Method for preparing battery grade ferromanganese phosphate by using titanium dioxide by-product ferrous chloride

Abstract

The invention discloses a method for preparing battery grade ferromanganese phosphate by using titanium dioxide by-product ferrous chloride, and relates to the technical field of production of lithium ferromanganese phosphate precursors. Comprising the following steps: removing impurities from a titanium dioxide by-product ferrous chloride crude product to obtain a ferrous chloride crude product, preparing a manganese source and a phosphorus source, and carrying out an oxidation reaction to obtain battery-grade ferromanganese phosphate, and the impurity removal comprises the following steps: dissolving the titanium dioxide by-product ferrous chloride crude product, carrying out primary filtration to obtain a filtrate, dropwise adding ammonia water while stirring until the pH value is 4, and carrying out secondary filtration to obtain the battery-grade ferromanganese phosphate. The content of the iron element is 40-55 wt%, and the content of the manganese element is 3-5 wt%. According to the method, the titanium dioxide by-product ferrous chloride crude product can be used for preparing the battery grade ferromanganese phosphate, the cyclic utilization of resources is realized, and the prepared ferromanganese phosphate is uniform in phase and high in cleanliness and is an excellent precursor for preparing a high-ferromanganese-phosphate lithium battery material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material preparation, and in particular, relates to the technical field of production of lithium manganese iron phosphate precursors. Background Art

[0002] With the rapid growth of demand for new energy vehicles and the continuous rise in raw material prices, the energy density of traditional lithium iron phosphate batteries (LFP) is limited by the 3.4V voltage platform and cannot be further improved, resulting in limited application. In order to overcome this limitation, researchers introduced manganese compounds into lithium iron phosphate to form lithium manganese iron phosphate batteries (LMFP). As an "upgraded version" of LFP (energy density can reach 4.1V), LMFP inherits the advantages of LFP such as low cost, high thermal stability and high safety, while making up for its shortcomings such as low energy density and poor low-temperature stability. As the key raw material for the positive electrode material of LMFP batteries, the quality of manganese iron phosphate is crucial. At present, the methods for preparing manganese iron phosphate mainly include solid phase production method, sol-gel method and coprecipitation method. However, the raw materials of the existing methods are all pure manganese salts, iron salts, etc., which are costly and cannot achieve good resource recycling.

[0003] Titanium dioxide, as a white pigment with the best performance, is widely used in coatings, plastics, papermaking, printing and rubber industries. The domestic production of titanium dioxide is mainly through the sulfuric acid process or titanium chloride. Among them, the production process of titanium dioxide chloride will produce a large amount of by-products whose main component is ferrous chloride. 2+ 、Al 3+ , Mn 2+ Mg 2+ Impurities such as chlorination and condensation make it impossible to be effectively utilized, which not only causes a waste of resources, but also greatly restricts the development of the chloride titanium dioxide industry.

[0004] The Chinese patent with application number CN202211623008.4 discloses a method for synthesizing an iron phosphate precursor from ferrous chloride, a byproduct of titanium dioxide, comprising: S1, reacting a solution of ferrous chloride, a byproduct of titanium dioxide, with an alkaline solution to obtain a solution A; S2, adding an acid regulator and an oxidant to solution A to obtain a solution B; S3, adding a phosphorus source to solution B to obtain a solution C; S4, adding the solution C and an alkali regulator to a reaction vessel pre-filled with a small amount of water as a base liquid, and after the reaction is completed, the iron phosphate precursor product is obtained by post-treatment. The patent proposes that the iron phosphate precursor can be synthesized from the byproduct of titanium dioxide ferrous chloride, and the quality indicators of the obtained iron phosphate can meet the requirements of the index of "HG / T4701-2014 Iron Phosphate for Batteries", and the utilization rate of iron in the titanium dioxide byproduct can be high without introducing new impurities, and ions such as chromium, aluminum, titanium, and vanadium can be better removed. However, the application only utilizes the ferrous chloride in the byproduct of titanium dioxide by the chloride process and prepares it as an iron phosphate electrode material. In fact, in addition to the iron source that can be utilized, the by-products also include impurity elements such as iron, calcium, magnesium, and manganese. When using the by-products to prepare iron phosphate precursors, it is often necessary to enrich only the iron element. The technical solution of this application does not indicate how to utilize the manganese element in the by-products, and it is often impossible to ensure that the manganese and iron elements are retained while removing other impurity elements. In addition, the preparation of ferromanganese phosphate not only requires a higher purity of the ferromanganese source, but also the impact of impurities on the preparation process is more serious.

