Manganese iron pyrophosphate, manganese iron lithium phosphate and preparation method and battery thereof

Abstract

The application discloses a manganese iron pyrophosphate with a laminated structure, and a specific preparation process is as follows: a manganese iron ammonium phosphate is prepared by carrying out a coprecipitation reaction on a phosphorus source and a mixed metal salt solution according to preset molar ratios of elements in the manganese iron ammonium phosphate, and then the manganese iron ammonium phosphate is calcined to obtain the manganese iron pyrophosphate; further, a manganese iron lithium phosphate is prepared by taking the manganese iron pyrophosphate as a raw material; and a battery comprising the manganese iron lithium phosphate as a positive electrode material.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of batteries, in particular to a manganese iron pyrophosphate, a lithium manganese iron phosphate and a preparation method thereof and a battery. BACKGROUND

[0002] With the continuous development of technology, the problems of resource waste and environmental pollution are becoming increasingly serious. Controlling carbon emissions and reducing the use of traditional vehicles have become important measures for energy conservation and emission reduction in many regions. Promoting the research and application of new energy vehicles has become a top priority. As the most widely researched and most practical energy material in new energy vehicles, lithium ion batteries have been applied in many fields.

[0003] The positive material is the main part that determines the performance and price of lithium ion batteries. Lithium iron phosphate and lithium manganese phosphate are currently commonly used positive materials, but the voltage platform and energy density of lithium iron phosphate are relatively low, and the conductivity of lithium manganese phosphate is poor.

[0004] Because manganese ions and iron ions have similar ionic radii, they can be infinitely miscible in the phosphate framework. The formation of lithium manganese iron phosphate by mixing manganese and iron can to some extent integrate the advantages and disadvantages of lithium iron phosphate and lithium manganese phosphate. However, the performance of lithium manganese iron phosphate is closely related to the precursor used in its preparation process. The lithium manganese iron phosphate positive material prepared by the existing precursor usually has a low compaction density and poor electrical performance.

[0005] In view of this, the present disclosure is proposed. SUMMARY

[0006] The present disclosure provides a manganese iron pyrophosphate, a lithium manganese iron phosphate and a preparation method thereof and a battery to solve or improve the above technical problems.

[0007] The present disclosure can be implemented as follows:

[0008] In a first aspect, the present disclosure provides a manganese iron pyrophosphate having a sheet structure.

[0009] In an optional embodiment, the manganese iron pyrophosphate has at least one of the following characteristics:

[0010] Characteristic one: In the manganese iron pyrophosphate, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 0.97:1-1.02:1, and the ratio of the number of moles of Mn to the number of moles of Fe is x:1-x, wherein 0.1≤x<1.

[0011] Characteristic two: The D50 of the manganese iron pyrophosphate is 5-20 μm. 50

[0012] In an optional embodiment, the manganese iron pyrophosphate is further doped with a doping element; the doping element includes at least one of Ti, V, Mg, Cr and Zr. ​

[0013] In an optional embodiment, the total doping amount of the doping elements is not more than 3000 ppm, based on the mass of the manganese iron pyrophosphate.

[0014] In a second aspect, the disclosure provides a method for preparing the manganese iron pyrophosphate according to any one of the preceding embodiments, comprising the following steps: calcining ammonium manganese iron phosphate to obtain manganese iron pyrophosphate.

[0015] The preparation of the ammonium manganese iron phosphate comprises: co-precipitation of a phosphorus source and a mixed metal salt solution according to a preset molar ratio of elements in the ammonium manganese iron phosphate.

[0016] The metals in the mixed metal salt solution include Mn and Fe.

[0017] In an optional embodiment, the ratio of the total number of moles of Mn and Fe to the number of moles of P in the ammonium manganese iron phosphate is 0.97:1-1.02:1, and the ratio of the number of moles of Mn to the number of moles of Fe is x:1-x, wherein 0.1≤x<1.

[0018] In an optional embodiment, the total concentration of Mn and Fe in the mixed metal salt solution is 0.6 mol / L-3 mol / L.

[0019] In an optional embodiment, the manganese source providing the Mn element is a divalent manganese source; and / or, the iron source providing the Fe element is a divalent iron source.

[0020] In an optional embodiment, the manganese source includes at least one of manganese sulfate, manganese nitrate, and manganese acetate; and / or, the iron source includes at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride.

[0021] In an optional embodiment, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and sodium hydrogen phosphate.

[0022] In an optional embodiment, when the manganese iron pyrophosphate contains doping elements, the metals in the mixed metal salt solution also include the doping elements.

[0023] In an optional embodiment, the co-precipitation reaction comprises at least one of the following characteristics:

[0024] Characteristic one: the pH value of the co-precipitation reaction is 6-7;

[0025] Characteristic two: the temperature of the co-precipitation reaction is 20°C-60°C;

[0026] Characteristic three: the time of the co-precipitation reaction is 0.5h-8h.

[0027] In an optional embodiment, the calcination has at least one of the following characteristics:

[0028] Feature 1: the calcination temperature is 500-600℃;

[0029] Feature 2: the calcination time is 2-10h;

[0030] Feature 3: the calcination is performed in a protective atmosphere.

