Magnesium-doped ferromanganese phosphate as well as preparation method and application thereof

Abstract

The invention discloses magnesium-doped ferromanganese phosphate as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) mixing a phosphorus source, a divalent manganese salt, manganese dioxide and a magnesium source to obtain a reaction mixture, the phosphorus source being selected from one or two of phosphate and phosphoric acid; (2) grinding the reaction mixture, and enabling the reaction mixture to be subjected to redox reaction to generate magnesium-doped manganese phosphate, so as to obtain slurry containing the magnesium-doped manganese phosphate; (3) separating the slurry to obtain magnesium-doped manganese phosphate particles; and 4) reacting the magnesium-doped manganese phosphate particles with an iron source to obtain the magnesium-doped ferromanganese phosphate. When the magnesium-doped ferromanganese phosphate is used as a precursor of a ferromanganese phosphate battery positive electrode material, the specific capacity of the positive electrode material can be improved, the dissolution of manganese is remarkably inhibited, and the cycle performance of the battery is remarkably improved.

Description

Technical Field

[0001] The invention relates to magnesium-doped ferromanganese phosphate and a preparation method and application thereof. Background Art

[0002] Lithium iron manganese phosphate has good electrochemical properties and is widely used in lithium ion batteries. In order to further improve its electrochemical properties, it is usually modified by nano-sizing, carbon coating and metal ion doping in the prior art. In the metal ion doping modification, magnesium ions can be added to modify it. However, when synthesizing magnesium-doped lithium iron manganese phosphate in the prior art, each raw material such as magnesium source, phosphorus source, manganese source, iron source and lithium source is usually fed together, resulting in uncertainty in the magnesium doping position in the final magnesium-doped lithium iron manganese phosphate product, and the doped magnesium ions do not necessarily occupy the manganese position. It is not enough to inhibit the dissolution of manganese in the final product and improve the cycle performance of the material. The electrical properties of the final product, especially the cycle performance, are not high enough. For the co-precipitation method in the prior art, due to the different solubility products of manganese salts and iron salts, it is difficult to carry out mixed precipitation according to the designed ratio, resulting in a large difference between the Mn / Fe ratio in the final lithium iron manganese phosphate product and that in the raw materials, and the degree of improvement in electrical performance is not high enough. Summary of the invention

[0003] In view of the shortcomings and deficiencies of the prior art, the present invention provides a method for preparing magnesium-doped ferromanganese phosphate, which can prepare improved magnesium-doped ferromanganese phosphate. When used as a precursor of manganese iron phosphate battery positive electrode material, it can increase the specific capacity of the positive electrode material, significantly inhibit manganese dissolution and significantly improve the battery cycle performance.

[0004] The present invention also provides an improved magnesium-doped ferromanganese phosphate, which can be used as a precursor of a manganese-ferrophosphate battery positive electrode material. The corresponding battery positive electrode material has a high specific capacity, significantly improved battery cycle performance, and significantly reduced manganese dissolution.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing magnesium-doped ferromanganese phosphate, the method comprising the following steps: 1) mixing a phosphorus source, a divalent manganese salt, manganese dioxide and a magnesium source to obtain a reaction mixture, wherein the phosphorus source is selected from one or both of phosphate and phosphoric acid; 2) grinding the reaction mixture to cause an oxidation-reduction reaction in the reaction mixture to generate magnesium-doped manganese phosphate, thereby obtaining a slurry containing magnesium-doped manganese phosphate; 3) separating the slurry to obtain magnesium-doped manganese phosphate particles; and 4) reacting the magnesium-doped manganese phosphate particles with an iron source to obtain the magnesium-doped ferromanganese phosphate.

[0007] In some embodiments, the phosphate is selected from one or two of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate and potassium dihydrogen phosphate. When the phosphorus source contains phosphate, the slurry also contains sulfate by-products, for example, when the phosphate is one or two of ammonium monohydrogen phosphate and ammonium dihydrogen phosphate, the slurry also contains ammonium sulfate; when the phosphate is one or two of sodium monohydrogen phosphate and sodium dihydrogen phosphate, the slurry also contains sodium sulfate; when the phosphate is one or two of potassium monohydrogen phosphate and potassium dihydrogen phosphate, the slurry also contains potassium sulfate. Ammonium sulfate, sodium sulfate and potassium sulfate are all usable by-products. Ammonium sulfate and potassium sulfate are economically valuable fertilizer raw materials.

[0008] In some embodiments, the molar amount of the phosphorus source is 5% to 15% in excess of the stoichiometric ratio of the divalent manganese salt.

[0009] In some embodiments, the phosphorus source is a mixture of phosphate and phosphoric acid.