[0005] The Chinese patent with application number CN201710336682.7 discloses a method for preparing battery-grade ferromanganese phosphate, including: mixing an iron source, a manganese source, a surfactant, and a carbon nanotube slurry in a reactor to obtain a slurry a, mixing a phosphate salt and an oxidant to obtain a phosphorus solution b and adding it to the reactor to react with the slurry a to obtain a seed crystal c; configuring an iron source and a manganese source mixed solution d and a phosphate salt and an oxidant mixed solution e, stirring c and d in the reactor, and then adding e to react, and then transforming, crystallizing, filtering, washing, drying, and crushing to obtain a battery-grade ferromanganese phosphate. The (iron + manganese) / phosphorus ratio, particle size and specific surface area of ​​the preparation method are controllable, and porous carbon nanotubes are further introduced in the case of adding a surfactant, which promotes the uniformity of particle size and conductive network, effectively shortens the ion transport channel, and improves the conductivity. It is an excellent precursor material for the manufacture of lithium ferromanganese phosphate. The application discloses how to prepare battery-grade ferromanganese phosphate from ferrous iron sources such as ferrous chloride, but the raw materials used in the application are still analytically pure iron salts and manganese salts. This is because for the prior art, the purity of battery-grade materials is often required to be high, and it is easier to obtain pure phase ferromanganese phosphate using pure manganese sources and iron sources. If there are too many impurities in the raw materials, it is easy to generate other impurities or generate ferromanganese phosphate doped with other elements. The appearance of impurities not only affects the purity of the battery-grade lithium iron manganese phosphate precursor, but also affects the discharge performance of the lithium iron manganese battery, causing safety hazards, and is not conducive to the later qualitative and quantitative element-doped ferromanganese phosphate to improve the performance of lithium iron manganese. Therefore, in order to avoid complex impurity removal operations and control production costs, the prior art usually gives priority to pure raw materials, and does not use titanium dioxide byproducts with more impurities for the preparation of battery materials.

[0006] The Chinese patent with application number CN202311854243.7 discloses a method and application for preparing lithium iron manganese phosphate / carbon composite positive electrode material from titanium dioxide byproducts. The invention utilizes the ferrous sulfate solution, a byproduct of titanium dioxide, and obtains a lithium iron manganese phosphate / carbon composite positive electrode material through the technology of "liquid phase coprecipitation-solid phase sand milling assisted spray granulation-high temperature sintering". It is matched with the negative electrode of lithium ion battery and can be used in lithium ion battery. The application proposes that the manganese element in the titanium dioxide byproduct ferrous sulfate can be retained after impurities are removed, and the lithium iron manganese phosphate / carbon composite positive electrode material can be prepared in combination with subsequent manganese sources and other raw materials. Although it is mentioned that the manganese element in the titanium dioxide byproduct is controlled to a certain content and then used, it does not indicate whether this is applicable to the chloride titanium dioxide byproduct. Obviously, in the ferrous chloride produced as a by-product of titanium dioxide, due to the high impurity content and the properties of most impurities being similar to those of iron, it is difficult to enrich iron to the level that can be used to prepare battery precursors. In other words, in the process of preparing titanium dioxide by the chlorination method, the impurities in its by-products are more difficult to remove and often cannot be used to prepare electrode materials.

