Doped modified manganese iron phosphate of nanoporous structure, and preparation method and use thereof

Abstract

The application discloses doped modified manganese iron phosphate with a nanoporous structure, a preparation method and application thereof. 1‑a‑b Fe a M b PO4, 0.01<=a<=0.98, 10 ‑4 <=b<=10 ‑2 M is a combination of one or more selected from magnesium, titanium, vanadium, chromium, cobalt, nickel, zinc, gallium, aluminum, zirconium, niobium, molybdenum, tin, antimony, calcium, barium, strontium, boron, ruthenium, silicon, tellurium, copper and lithium, and the particle size is below 50 nm, and the material also has a porous structure. The material can be used for preparation of lithium manganese iron phosphate positive electrode materials in lithium ion batteries, and the specific capacity, rate and cycle performance of the obtained positive electrode materials are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a doped modified manganese iron phosphate with a nanoporous structure and a preparation method and use thereof. BACKGROUND

[0002] In recent decades, nanomaterials and porous materials are functional materials with special structures, which play a unique role and value in many application fields such as photocatalysis, solar cells, electromagnetism, optics, etc., attracting the attention of researchers. Manganese iron phosphate material can be used as a phosphating agent to prevent rust and corrosion of steel products; it can also be used as an ion exchanger, a sensor, an adsorbent, a magnetic material, etc., and is a very important non-metallic inorganic material. In addition, manganese iron phosphate can also be used as an important precursor of manganese iron phosphate positive electrode material in lithium ion batteries. Since manganese and iron in manganese iron phosphate material have a uniform mixing degree at the atomic level, when used to prepare manganese iron phosphate positive electrode material, the manganese and iron metal elements in the positive electrode material are also uniformly distributed at the atomic level, which is beneficial to improving the rate performance and cycle stability of manganese iron phosphate lithium ion batteries, and improving the voltage drop and manganese dissolution phenomenon.

[0003] Elemental doping is a common technical means for modifying materials, and one or more elements are usually selected for doping to improve the performance of the material. Through special chemical methods, a small amount of metal or non-metal elements enter the crystal lattice of the material and replace the positions of manganese or iron elements in the manganese iron phosphate crystal lattice, and the type of metal or non-metal elements can be one or a combination of multiple types. Since the doping elements enter the crystal interior, the crystal structure of the material changes to some extent, which in turn has a series of effects on the properties of the material.

[0004] Currently, there are few reports on the preparation of manganese iron phosphate, and there are even fewer reports on manganese iron phosphate with a nanoporous structure. Chinese patent CN111908442A discloses manganese iron phosphate and a preparation method thereof. In this method, manganese dioxide, ferrous oxalate and phosphoric acid are reacted in the presence of a reducing agent to obtain (Mn 1-x Fe x ) a PO4·H2O crystals, which are then filtered, washed and sintered at high temperature to obtain amorphous (Mn 1-x Fe x ) a PO4 powder with a particle size of about 2 um. This method requires the introduction of a reducing agent and heating during the reaction process. The prepared manganese iron phosphate material has a large particle size, which is in the micron level, and the particles have high density and no porous structure. There are almost no reports on doped modified manganese iron phosphate materials with a nanoporous structure.

[0005] Methods for preparing manganese phosphate mentioned in the literature include oxidation-precipitation method, reduction-precipitation method, hydrothermal method, etc. Most of the manganese phosphate particles prepared by these methods are micron-sized, and the particle size is too large; and the product solution contains a large amount of metal ions, and the purity is not high. In addition, the manganese phosphate prepared by the preparation method of manganese phosphate may not necessarily obtain pure-phase manganese phosphate iron, and it is most likely a mixture of manganese phosphate and iron phosphate. SUMMARY

[0006] In view of the defects and deficiencies of the prior art, the present application provides a doped modified manganese iron phosphate with a nanoporous structure. The particle size of the manganese iron phosphate material is small, at the nanometer level, and the particles have a porous structure. When used as a precursor of a doped manganese iron lithium battery cathode material, the manganese iron phosphate can improve the specific capacity of the cathode material and improve the rate and cycle performance of the battery.

[0007] The present application also provides a preparation method of a doped modified manganese iron phosphate with a nanoporous structure. The preparation method does not require the use of a reducing agent and a soluble manganese salt, has mild reaction conditions, and can obtain a doped modified manganese iron phosphate with high purity.

[0008] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0009] A doped modified manganese iron phosphate, the chemical general formula of the doped modified manganese iron phosphate is Mn 1-a- b Fe a M b PO4, wherein M is a combination of one or more selected from magnesium, titanium, vanadium, chromium, cobalt, nickel, zinc, gallium, aluminum, zirconium, niobium, molybdenum, tin, antimony, calcium, barium, strontium, boron, ruthenium, silicon, tellurium, copper and lithium, and 0.01≤a≤0.98, 10 -4 ≤b≤10 -2 , the particle size of the doped modified manganese iron phosphate is 50 nm or less, and the doped modified manganese iron phosphate has a porous structure.

[0010] In some embodiments, the particle size of the doped modified manganese iron phosphate is 40 nm or less, further preferably 5-40 nm, and more further preferably 10-30 nm.

[0011] In some embodiments, the pore size of the doped modified manganese iron phosphate is 2-10 nm; preferably, the pore size of the doped modified manganese iron phosphate is 3-5 nm.