[0031] In a third aspect, the present disclosure provides a lithium manganese iron phosphate, which is prepared from a raw material including the pyrophosphate manganese iron of any of the preceding embodiments.

[0032] In an optional embodiment, the lithium manganese iron phosphate has a tap density of not less than 2.3g / cm 3 .

[0033] In a fourth aspect, the present disclosure provides a method for preparing the lithium manganese iron phosphate of the preceding embodiments, which includes the step of sintering the pyrophosphate manganese iron with a lithium source.

[0034] In an optional embodiment, the sintering has at least one of the following features:

[0035] Feature 1: the sintering temperature is 600-750℃;

[0036] Feature 2: the sintering time is 2-10h;

[0037] Feature 3: the sintering is performed in an inert atmosphere.

[0038] In an optional embodiment, the ratio of the moles of Li in the lithium source to the total moles of Mn and Fe in the pyrophosphate manganese iron is (0.98:1)-(1.02:1).

[0039] In an optional embodiment, the lithium source includes at least one of lithium hydroxide and lithium carbonate.

[0040] In an optional embodiment, before the sintering, the method further includes sand milling and spray drying the mixture of the pyrophosphate manganese iron and the lithium source.

[0041] In an optional embodiment, the sand milling is to mill the mixture to a D 50 of 400-600nm.

[0042] In an optional embodiment, the spray drying temperature is 180-210℃.

[0043] In an optional embodiment, the raw material for preparing the lithium manganese iron phosphate further includes a carbon source, and the sintering is performed on the pyrophosphate manganese iron, the phosphorus source and the carbon source together.

[0044] In an optional embodiment, the carbon source includes at least one of glucose, starch, ascorbic acid and citric acid.

[0045] In an optional embodiment, the lithium manganese iron phosphate contains 1wt%-2wt% of carbon.

[0046] In a fifth aspect, the present disclosure provides a battery, the positive electrode material of which comprises the lithium manganese iron phosphate of the preceding embodiments.

[0047] The beneficial effects of the present disclosure include:

[0048] The present disclosure first proposes a manganese iron pyrophosphate in a sheet structure, and accordingly provides a preparation method of the manganese iron pyrophosphate. By using the above-mentioned manganese iron pyrophosphate as a precursor to prepare lithium manganese iron phosphate, the generation of gas and the defects such as pores caused by the generation of gas in the sintering process can be avoided, so that the compaction density of the lithium manganese iron phosphate can be effectively improved. Further, by using the lithium manganese iron phosphate to prepare a lithium ion battery, the battery can have good capacity and initial efficiency and other performances at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0050] Figure 1 The preparation process flow chart of the lithium manganese iron phosphate in Example 7 of the present disclosure is shown in the following figure:

[0051] Figure 2 The SEM image of the manganese iron pyrophosphate obtained in Example 5 of the test example of the present disclosure is shown in the following figure:

[0052] Figure 3 The XRD image of the manganese iron pyrophosphate obtained in Example 5 of the test example of the present disclosure is shown in the following figure:

[0053] Figure 4 The XRD image of the lithium manganese iron phosphate obtained in Example 7 of the test example of the present disclosure is shown in the following figure. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be described clearly and completely. The specific conditions in the embodiments are not specified, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased in the market.

[0055] The manganese iron pyrophosphate, lithium manganese iron phosphate and the preparation method and battery thereof provided by the present disclosure will be described in detail below.

[0056] The inventors have found that the reason why the current existing lithium manganese iron phosphate positive electrode material has a low tap density is that the existing technology usually uses manganese iron oxalate and manganese ammonium phosphate as a precursor to prepare lithium manganese iron phosphate. The precursor releases gas (such as ammonia, water vapor, carbon monoxide, or carbon dioxide) during calcination, which increases the number of pores and the degree of looseness of the material, resulting in an insignificant tap effect and a relatively low tap density, and thus a low tap density of the obtained positive electrode material. The present disclosure creatively uses manganese iron pyrophosphate as a precursor to prepare lithium manganese iron phosphate. By using manganese iron pyrophosphate as a precursor, the generation of gas during sintering and the defects such as pores caused by the generation of gas can be avoided, which is beneficial to improve the tap density of the positive electrode material.

[0057] The chemical formula of the manganese iron pyrophosphate is (Mn x Fe 1-x )2P2O7, 0.1≤x<1, that is, the manganese iron pyrophosphate is a substance formed by replacing part of manganese in manganese pyrophosphate with iron. It should be noted that the manganese iron pyrophosphate in the current existing technology does not have a fixed morphology, and is usually an amorphous powder. If such manganese iron pyrophosphate is used to prepare lithium manganese iron phosphate, the obtained lithium manganese iron phosphate has poor performance. The manganese iron pyrophosphate used in the present disclosure has a specific morphology, which is a lamellar structure. By using the manganese iron pyrophosphate as a precursor, a lithium manganese iron phosphate positive electrode material with good performance can be obtained. A lithium ion battery prepared from the lithium manganese iron phosphate has good capacity and initial efficiency.

[0058] For reference, in the manganese iron pyrophosphate provided by the present disclosure, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 0.97:1-1.02:1, and the ratio of the number of moles of Mn to the number of moles of Fe is x:1-x, wherein 0.1≤x<1.