[0007] In summary, although the above patents disclose that titanium dioxide byproducts can be recycled for the preparation of battery materials, including titanium dioxide byproduct ferrous sulfate and titanium dioxide byproduct ferrous chloride, there is no technology for using titanium dioxide byproduct ferrous chloride to prepare lithium iron manganese phosphate electrode materials. This is because the presence of complex impurity elements such as manganese, magnesium, and aluminum in titanium dioxide byproduct ferrous chloride makes it impossible to be directly used to synthesize battery-grade ferromanganese phosphate, and the mutual influence between impurity elements also makes the impurity removal process difficult. Usually, only the main component ferrous chloride can be simply retained, and it cannot be prepared into a more difficult battery-grade ferromanganese phosphate. Therefore, how to better realize the resource application of byproducts in the titanium dioxide production process so that it can become another solution for lithium iron manganese phosphate battery materials has become a technical problem that needs to be solved by those skilled in the art. Summary of the invention

[0008] In view of the problem that the existing technology cannot utilize ferrous chloride, a by-product of titanium dioxide, and often needs to rely on pure raw materials to prepare battery-grade ferromanganese phosphate precursors, resulting in high production costs, the present invention provides a method that can overcome the influence of impurity elements in ferrous chloride, a by-product of titanium dioxide, on the enrichment of ferromanganese, and prepare the by-products in the titanium dioxide production process into a battery-grade ferromanganese phosphate precursor, thereby realizing the recycling of resources.

[0009] The technical solution adopted by the present invention to solve the technical problem is:

[0010] A method for preparing battery-grade ferromanganese phosphate using ferrous chloride produced as a byproduct of titanium dioxide, comprising the following steps:

[0011] S1: Impurity removal: Heat the titanium dioxide by-product to 30-60°C and dissolve it in ultrapure water, filter it once to obtain a filtrate, add ammonia water dropwise while stirring until the pH value is 4, filter it twice, collect the filtrate, evaporate and crystallize it, and obtain crude ferrous chloride, whose iron content is 40-55wt%, and the manganese content is 3-5wt%. The iron content in the above titanium dioxide by-product is 18-20wt%.

[0012] S2: Prepare manganese source: prepare the above crude ferrous chloride and divalent manganese salt into divalent manganese ferroic mixed solution, where Mn 2+ and Fe 2+ The molar ratio is 6.5:3.5.

[0013] S3: preparing a phosphorus source: preparing a phosphorus source solution, adjusting the pH value to 3-10, and adding a surfactant in an amount of 5-8 g / L.

[0014] S4: preparing divalent manganese iron phosphate suspension: adding the divalent manganese iron mixed solution to the phosphorus source solution within 30 to 180 minutes at 25 to 70° C., stirring continuously at a speed of 200 to 500 rpm, to obtain a divalent manganese iron phosphate suspension.

[0015] S5: Oxidation reaction: at 25-70° C., an oxidant is introduced into the above divalent ferromanganese phosphate suspension within 30-180 min to obtain an oxidized ferromanganese phosphate suspension, wherein the manganese and iron elements are trivalent.

[0016] S6: Preparation of battery-grade ferromanganese phosphate: Filter the above ferromanganese phosphate suspension using a vacuum filter or a filter press, wash with ultrapure water to reduce the conductivity to 1000 μs / cm, dry at 70-120° C., and calcine at 300-700° C. to obtain battery-grade ferromanganese phosphate.

[0017] Usually, battery-grade materials have high requirements for the purity of precursors, and pure raw materials are generally selected for preparation. High impurity content will lead to poor discharge performance of battery materials and cause safety hazards. In the crude ferrous chloride byproduct of titanium dioxide, in addition to the two elements of iron and manganese that can be used, it also contains many other impurity elements, such as calcium, magnesium, aluminum, etc. When using an alkaline precipitant to remove impurities, the manganese element is usually removed, and it is difficult to be enriched with the iron element at the same time. In this application, in the crude ferrous chloride after the titanium dioxide byproduct is removed, the content of iron is 40-55wt%, and the content of manganese is 3-5wt%, so that the titanium dioxide byproduct with ferrous chloride as the main component can be used as a qualified iron source to prepare a battery-grade ferromanganese phosphate precursor. And after removing impurities, the manganese source and phosphorus source are first configured and then synthesized and oxidized with the iron source, which can effectively prevent impurities from mixing into the crude ferromanganese phosphate, so that the purity of the finished ferromanganese phosphate is good and the particle size distribution is uniform. The purity of the ferromanganese phosphate precursor prepared in the present application can generally reach the content of elements such as sodium, potassium, magnesium, and calcium less than 100ppm, and the content of copper element less than 5ppm. It can be understood that as long as the impurity content in the ferromanganese phosphate material is controlled, that is, the purity is good, it can be used as a precursor of the electrode material lithium manganese iron phosphate without affecting the electrical performance.

