:1.1 - 1.2:0.1 - 0.3:0.6 - 0.8.

[0010] Further, in Step 3, the oxidant is at least one of hydrogen peroxide, air, oxygen, ozone, and sodium peroxide. Sodium peroxide can be added in the form of solid powder or mixed with water and then added.

[0011] Further, in Step 3, the phosphorus content of the phosphorus source solution is 1.1 - 1.5 mol / L, the concentration of ammonia water is 0.4 - 0.5 mol / L, the oxidant is hydrogen peroxide, and the concentration of hydrogen peroxide is 0.6 - 0.8 mol / L.

[0012] Further, in Step 3, the addition duration of the titanium-containing iron source solution, phosphorus source solution, ammonia water, and oxidant is 1.5 - 2 h.

[0013] Further, in Step 7, the drying temperature is 105 - 110 °C, the sintering temperature is 550 - 650 °C, and the sintering time is 3 - 5 h.

[0014] Further, in step seven, the titanium doping amount of the iron phosphate product is 3000 - 4000 ppm.

[0015] The beneficial effects of the present invention are as follows: The present invention provides a method for doping titanium in iron phosphate. By using the by - product ferrous sulfate powder of titanium dioxide as both the iron source and the titanium source, the cost of purchasing external iron sources and titanium sources is saved. The by - product ferrous sulfate powder of titanium dioxide containing impurities such as titanium element and aluminum element is dissolved in water to prepare a titanium - containing iron source solution, which is then directly subjected to an oxidation - precipitation synergistic reaction with a phosphorus source solution, ammonia water, and an oxidant. The aqueous solution of the by - product ferrous sulfate of titanium dioxide is acidic with a pH value of 2 - 3, and titanium exists as ionic titanium in the acidic solution. This method makes full use of the residual titanium element in the by - product ferrous sulfate powder of titanium dioxide, omits the titanium removal process of the by - product ferrous sulfate powder of titanium dioxide, reduces the treatment cost and energy consumption while realizing the reuse of the by - product of titanium dioxide. For the impurity containing aluminum element, in the process of preparing iron phosphate by the two - step method of the present invention, through the precipitation reaction of preparing the primary slurry, two precipitations and two washings of washing and heat preservation reaction after the reaction, and the purification effect in the process of white - turning crystallization, the aluminum content in the iron phosphate finished product is reduced, and the purity of the titanium - doped iron phosphate finished product is improved. In addition, the present invention dopes titanium at the iron phosphate stage, reduces the difficulty of titanium doping, makes the titanium element uniformly doped into the iron phosphate lattice while reducing energy consumption, and improves the electrochemical performance of lithium iron phosphate.

[0016] In summary, the present invention not only effectively reduces the raw material cost and process cost of titanium doping in the synthesis of iron phosphate, but also significantly improves the uniformity of titanium doping in the synthesis process of lithium iron phosphate. Using the method provided by the present invention for titanium doping has both cost advantages and advantages in improving the performance of lithium iron phosphate due to the uniform titanium doping. By controlling the dosage of the by - product ferrous sulfate powder of titanium dioxide, the concentration of ferrous sulfate in the titanium - containing iron source solution, the ratio of the by - product ferrous sulfate powder of titanium dioxide to the phosphorus source, etc., the titanium doping amount of iron phosphate can be regulated. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is the XRD pattern of the iron phosphate product prepared in Example 3 and the standard card of iron phosphate.

[0019] Figure 2 It is the SEM image (magnified 5000 times) of the iron phosphate product prepared in Example 3.

[0020] Figure 3 It is the SEM image (magnified 50,000 times) of the iron phosphate product prepared in Example 3.

[0021] Figure 4 It is the XRD pattern of the iron phosphate product prepared in Example 5 and the standard card of iron phosphate.

[0022] Figure 5 It is the SEM image (magnified 5,000 times) of the iron phosphate product prepared in Example 5.

[0023] Figure 6 It is the SEM image (magnified 50,000 times) of the iron phosphate product prepared in Example 5.

[0024] Figure 7 It is the XRD pattern of the iron phosphate product prepared in Comparative Example 1 and the standard card of iron phosphate.

[0025] Figure 8 It is the SEM image (magnified 5,000 times) of the secondary agglomerates of the iron phosphate product prepared in Comparative Example 1.

[0026] Figure 9 It is the SEM image (magnified 50,000 times) of the primary particles of the iron phosphate product prepared in Comparative Example 1.

[0027] Figure 10 It is the XRD pattern of the iron phosphate product prepared in Comparative Example 2 and the standard card of iron phosphate.

[0028] Figure 11 It is the SEM image of the secondary agglomerates of the iron phosphate product prepared in Comparative Example 2 (magnified 5,000 times).

[0029] Figure 12 It is the SEM image of the primary particles of the iron phosphate product prepared in Comparative Example 2 (magnified 50,000 times).

[0030] Figure 13 It is the XRD pattern of the iron phosphate product prepared in Comparative Example 3 and the standard card of iron phosphate.

[0031] Figure 14 It is the SEM image of the secondary agglomerates of the iron phosphate product prepared in Comparative Example 3 (magnified 5,000 times).