[0059] The ratio of the total number of moles of Mn and Fe to the number of moles of P can be 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, or 1.02:1, or any other value within the range of 0.97:1-1.02:1. In some typical embodiments, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 1:1. In the present disclosure, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 0.97:1-1.02:1. This manganese iron pyrophosphate is more consistent with the element ratio of lithium manganese iron phosphate after sintering, and does not need to supplement phosphorus source later, which is more conducive to the simplification of the process and the uniform distribution of elements.

[0060] The manganese iron pyrophosphate provided by the present disclosure has a wide particle size distribution. In some embodiments, the D 50 of the manganese iron pyrophosphate is 5 μm to 20 μm, such as D 50It can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, etc., or any other value in the range of 5 μm to 20 μm.

[0061] In some optional embodiments, the manganese iron pyrophosphate provided by the present disclosure can also be doped with a doping element as needed. The doping element can exemplarily but non-limitingly include at least one of Ti, V, Mg, Cr and Zr.

[0062] In some embodiments, the doping amount of the doping element M is not more than 3000 ppm, for example, it can be 3000 ppm, 2800 ppm, 2500 ppm, 2200 ppm, 2000 ppm, 1800 ppm, 1500 ppm, 1200 ppm, 1000 ppm, 800 ppm, 500 ppm, 200 ppm, 100 ppm, 80 ppm, 50 ppm, 20 ppm, 10 ppm or 5 ppm, etc., based on the mass of the manganese iron pyrophosphate.

[0063] Correspondingly, the present disclosure provides a preparation method of the above-mentioned manganese iron pyrophosphate, which can include the following steps: calcining ammonium manganese iron phosphate to obtain manganese iron pyrophosphate.

[0064] The preparation of the above-mentioned ammonium manganese iron phosphate includes: co-precipitation reaction of a phosphorus source and a mixed metal salt solution according to a preset molar ratio of elements in the ammonium manganese iron phosphate; the metals in the mixed metal salt solution include Mn and Fe.

[0065] It should be noted that the ammonium manganese iron phosphate is prepared by the liquid phase method, and then the obtained ammonium manganese iron phosphate is calcined to obtain manganese iron pyrophosphate, which can make the element distribution more uniform than the solid state ball milling method, and a solid solution with atomic level uniform distribution of manganese and iron can be obtained, and the atomic level uniform mixing of manganese and iron is an important prerequisite for improving the lithium battery performance and cycle number of the ammonium manganese iron phosphate.

[0066] Corresponding to the above-mentioned manganese iron pyrophosphate, in the ammonium manganese iron phosphate, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 0.97:1-1.02:1, and the ratio of the number of moles of Mn to the number of moles of Fe is x:1-x, wherein 0.1≤x<1.

[0067] For reference, the total concentration of Mn and Fe in the mixed metal salt solution can be 0.6 mol / L-3 mol / L, such as 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc., or any other value in the range of 0.6 mol / L-3 mol / L.

[0068] In some embodiments, the manganese source providing the Mn element is a divalent manganese source, which exemplarily but non-limitatively can include at least one of manganese sulfate, manganese nitrate and manganese acetate. In other embodiments, the manganese source can also be other manganese-containing substances in which the manganese element is not divalent.

[0069] In some embodiments, the iron source providing the Fe element is a divalent iron source, which exemplarily but non-limitatively can include at least one of ferrous sulfate, ferrous nitrate and ferrous chloride. In other embodiments, the iron source can also be other iron-containing substances in which the iron element is not divalent.

[0070] The phosphorus source can exemplarily but non-limitatively include at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and sodium hydrogen phosphate.

[0071] Corresponding to manganese pyrophosphate iron, when the manganese pyrophosphate iron contains a doping element, the metals in the mixed metal salt solution also include the doping element.

[0072] For reference, the pH value of the coprecipitation reaction can be 6-7, such as 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7, etc., and can also be any other value within the range of 6-7. In specific operation, the pH value can be adjusted by adding ammonia water.

[0073] The temperature of the coprecipitation reaction can be 20-60°C, such as 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc., and can also be any other value within the range of 20-60°C.

[0074] The time of the coprecipitation reaction can be 0.5-8h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, etc., and can also be any other value within the range of 0.5-8h.

[0075] After the coprecipitation reaction is completed, the solid-liquid mixture obtained by the reaction is subjected to solid-liquid separation, and the obtained solid is washed and dried, to obtain the manganese iron ammonium phosphate.

[0076] For reference, the temperature of the calcination for preparing the manganese pyrophosphate iron from the manganese iron ammonium phosphate can be 500-600°C, such as 500°C, 520°C, 550°C, 580°C or 600°C, etc., and can also be any other value within the range of 500-600°C.

[0077] It should be noted that if the calcination temperature is lower than 500℃, the ammonium manganese iron phosphate will not be completely de-crystallized, the ammonia molecules cannot be completely removed, and the ammonium manganese iron phosphate cannot be completely converted into manganese iron pyrophosphate. If the calcination temperature is higher than 600℃, the morphology of the manganese pyrophosphate will be affected, the ammonia gas generated will be decomposed, the recycling thereof will be affected, and the lattice structure of the manganese pyrophosphate will be damaged due to the excessively high sintering temperature.