[0018] Specifically, in the impurity removal stage of S1, the crude ferrous chloride product of titanium dioxide byproduct is first heated to 30-60°C and dissolved, and then filtered once to remove the insoluble matter with larger particles, and then alkali is added to precipitate the impurity metals in the crude product, and the pH value is controlled to 4 to make the impurity precipitation more complete, and the temperature is controlled to accelerate the dissolution of the crude product, and the manganese iron element and other impurity ions are better dissolved in water. When the alkali is added, the impurity elements can be completely precipitated to improve the purity of the finished product. After that, the filtrate is evaporated and crystallized by secondary filtration to obtain a crude ferrous chloride product with good purity, wherein the iron element can be enriched to a content of 40-55wt%, the content of manganese element accounts for 3-5wt%, and the content of impurities has little effect on the electrode material. At this content, the crude ferrous chloride product can be used as a qualified iron source to participate in the preparation of battery-grade manganese iron phosphate precursor, and the manganese element therein is used as a supplementary manganese source, which can reduce the amount of subsequent manganese source addition, save costs, and improve the utilization rate of by-products. Among them, using ammonia water as an alkaline precipitant will not bring new impurities and is easier to recycle and process; using ultrapure water as a solvent can also reduce the introduction of impurities. The present application preferably uses a titanium dioxide byproduct with an iron content of 18-20wt%, which can reduce the difficulty of impurity removal.

[0019] After removing impurities from the titanium dioxide byproduct, S2 of this application is used to configure a manganese source. Usually, when preparing a manganese iron phosphate precursor, the discharge performance of manganese iron lithium phosphate with different manganese iron ratios is different. Theoretically, within a certain range, the higher the manganese content, the higher the energy density of the manganese iron lithium battery, that is, the higher the rate, but the addition of too high a content of manganese will also cause the cycle life of the manganese iron lithium battery to decrease. By adding an external manganese source and controlling the ratio of manganese iron elements, the electrical properties of the battery material can be guaranteed. Specifically, the crude ferrous chloride already contains some manganese elements that can be used as a manganese source. A divalent manganese salt is added to S2 as a supplementary manganese source, and it is prepared into a divalent manganese iron mixed solution with the above-mentioned crude ferrous chloride, and the Mn 2+ and Fe 2+ The molar ratio of Mn is 6.5:3.5. Under this ratio, the purity and discharge performance of the generated precursor are better. The final product is Mn 0.65 Fe 0.35 PO4.

[0020] Afterwards, in S3, the soluble phosphorus source is prepared into a phosphorus source solution, and the pH value is adjusted to 3-10, so that no manganese pyrophosphate / iron is generated in the calcined product, and the purity is good. In the process of preparing the phosphorus source solution, 5-8g of surfactant is added per liter of phosphorus source solution, so that the phosphorus source can be better dispersed and dissolved in the solution, the particles are prevented from aggregating, the subsequent reaction process is more sufficient, and the appearance of impurities is reduced.

[0021] Preferably, the phosphorus source in S3 includes phosphoric acid, disodium hydrogen phosphate or diammonium hydrogen phosphate; the surfactant includes sodium dodecyl sulfate, gelatin, salicylic acid, sodium gluconate, diethanolamine, coconut oil diethanolamine or oxalic acid. It is preferred that the above common phosphorus sources and surfactants are used to prepare the phosphorus source solution, so that the preparation process is easy to control, the post-treatment is simple, and the possibility of impurities can be reduced.