[0032] Figure 15 It is the SEM image of the primary particles of the iron phosphate product prepared in Comparative Example 3 (magnified 50,000 times).

[0033] Figure 16 It is the XRD pattern of the lithium iron phosphate LFP-5 prepared in Example 5 and the standard card of iron phosphate.

[0034] Figure 17 It is the SEM image (magnified 5000 times) of the secondary agglomerates of lithium iron phosphate LFP-5 prepared in Example 5.

[0035] Figure 18 It is the SEM image (magnified 50000 times) of the primary particles of lithium iron phosphate LFP-5 prepared in Example 5.

[0036] Figure 19 It is the XRD pattern of lithium iron phosphate LFP-7 prepared in Comparative Example 2 and the standard card of iron phosphate.

[0037] Figure 20 It is the SEM image (magnified 5000 times) of the secondary agglomerates of lithium iron phosphate LFP-7 prepared in Comparative Example 2.

[0038] Figure 21 It is the SEM image (magnified 50000 times) of the primary particles of lithium iron phosphate LFP-7 prepared in Comparative Example 2.

[0039] Figure 22 It is the comparison chart of the rate performance of the 3# button cell, 5# button cell, 6# button cell, 7# button cell, 8# button cell and 9# button cell in Application Example 1.

[0040] Figure 23 It is the energy density of LFP-3, LFP-5, LFP-6, LFP-7, LFP-8 and LFP-9 at different rates.

[0041] Figure 24 It is the volume energy density of LFP-3, LFP-5, LFP-6, LFP-7, LFP-8 and LFP-9 at different rates. Detailed implementation manners

[0042] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] Example 1 A method for doping titanium into iron phosphate includes the following steps: Step 1: Dissolve the by-product ferrous sulfate powder of titanium dioxide in pure water to prepare 5 L of a titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2900 ppm; the ferrous ion concentration of the titanium-containing iron source solution is 1.2 mol / L, and the titanium content is 689 ppm.

[0044] Step 2: Add water into the reactor. The mass ratio of the water added into the reactor to the mass of the ferrous sulfate powder is 2:1. Then stir at a speed of 50 rpm, with the stirring paddle being able to agitate the water appropriately.

[0045] Step 3: Under the stirring state, simultaneously add a titanium-containing iron source solution, 6 L of a phosphorus source solution, 3 L of ammonia water, and 5.15 L of an oxidant into the reactor through four pipelines respectively for reaction to obtain a primary slurry. The reaction temperature is 50 °C. Control the feeding speeds of the titanium-containing iron source solution, the phosphorus source solution, the ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time of adding the titanium-containing iron source solution, the phosphorus source solution, the ammonia water, and the oxidant are the same. The feeding duration of the titanium-containing iron source solution, the phosphorus source solution, the ammonia water, and the oxidant is all 1.5 h. Among them, the phosphorus source solution is an ammonium dihydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of the ammonia water is 0.4 mol / L.

[0046] Step 4: Filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, and then add water to make a secondary slurry. The iron concentration of the secondary slurry is 1.2 mol / L.

[0047] Step 5: Add phosphoric acid to the reactor for bottoming and heat up to 60 - 70 °C. The mass concentration of the phosphoric acid is 85%.

[0048] Step 6: Under the stirring state, add the secondary slurry into the reactor for heat preservation reaction with the phosphoric acid. Among them, the stirring speed is 50 - 150 rpm, the temperature of the heat preservation reaction is 95 °C, and the time of the heat preservation reaction is 3 h. After the addition of the secondary slurry into the reactor is completed, the pH value of the liquid in the reactor is 1.56.

[0049] Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, and then carry out drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 550 °C, and the sintering time is 5 h.

[0050] Example 2 A method for doping titanium in iron phosphate, comprising the following steps: Step 1: Dissolve the by-product ferrous sulfate powder of titanium dioxide in pure water to prepare 10 L of a titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2700 ppm; the ferrous ion concentration of the titanium-containing iron source solution is 1.2 mol / L, and the titanium content is 676 ppm.

[0051] Step 2: Add water into the reactor. The mass ratio of the water added into the reactor to the mass of the ferrous sulfate powder is 2:1. Then stir at a speed of 100 rpm, with the stirring paddle being able to agitate the water appropriately.

[0052] Step 3: Under stirring, add a titanium-iron source solution, 12 L of a phosphorus source solution, 6 L of ammonia water, and 12 L of an oxidant into the reactor simultaneously through four pipelines for reaction to obtain a primary slurry. The reaction temperature is 50°C. Control the feeding rates of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time of adding the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant are the same, and the feeding duration of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant is 1.7 h. Among them, the phosphorus source solution is a diammonium hydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of the ammonia water is 0.4 mol / L.

[0053] Step 4: Filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, and then add water to make a secondary slurry. The iron concentration of the secondary slurry is 1.3 mol / L.

[0054] Step 5: Add phosphoric acid to the reactor for bottoming and heat up to 60 - 70°C. The mass concentration of the phosphoric acid is 85%.