[0012] In some embodiments, the specific surface area of the doped modified manganese iron phosphate is 10-30 m 2 / g; preferably, the specific surface area of the doped modified manganese iron phosphate is 12-18 m 2 / g.

[0013] In some embodiments, 0.2≤a≤0.5, 10 -3 ≤b≤10 -2 .

[0014] In some embodiments, the doped modified manganese iron phosphate is monoclinic.

[0015] In some embodiments, the M is cobalt; or, the M is magnesium and boron; or, the M is molybdenum, niobium and boron; or, the M is cobalt, vanadium, nickel and boron; or, the M is magnesium; or, the M is vanadium and titanium.

[0016] In some embodiments, the doped modified manganese iron phosphate has a chemical formula of Mn 1-a-b Fe a Co b PO4;

[0017] or Mn 1-a-b Fe a Mg b1 B b2 PO4, wherein b1+b2=b;

[0018] or Mn 1-a-b Fe a Mo b1 Nb b2 B b3 PO4, wherein b1+b2+b3=b;

[0019] or Mn 1-a-b Fe a Co b1 V b2 Ni b3 B b4 PO4, wherein b1+b2+b3+b4=b;

[0020] or Mn 1-a-b Fe a Mg b PO4;

[0021] or Mn 1-a-b Fe a V b1 Ti b2 PO4, wherein b1+b2=b;

[0022] wherein, 10 -4 ≤b1≤10 -2 , 10 -4 ≤b2≤10 -2 , 10 -4 ≤b3≤10 -2 , 10-4≤b4≤10 -2.

[0023] In some embodiments, the doped modified manganese iron phosphate has a chemical formula of Mn 0.6 Fe 0.395 Co 0.005 PO4or Mn 0.65 Fe 0.344 Mg 0.005 B 0.001 PO4or Mn 0.7 Fe 0.293 Mo 0.003 Nb 0.003 B 0.001 PO4or Mn 0.8 Fe 0.19 Co 0.005 V 0.001 Ni 0.00 1B 0.003 PO4or Mn 0.5 Fe 0.495 Mg 0.005 PO4or Mn 0.65 Fe 0.34 V 0.005 Ti 0.005 PO4.

[0024] The present application also provides a method for preparing the aforementioned doped modified manganese iron phosphate, which comprises the following steps: 1) mixing manganese iron oxide and a compound of element M with phosphoric acid to obtain a reaction mixture; 2) grinding the reaction mixture to make the reaction mixture react to generate phosphate, thereby obtaining a slurry containing phosphate, wherein the particle size of the phosphate in the slurry is below 100 nm; 3) separating the slurry to obtain phosphate particles; and 4) drying and sintering the phosphate particles to obtain the doped modified manganese iron phosphate.

[0025] In some embodiments, the particle size of the manganese iron oxide is 1-20 microns, preferably, the particle size of the manganese iron oxide is 2-7 microns.

[0026] In some embodiments, the manganese iron oxide has a molecular formula of (Mn x Fe y )3O4, wherein 0.50≤x≤0.81, 0.19≤y≤0.50.

[0027] In some embodiments, the manganese iron oxide has a molecular formula of (Mn 0.60 Fe 0.40 )3O4, (Mn 0.65 Fe 0.35 )3O4, (Mn 0.70 Fe 0.30 )3O4, (Mn0.81 Fe 0.19 )3O4, (Mn 0.50 Fe 0.50 )3O4 or (Mn 0.66 Fe 0.34 )3O4.

[0028] In some embodiments, the phosphoric acid is in the form of an aqueous solution of phosphoric acid, and the mass concentration of the aqueous solution of phosphoric acid is 10% to 70%, preferably 20% to 40%.

[0029] In some embodiments, in step 1), the mixing is carried out under mechanical stirring and at a temperature of 20 to 40°C.

[0030] In some embodiments, in step 1), the mixing is carried out for 1 to 12 hours.

[0031] In some embodiments, in step 2), the grinding is carried out in a sand mill, and the temperature of the grinding is 20 to 40°C.

[0032] In some embodiments, in step 2), the grinding is carried out for 0.5 to 3 hours.

[0033] In some embodiments, in step 4), the drying is carried out at a temperature of 100 to 120°C.

[0034] In some embodiments, in step 4), the drying is carried out for 10 hours.

[0035] In some embodiments, in step 4), the sintering is carried out at a temperature of 300 to 400°C.

[0036] In some embodiments, in step 4), the sintering is carried out for 1 to 4 hours.

[0037] In some embodiments, step 3) comprises filtering and washing the phosphate slurry.

[0038] In some embodiments, step 4) comprises drying the phosphate particles to obtain doped modified manganese iron phosphate monohydrate crystals with a particle size of less than 100 nm, and sintering the doped modified manganese iron phosphate monohydrate crystals to obtain the doped modified manganese iron phosphate.

[0039] In some embodiments, the ratio of the amount of substance of the manganese iron oxide and the compound of the element M to the amount of substance of the phosphoric acid is 1:1 to 2.

[0040] In some embodiments, the preparation method further comprises a step of dispersing the manganese iron oxide into an aqueous dispersant solution prior to the step 1).

[0041] In some embodiments, the dispersant is selected from a combination of one or more of polyvinylpyrrolidone, polyethylene glycol, and TC130 dispersant.

[0042] In some embodiments, the aqueous dispersant solution has a mass concentration of 0.01% to 5%.