[0022] In S4, at 25-70°C, the above-mentioned divalent manganese iron mixed solution is added to the above-mentioned phosphorus source solution within 30-180min. At this temperature, the manganese iron mixed solution and the phosphorus source solution can react well to obtain a divalent manganese iron phosphate precipitate with good purity. Limiting the addition time of the phosphorus source solution, stirring continuously during the period, the rotation speed is 200-500rpm, and the degree of complexation of manganese iron phosphate can be further controlled. If the addition time is too short, manganese iron cannot be precipitated together, and iron phosphate and manganese phosphate are easily generated, and the particle size of manganese iron phosphate particles is too small, and the discharge performance of the finished product is poor; on the contrary, if the addition time is too long, the particle size of manganese iron phosphate is too large, and the efficiency is reduced. In the process of preparing divalent manganese iron phosphate suspension, limiting the temperature, addition time, and stirring speed can obtain manganese iron phosphate particles with suitable particle size, which can make the phase sintering uniform in the subsequent process, and control the addition time of the material to reduce the generation of other impurity products, so that the complexation process generates more divalent manganese iron phosphate products, and further improve the purity of the finished product.

[0023] After the divalent manganese ferrophosphate suspension is prepared, an oxidant is added thereto to oxidize the divalent iron to trivalent iron. Since the oxidation reaction is an exothermic reaction, the introduction of the oxidant at 25 to 70°C can make the oxidation reaction proceed relatively smoothly. The oxidant is controlled to be introduced within 30 to 180 minutes. When the oxidant is introduced for too short a time and at too fast a speed, a large amount of heat is released instantly in the reaction, causing the temperature of the solution to rise sharply. At this time, the manganese ferrophosphate is still in an amorphous state and is easily destroyed, and some oxidants such as hydrogen peroxide, oxygen, ozone, and sodium hypochlorite will be decomposed or eliminated by high temperature before they have time to react, and cannot achieve a good oxidation effect; when the speed is too slow, the amorphous manganese ferrophosphate will gradually transform into crystals, increasing the difficulty of its oxidation, and incomplete oxidation is prone to occur, and the too long addition process seriously reduces the preparation efficiency.

[0024] Different from the traditional strategy of adding phosphorus source after oxidation, the present application adopts the method of adding phosphorus source solution first to generate divalent ferromanganese phosphate precipitation and then oxidizing to generate ferromanganese phosphate, which can guarantee the purity and yield of finished product ferromanganese phosphate to the maximum extent. First, the present application is divalent in the preparation of ferrous chloride crude product and added manganese source, and first prepares it as divalent ferromanganese phosphate and then performs oxidation reaction, so that it will not be oxidized to trivalent manganese ion, because the state of trivalent manganese ion is unstable, it is very easy to be disproportionated into tetravalent manganese and divalent manganese, and reducing the appearance of trivalent manganese ion can avoid the situation of manganese valence state mixing in finished product. Secondly, if divalent iron is first oxidized to ferric iron, because ferric iron ion is very easy to hydrolyze into ferric hydroxide under weak acid conditions, and the Ksp of ferric hydroxide is much smaller than ferric phosphate, it may face the phenomenon of being unable to be completely converted in subsequent preparation, resulting in impurities such as ferric oxide appearing in the finished product; if reacted under strong acid conditions, precipitation reaction is less, and the finished product yield will be reduced by more than half. In addition, if the oxidation reaction is carried out without ferromanganese phosphate precipitation, amorphous substances are easily produced in the process, and it may be impossible to determine whether the final product is ferromanganese phosphate. As a result, there will be more impurities in the finished product and unstable discharge performance.

[0025] Preferably, the oxidant in S5 above includes: hydrogen peroxide, oxygen, ozone, sodium hypochlorite, potassium permanganate or nitric acid. Since the strategy of first preparing a divalent manganese ferrophosphate suspension and then oxidizing the divalent iron to trivalent iron is adopted, the above oxidants with strong oxidizing properties can better oxidize the solid divalent manganese ferrophosphate.

[0026] After the oxidation reaction, since the suspension prepared in S5 has a high purity of ferromanganese phosphate and very little impurity content, no other post-treatment is required in S6. It is only necessary to control the temperature and other conditions. The suspension can be filtered, washed, dried, and calcined to obtain a qualified battery-grade ferromanganese phosphate precursor, which can use relatively simple operation steps to improve production efficiency. Specifically, since the particle size of the ferromanganese phosphate precipitate is small, the precipitate of the above-mentioned ferromanganese phosphate suspension is filtered using a vacuum filter or a filter press, which can make the filtration effect of the target ferromanganese phosphate precipitate good. After that, the conductivity is controlled to 1000μs / cm using ultrapure water during the washing process, which can wash away more insoluble impurities and excess phosphorus, ensure the purity of the finished product and control the value of Me / P. After drying at a temperature of 70 to 120°C, calcining at 300 to 700°C can make the drying and calcining efficiency higher while avoiding the finished product from being burned and damaged due to excessive temperature.