[0055] Step 6: Under stirring, add the secondary slurry into the reactor for heat preservation reaction with the phosphoric acid. Among them, the stirring speed is 50 - 150 rpm, the temperature of the heat preservation reaction is 95°C, and the time of the heat preservation reaction is 4 h. After the addition of the secondary slurry into the reactor is completed, the pH value of the liquid in the reactor is 1.65.

[0056] Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, and then carry out drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105°C, the drying time is 3 h, the sintering temperature is 570°C, and the sintering time is 3 h.

[0057] Example 3 A method for doping titanium in iron phosphate, comprising the following steps: Step 1: Dissolve titanium white by-product ferrous sulfate powder in pure water to prepare 100 L of a titanium-iron source solution for standby. The titanium content of the ferrous sulfate powder is 2300 ppm; the ferrous ion concentration of the titanium-iron source solution is 1.2 mol / L, and the titanium content is 654 ppm.

[0058] Step 2: Add water into the reactor. The mass ratio of the water added into the reactor to the mass of the ferrous sulfate powder is 2:1, and then carry out stirring. The stirring speed is 150 rpm, and it is appropriate that the stirring paddle can stir up the water.

[0059] Step 3: Under stirring, add a titanium-iron source solution, 120 L of a phosphorus source solution, 60 L of ammonia water, and 120 L of an oxidant into the reaction kettle simultaneously through four pipelines for reaction to obtain a primary slurry, with the reaction temperature being 50 °C. Control the feeding rates of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time for adding the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant are the same, and the feeding duration for the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium dihydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of the ammonia water is 0.4 mol / L.

[0060] Step 4: Filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, and then add water to make a secondary slurry, with the iron concentration of the secondary slurry being 1.3 mol / L.

[0061] Step 5: Add phosphoric acid to the reaction kettle for priming and heat up to 60 - 70 °C, with the mass concentration of the phosphoric acid being 85%.

[0062] Step 6: Under stirring, add the secondary slurry into the reaction kettle to carry out a heat-preservation reaction with the phosphoric acid. Among them, the stirring speed is 50 - 150 rpm, the temperature for the heat-preservation reaction is 95 °C, the time for the heat-preservation reaction is 5 h. After the addition of the secondary slurry to the reaction kettle is completed, the pH value of the liquid in the reaction kettle is 1.70.

[0063] Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, and then carry out drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0064] Perform XRD testing and SEM testing on the iron phosphate product prepared in this example. The XRD pattern of the iron phosphate product prepared in this example and the standard card of iron phosphate are as Figure 1 shown. The SEM images of the iron phosphate product prepared in this example at different magnifications are as Figure 2 and Figure 3 shown. Figure 2 、 Figure 3 The magnifications are 5000 times and 50000 times respectively.

[0065] It can be seen from Figure 1 that the titanium-doped iron phosphate product prepared in this example is a pure-phase high-crystallinity iron phosphate. It can be seen from Figure 2 and Figure 3It can be seen that the primary particles of the titanium-doped iron phosphate product are relatively large and are irregularly spherical. During the sintering process, the primary particles fuse together to form aggregated secondary particles. Herein, the primary particle refers to the smallest particle in the SEM image, and the secondary particle refers to the particle formed by the aggregation of primary particles.

[0066] Example 4 A method for doping titanium into iron phosphate includes the following steps: Step 1: Dissolve the by-product ferrous sulfate powder of titanium dioxide in pure water to prepare 100 L of a titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2500 ppm; the ferrous ion concentration of the titanium-containing iron source solution is 1.2 mol / L, and the titanium content is 675 ppm.

[0067] Step 2: Add water to the reaction kettle. The mass ratio of the water added to the reaction kettle to the mass of the ferrous sulfate powder is 2:1, and then stir at a stirring speed of 150 rpm, with the stirring paddle being able to stir up the water being appropriate.

[0068] Step 3: Under the stirring state, simultaneously add the titanium-containing iron source solution, 120 L of the phosphorus source solution, 60 L of ammonia water, and 120 L of the oxidant to the reaction kettle through four pipelines for reaction to obtain a primary slurry, with the reaction temperature being 50 °C. Control the feeding speeds of the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time of adding the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant are the same, and the feeding duration of the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of ammonia water is 0.4 mol / L.

[0069] Step 4: Press-filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, and then add water to make a secondary slurry, with the iron concentration of the secondary slurry being 1.3 mol / L.

[0070] Step 5: Add phosphoric acid to the reaction kettle and heat it up to 60 - 70 °C. The mass concentration of phosphoric acid is 85%.

[0071] Step 6: Under the stirring state, add the secondary slurry to the reaction kettle and carry out a heat-preservation reaction with phosphoric acid. Among them, the stirring speed is 150 rpm, the temperature of the heat-preservation reaction is 95 °C, and the time of the heat-preservation reaction is 5 h. After the addition of the secondary slurry to the reaction kettle is completed, the pH value of the liquid in the reaction kettle is 1.70.