[0043] In some embodiments, the preparation method further comprises a step of preparing the phosphoric acid by reacting phosphorus pentoxide with water prior to the step 1). That is, the present application can use phosphoric acid or phosphorus pentoxide as the phosphorus source for preparing the phosphate-based material.

[0044] In some embodiments, the compound of the M element is selected from a combination of one or more of a compound of magnesium, a compound of titanium, a compound of vanadium, a compound of cobalt, a compound of nickel, a compound of zinc, a compound of gallium, a compound of aluminum, a compound of zirconium, a compound of niobium, a compound of molybdenum, a compound of tin, a compound of antimony, a compound of calcium, a compound of barium, a compound of strontium, a compound of boron, a compound of ruthenium, a compound of silicon, a compound of tellurium, a compound of copper, and a compound of lithium.

[0045] In some embodiments, the compound of the M element is selected from a combination of one or more of an oxide, a carbonate, an oxalate, a nitrate, a sulfate, a chloride, and an organic acid salt of the M element.

[0046] In some embodiments, the organic acid salt of the M element is selected from a combination of one or more of an organic phosphate, an acetate, an organic sulfonate, an alkyl salt, and an ester salt of the M element.

[0047] In some embodiments, the compound of the M element is cobalt chloride; or a combination of magnesium oxide and boric acid, or a combination of molybdenum trioxide, niobium oxalate, and boric acid; or a combination of cobalt acetate, ammonium metavanadate, nickel sulfate, and boric acid; or magnesium acetate; or a combination of vanadyl oxalate and titanium chloride.

[0048] The present application also provides a use of the aforementioned doped modified manganese iron phosphate for preparing a battery cathode material.

[0049] The present application also provides a doped lithium manganese iron phosphate cathode material, which is prepared by a high-temperature sintering reaction of raw materials comprising the aforementioned doped modified manganese iron phosphate and a lithium source compound and optionally an organic carbon source.

[0050] Furthermore, the lithium source compound is selected from one or more combinations of lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium acetate.

[0051] Furthermore, the organic carbon source is selected from one or more combinations of glucose, sucrose, fructose, citric acid, polyethylene glycol, polyvinylpyrrolidone, ethylenediaminetetraacetic acid, and ascorbic acid.

[0052] The present invention also provides a lithium-ion battery, including a positive electrode material, wherein the positive electrode material includes the aforementioned doped lithium manganese iron phosphate positive electrode material.

[0053] Furthermore, the lithium-ion battery exhibits a discharge specific capacity of over 145 mAh / g at 0.1C, a discharge specific capacity of over 135 mAh / g at 1C, and a capacity retention rate of over 92% after 200 charge-discharge cycles at 1C. This demonstrates the excellent cycle performance of this lithium-ion battery.

[0054] Compared with the prior art, the present invention has the following advantages:

[0055] The doped and modified manganese iron phosphate of this invention has a nano-scale particle size, small size, and porous structure. When used as a precursor for the doped manganese iron phosphate battery cathode material, the doped manganese iron phosphate battery cathode material prepared can significantly improve the specific capacity, rate capability, and cycle performance of lithium-ion batteries. Attached Figure Description

[0056] Figure 1 The image shows the XRD pattern of the manganese iron oxide raw material used in Example 1.

[0057] Figures 2-3 The images are SEM images of the manganese iron oxide raw material used in Example 1, with different scales.

[0058] Figure 4 The image shows the XRD pattern of the doped and modified manganese iron phosphate monohydrate in Example 1.

[0059] Figures 5-6 The images are SEM images of the doped and modified manganese iron phosphate monohydrate in Example 1, with scale bars of 1 μm and 2 μm, respectively.

[0060] Figure 7 The XRD pattern of the doped and modified manganese iron phosphate prepared in Example 1;

[0061] Figure 8 SEM image of the doped and modified manganese iron phosphate prepared in Example 1;

[0062] Figure 9 The XRD pattern of the product from step 2) in Comparative Example 1;

[0063] Figures 10-11 SEM image of the product of step 2) in Comparative Example 1, the scales are different;

[0064] Figure 12 XRD image of the final product in Comparative Example 1;

[0065] Figure 13 SEM image of the final product in Comparative Example 1.

[0066] Figure 14 Adsorption-desorption curve of the doped modified manganese iron phosphate prepared in Example 1;

[0067] Figure 15 Pore size distribution of the doped modified manganese iron phosphate prepared in Example 1;

[0068] Figure 16 Rate test results of the doped modified manganese iron phosphate prepared in Example 1 for button cell;

[0069] Figure 17 Cycle test results of the doped modified manganese iron phosphate prepared in Example 1 for button cell. DETAILED DESCRIPTION

[0070] The present application provides an improved doped modified manganese iron phosphate, the main innovation of the product is that the particle size is controlled to be less than 50 nm, and the product has a porous structure.

[0071] Although the prior art discloses manganese iron phosphate, the particle size is micron level, the particle size is large, and the manganese iron phosphate particles in the prior art have high density, usually have no porous structure, and are not doped and modified by metal or non-metal elements.