[0010] Preferably, based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.05-0.15 equivalents. More preferably, the phosphate is 1 equivalent; and the phosphoric acid is 0.1 equivalents.

[0011] In some embodiments, the divalent manganese salt is selected from a combination of one or more of manganese sulfate, manganese chloride, and manganese nitrate.

[0012] In some embodiments, the magnesium source is selected from a combination of one or more of magnesium oxide, magnesium phosphate, magnesium carbonate, magnesium sulfate, magnesium oxalate, magnesium nitrate and magnesium chloride.

[0013] In some embodiments, the iron source is selected from a combination of one or more of ferrous oxalate, ferrous acetate, ferric phosphate dihydrate, ferric phosphate, ferric oxide and ferrous sulfate.

[0014] In some embodiments, the molar amount of magnesium in the magnesium source accounts for 0.1%-5% of the total molar amount of manganese in the divalent manganese salt and manganese dioxide; preferably 0.1%-2%.

[0015] In some embodiments, in the slurry, the D50 particle size of the magnesium-doped manganese phosphate is less than 0.3 μm.

[0016] In some embodiments, 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% to 70%, preferably 20% to 40%.

[0017] In some embodiments, the phosphate is present in the form of an aqueous phosphate solution.

[0018] In some embodiments, the divalent manganese salt is present in the form of a divalent manganese salt aqueous solution.

[0019] In some embodiments, the step 4) is specifically to disperse and mix the magnesium-doped manganese phosphate particles and the iron source in water, filter, wash, dry and sinter to obtain the magnesium-doped manganese iron phosphate.

[0020] Preferably, the washing is performed with a phosphoric acid aqueous solution.

[0021] More preferably, the mass concentration of the phosphoric acid aqueous solution for washing is 0.5%-2%. Here, the filter cake after filtration is washed with a dilute phosphoric acid aqueous solution, which can better remove the residual impurities in the filter cake and accurately control the Mn / P ratio in the manganese precursor (magnesium-doped manganese phosphate) to further improve the quality of the subsequent finished product lithium manganese iron phosphate.

[0022] In some embodiments, in step 1), the mixing temperature is set at 20-40°C.

[0023] In some embodiments, in step 2), the grinding is performed in a sand mill, and the grinding temperature is 20-60°C.

[0024] In some embodiments, in step 4), the drying temperature is 100-120°C.

[0025] In some embodiments, in step 4), the sintering temperature is 500-800°C.

[0026] In some embodiments, the step 3) includes filtering and washing the slurry.

[0027] Preferably, washing is performed until the conductivity of the washing liquid is ≤500 μS / cm.

[0028] Preferably, by-products such as ammonium sulfate, sodium sulfate or potassium sulfate are recovered during filtration.

[0029] In some embodiments, the ratio of the molar amount of manganese in the magnesium-doped manganese phosphate particles to the molar amount of iron in the iron source is 5-8:2-5.

[0030] The present invention also provides a magnesium-doped ferromanganese phosphate, which is prepared by the above-mentioned preparation method and has a chemical formula of Mn 1-a-b Fe a Mg b PO4, and 0.2≤a≤0.5, 0.001≤b≤0.04.

[0031] The present invention also provides a use of the magnesium-doped ferromanganese phosphate for preparing a positive electrode material for a battery.

[0032] The present invention also provides a manganese iron phosphate battery positive electrode material, which is prepared by high-temperature sintering reaction of the above-mentioned magnesium-doped manganese iron phosphate and raw materials of a lithium source compound, an optional organic carbon source and an optional compound of other dopants.

[0033] In some embodiments, the chemical formula of the manganese iron phosphate battery positive electrode material is Li 1-x M x Mn 1-a- b Mg b Fe a-c X c P 1-d Y d O 4-e Z e , wherein M is a lithium dopant, X is an iron dopant, Y is a phosphorus dopant, Z is an oxygen dopant, and 0.001≤x≤0.03, 0.2≤a≤0.5, 0.001≤b≤0.04, 0.001≤c<0.5, 0.001≤d<1, and 0.001≤e<4.

[0034] In some embodiments, 0.001≤x≤0.01, 0.2≤a≤0.5, 0.001≤b≤0.04, 0.001≤c≤0.01, 0.001≤d≤0.01, and 0.001≤e≤0.01.

[0035] In some embodiments, 0.001≤x≤0.004, 0.2≤a≤0.5, 0.001≤b≤0.04, 0.001≤c≤0.004, 0.001≤d≤0.004, and 0.001≤e≤0.004.