[0072] Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, then carry out drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0073] Example 5 A method for doping titanium in iron phosphate, comprising the following steps: Step 1: Dissolve the by-product ferrous sulfate powder of titanium dioxide in pure water to prepare 100 L of a titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2450 ppm; the ferrous concentration of the titanium-containing iron source solution is 1.2 mol / L, and the titanium content is 675 ppm.

[0074] Step 2: Add water to the reaction kettle. The mass ratio of the water added to the reaction kettle to the mass of the ferrous sulfate powder is 2:1, and then stir at a stirring speed of 150 rpm, with the stirring paddle being able to stir up the water being appropriate.

[0075] Step 3: Under the stirring state, simultaneously add the titanium-containing iron source solution, 120 L of the phosphorus source solution, 60 L of ammonia water, and 120 L of the oxidant to the reaction kettle through four pipelines for reaction to obtain a primary slurry, and the reaction temperature is 50 °C. Control the addition speeds of the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant to be synchronous by regulating the flow rate. The starting time and the ending time of the addition of the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant are the same, and the addition duration of the titanium-containing iron source solution, the phosphorus source solution, ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of ammonia water is 0.4 mol / L.

[0076] Step 4: Press-filter and wash the primary slurry until the conductivity ≤ 2000 us / cm, and then add water to make a secondary slurry. The iron concentration of the secondary slurry is 1.3 mol / L.

[0077] Step 5: Add phosphoric acid to the reaction kettle and heat up to 60 - 70 °C. The mass concentration of phosphoric acid is 85%.

[0078] Step 6: Under the stirring state, add the secondary slurry to the reaction kettle for heat preservation reaction with phosphoric acid. Among them, the stirring speed is 150 rpm, the temperature of the heat preservation reaction is 95 °C, the time of the heat preservation reaction is 5 h. After the addition of the secondary slurry to the reaction kettle is completed, the pH value of the liquid in the reaction kettle is 1.70.

[0079] Step 7: Filter and wash the reaction product obtained in Step 6 until the conductivity ≤ 500 us / cm, then perform drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0080] Perform XRD test and SEM test on the iron phosphate product prepared in this example. The XRD pattern of the iron phosphate product prepared in this example and the standard card of iron phosphate are as Figure 4 shown. The SEM images of the iron phosphate product prepared in this example at different magnifications are as Figure 5 and Figure 6 shown. Figure 5 、 Figure 6 The magnifications of

[0081] are 5000 times and 50000 times respectively. Figure 4 As can be seen from Figure 5 and Figure 6 the titanium-doped iron phosphate product prepared in this example is a pure-phase high-crystallinity iron phosphate. As can be seen from

[0082] Comparative Example 1 A method for doping titanium in iron phosphate includes the following steps: Step 1: Dissolve the by-product ferrous sulfate powder of titanium dioxide in pure water, and after impurity removal treatment, prepare 100 L of an iron source solution for standby. The titanium content of the ferrous sulfate powder is 2450 ppm; the ferrous ion concentration of the iron source solution is 1.2 mol / L, and the titanium content is 4 ppm.

[0083] Step 2: Add water to the reaction kettle. The mass ratio of the water added to the reaction kettle to the mass of the ferrous sulfate powder is 2:1, and then stir at a stirring speed of 150 rpm, with the stirring paddle being able to stir up the water appropriately.

[0084] Step 3: Under the stirring state, simultaneously add the iron source solution, 120 L of the phosphorus source solution, 60 L of ammonia water, and 120 L of the oxidant to the reaction kettle through four pipelines for reaction to obtain a primary slurry. The reaction temperature is 50 °C. Control the addition speeds of the titanium-iron source solution, the phosphorus source solution, ammonia water, and the oxidant to be synchronous by regulating the flow rate. The starting time and the ending time of the addition of the titanium-iron source solution, the phosphorus source solution, ammonia water, and the oxidant are the same, and the addition duration of the titanium-iron source solution, the phosphorus source solution, ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium dihydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of ammonia water is 0.4 mol / L.

[0085] Step 4: Add phosphoric acid with a mass concentration of 85% into the reaction kettle. After addition, the pH value of the liquid in the reaction kettle is 1.70. Then, heat up to 95 °C for heat preservation reaction, and the heat preservation reaction time is 5 h.

[0086] Step 5: Filter and wash the reaction product obtained in Step 4 until the conductivity ≤ 500 us / cm, and then perform drying and sintering to obtain iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0087] Perform XRD test and SEM test on the iron phosphate product prepared in this comparative example. The XRD pattern of the iron phosphate product prepared in this comparative example and the standard card of iron phosphate are as Figure 7 shown. The SEM images of the iron phosphate product prepared in this comparative example at different magnifications are as Figure 8 and Figure 9 shown. Figure 8 、 Figure 9 The magnifications of 、 are 5000 times and 50000 times respectively.

[0088] It can be seen from Figure 7 that the iron phosphate product prepared in this comparative example is pure-phase iron phosphate with high crystallinity. It can be seen from Figure 8 and Figure 9 that the primary particles of the iron phosphate product are relatively fine and irregular spherical in shape. The primary particles are fused and form aggregated secondary particles during the sintering process. Although the iron phosphate product prepared in this comparative example is not doped with titanium, its microscopic morphology is close to that of the iron phosphate products prepared in Examples 1 - 5, indicating that titanium doping has little effect on the microscopic morphology of the iron phosphate product.