[0072] The specific capacity, charge-discharge rate and cycle performance of a lithium ion battery including the doped manganese iron phosphate salt-based positive electrode material can be significantly improved. The manganese iron active element in the positive electrode material structure is partially occupied by one or more other elements, which changes the physical and chemical properties of the positive electrode material, which is manifested as follows: 1) higher electrochemical activity of the material. When another cation with a different valence is incorporated into the positive electrode material, the concentration of ion defects and electron defects in the material lattice increases due to the interaction between the cations and the redistribution of charges, thereby increasing the activity of the material; 2) higher cycle stability of the material. During the cycle charge-discharge of the positive electrode material, lithium ions are rapidly transported along one-dimensional channels in the crystal structure. When the cycle reaches several hundred cycles, ion mixing or crystal structure collapse deformation occurs in the crystal structure, causing the lithium ion transport channel to be unsmooth, and the cycle performance to decrease. When other metal or non-metal elements are incorporated into the positive electrode material, the ions in the crystal structure will be rearranged, and the rearranged crystal structure is more conducive to the transport of lithium ions, thereby improving the cycle stability of the material. Therefore, the performance of the doped phosphate-based positive electrode material is far superior to that of the undoped manganese iron phosphate-based positive electrode material. The doped manganese iron phosphate-based positive electrode material not only has a more stable crystal structure, but also makes it more difficult for manganese and other metal ions to dissolve, thereby improving the cycle performance of the material; and in the presence of multiple active metals and the synergistic effect between multiple active metals, the positive electrode material has more electrochemical platforms, and the connection between the platforms is more gentle, eliminating the phenomenon of steep decline at the end of the discharge platform. In addition, the electronic and ionic conduction speed of the doped manganese iron phosphate-based positive electrode material can also be higher, and the rate performance of the lithium ion battery is better.

[0073] Another innovation of the present application is the preparation process of the doped modified manganese iron phosphate material. The manganese iron oxide, one or more compounds of other doped metal elements and phosphoric acid are directly mixed, and then grinding is performed to accelerate the reaction rate between them, so that the reaction between them generates a nano-sized phosphate slurry, and the doped ions are incorporated into the phosphate material. After the particles are separated from the slurry, the particles are dried to obtain the nano-sized doped modified manganese iron phosphate monohydrate crystals, and finally sintering is performed to obtain the nano-porous doped modified manganese iron phosphate of the present application. Compared with the prior art, the preparation process does not require a reducing agent or a soluble ferrous salt as a raw material, but directly reacts the manganese iron oxide, which is a compound of manganese iron elements uniformly mixed at an atomic level, with phosphoric acid to obtain high-purity manganese iron phosphate, and the process is simple. The doped ion compounds also react with phosphoric acid, enter the phosphate material in the form of ion doping while the manganese iron phosphate material is gradually generated, and finally the doped modified manganese iron phosphate material is obtained. The aforementioned grinding can accelerate the reaction rate. If grinding is not performed, the reaction between the manganese iron oxide, the doped ion compounds and the phosphoric acid is very slow, the reaction period is very long and it is difficult to react completely, and the ion doping is very uneven.

[0074] Another innovation of the present application is that the dissolution rate of the manganese iron oxide and the nucleation rate of the manganese iron phosphate can be adjusted by changing the concentration of the phosphoric acid, and then the crystal particle size of the manganese iron phosphate is regulated. The phosphoric acid can also be prepared by reacting phosphorus pentoxide with water, that is, the phosphorus source for preparing the manganese iron phosphate of the present application can be phosphoric acid or phosphorus pentoxide.

[0075] The present application will be further described below in conjunction with examples. However, the present application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not mentioned are conventional conditions in the industry. The technical features involved in each embodiment of the present application can be combined with each other as long as there is no conflict between them.

[0076] Example 1

[0077] The present embodiment provides a doped modified manganese iron phosphate with a nano-porous structure, which has a chemical formula of Mn 0.6 Fe 0.395 Co 0.005 PO4, and the preparation process is as follows:

[0078] 1) A concentrated phosphoric acid solution and deionized water are sequentially added into a glass beaker, and after stirring, a phosphoric acid aqueous solution with a mass concentration of 35% is prepared; according to the molar ratio of Mn and Fe to P element of 1:1.5, 114.95g of micron-sized manganese iron oxide (molecular formula is (Mn 0.60Fe 0.40 Fe2O3, purchased from Sichuan Qingyuan New Material Co., Ltd., average particle size of 7 microns), 1.190 g of cobalt chloride hexahydrate, mechanical stirring for 12 hours to obtain a reaction mixture;

[0079] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a green slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a green powder (manganese iron cobalt phosphate monohydrate);

[0080] 3) Sinter the manganese iron cobalt phosphate monohydrate in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder of manganese iron cobalt phosphate.

[0081] The XRD pattern and SEM image of the manganese iron oxide are shown in Figure 1 , 2 -3, and it can be seen that the manganese iron oxide has a crystal structure. The XRD pattern and SEM image of the manganese iron cobalt phosphate monohydrate obtained in step 2) are shown in Figure 4 , 5 -6, and it can be seen that it has a monoclinic crystal structure of MnPO4·H2O. The particle size of the manganese iron cobalt phosphate monohydrate is 20 nm, as measured by a scanning electron microscope (SEM) test method. The XRD pattern and SEM image of the manganese iron cobalt phosphate obtained in step 3) are shown in Figure 7 , 8 , and it can be seen that the manganese iron cobalt phosphate has a certain degree of crystallinity, and a large number of porous structures are distributed between the particles. The crystal phase still maintains a monoclinic crystal structure, as measured by an XRD test. The particle size of the manganese iron cobalt phosphate is 40 nm, as measured by a scanning electron microscope (SEM) test method. The adsorption-desorption test and analysis of the manganese iron cobalt phosphate were performed using a specific surface area and pore size tester, as shown in Figure 14 , 15 , and it can be seen that the manganese iron cobalt phosphate has a mesoporous structure, with a pore size mainly distributed at about 3-5 nm, and a specific surface area of about 15.1 m 2 / g.