[0027] Compared with the prior art, the technical solution of the present application has at least the following beneficial effects:

[0028] 1. The present invention adopts two filtrations and evaporation crystallization to obtain crude ferrous chloride, wherein the content of iron is controlled to be 40-55wt%, and the content of manganese is controlled to be 3-5wt%, so that the crude ferrous chloride produced as a byproduct of titanium dioxide can be used to prepare battery-grade manganese phosphate with good purity, thereby realizing the recycling of resources.

[0029] 2. In the process of preparing ferromanganese phosphate, the present invention adopts the operation sequence of first preparing the phosphorus source and then oxidizing the divalent iron, which can make more manganese elements generate ferromanganese phosphate and reduce the appearance of impurities in the finished product.

[0030] 3. The present invention uses ferrous chloride in the byproduct of titanium dioxide to prepare ferromanganese phosphate, which realizes resource recycling, is conducive to cost saving and improves resource utilization. In addition, the present invention has low reaction temperature, is easy to control, has simple process operation, and can recycle wastewater, which is easy to industrialize and apply; the prepared ferromanganese phosphate has uniform particle size distribution, pure phase, and high cleanliness, and is an excellent precursor for preparing high-ferromanganese phosphate lithium battery materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments and comparative examples. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The Mn prepared in Example 1 of the present invention 0.65 Fe 0.35 The SEM image of PO4 precursor is a scanning electron microscope image. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0034] A method for preparing battery-grade ferromanganese phosphate using ferrous chloride produced as a byproduct of titanium dioxide, comprising the following steps:

[0035] S1: Impurity removal: Heat the titanium dioxide by-product to 30-60°C and dissolve it in ultrapure water, filter it once to obtain a filtrate, add ammonia water dropwise while stirring until the pH value is 4, filter it twice, collect the filtrate, evaporate and crystallize it, and obtain crude ferrous chloride, whose iron content is 40-55wt%, and the manganese content is 3-5wt%. The iron content in the above titanium dioxide by-product is 18-20wt%.

[0036] S2: Prepare manganese source: prepare the above crude ferrous chloride and divalent manganese salt into divalent manganese ferroic mixed solution, where Mn 2+ and Fe 2+ The molar ratio is 6.5:3.5.

[0037] S3: preparing a phosphorus source: preparing a phosphorus source solution, adjusting the pH value to 3-10, and adding a surfactant in an amount of 5-8 g / L.

[0038] S4: preparing divalent manganese iron phosphate suspension: adding the divalent manganese iron mixed solution to the phosphorus source solution within 30 to 180 minutes at 25 to 70° C., stirring continuously at a speed of 200 to 500 rpm, to obtain a divalent manganese iron phosphate suspension.

[0039] S5: Oxidation reaction: at 25-70° C., an oxidant is introduced into the above divalent ferromanganese phosphate suspension within 30-180 min to obtain an oxidized ferromanganese phosphate suspension, wherein the manganese and iron elements are trivalent.

[0040] S6: Preparation of battery-grade ferromanganese phosphate: Filter the above ferromanganese phosphate suspension using a vacuum filter or a filter press, wash with ultrapure water to reduce the conductivity to 1000 μs / cm, dry at 70-120° C., and calcine at 300-700° C. to obtain battery-grade ferromanganese phosphate.

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0042] Example

[0043] The embodiments of the present invention are all implemented according to the technical solutions in the above-mentioned embodiments. The specific implementation conditions are shown in Table 1. The purity of the battery-grade ferromanganese phosphate precursor obtained in Example 2 is tested, and the specific test results are shown in Table 2.