[0089] Comparative Example 2 A method for doping titanium in iron phosphate, comprising the following steps: Step 1: Dissolve titanium white by-product ferrous sulfate powder in pure water to prepare 100 L of titanium-containing iron source solution for standby. The titanium content of the ferrous sulfate powder is 2350 ppm; the ferrous concentration of the titanium-containing iron source solution is 1.2 mol / L, and the titanium content is 654 ppm.

[0090] Step 2: Add water into the reaction kettle. The mass ratio of the water added into the reaction kettle to the mass of the ferrous sulfate powder is 2:1. Then, perform stirring, and the stirring speed is 150 rpm, so that the water can be stirred up by the stirring paddle.

[0091] Step 3: Under stirring conditions, add a titanium-iron source solution, 120 L of a phosphorus source solution, 60 L of ammonia water, and 120 L of an oxidant into the reaction kettle simultaneously through four pipelines for reaction to obtain a primary slurry. The reaction temperature is 50 °C. Control the feeding rates of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time of adding the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant are the same, and the feeding duration of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium dihydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of the ammonia water is 0.4 mol / L.

[0092] Step 4: Add phosphoric acid with a mass concentration of 85% into the reaction kettle. After adding, the pH value of the liquid in the reaction kettle is 1.70, and then heat it up to 95 °C for heat preservation reaction. The time for the heat preservation reaction is 5 h.

[0093] Step 5: Filter and wash the reaction product obtained in Step 4 until the conductivity ≤ 500 us / cm, and then carry out drying and sintering to obtain a ferric phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0094] Perform XRD test and SEM test on the ferric phosphate product prepared in this comparative example. The XRD pattern of the ferric phosphate product prepared in this comparative example and the standard card of ferric phosphate are as Figure 10 shown. The SEM images of the ferric phosphate product prepared in this comparative example at different magnifications are as Figure 11 and Figure 12 shown. Figure 11 、 Figure 12 The magnifications are 5000 times and 50000 times respectively.

[0095] It can be seen from Figure 10 that the ferric phosphate product prepared in this comparative example is a high-crystallinity ferric phosphate of pure phase. It can be seen from Figure 11 and Figure 12 that the primary particles of the ferric phosphate product are small and irregular spherical, and the primary particles are fused and form aggregated secondary particles during the sintering process.

[0096] Comparative Example 3 A method for doping titanium into ferric phosphate, comprising the following steps: Step 1: Dissolve titanium white by-product ferrous sulfate powder in pure water, and then after impurity removal treatment, prepare 100 L of an iron source solution. The ferrous concentration of the iron source solution is 1.2 mol / L, the titanium content is 4 ppm, and the titanium content of the ferrous sulfate powder is 2350 ppm. Add 59 g of industrial-grade titanyl sulfate with a purity of 98% into the iron source solution, and mix evenly to obtain a titanium-iron source solution for standby.

[0097] Step 2: Add water into the reactor. The mass ratio of the water added into the reactor to the mass of ferrous sulfate powder is 2:1, and then stir at a stirring speed of 150 rpm, with the stirring paddle being able to stir up the water being appropriate.

[0098] Step 3: Under the stirring state, simultaneously add a titanium-iron source solution, 120 L of a phosphorus source solution, 60 L of ammonia water, and 120 L of an oxidant into the reactor through four pipelines for reaction to obtain a primary slurry, with the reaction temperature being 50 °C. Control the feeding speeds of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant to be synchronous by regulating the flow rates. The starting time and the ending time of adding the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant are the same, and the feeding duration of the titanium-iron source solution, the phosphorus source solution, the ammonia water, and the oxidant is all 2 h. Among them, the phosphorus source solution is a sodium dihydrogen phosphate solution with a concentration of 1.2 mol / L, the oxidant is hydrogen peroxide with a concentration of 0.7 mol / L, and the concentration of the ammonia water is 0.4 mol / L.

[0099] Step 4: Add phosphoric acid with a mass concentration of 85% into the reactor. After adding, the pH value of the liquid in the reactor is 1.70, and then heat up to 95 °C for heat preservation reaction, with the heat preservation reaction time being 5 h.

[0100] Step 5: Filter and wash the reaction product obtained in Step 4 until the conductivity ≤ 500 us / cm, and then carry out drying and sintering to obtain a titanium-doped iron phosphate product. The drying temperature is 105 °C, the drying time is 3 h, the sintering temperature is 600 °C, and the sintering time is 5 h.

[0101] Perform XRD testing and SEM testing on the iron phosphate product prepared in this comparative example. The XRD pattern of the iron phosphate product prepared in this comparative example and the standard card of iron phosphate are as Figure 13 shown. The SEM images of the iron phosphate product prepared in this comparative example at different magnifications are as Figure 14 and Figure 15 shown. Figure 14 、 Figure 15 The magnifications of

[0102] are 5000 times and 50000 times respectively. Figure 13 It can be seen from Figure 14 and Figure 15 that the iron phosphate product prepared in this comparative example is a pure-phase high-crystallinity iron phosphate. It can be seen from

[0103] that the primary particles of the iron phosphate product are relatively large, showing an irregular spherical shape, and the primary particles are fused and form aggregated secondary particles during the sintering process.