[0082] Example 2

[0083] This example provides a doped modified manganese iron phosphate with a nanoporous structure, which has a chemical formula of Mn 0.65 Fe 0.344 Mg 0.005 B 0.001 PO4, and the preparation process is as follows:

[0084] 1) In a glass beaker, add concentrated phosphoric acid solution and deionized water in turn, and after stirring evenly, prepare a 30% mass concentration phosphoric acid aqueous solution; according to the molar ratio of Mn and Fe total: P element is 1:1.5, pour 114.88g micron-sized manganese iron oxide (molecular formula is (Mn 0.65 Fe 0.35 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns) into 735mL of the above phosphoric acid aqueous solution, 0.201g magnesium oxide, 0.062g boric acid, and mechanically stir for 12 hours to obtain a reaction mixture;

[0085] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark green slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark green powder (magnesium-boron-doped manganese iron phosphate monohydrate);

[0086] 3) Sinter the magnesium-boron-doped manganese iron phosphate monohydrate in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder.

[0087] After testing and analysis, the obtained magnesium-boron-doped manganese iron phosphate monohydrate is MnPO4·H2O with a monoclinic crystal structure, with a particle size of 25nm; the magnesium-boron-doped manganese iron phosphate after heat treatment has a certain degree of crystallinity, and the crystal phase still maintains a monoclinic crystal structure; a large number of porous structures are distributed between the particles, and the particle size is 45nm; the magnesium-boron-doped manganese iron phosphate has a mesoporous structure, with a pore size mainly distributed around 4-6nm, and a specific surface area of about 14.8m 2 / g.

[0088] Example 3

[0089] This example provides a doped and modified manganese iron phosphate with a nanoporous structure, with a chemical formula of Mn 0.7 Fe 0.293 Mo 0.003 Nb 0.003 B 0.001 PO4, and the preparation process is as follows:

[0090] 1) In a glass beaker, add concentrated phosphoric acid solution and deionized water in turn, and after stirring evenly, prepare a 25% mass concentration phosphoric acid aqueous solution; according to the molar ratio of Mn and Fe total: P element is 1:1.5, pour 114.81g micron-sized manganese iron oxide (molecular formula is (Mn 0.70 Fe 0.30 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns) into 882mL of the above phosphoric acid aqueous solution, 0.432g molybdenum trioxide, 1.614g niobium oxalate, 0.062g boric acid, and mechanically stir for 12 hours to obtain a reaction mixture;

[0091] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark green slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark green powder (molybdenum-niobium-boron-doped manganese iron phosphate monohydrate);

[0092] 3) Sinter the molybdenum-niobium-boron-doped manganese iron phosphate monohydrate in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder.

[0093] After testing and analysis, the obtained molybdenum-niobium-boron-doped manganese iron phosphate monohydrate is MnPO4·H2O with a monoclinic crystal structure, and the particle size is 30 nm; the molybdenum-niobium-boron-doped manganese iron phosphate after heat treatment has a certain degree of crystallinity, and the crystal phase still maintains a monoclinic crystal structure; a large number of porous structures are distributed between the particles, and the particle size is 50 nm; the molybdenum-niobium-boron-doped manganese iron phosphate has a mesoporous structure, and the pore size mainly distributes around 4-6 nm, and the specific surface area is about 14.1 m 2 / g.

[0094] Example 4

[0095] This example provides a doped and modified manganese iron phosphate with a nanoporous structure, which has a chemical formula of Mn 0.8 Fe 0.19 Co 0.005 V 0.001 Ni 0.001 B 0.003 PO4, and the preparation process is as follows:

[0096] 1) In a glass beaker, add a concentrated phosphoric acid solution and deionized water in sequence, and after stirring uniformly, prepare a phosphoric acid aqueous solution with a mass concentration of 30%; according to the molar ratio of Mn and Fe to P element of 1:1.5, pour 114.66 g of micron-sized manganese iron oxide (molecular formula (Mn 0.81 Fe 0.19 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns), 1.245 g of cobalt acetate tetrahydrate, 0.117 g of ammonium metavanadate, 0.263 g of nickel sulfate hexahydrate, and 0.185 g of boric acid into 735 mL of the above phosphoric acid aqueous solution, and mechanically stir for 12 hours to obtain a reaction mixture;

[0097] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark green slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark green powder (molybdenum-niobium-boron-doped manganese iron phosphate monohydrate);

[0098] 3) Sinter the molybdenum-niobium-boron-doped manganese iron phosphate monohydrate in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder.

[0099] The MnPO4.H2O obtained through testing analysis is a monoclinic crystal phase structure, with a particle size of 20 nm; the MnPO4.H2O obtained through heat treatment has a certain crystallinity, and the crystal phase still maintains a monoclinic crystal phase structure; a large number of porous structures are distributed between the particles, and the particle size is 40 nm; the MnPO4.H2O has a mesoporous structure, and the pore size mainly distributes at about 3-5 nm, and the specific surface area is about 15.8 m 2 / g.