[0078] The calcination time can be 2h-10h, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., or any other value within the range of 2h-10h.

[0079] The calcination is performed in a protective atmosphere, which can be nitrogen, argon or helium, etc.

[0080] In addition, the present disclosure also provides a lithium manganese iron phosphate, the raw material for preparing the lithium manganese iron phosphate comprising the manganese iron pyrophosphate.

[0081] By using the manganese iron pyrophosphate as the precursor for preparing the lithium manganese iron phosphate, the molar ratio of manganese iron to phosphorus in the manganese iron pyrophosphate is approximately 1:1, and the manganese and iron are uniformly mixed at the atomic level. Using the manganese iron pyrophosphate as the precursor for preparing the lithium manganese iron phosphate can exclude the ammonium and water molecules in the ammonium manganese iron phosphate in advance, avoid the generation of pores due to the generation of a large amount of gas during the mixing and sintering of the lithium source, and be beneficial to improving the tap density of the lithium manganese iron phosphate and the initial efficiency and capacity of the corresponding battery.

[0082] In some embodiments, the tap density of the lithium manganese iron phosphate is not less than 2.3g / cm 3 The lithium manganese iron phosphate has a higher tap density than the existing lithium manganese iron phosphate.

[0083] Correspondingly, the present disclosure also provides a preparation method of the lithium manganese iron phosphate, which can comprise the following steps: sintering the manganese iron pyrophosphate and a lithium source.

[0084] For reference, the ratio of the number of moles of Li in the lithium source to the total number of moles of Mn and Fe in the manganese iron pyrophosphate can be (0.98:1)-(1.02:1), such as 0.98:1, 0.99:1, 1:1, 1.01:1 or 1.02:1, etc. The lithium source exemplarily but non-limitingly can comprise at least one of lithium hydroxide and lithium carbonate.

[0085] In some embodiments, the raw material for preparing the lithium manganese iron phosphate can also comprise a carbon source, and correspondingly, the sintering is performed by treating the manganese iron pyrophosphate, the phosphorus source and the carbon source together.

[0086] The carbon source can exemplarily but non-limitatively include at least one of glucose, starch, ascorbic acid and citric acid. The lithium manganese iron phosphate can contain 1wt%-2wt% (such as 1wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%, etc.) of carbon. In some typical embodiments, the lithium manganese iron phosphate can contain 1.4wt%-1.6wt% of carbon.

[0087] By adding the carbon source in the preparation process, a carbon coating layer can be formed, which is beneficial to improve the conductivity, capacity and cycle performance of the positive electrode material, etc.

[0088] In some embodiments, before sintering, the mixture of manganese iron pyrophosphate and lithium source is further subjected to sand milling and spray drying. When the raw material also has a carbon source, before sintering, the mixture of manganese iron pyrophosphate, lithium source and carbon source is subjected to sand milling and spray drying.

[0089] Exemplarily, the sand milling can be to grind the mixture to D 50 400nm to 600nm, such as 400nm, 450nm, 500nm, 550nm or 600nm, etc. In addition, the mixture can also be ground to D 50 less than 500nm and D 90 greater than 1μm.

[0090] By sand milling, on the one hand, the fineness of the mixture can be improved, which is beneficial to make the mixture more fully react in the sintering process, and on the other hand, it is also beneficial to improve the uniformity of the element distribution in the product.

[0091] Exemplarily, the temperature of spray drying can be 180°C-210°C, such as 180°C, 185°C, 190°C, 195°C, 200°C, 205°C or 210°C, etc., or other arbitrary values in the range of 180°C-210°C.

[0092] For reference, the temperature of sintering can be 600°C-750°C, such as 600°C, 620°C, 650°C, 680°C, 700°C, 720°C or 750°C, etc., or other arbitrary values in the range of 600°C-750°C.

[0093] The time of sintering can be 2h-10h, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., or other arbitrary values in the range of 2h-10h.

[0094] The sintering can be carried out under inert atmosphere (such as nitrogen, argon or helium, etc.).

[0095] Further, the present disclosure also provides a battery, the positive electrode material of which comprises the above lithium manganese iron phosphate. The battery has good capacity and initial efficiency.

[0096] The features and performance of the present disclosure are further described in detail below in conjunction with the embodiments.

[0097] Embodiment 1

[0098] This embodiment provides a manganese iron pyrophosphate, whose molecular formula is: (Mn 0.6 Fe 0.4 )2P2O7.

[0099] The preparation of the manganese iron pyrophosphate includes:

[0100] S1: 507g of manganese sulfate monohydrate and 556g of ferrous sulfate heptahydrate are dissolved in 2L of pure water to obtain a mixed metal salt solution (denoted as solution A). In solution A, the molar ratio of Mn to Fe is 6:4, and the total concentration of Mn and Fe is 2.5mol / L;

[0101] S2: 780g of diammonium hydrogen phosphate is weighed and dissolved in 4L of pure water to prepare solution B;

[0102] S3: 408g of ammonia water is weighed and dissolved in 2L of pure water to prepare solution C;

[0103] S4: solution A, solution B and solution C are simultaneously added to the reaction kettle for co-precipitation reaction, and the flow rate is 25min. During the flow rate, the flow rate of solution A is 80ml / min, the flow rate of solution B is 160ml / min, and the flow rate of ammonia water is controlled so that the pH value of the mixed solution in the reaction kettle is always kept at 7. The temperature of the co-precipitation reaction is room temperature 25℃, and the time is 4h. After the co-precipitation reaction is completed, the solid-liquid mixture obtained by the reaction is filtered, and the solid obtained by the filtration is washed and dried to obtain powder manganese iron ammonium phosphate;

[0104] S5: the obtained manganese iron ammonium phosphate powder is placed in a muffle furnace under nitrogen protection, calcined at 550℃ for 8h to obtain manganese iron pyrophosphate (Mn 50 Fe 0.6 )2P2O7with a particle size of D 0.4 =15μm.