[0104] Table 1 ICP Results of Iron Phosphate Prepared in Examples and Comparative Examples

[0105] As can be seen from Table 1, the titanium incorporation amounts in Examples 1 - 5 and Comparative Examples 2 - 3 are all in the range of 3400 - 3600 ppm. Compared with Comparative Examples 2 - 3, the impurity contents in Examples 1 - 5 are significantly lower, indicating that although the by - product ferrous sulfate powder of titanium dioxide was not subjected to impurity removal treatment in Examples 1 - 5, the impurities in the prepared titanium - doped iron phosphate products are still very low and can meet the product index requirements.

[0106] Application Example 1 Take the iron phosphate products prepared in Examples 1 - 5 and Comparative Examples 1 - 3, and prepare them into lithium iron phosphate under the same conditions, and name them lithium iron phosphate LFP - 1, lithium iron phosphate LFP - 2, lithium iron phosphate LFP - 3, lithium iron phosphate LFP - 4, lithium iron phosphate LFP - 5, lithium iron phosphate LFP - 6, lithium iron phosphate LFP - 7, and lithium iron phosphate LFP - 8 in turn. Take another part of the iron phosphate product without titanium doping in Comparative Example 1, prepare it into lithium iron phosphate under the same conditions, use nanoscale titanium dioxide as the titanium source, incorporate 3500 ppm of titanium at the lithium iron phosphate end, add nanoscale titanium dioxide during sanding, and obtain titanium - doped lithium iron phosphate through spray drying and high - temperature sintering, and name it lithium iron phosphate LFP - 9. The specific preparation method of lithium iron phosphate is as follows: Step (1): Mix iron phosphate, deionized water, lithium carbonate, and glucose evenly according to a molar ratio of 1:2:0.51:0.03 to obtain a mixed slurry.

[0107] Step (2): Sand the mixed slurry until the particle size reaches 350 nm, and then spray - dry the sanded mixed slurry.

[0108] Step (3): Sinter the material obtained in Step (2) in a nitrogen atmosphere at 720 °C for 20 h to obtain lithium iron phosphate.

[0109] Perform XRD tests and SEM tests on lithium iron phosphate LFP - 5 and lithium iron phosphate LFP - 7 respectively. The XRD pattern of lithium iron phosphate LFP - 5 and the standard card of iron phosphate are as Figure 16 shown, the SEM image of the secondary agglomerates of lithium iron phosphate LFP - 5 is as Figure 17 shown, and the SEM image of the primary particles of lithium iron phosphate LFP - 5 is as Figure 18 shown. The XRD pattern of lithium iron phosphate LFP - 7 and the standard card of iron phosphate are as Figure 19 shown, and the SEM image of the secondary agglomerates of lithium iron phosphate LFP - 7 is as Figure 20As shown, the SEM image of the primary particles of lithium iron phosphate LFP-7 is as Figure 21 shown. XRD tests were respectively carried out on lithium iron phosphate LFP-3, lithium iron phosphate LFP-6, lithium iron phosphate LFP-8, and lithium iron phosphate LFP-9.

[0110] It can be seen from Figure 16 that lithium iron phosphate LFP-5 is a pure-phase lithium iron phosphate with high crystallinity. As shown by Figure 17 - Figure 18 the primary particles of lithium iron phosphate LFP-5 are spherical, with a high sphericity, and the size of the primary particles is 200 - 400 nm. As shown by Figure 19 lithium iron phosphate LFP-7 is also a pure-phase lithium iron phosphate, but it can be seen from Figure 20 - Figure 21 that there are some aggregated large particles in lithium iron phosphate LFP-7, with the size of the large particles being 5 - 20 μm. The existence of these large particles makes the transmission path of lithium ions longer, thus having an adverse effect on the electrical properties of the cathode material.

[0111] The XRD test results of lithium iron phosphate LFP-3, lithium iron phosphate LFP-5, lithium iron phosphate LFP-6, lithium iron phosphate LFP-7, lithium iron phosphate LFP-8, and lithium iron phosphate LFP-9 were refined respectively to obtain the corresponding unit cell parameters. The refined results of the unit cell parameters of lithium iron phosphate LFP-3, lithium iron phosphate LFP-5, lithium iron phosphate LFP-6, lithium iron phosphate LFP-7, lithium iron phosphate LFP-8, and lithium iron phosphate LFP-9 are shown in Table 2.