[0100] Example 5

[0101] The present example provides a doped modified manganese iron phosphate with a nanoporous structure, which has a chemical formula of Mn 0.5 Fe 0.495 Mg 0.005 PO4, and the preparation process is as follows:

[0102] 1) A concentrated phosphoric acid solution and deionized water are sequentially added into a glass beaker, and a 25% mass concentration phosphoric acid aqueous solution is prepared after stirring; 115.08 g of micron-sized manganese iron oxide (molecular formula is (Mn 0.50 Fe 0.50 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns) and 1.072 g of magnesium acetate tetrahydrate are poured into 882 mL of the above phosphoric acid aqueous solution according to a molar ratio of Mn and Fe to P of 1:1.5, and mechanical stirring is performed for 12 hours to obtain a reaction mixture;

[0103] 2) The reaction mixture is poured into a sand mill and sand milled for 1 hour to obtain a dark green slurry; the slurry is filtered and washed to obtain particles, and the particles are dried at 100°C to obtain a dark green powder (manganese iron magnesium phosphate monohydrate);

[0104] 3) The manganese iron magnesium phosphate monohydrate is sintered in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder.

[0105] The MnPO4.H2O obtained through testing analysis is a monoclinic crystal phase structure, with a particle size of 20 nm; the MnPO4.H2O obtained through heat treatment has a certain crystallinity, and the crystal phase still maintains a monoclinic crystal phase structure; a large number of porous structures are distributed between the particles, and the particle size is 40 nm; the MnPO4.H2O has a mesoporous structure, and the pore size mainly distributes at about 3-5 nm, and the specific surface area is about 15.8 m 2 / g.

[0106] Example 6

[0107] The present example provides a doped modified manganese iron phosphate with a nanoporous structure, which has a chemical formula of Mn0.65 Fe 0.34 V 0.005 Ti 0.005 PO4, prepared as follows:

[0108] 1) In a glass beaker, add concentrated phosphoric acid solution and deionized water in turn, and after stirring evenly, prepare a 25% mass concentration phosphoric acid aqueous solution; according to the molar ratio of Mn and Fe total: P element of 1:1.5, pour 114.87g micron-sized manganese iron oxide (molecular formula is (Mn 0.66 Fe 0.34 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns), 1.225g vanadyl oxalate, 0.948g titanium chloride, and mechanically stir for 12 hours to obtain a reaction mixture;

[0109] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark green slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark green powder (vanadium-titanium-doped manganese iron phosphate monohydrate);

[0110] 3) Sinter the vanadium-titanium-doped manganese iron phosphate monohydrate in a muffle furnace at 400°C for 2 hours to obtain a red-brown powder.

[0111] After testing and analysis, the obtained vanadium-titanium-doped manganese iron phosphate monohydrate is MnPO4·H2O with a monoclinic crystal structure, with a particle size of 25nm; the vanadium-titanium-doped manganese iron phosphate after heat treatment has a certain degree of crystallinity, and the crystal phase still maintains a monoclinic crystal structure; a large number of porous structures are distributed between the particles, with a particle size of 45nm; the vanadium-titanium-doped manganese iron phosphate has a mesoporous structure, with a pore size mainly distributed around 4-6nm, and a specific surface area of about 14.8m 2 / g.

[0112] Comparative Example 1

[0113] This comparative example provides a comparative phosphate material, which is prepared basically the same as Example 1, as follows:

[0114] 1) In a glass beaker, add concentrated phosphoric acid solution and deionized water in turn, and after stirring evenly, prepare a 25% mass concentration phosphoric acid aqueous solution; according to the molar ratio of Mn and Fe total: P element of 1:1.5, pour 114.87g micron-sized manganese iron oxide (molecular formula is (Mn

[0115] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark brown slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark brown product;

[0116] 3) Sinter the product of step 2) in a muffle furnace at 400°C for 2 hours to obtain a dark brown final product.

[0117] The XRD pattern and SEM image of the product obtained in step 2) are shown in FIGS. 11 and 12, respectively, which shows that the product is a mixture of cobalt-doped manganese monohydrate phosphate MnPO4·H2O and iron oxide, and the particle size distribution of the product is not uniform, being between 30-2000 nm, with small particles of about 30 nm being cobalt-doped manganese monohydrate phosphate and large particles of about 2000 nm being iron oxide. Figure 9 、 10 The XRD pattern and SEM image of the final product obtained in step 3) are shown in FIGS. 13 and 14, respectively, which shows that the final product is a mixture of cobalt-doped manganese phosphate with low crystallinity and iron oxide, and the particle size distribution of the final product is also not uniform, being mainly distributed between 50-2000 nm, with small particles having more pore structures, but large particles being denser. Figure 12 、 13 The XRD pattern and SEM image of the final product obtained in step 3) are shown in FIGS. 13 and 14, respectively, which shows that the final product is a mixture of cobalt-doped manganese phosphate with low crystallinity and iron oxide, and the particle size distribution of the final product is also not uniform, being mainly distributed between 50-2000 nm, with small particles having more pore structures, but large particles being denser.

[0118] Comparative Example 2

[0119] This comparative example provides a comparative phosphate material, which is prepared in a process substantially the same as that of Example 1, except that no cobalt chloride hexahydrate is added in step 1), and the preparation process is as follows:

[0120] 1) In a glass beaker, add a concentrated phosphoric acid solution and deionized water in sequence, and after stirring uniformly, prepare a phosphoric acid aqueous solution with a mass concentration of 35%; according to the molar ratio of Mn and Fe to P elements being 1:1.5, pour 114.95 g of micron-sized manganese-iron oxide (molecular formula (Mn 0.60 Fe 0.40 )3O4, purchased from Sichuan Qingyuan New Material Co., Ltd., with an average particle size of 7 microns) into 630 mL of the above phosphoric acid aqueous solution, and mechanically stir for 12 hours to obtain a reaction mixture;

[0121] 2) Pour the reaction mixture into a sand mill and sand mill for 1 hour to obtain a dark brown slurry; filter and wash the slurry to obtain particles, and then dry the particles at 100°C to obtain a dark brown product;

[0122] 3) Sinter the product of step 2) in a muffle furnace at 400°C for 2 hours to obtain a dark brown final product.