[0036] In some embodiments, the lithium-site dopant M is selected from a combination of one or more of sodium, potassium and niobium.

[0037] In some embodiments, the iron-site dopant X is selected from a combination of one or more of vanadium, cobalt and titanium.

[0038] In some embodiments, the phosphorus-site dopant Y is selected from one or both of boron and silicon.

[0039] In some embodiments, the oxygen-site dopant Z is selected from one or both of fluorine and bromine.

[0040] In some embodiments, the compound of M is selected from one or more combinations of sodium carbonate, sodium hydroxide, sodium fluoride, potassium hydroxide, potassium bromide, potassium carbonate, niobium fluoride, niobium oxalate, niobium hydroxide, and niobium oxide.

[0041] In some embodiments, the compound of X is selected from a combination of one or more of vanadium oxide, ammonium metavanadate, vanadyl oxalate, cobalt oxide, cobalt acetate tetrahydrate, cobalt oxalate, cobalt carbonate, titanium dioxide and titanium hydroxide.

[0042] In some embodiments, the compound of Y is selected from a combination of one or more of boric acid, boron oxide, boron tribromide, silicic acid, and silicon dioxide.

[0043] In some embodiments, the compound of Z is selected from a combination of one or more of lithium fluoride, sodium fluoride, magnesium fluoride, lithium bromide, potassium bromide, bromic acid and sodium bromide.

[0044] In some embodiments, 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.

[0045] In some embodiments, the organic carbon source is selected from a combination of one or more of glucose, sucrose, fructose, citric acid, polyethylene glycol, polyvinyl pyrrolidone, ethylenediaminetetraacetic acid and ascorbic acid.

[0046] The present invention also provides a lithium-ion battery, comprising a positive electrode material, wherein the positive electrode material comprises the above-mentioned manganese iron phosphate positive electrode material.

[0047] Furthermore, the lithium ion battery has a discharge capacity of 155 mAh / g or more at 0.1C, a discharge capacity of 145 mAh / g or more at 1C, a capacity retention rate of 98% or more after 200 cycles of charge and discharge at 1C, and a manganese dissolution amount of 0.03 ppm or less after 200 cycles of charge and discharge at 1C. It can be seen that the lithium ion battery has excellent cycle performance and the manganese dissolution level is significantly suppressed.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] The present invention firstly subjects a divalent manganese salt, manganese dioxide and a phosphorus source to an oxidation-reduction reaction, and then adds a magnesium source to dope manganese to obtain magnesium-doped manganese phosphate, which is then reacted with an iron source to prepare magnesium-doped manganese iron phosphate.

[0050] When used as a precursor of the positive electrode material of manganese iron phosphate battery, it can increase the specific capacity of the positive electrode material, significantly inhibit manganese dissolution and significantly improve the battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the preparation process of Example 1;

[0052] Figure 2 This is a SEM image of the magnesium-doped ferromanganese phosphate prepared in Example 1;

[0053] Figure 3 This is a SEM image of the magnesium-doped lithium manganese iron phosphate prepared in Example 1;

[0054] Figure 4 This is a rate curve diagram of the magnesium-doped lithium manganese iron phosphate prepared in Example 1 at 0.1C and 1C;

[0055] Figure 5 This is a cycle curve of the magnesium-doped lithium manganese iron phosphate prepared in Example 1 at 1C. DETAILED DESCRIPTION

[0056] When synthesizing magnesium-doped lithium manganese iron phosphate in the prior art, various raw materials such as magnesium source, phosphorus source, manganese source, iron source and lithium source are usually fed together, resulting in uncertainty in the magnesium doping position in the final magnesium-doped lithium manganese iron phosphate product, and the doped magnesium ions do not necessarily occupy the manganese position, which is not enough to inhibit the dissolution of manganese in the final product and improve the cycle performance of the material. The electrical properties of the final product, especially the cycle performance, are not high enough. For the co-precipitation method in the prior art, due to the different solubility products of manganese salts and iron salts, it is difficult to mix and precipitate according to the designed ratio, resulting in a large difference in the Mn / Fe ratio in the final lithium manganese iron phosphate product from that in the raw materials, and the degree of improvement in electrical performance is not high enough.

[0057] The present invention provides an improved method for preparing magnesium-doped ferromanganese phosphate, wherein the method comprises first subjecting a divalent manganese salt, manganese dioxide and a phosphorus source to an oxidation-reduction reaction, and then adding a magnesium source to dope manganese, first obtaining magnesium-doped manganese phosphate, and then reacting the manganese phosphate with an iron source to prepare magnesium-doped ferromanganese phosphate. When the magnesium-doped ferromanganese phosphate is used as a precursor of a positive electrode material of a manganese iron phosphate battery, the specific capacity of the positive electrode material can be increased, and manganese dissolution can be significantly inhibited and battery cycle performance can be significantly improved.