[0112] Table 2 Test results of the unit cell parameters of lithium iron phosphate samples

[0113] It can be seen from Table 2 that lithium iron phosphate LFP-6 is a sample without titanium doping, and its lattice parameter and unit cell volume are the largest. Compared with undoped lithium iron phosphate LFP-6, due to titanium doping in lithium iron phosphate LFP-3, lithium iron phosphate LFP-5, lithium iron phosphate LFP-7, lithium iron phosphate LFP-8, and lithium iron phosphate LFP-9, the lattice parameter decreases and the unit cell volume becomes smaller. This is mainly because in the lattice of lithium iron phosphate, Ti with a smaller ionic radius 4+ (0.068 nm) replaces Fe with a larger ionic radius 2+(0.074 nm), resulting in a decrease in lattice parameter and a contraction of the unit cell volume. As can be seen from Table 2, the lattice parameters and unit cell volumes of Examples 3 and 5 (LiFePO₄ LFP-3 and LiFePO₄ LFP-5) are the smallest, indicating that more titanium ions substituting ferrous ions are incorporated into the lattice, and the doping effect is better. For LiFePO₄ LFP-7, one-step titanium-doped iron phosphate is used, and the titanium doping effect is worse than that of LiFePO₄ LFP-3 and LiFePO₄ LFP-5, with a larger unit cell volume. It may be that other impurity ions have an impact on the titanium doping effect. LiFePO₄ LFP-8 is prepared by two-step titanium doping using titanium oxysulfate as the titanium source. It can be seen that its lattice parameters and unit cell volume are larger than those of LiFePO₄ LFP-3 and LiFePO₄ LFP-5, indicating that the titanium doping effect of LiFePO₄ LFP-8 is inferior to that of LiFePO₄ LFP-3 and LiFePO₄ LFP-5. LiFePO₄ LFP-9 is not doped with titanium at the iron phosphate end but at the LiFePO₄ end. It can be seen that its lattice parameters and unit cell volume are smaller than those of the undoped LFP-6 sample and larger than those of the samples doped with titanium at the iron phosphate end. This shows that the doping effect at the iron phosphate end is better than that of crystal form doping at the LiFePO₄ end, and the titanium doping effect at the iron phosphate end is better. As can be seen from Table 2, using the method of the present invention, more titanium is doped into the lattice of LiFePO₄ compared with the comparative examples.

[0114] According to the conventional method, the iron phosphate products obtained from Examples 1-5 and Comparative Examples 1-3 were respectively prepared into button cells under the same conditions, and were named 1# button cell, 2# button cell, 3# button cell, 4# button cell, 5# button cell, 6# button cell, 7# button cell, and 8# button cell in sequence. In addition, LiFePO₄ LFP-9 was used as the cathode material to prepare a button cell named 9# button cell. Then, according to the conventional method in the art (reference standard: GB42260-2022), the electrical properties and rate performance of 1# button cell - 9# button cell were respectively tested under the same conditions. The test results of the electrical properties of 1# button cell - 9# button cell are shown in Table 3, and the test results of the rate performance of 1# button cell - 9# button cell are shown in Table 4.

[0115] Table 3 Test results of the electrical properties of 1# button cell - 9# button cell

[0116] As can be seen from Table 3, the initial charge capacity of Coin Cells 1# - 5# is 2 - 3 mAh / g higher than that of Coin Cells 6# - 9#, the initial discharge capacity is 3 - 4 mAh / g higher, and the discharge efficiency is also 2% higher. This is mainly because the iron phosphate prepared in Examples 1 - 5 is uniformly titanium-doped iron phosphate. From the perspectives of thermodynamics and kinetics, compared with Coin Cell 6# prepared from undoped iron phosphate, the incorporation of titanium is beneficial to simultaneously improve the electronic conductivity and ionic conductivity, thereby enhancing the electrical performance of the coin cell. Compared with the titanium-doped iron phosphate prepared by the one-step method in Comparative Example 2, the titanium-doped iron phosphate prepared by the two-step method in Examples 1 - 5 has a lower impurity content, thus reducing the adverse effects of impurities on the electrical performance of the coin cell and improving the electrical performance of the coin cell. Compared with the iron phosphate prepared using titanium oxysulfate as the titanium source in Comparative Example 3, since the hydrolysis degree of titanium oxysulfate in water may vary, it may lead to uneven distribution of titanium in the solution, thereby affecting the electrical performance. Compared with Coin Cell 9# with titanium doping at the lithium iron phosphate end, when titanium doping is carried out using the residual titanium in the titanium dioxide by-product at the iron phosphate end, the incorporation of titanium is more uniform. However, due to the solid-phase reaction at the lithium iron phosphate end, the doping uniformity of titanium is relatively poor, which also results in poorer electrical performance of Coin Cell 9#.

[0117] Table 4 lists the comparison of the rate performance of Coin Cells 3#, 5#, 6# - 9#. From Table 4 and Figure 22 it can be seen that the rate performance of Coin Cells 3# and 5# is significantly better than that of Coin Cells 6# - 9#. Moreover, Coin Cells 3# and 5# still have a capacity of 126 - 128 mAh / g at a 5C rate and 97 - 98 mAh / g at a 10C rate, which is significantly better than the capacity in Coin Cells 6# - 9# (5C: 97 - 102 mAh / g, 10C: 63 - 67 mAh / g).