[0123] The greenish black powder obtained in step 2) is analyzed by XRD and SEM, and the crystal phase of the material is MnPO4.H2O with a monoclinic structure, and the particle size is 20 nm.

[0124] The red-brown powder obtained in step 3) is analyzed by XRD and SEM, and the crystal phase of the material is still a monoclinic structure, and the particle size is 40 nm. The manganese iron phosphate material has a mesoporous structure, and the pore size is mainly distributed at about 3-5 nm, and the specific surface area is about 15.0 m 2 / g.

[0125] Application Example 1

[0126] The phosphate materials prepared in Examples 1-6 and Comparative Examples 1-2 are used to prepare lithium manganese iron phosphate, and the specific operation is as follows:

[0127] 1) According to the element molar ratio of Li:(Mn+Fe):P being 1.02:1:1, 113 g of lithium carbonate, 450.9 g of the phosphate material, 68.3 g of glucose and other raw materials are weighed;

[0128] 2) 2.5 Kg of water and the weighed glucose are poured into a sand mill, and mechanically stirred for 10 min until the glucose is completely dissolved;

[0129] 3) The weighed phosphate material and lithium carbonate are poured into the sand mill, and sand milling is performed for 2 h;

[0130] 4) The slurry obtained by sand milling is subjected to spray drying to obtain a precursor powder of lithium manganese iron phosphate (LMFP) / C;

[0131] 5) The LMFP / C precursor powder is first pre-fired at 350°C for 2 h under an inert atmosphere, and then secondarily sintered at 600°C for 10 h to obtain a LMFP / C positive electrode material.

[0132] The above LMFP / C positive electrode material, conductive agent carbon nanotube, conductive agent carbon black, binder polyvinylidene fluoride and solvent N-methyl pyrrolidone are configured into a positive electrode slurry, and the mass ratio of the LMFP / C positive electrode material, conductive agent carbon nanotube, conductive agent carbon black and binder polyvinylidene fluoride is 91.5:1.5:1.0:6; the positive electrode slurry is coated on an aluminum foil, vacuum baked, punched, and finally a LMFP / C positive electrode sheet is prepared. A button cell is assembled by using LMFP / C as a positive electrode, lithium sheet as a negative electrode, and 1 mol / L LiPF6 EC / DMC / EMC solution as an electrolyte, and the cell is subjected to charge and discharge test (charge and discharge window is 2.5V-4.3V) to obtain the electrical performance of lithium manganese iron phosphate. The results are shown in Table 1, and the results of Example 1 are also shown in Table 1. Figures 16-17 .

[0133] Table 1 Lithium iron manganese phosphate electrical performance

[0134]

[0135]

[0136] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

[0137] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not, in some cases, critical to the present application. Any numerical value, however, can be expressed as a range to include any and all expressed values between the two values. In some cases, the endpoints of the ranges are presented as a range between two values, and this range is a "Floor" and a "Ceil" of the continuous range between the two values. The disclosure of a single value of a parameter or characteristic can be presented as a "Floor" and a "Ceil" to the same value. The endpoints of these ranges are based on the value of the lower and the upper range and are obtained by deeming the lower range as a "Floor" and the upper range as a "Ceil" of the continuous range between the two values, and the same is applied to the disclosure of a single numerical value.

Claims

1. A doped modified manganese iron phosphate characterized in that: The chemical general formula of the doped modified manganese iron phosphate is Mn 1-a-b Fe a M b PO4, 0.01≤a≤0.98, 10 -4 ≤b≤10 -2 The particle size of the doped modified manganese iron phosphate is below 50nm, and it has a porous structure; the specific surface area of the doped modified manganese iron phosphate is 10-30m 2 / g, and the pore size is 2-10nm. The M is cobalt; or, the M is magnesium and boron; or, the M is molybdenum, niobium and boron; or, the M is cobalt, vanadium, nickel and boron; or, the M is magnesium; or, the M is vanadium and titanium. The doped modified manganese iron phosphate is prepared by a preparation method comprising the following steps: 1) mixing manganese iron oxide and a compound of M element with phosphoric acid to obtain a reaction mixture; 2) grinding the reaction mixture, so that the reaction mixture reacts to generate phosphate, to obtain a slurry containing phosphate, wherein the particle size of the phosphate in the slurry is below 100 nm; 3) separating the slurry to obtain phosphate particles; and 4) drying and sintering the phosphate particles to obtain the doped modified manganese iron phosphate.

2. The doped modified manganese iron phosphate of claim 1, wherein, The particle size of the doped modified manganese iron phosphate is below 40 nm.

3. The doped modified manganese iron phosphate of claim 1, wherein, The particle size of the doped modified manganese iron phosphate is 5-40 nm.

4. The doped modified manganese iron phosphate of claim 1, wherein, The specific surface area of the doped modified manganese iron phosphate is 12-18 m 2 / g, and the pore size is 3-5 nm.