[0105] Embodiment 2

[0106] This embodiment provides a manganese iron pyrophosphate, whose molecular formula is: (Mn 0.9 Fe 0.1 )2P2O7.

[0107] The preparation of the manganese iron pyrophosphate includes:

[0108] S1: 76 g of manganese sulfate monohydrate and 10 g of ferrous chloride tetrahydrate were dissolved in 400 mL of pure water to obtain a mixed metal salt solution (denoted as solution A). In solution A, the molar ratio of Mn to Fe was 9:1, and the total concentration of Mn and Fe was 1.25 mol / L;

[0109] S2: 65 g of phosphoric acid was dissolved in 400 mL of pure water to form solution B;

[0110] S3: 76 g of ammonia was weighed and dissolved in 200 mL of pure water to form solution C;

[0111] S4: The ammonia was added to the reaction kettle, and then solution A and solution B were simultaneously added to the reaction kettle for co-precipitation reaction. The flow rate of solution A was 40 mL / min, and the flow rate of solution B was 40 mL / min. The temperature of the co-precipitation reaction was 40°C, the time was 6 h, and the pH value after feeding was 6.0. After the co-precipitation reaction was completed, the solid-liquid mixture obtained by the reaction was filtered, and the solid obtained by the filtration was washed and dried to obtain a powder of manganese iron ammonium phosphate;

[0112] S5: The obtained manganese iron ammonium phosphate powder was placed in a muffle furnace under nitrogen protection and calcined at 500°C for 6 h to obtain D 50 = 5 μm of manganese iron pyrophosphate (Mn 0.9 Fe 0.1 )2P2O7.

[0113] Example 3

[0114] This example provides a manganese iron pyrophosphate, the molecular formula of which is: (Mn 0.8 Fe 0.2 )2P2O7.

[0115] The preparation of the manganese iron pyrophosphate includes:

[0116] S1: 85.9 g of 50% (w / w) manganese nitrate and 16.68 g of ferrous sulfate heptahydrate were dissolved in 300 mL of pure water to obtain a mixed metal salt solution (denoted as solution A). In solution A, the molar ratio of Mn to Fe was 8:2, and the total concentration of Mn and Fe was 1 mol / L.

[0117] S2: 65 g of diammonium hydrogen phosphate was dissolved in 200 mL of pure water, and 34 g of ammonia was added to form solution B;

[0118] S3: Solution A and solution B are added into the reactor for coprecipitation reaction in parallel flow, and the flow adding time is 25 min. During the flow adding process, the adding speed of solution A is 12 ml / min, and the adding speed of solution B is 8 ml / min. The temperature of the coprecipitation reaction is 30°C, the time is 2 h, and the pH value is 6.1. After the coprecipitation reaction is completed, the solid-liquid mixture obtained by the reaction is filtered, and the solid obtained by the filtration is washed and dried to obtain the powder of ammonium manganese iron phosphate;

[0119] S4: The obtained ammonium manganese iron phosphate powder is placed in a muffle furnace under nitrogen protection, calcined at 550°C for 4 h to obtain D 50 = 13 μm of manganese iron pyrophosphate (Mn 0.8 Fe 0.2 )2P2O7.

[0120] Example 4

[0121] This example provides a manganese iron pyrophosphate, and the molecular formula of the manganese iron pyrophosphate is: (Mn 0.8 Fe 0.2 )2P2O7.

[0122] The preparation of the manganese iron pyrophosphate comprises:

[0123] S1: 58.8 g of manganese acetate tetrahydrate and 16.68 g of ferrous sulfate heptahydrate are dissolved in 300 mL of pure water to obtain a mixed metal salt solution (denoted as solution A). In the solution A, the molar ratio of Mn to Fe is 8:2, and the total concentration of Mn and Fe is 1 mol / L;

[0124] S2: 57 g of ammonium dihydrogen phosphate is dissolved in 100 mL of pure water to form solution B;

[0125] S3: 68 g of ammonia is weighed and dissolved in 100 mL of pure water to prepare solution C;

[0126] S4: Solution A, solution B and solution C are simultaneously added into the reactor for coprecipitation reaction, and the flow adding time is 15 min. During the flow adding process, the adding speed of solution A is 20 ml / min, the adding speed of solution B is 6.66 ml / min, and the adding speed of ammonia is controlled so that the pH value of the mixed solution in the reactor is always maintained at 6.5. The temperature of the coprecipitation reaction is 30°C, the time is 3 h, and the stirring frequency is 400 rpm. After the coprecipitation reaction is completed, the solid-liquid mixture obtained by the reaction is filtered, and the solid obtained by the filtration is washed and dried to obtain the powder of ammonium manganese iron phosphate.