[0058] The present invention ensures that magnesium is doped at the manganese position by adding a magnesium compound during the preparation of the precursor, and the position of the doped magnesium can be confirmed because Mg 2+ The stable ionic radius is Between Mn 3+ The ionic radius and Mn 2+ The ionic radius The valence is not changed, which has a stabilizing effect on the structure. The confirmation of the position of magnesium ions ensures that manganese is doped, which can significantly inhibit the manganese dissolution of the final positive electrode material doped with lithium manganese iron phosphate and improve its cycle performance. Compared with the prior art in which magnesium is doped, all raw materials are fed together, and the performance of the final positive electrode material is improved.

[0059] The present invention first prepares magnesium-doped manganese phosphate through the redox reaction of manganese in two valence states, and then adds iron phosphate to mix and wash, which can accurately control the Mn / Fe ratio content, and the preparation process does not use explosive strong oxidant hydrogen peroxide and highly corrosive pH regulator ammonia water, and the doped manganese phosphate and iron source are then calcined at high temperature to generate a manganese iron phosphate precursor, and then the precursor and the lithium source are calcined at high temperature to generate a manganese iron phosphate lithium positive electrode material, and the mutual solubility of the material is greatly improved, showing excellent electrochemical performance. For the coprecipitation method in the prior art, due to the different solubility products of manganese salts and iron salts, it is difficult to carry out mixed precipitation according to the designed ratio, resulting in a large difference between the Mn / Fe ratio in the final manganese iron phosphate lithium product and that in the raw material.

[0060] The present invention can produce synergistic effects by selecting different elements to be doped at different points through secondary doping, and jointly improve the performance of the final lithium iron manganese phosphate positive electrode material to obtain a lithium iron manganese phosphate product with excellent comprehensive performance. Magnesium ions have been doped into the manganese position in the magnesium-doped iron manganese phosphate precursor. During the secondary doping during the synthesis of lithium iron manganese phosphate, vanadium, cobalt, titanium, etc. with similar ion radius can be doped into the iron position (high-priced metal cation doping can induce lattice distortion, stabilize the crystal structure of the material, optimize the material band structure and reduce the band gap width, reduce the lithium ion diffusion barrier so that lithium ions can be quickly deintercalated inside the material, and improve the rate performance), boron, silicon, etc. are doped into the phosphorus position (reducing material lattice distortion, reducing lithium ion diffusion resistance, and improving ion conductivity), fluorine and bromine are doped into the oxygen position, and sodium, potassium, niobium, etc. are doped into the lithium position (improving the electronic conductivity of the material, improving the lithium ion diffusion coefficient, and expanding the lithium ion diffusion migration path, thereby improving the electrochemical performance of the material).

[0061] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0062] Example 1

[0063] This embodiment provides a magnesium-doped manganese iron phosphate and the use thereof to prepare lithium manganese iron phosphate. The preparation process is as follows: the chemical formula of magnesium-doped manganese iron phosphate is Mn 0.595 Fe 0.4 Mg 0.005 PO4:

[0064] 1) Weigh the raw materials: 184.66 kg of ammonium dihydrogen phosphate and 135.66 kg of manganese sulfate monohydrate, dissolve and filter them respectively with 200.0 kg of pure water, and add 18.50 kg of concentrated phosphoric acid (mass percentage is 10%) to the ammonium dihydrogen phosphate solution;

[0065] 2) Put the mixed solution of ammonium dihydrogen phosphate and concentrated phosphoric acid into the feeding tank of the sand mill, set the speed of the sand mill, start the circulation, add the aforementioned manganese sulfate solution, 69.79 kg of manganese dioxide, and 543.72 g of magnesium oxide into the sand mill in sequence, and sand grind until the particle size D50 of the slurry is ≤0.3 μm;

[0066] 3) The sand-milled slurry is put into a plate-and-frame filter press for filter pressing and water washing, and then the byproduct ammonium sulfate is recovered, and the filter cake is continuously washed with water until the conductivity of the washing liquid is ≤500 μS / cm, and the filter cake is removed;

[0067] 4) According to the Mn / Fe molar ratio of 6 / 4, the filter cake, dihydrate ferric phosphate and pure water are dispersed and mixed, and the filter cake is filtered. The filter cake is washed with a phosphoric acid aqueous solution with a mass concentration of about 1%, and then calcined in a rotary kiln after drying. The furnace temperature is controlled at 600° C. to finally obtain a magnesium-doped ferromanganese phosphate precursor.