5. The doped modified manganese iron phosphate of claim 1, wherein, The doped modified manganese iron phosphate is monoclinic.

6. The doped modified manganese iron phosphate of claim 1, wherein, The doped modified manganese iron phosphate has a chemical formula of Mn 1-a-b Fe a Co b PO4; or Mn 1-a-b Fe a Mg b1 B b2 PO4, where b1 + b2 = b; or Mn 1-a-b Fe a Mo b1 Nb b2 B b3 PO4, where b1+b2+b3=b; or Mn 1-a-b Fe a Co b1 V b2 Ni b3 B b4 PO4, where b1+b2+b3+b4=b; or Mn 1-a-b Fe a Mg b PO4; or Mn 1-a-b Fe a V b1 Ti b2 PO4, where b1 + b2 = b; wherein, 10 -4 ≤ b1≤ 10 -2 , 10 -4 ≤ b2≤ 10 -2 , 10 -4 ≤ b3≤ 10 -2 , 10 -4 ≤ b4≤ 10 -2 .

7. The doped modified manganese iron phosphate of claim 1, wherein, The doped modified manganese iron phosphate has a chemical formula of Mn 0.6 Fe 0.395 Co 0.005 PO4 or Mn 0.65 Fe 0.344 Mg 0.005 B 0.001 PO4 or Mn 0.7 Fe 0.293 Mo 0.003 Nb 0.00 3B 0.001 PO4 or Mn 0.8 Fe 0.19 Co 0.005 V 0.001 Ni 0.001 B 0.003 PO4 or Mn 0.5 Fe 0.495 Mg 0.005 PO4 or Mn 0.65 Fe 0.34 V 0.005 Ti 0.005 PO4.

8. A method for producing the doped modified manganese iron phosphate according to any one of claims 1 to 7, characterized in that, The preparation method comprises the following steps: 1) mixing manganese iron oxide and a compound of M element with phosphoric acid to obtain a reaction mixture; 2) grinding the reaction mixture, so that the reaction mixture reacts to generate phosphate, to obtain a slurry containing phosphate, wherein the particle size of the phosphate in the slurry is below 100 nm; 3) separating the slurry to obtain phosphate particles; and 4) drying and sintering the phosphate particles to obtain the doped modified manganese iron phosphate.

9. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: The particle size of the manganese iron oxide is 1-20 microns; and / or, the phosphoric acid is in the form of a phosphoric acid aqueous solution, and the mass concentration of the phosphoric acid aqueous solution is 10%-70%. ​ 10. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: In step 1), the mixing is performed under mechanical stirring at a temperature of 20-40°C; and / or, in step 2), the grinding is performed in a sand mill, and the temperature of the grinding is 20-40°C; and / or, in step 4), the temperature of the drying is 100-120°C; and / or, in step 4), the temperature of the sintering is 300-400°C; and / or, the step 3) comprises filtering and washing the phosphate slurry. ​ 11. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: The step 4) comprises drying the phosphate particles to obtain doped modified manganese iron phosphate monohydrate crystals, wherein the particle size of the doped modified manganese iron phosphate monohydrate crystals is below 100 nm, and then sintering the doped modified manganese iron phosphate monohydrate crystals to obtain the doped modified manganese iron phosphate. ​ 12. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: The ratio of the amount of substance of the manganese iron oxide and the compound of M element to the amount of substance of the phosphoric acid is 1:1-2. ​ 13. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: The preparation method further comprises, before the step 1), a step of dispersing the manganese iron oxide in a dispersant aqueous solution. ​ 14. The method of claim 13, wherein the doped modified manganese iron phosphate material is prepared by: The dispersant is selected from a combination of one or more of polyvinylpyrrolidone, polyethylene glycol and TC130 dispersant; and / or, the mass concentration of the dispersant aqueous solution is 0.01%-5%.

15. The method of claim 8, wherein the doped modified manganese iron phosphate is prepared by the steps of: The preparation method further comprises, before the step 1), a step of preparing the phosphoric acid by reacting phosphorus pentoxide with water. ​ 16. The method of claim 8 to 15, wherein the method is characterized by: The compound of the M element is selected from a combination of one or more of oxides, carbonates, oxalates, nitrates, sulfates, chlorides and organic acid salts of the M element.

17. The method of claim 8 to 15, wherein the method is characterized by: The compound of the M element is cobalt chloride; or a combination of magnesium oxide and boric acid, or a combination of molybdenum trioxide, niobium oxalate and boric acid; or a combination of cobalt acetate, ammonium metavanadate, nickel sulfate and boric acid; or magnesium acetate; or a combination of vanadyl oxalate and titanium chloride.

18. Use of the doped modified manganese iron phosphate of any one of claims 1-7 for preparing a lithium ion battery cathode material.

19. A doped lithium iron manganese phosphate cathode material, characterized in that: The doped manganese iron phosphate cathode material is prepared by a high-temperature sintering reaction of raw materials including the doped modified manganese iron phosphate of any one of claims 1-7, a lithium source compound and optionally an organic carbon source.

20. A lithium-ion battery comprising a cathode material, characterized in that: The cathode material includes the doped manganese iron phosphate lithium cathode material of claim 19.

21. The lithium-ion battery of claim 20, wherein: The lithium ion battery has a discharge specific capacity of 145 mAh / g or more at 0.1C, a discharge specific capacity of 135 mAh / g or more at 1C, and a capacity retention rate of 92% or more after 200 cycles of charging and discharging at a 1C rate.

Images