[0127] S5: The obtained ammonium manganese iron phosphate powder is placed in a muffle furnace under nitrogen protection, calcined at 500°C for 8 h to obtain D 50 = 6.5 μm of manganese iron pyrophosphate (Mn 0.8 Fe0.2 )2P2O7.

[0128] Example 5

[0129] This embodiment provides a manganese ferric pyrophosphate with the molecular formula: (Mn 0.6 Fe 0.4 )2P2O7.

[0130] The preparation of this ferromanganese pyrophosphate includes:

[0131] S1: Dissolve 507g of manganese sulfate monohydrate and 556g of ferrous sulfate heptahydrate in 5L of pure water to obtain a mixed metal salt solution (i.e., manganese-iron metal solution, denoted as solution A). In solution A, the molar ratio of Mn to Fe is 6:4, and the total concentration of Mn and Fe is 1mol / L.

[0132] S2: Weigh 780g of diammonium hydrogen phosphate and dissolve it in 2L of pure water to prepare solution B;

[0133] S3: Weigh 408g of ammonia water and dissolve it in 2L of pure water to prepare solution C;

[0134] S4: Solutions A, B, and C were simultaneously added to the reactor (with 2L of pure water added as a base solution) for a co-precipitation reaction over a period of 40 minutes. During the addition, the feed rate of solution A was 125 ml / min, and the feed rate of solution B was 50 ml / min. The feed rate of ammonia was controlled to maintain the pH of the mixed solution in the reactor at 7. After the addition was complete, the mixture was stirred and aged at room temperature (30℃) for 2 hours. After the co-precipitation reaction was completed, the solid and liquid mixture was filtered. The filtered solid was washed and dried to obtain powdered ferric ammonium manganese phosphate.

[0135] S5: The obtained manganese ferric ammonium phosphate powder was placed in a muffle furnace under nitrogen protection and calcined at 550℃ for 8 hours to obtain D. 50 =14μm manganese iron pyrophosphate (Mn 0.6 Fe 0.4 )2P2O7.

[0136] Example 6

[0137] This embodiment provides a titanium-doped manganese iron pyrophosphate with the molecular formula: (Mn 0.7 Fe 0.3 )2P2O7.

[0138] The preparation of this ferromanganese pyrophosphate includes:

[0139] S1: 591.5 g of manganese sulfate monohydrate and 417 g of ferrous sulfate heptahydrate were dissolved in 2.5 L of pure water to obtain a mixed metal salt solution (i.e., a manganese-iron metal solution, denoted as solution A), and 6.87 g of titanium trichloride was added thereto. In solution A, the molar ratio of Mn to Fe was 7:3, and the total concentration of Mn and Fe was 2 mol / L;

[0140] S2: 780 g of diammonium hydrogen phosphate was weighed and dissolved in 2 L of pure water to prepare solution B;

[0141] S3: 408 g of ammonia water was weighed and dissolved in 2 L of pure water to prepare solution C;

[0142] S4: Solution A, solution B and solution C were simultaneously fed into a reaction kettle (2 L of pure water was first added into the reaction kettle as a bottom liquid) to perform a co-precipitation reaction. The feeding time was 30 min. During the feeding process, the feeding speed of solution A was 83.3 ml / min, the feeding speed of solution B was 66.67 ml / min, and the feeding speed of ammonia water was controlled so that the pH value of the mixed solution in the reaction kettle was always maintained at 7. After the feeding was completed, the reaction was stirred at room temperature (30°C) for 4 h. After the co-precipitation reaction was completed, the solid-liquid mixture obtained in the reaction was filtered, and the obtained solid was washed and dried to obtain a powder of ammonium manganese iron phosphate;

[0143] S5: The obtained ammonium manganese iron phosphate powder was placed in a muffle furnace under nitrogen protection, and calcined at 550°C for 8 h to obtain D 50 = 14 μm, and the Ti content was 3000 ppm. 0.7 Fe 0.3 )2P2O7.

[0144] Example 7

[0145] Please refer to Figure 1 , the present embodiment provides a carbon-coated lithium manganese iron phosphate, denoted as LiMn 0.6 Fe 0.4 PO4 / C, and a preparation method thereof is as follows:

[0146] 500 g of the manganese iron pyrophosphate obtained in Example 5 was weighed as a precursor, 130 g of lithium carbonate and 28.35 g of anhydrous glucose were added and mixed to obtain a mixture (the molar ratio of Li in lithium carbonate to the total moles of Mn and Fe in manganese iron pyrophosphate was 1.02:1). The mixture was placed in 7 L of pure water and sand-milled for 4 h, and the sand-milling was ended when the particle size D 50 of the mixture was less than 500 nm and D 90 was greater than 1 μm. The mixture was spray-dried at 200°C, and then the dried particles were sintered in a box-type furnace under nitrogen protection at 720°C for 10 h. After being crushed, a carbon-coated lithium manganese iron phosphate (containing 1.3 wt% of carbon) was obtained.

[0147] Example 8

[0148] The difference between this example and Example 7 is that no carbon coating is carried out, that is, the raw material for preparing lithium manganese iron phosphate does not contain a carbon source.