[0044] Table 1 Specific implementation of the embodiment

[0045]

[0046] Table 2 Performance test results of battery-grade ferromanganese phosphate precursor prepared in Example 2

[0047]

[0048] It can be seen from the test results in Table 2 that the technical solution of the present application can effectively prepare ferromanganese phosphate from the crude ferrous chloride byproduct of titanium dioxide, wherein the total amount of metal elements (Me) and phosphorus elements have a suitable ratio, and the ratio of manganese to iron is 6.5:3.5, indicating that the manganese element is well utilized, and the other impurity content, tap density, particle size, etc. of the ferromanganese phosphate precursor have reached the standards for the precursor of battery-grade lithium manganese iron phosphate. The ferromanganese phosphate of Example 1 was scanned by electron microscope, and the SEM image was obtained as follows Figure 1 As shown, it can be seen that the ferromanganese phosphate obtained in the present application has a relatively uniform morphology and can be used as a battery-grade precursor material.

[0049] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the application claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride, a byproduct of titanium dioxide, characterized in that: The method comprises removing impurities from titanium dioxide byproducts to obtain a crude ferrous chloride product, wherein the crude ferrous chloride product has an iron content of 40-55wt% and a manganese content of 3-5wt%, and then a manganese source and a phosphorus source are prepared, and synthesis and oxidation reactions are carried out to obtain battery-grade ferromanganese phosphate.

2. The method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride produced as a byproduct of titanium dioxide according to claim 1, characterized in that: The following steps are involved: S1: impurity removal: heating the titanium dioxide by-product to 30-60° C. and dissolving it in ultrapure water, filtering once to obtain a filtrate, adding ammonia water dropwise while stirring until the pH value is 4, filtering twice, collecting the filtrate, evaporating and crystallizing to obtain the crude ferrous chloride, wherein the iron content in the titanium dioxide by-product is 18-20wt%; S2: preparing a manganese source: preparing the crude ferrous chloride and a divalent manganese salt into a divalent manganese-iron mixed solution; S3: preparing a phosphorus source: preparing a phosphorus source solution, adjusting the pH value to 3-10, and adding a surfactant in an amount of 5-8 g / L; S4: preparing a divalent ferromanganese phosphate suspension: adding the divalent ferromanganese mixed solution to the phosphorus source solution within 30 to 180 minutes at 25 to 70° C., stirring continuously during the period at a speed of 200 to 500 rpm, to obtain a divalent ferromanganese phosphate suspension; S5: oxidation reaction: at 25-70° C., introducing an oxidant into the divalent ferromanganese phosphate suspension within 30-180 min to obtain an oxidized ferromanganese phosphate suspension, wherein the manganese and iron elements are trivalent; S6: preparing battery-grade ferromanganese phosphate: filtering, washing, drying and calcining the ferromanganese phosphate suspension to obtain battery-grade ferromanganese phosphate.

3. The method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride, a byproduct of titanium dioxide, according to claim 2, characterized in that: In the divalent manganese iron mixed solution of S2, Mn 2+ and Fe 2+ The molar ratio is 6.5:3.

5.

4. The method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride, a byproduct of titanium dioxide, according to claim 2, characterized in that: The phosphorus source in S3 includes phosphoric acid, disodium hydrogen phosphate or diammonium hydrogen phosphate.

5. A method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride produced as a byproduct of titanium dioxide according to claim 2 or 4, characterized in that: The surfactant in S3 includes: sodium dodecyl sulfate, gelatin, salicylic acid, sodium gluconate, diethanolamine, coconut oil diethanolamine or oxalic acid.

6. The method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride produced as a byproduct of titanium dioxide according to claim 2, characterized in that: The oxidant in S5 includes: hydrogen peroxide, oxygen, ozone, sodium hypochlorite, potassium permanganate or nitric acid.

7. The method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride produced as a byproduct of titanium dioxide according to claim 2, characterized in that: In S6, the filtration is performed using a vacuum filter or a filter press.

8. A method for preparing a battery-grade ferromanganese phosphate precursor using ferrous chloride produced as a byproduct of titanium dioxide according to claim 2 or 7, characterized in that: In the S6, the washing includes: washing with ultrapure water to reduce the conductivity to 1000 μs / cm, the drying temperature is 70 to 120°C, and the calcining temperature is 300 to 700°C.

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