[0118] Table 4 Comparison of the Rate Performance of Coin Cell Samples (mAh / g)

[0119] Figure 23 - 24 respectively show the energy density and volume energy density of lithium iron phosphate LFP-3, lithium iron phosphate LFP-5, lithium iron phosphate LFP6 - lithium iron phosphate LFP-9 at different rates. The calculation method for energy density is energy density = discharge capacity × discharge voltage; the calculation method for volume energy density is volume energy density = tap density × discharge capacity × discharge voltage. From Figure 23 - Figure 24It can be seen that the energy density and volumetric energy density of the 3# button cell and 5# button cell at different rates are significantly higher than those of the 6# button cell - 9# button cell. For example, at the 1C rate, the energy density of lithium iron phosphate LFP-5 with titanium doped at the iron phosphate end is 482 Wh / kg, while the energy density of lithium iron phosphate LFP-6 without titanium doping is only 391 Wh / kg. At the high rate of 10C, the energy density of lithium iron phosphate LFP-5 with titanium doped at the iron phosphate end is 324 Wh / kg, while the energy density of lithium iron phosphate LFP-6 without titanium doping is only 166 Wh / kg. The energy density of other comparative samples is also significantly lower than that of the examples. From the perspective of volumetric energy density, at the 1C rate, the volumetric energy density of lithium iron phosphate LFP-5 with titanium doped at the iron phosphate end is 1259 Wh / L, while the energy density of lithium iron phosphate LFP-6 without titanium doping is 908 Wh / L. At the high rate of 10C, the energy density of lithium iron phosphate LFP-5 with titanium doped at the iron phosphate end is 846 Wh / L, while the energy density of lithium iron phosphate LFP-6 without titanium doping is only 385 Wh / L, less than half of the energy density of lithium iron phosphate LFP-5. The volumetric energy density of other comparative samples at the 10C rate is also less than half of that of the examples. For lithium-ion batteries, energy density and volumetric energy density are very important indicator parameters, which determine the driving range of electric vehicles. For example, if an electric vehicle uses the sample prepared in the comparative example as the power battery and its driving range is 500 kilometers, then the driving range of another electric vehicle using the sample prepared in the example as the power battery can reach 1000 kilometers, which can well solve the range anxiety of existing electric vehicles.

[0120] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A method for doping titanium with iron phosphate, characterized in that: The steps include: Step 1: dissolving ferrous sulfate powder, a byproduct of titanium dioxide, in water to prepare a titanium-iron source solution for standby use, wherein the titanium content of the ferrous sulfate powder is 2000-3000ppm; Step 2: Add water into the reaction kettle and then stir; Step 3: Under stirring, add a titanium-iron source solution, a phosphorus source solution, ammonia water and an oxidant to the reactor to react to obtain a primary slurry, and control the addition speed of the titanium-iron source solution, the phosphorus source solution, ammonia water and the oxidant to be synchronized, and the start time and end time of the addition are the same; Step 4: filter and wash the primary slurry until the conductivity is ≤2000us / cm, then add water to make a secondary slurry, the iron concentration of the secondary slurry is 1.1-1.5mol / L; Step 5: Add phosphoric acid to the reactor as a base and heat to 60-70°C, with a mass concentration of 85% phosphoric acid; Step 6: Under stirring, add the secondary slurry into the reactor and carry out heat preservation reaction with phosphoric acid, the temperature of the heat preservation reaction is 80-95°C, and the heat preservation reaction time is 3-5h; Step 7: Filter and wash the reaction product obtained in step 6 until the conductivity is ≤500us / cm, and then dry and sinter to obtain a titanium-doped iron phosphate product.

2. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step 1, the ferrous iron concentration of the titanium-containing ferro source solution is 1.1-1.5 mol / L, and the titanium content is 600-700 ppm.

3. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step 2 and step 6, the stirring speed is 50-150 rpm; in step 2, the ratio of the mass of water added to the reactor to the mass of ferrous sulfate powder is 1-3:

1.

4. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step three, the phosphorus source solution is an aqueous solution of a phosphorus source, and the phosphorus source is at least one of monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate and trisodium phosphate; in step three, the reaction temperature is 40-60°C.

5. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step three, the molar ratio of iron, phosphorus, ammonia and oxidant in the titanium-iron source solution, phosphorus source solution, ammonia water and oxidant is 1:1.1-1.2:0.1-0.3:0.6-0.

8.

6. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step three, the oxidant is at least one of hydrogen peroxide, air, oxygen, ozone and sodium peroxide.

7. The method for doping titanium with iron phosphate as claimed in claim 6, characterized in that: In step 3, the phosphorus content of the phosphorus source solution is 1.1-1.5 mol / L, the concentration of ammonia water is 0.4-0.5 mol / L, the oxidant is hydrogen peroxide, and the concentration of hydrogen peroxide is 0.6-0.8 mol / L.

8. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step 3, the titanium-iron source solution, phosphorus source solution, ammonia water and oxidant are added for 1.5-2 hours.

9. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step seven, the drying temperature is 105-110°C, the sintering temperature is 550-650°C, and the sintering time is 3-5h.

10. The method for doping titanium with iron phosphate according to claim 1, characterized in that: In step seven, the titanium doping amount of the ferrophosphate product is 3000-4000ppm.

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