[0149] Example 9

[0150] The difference between this example and Example 7 is that the sintering temperature is 600°C and the sintering time is 8h. The sand milling is to mill the mixture to D 50 = 600nm. The temperature for spray drying is 180°C. The carbon source is citric acid. The lithium manganese iron phosphate contains 1wt% of carbon.

[0151] Example 10

[0152] The difference between this example and Example 7 is that the sintering temperature is 750°C and the sintering time is 2h. The sand milling is to mill the mixture to D 50 = 500nm. The temperature for spray drying is 210°C. The carbon source is starch. The lithium manganese iron phosphate contains 2wt% of carbon.

[0153] Comparative Example 1

[0154] The difference between this comparative example and Example 5 is that in S5, the calcination temperature is 400°C.

[0155] Comparative Example 2

[0156] The difference between this comparative example and Example 5 is that in S5, the calcination temperature is 900°C.

[0157] Comparative Example 3

[0158] The difference between this comparative example and Example 7 is that the ammonium manganese iron phosphate obtained in S4 of Example 5 is directly used to prepare lithium manganese iron phosphate with a carbon source and a lithium source.

[0159] That is, the ammonium manganese iron phosphate is not prepared into manganese iron pyrophosphate as a precursor of lithium manganese iron phosphate, but is directly used as a precursor of lithium manganese iron phosphate.

[0160] Comparative Example 4

[0161] The difference between this comparative example and Example 7 is that no sand milling treatment is carried out, and the mixture of manganese iron pyrophosphate, a carbon source and a lithium source is directly dried and sintered.

[0162] Comparative Example 5

[0163] The difference between this comparative example and Example 7 is that the manganese iron pyrophosphate obtained by a solid phase method (refer to patent CN201510847231.0) is used instead of the manganese iron pyrophosphate with a layered structure in Example 7.

[0164] Test Example

[0165] ①, the manganese iron pyrophosphate obtained in Example 5 and Comparative Example 1-2 is compared.

[0166] The SEM image of the manganese iron pyrophosphate obtained in Example 5 is shown in Figure 2 It can be seen that the manganese iron pyrophosphate has a layered structure and a certain degree of microporous surface. Figure 2

[0167] Comparative Example 1 fails to completely dehydrate and deammoniate, and the crystal form is not completely converted; Comparative Example 2 has a too high sintering temperature, causing the crystal form to be destroyed.

[0168] ②, the manganese iron pyrophosphate involved in Examples 1-6 is compared in terms of element content, and the results are shown in Table 1.

[0169] Table 1 Comparison Results

[0170] Mn % Fe % P％ Mn:Fe (Mn+Fe):P Example 1 23.23 15.71 21.7 60.1:39.9 1.004 Example 2 34.53 3.93 21.3 89.9:10.1 1.016 Example 3 31.12 7.81 21.8 80.2:19.8 1.003 Example 4 30.57 7.87 21.7 79.8:20.2 0.994 Example 5 23.25 15.78 21.8 60.0:40.0 1.002 Example 6 27.18 11.64 21.6 70.4:29.6 1.008

[0171] As can be seen from Table 1, the actual ratios of Mn and Fe and the actual ratio of Mn+Fe to P in the manganese iron pyrophosphates of the examples are basically consistent with the theoretical added ratios, which is conducive to stabilizing the structure of the manganese iron pyrophosphate.

[0172] In addition, the XRD pattern of the manganese iron pyrophosphate prepared in Example 5 is shown in Figure 3 The results show that the XRD information of the prepared manganese iron pyrophosphate completely matches the standard card of manganese pyrophosphate.

[0173] Further, the XRD pattern of the manganese iron lithium phosphate prepared in Example 7 is shown in Figure 4 The results show that the XRD information of the prepared manganese iron lithium phosphate completely matches the standard card of manganese iron lithium phosphate.

[0174] ③, the manganese iron lithium phosphate obtained in Example 7 and Comparative Examples 3-5 is compared in terms of tap density, and the results are shown in Table 2.

[0175] Table 2 Comparison Results

[0176] Compacted density g / cm 3 ]]> Example 7 2.42 Comparative Example 3 2.23 Comparative Example 4 1.56 Comparative Example 5 2.15

[0177] As can be seen from Table 2, before sintering the lithium-doped manganese ammonium phosphate, pre-sintering the manganese iron pyrophosphate to further prepare the manganese iron lithium phosphate can effectively improve the tap density of the manganese iron lithium phosphate. In addition, having a sanding treatment during the preparation of the manganese iron lithium phosphate is also conducive to improving the tap density of the manganese iron lithium phosphate. Further, using the manganese iron pyrophosphate having a layered structure, or using the manganese iron pyrophosphate having the specific element ratio provided by the present disclosure can also improve the tap density of the manganese iron lithium phosphate. ​

[0178] IV. The lithium manganese iron phosphate involved in Example 7 and Comparative Examples 3-5 was prepared into lithium ion button-type half-batteries in the following manner, and the 0.1C cycle capacity and initial efficiency of the half-batteries were compared, with the results shown in Table 3. The determination conditions for the 0.1C cycle capacity and initial efficiency included: normal temperature 25℃, voltage 2-4.3V, and 0.1C three cycles.

[0179] The lithium ion battery was prepared according to the following method: LiPF6 and diethyl carbonate (DEC) were used as electrolyte, the concentration of LiPF6 was 1 mol / L, and a lithium sheet was used as the negative electrode to prepare a button-type half-battery.

[0180] Table 3 comparison results

[0181] 0.1 C cycle capacity mAh / g Initial efficiency % Example 7 156.8 96.1 Comparative Example 3 155.4 95.3 Comparative Example 4 120.6 89.7 Comparative Example 5 151.8 94.7

[0182] As can be seen from Table 3, the lithium manganese iron phosphate provided by the embodiments of the present disclosure can be more conducive to improving the cycle capacity and initial efficiency of the corresponding battery than the lithium manganese iron phosphate provided by the comparative examples.

[0183] Industrial applicability

[0184] The present disclosure first proposes manganese iron pyrophosphate in a sheet structure, and correspondingly provides a preparation method of the manganese iron pyrophosphate. In addition, the present disclosure generates manganese iron pyrophosphate by pre-sintering before sintering lithium-doped manganese iron ammonium phosphate, and then prepares lithium manganese iron phosphate by using manganese iron pyrophosphate as a precursor. This can avoid the generation of gas and defects such as pores during the sintering process, and effectively improve the compaction density of lithium manganese iron phosphate. Further, the lithium ion battery prepared from the lithium manganese iron phosphate can have good capacity and initial efficiency and other performances.

Claims

1. A manganese iron pyrophosphate characterized in that, The manganese iron pyrophosphate has a laminar structure. The preparation of the manganese iron pyrophosphate comprises the following steps: calcining ammonium manganese iron phosphate to obtain manganese iron pyrophosphate; wherein the preparation of the ammonium manganese iron phosphate comprises: co-precipitation reaction of a phosphorus source and a mixed metal salt solution according to a preset molar ratio of elements in the ammonium manganese iron phosphate; the metals in the mixed metal salt solution include Mn and Fe; The pH value of the co-precipitation reaction is 6-7; the temperature of the co-precipitation reaction is 20-60°C; and the time of the co-precipitation reaction is 0.5-8h. The calcination temperature is 500-600°C; the calcination time is 2-10h; and the calcination is performed in a protective atmosphere.

2. The manganese iron pyrophosphate of claim 1, wherein, The manganese iron pyrophosphate has at least one of the following characteristics: Characteristic one: in the manganese iron pyrophosphate, the ratio of the total number of moles of Mn and Fe to the number of moles of P is 0.97:1-1.02:1, and the ratio of the number of moles of Mn to the number of moles of Fe is x:1-x, wherein 0.1≤x<1; Feature two: the D50 of the manganese iron pyrophosphate is 5 μm to 20 μm. 50 5 μm to 20 μm.

3. A method of producing manganese iron pyrophosphate as claimed in claim 1 or 2, characterized in that, The preparation of the manganese iron pyrophosphate comprises the following steps: calcining ammonium manganese iron phosphate to obtain manganese iron pyrophosphate; The preparation of the ammonium manganese iron phosphate comprises: co-precipitation reaction of a phosphorus source and a mixed metal salt solution according to a preset molar ratio of elements in the ammonium manganese iron phosphate; The metals in the mixed metal salt solution include Mn and Fe; The pH value of the co-precipitation reaction is 6-7; the temperature of the co-precipitation reaction is 20-60°C; and the time of the co-precipitation reaction is 0.5-8h. The calcination temperature is 500-600°C; the calcination time is 2-10h; and the calcination is performed in a protective atmosphere.

4. A lithium iron manganese phosphate characterized by, The raw material for preparing the lithium manganese iron phosphate comprises the manganese iron pyrophosphate according to claim 1 or 2.

5. The lithium iron manganese phosphate of claim 4, wherein, The compaction density of the lithium manganese iron phosphate is not less than 2.3 g / cm 3 .

6. The method of producing lithium iron manganese phosphate as claimed in claim 4 or 5, characterized in that, The preparation of the lithium manganese iron phosphate comprises the following steps: Sintering the manganese iron pyrophosphate and a lithium source.

7. The production method according to claim 6, wherein The sintering has at least one of the following characteristics: Characteristic one: the sintering temperature is 600-750°C; Characteristic two: the sintering time is 2-10h; Characteristic three: the sintering is performed in an inert atmosphere.

8. The production method according to claim 6 or 7, characterized by, Before sintering, the mixture of the manganese iron pyrophosphate and the lithium source is further subjected to sand milling and spray drying.

9. The production method according to claim 8, characterized by, The sanding is to D 50 400 nm to 600 nm.

10. The preparation method according to claim 8, characterized in that, The temperature of the spray drying is 180-210°C.

11. The method of claim 6, wherein, The raw material for preparing the lithium manganese iron phosphate further comprises a carbon source, and the sintering is performed on the manganese iron pyrophosphate, the phosphorus source and the carbon source.

12. The method of claim 11, wherein, The lithium manganese iron phosphate contains 1wt%-2wt% of carbon.

13. A battery, characterized by The positive electrode material of the battery comprises the lithium manganese iron phosphate according to claim 4 or 5.

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