[0068] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028 Na 0.002 Mn 0.595 Mg 0.005 Fe 0.399 Co 0.001 P 0.995 B 0.00 5O 3.998 F 0.002 / C:

[0069] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and sequentially add 130.78 kg of the magnesium-doped ferromanganese phosphate precursor prepared above, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 227.89 g of cobalt acetate tetrahydrate, 160.87 g of boron oxide and 76.83 g of sodium fluoride, and sand grind until the particle size D50 of the slurry is ≤0.4 μm;

[0070] 6) Drying with a sprayer, setting the inlet air temperature of the sprayer to 240°C and the outlet air temperature to 110°C, spray drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0071] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0072] The above process is as follows Figure 1 The SEM image of the magnesium-doped manganese iron phosphate precursor is shown in Figure 2 The SEM image of the final sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate is shown in Figure 3 shown.

[0073] Example 2

[0074] This embodiment provides a magnesium-doped ferromanganese phosphate and uses it to prepare lithium ferromanganese phosphate. The magnesium-doped ferromanganese phosphate is the same as that in Example 1.

[0075] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028 Na 0.002 Mn 0.595 Mg 0.005 Fe 0.399 V 0.001 P 0.997 B 0.003 O 3.99 8F 0.002 / C:

[0076] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and add 131.04 kg of magnesium-doped ferromanganese phosphate precursor, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 141.78 g of vanadyl oxalate, 96.52 g of boron oxide and 76.83 g of sodium fluoride in sequence, and sand grind until the particle size of the slurry is ≤ 0.4 μm;

[0077] 6) Using a spray machine to dry, setting the air inlet temperature to 240°C and the air outlet temperature to 110°C, spray-drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0078] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-vanadium-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0079] Example 3

[0080] This embodiment provides a magnesium-doped ferromanganese phosphate and uses it to prepare lithium ferromanganese phosphate. The magnesium-doped ferromanganese phosphate is the same as that in Example 1.

[0081] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.029 Na 0.001 Mn 0.595 Mg 0.005 Fe 0.39 Co 0.01 P 0.997 B 0.003 O 3.99 8F 0.003 / C:

[0082] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and add 130.91 kg of magnesium-doped ferromanganese phosphate precursor, 34.42 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 2278.97 g of cobalt acetate tetrahydrate, 160.87 g of boron oxide, 47.46 g of lithium fluoride and 38.42 g of sodium fluoride in sequence, and sand grind until the particle size of the slurry is ≤ 0.4 μm;

[0083] 6) Using a spray machine to dry, setting the air inlet temperature to 240°C and the air outlet temperature to 110°C, spray-drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0084] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0085] Example 4

[0086] This embodiment provides a magnesium-doped manganese iron phosphate and the use thereof to prepare lithium manganese iron phosphate. The preparation process is as follows: the chemical formula of magnesium-doped manganese iron phosphate is Mn 0.590 Fe 0.4 Mg 0.01 PO4:

[0087] 1) Weigh the raw materials: 183.11 kg of ammonium dihydrogen phosphate and 134.52 kg of manganese sulfate monohydrate, dissolve and filter them respectively with 200.0 kg of pure water, and add 18.35 kg of concentrated phosphoric acid (mass percentage is 10%) to the ammonium dihydrogen phosphate solution;

[0088] 2) Put the mixed solution of ammonium dihydrogen phosphate and concentrated phosphoric acid into the feeding tank of the sand mill, set the speed of the sand mill, start the circulation, add the aforementioned manganese sulfate solution, 69.20 kg of manganese dioxide and 1087.44 g of magnesium oxide into the sand mill in sequence, and sand grind until the particle size D50 of the slurry is ≤0.3 μm;

[0089] 3) The sand-milled slurry is put into a plate-and-frame filter press for filter pressing and water washing, and then the byproduct ammonium sulfate is recovered, and the filter cake is continuously washed with water until the conductivity of the washing liquid is ≤500 μS / cm, and the filter cake is removed;

[0090] 4) According to the Mn / Fe molar ratio of 6 / 4, the filter cake, dihydrate ferric phosphate and pure water are dispersed and mixed, and the filter cake is filtered. The filter cake is washed with a phosphoric acid aqueous solution with a mass concentration of about 1%, and then dried and calcined in a rotary kiln with the furnace temperature controlled at 600°C to finally obtain a magnesium-doped ferromanganese phosphate precursor with a manganese iron to phosphorus molar ratio of about 0.975.

[0091] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028Na 0.002 Mn 0.590 Mg 0.01 Fe 0.398 Ti 0.002 P 0.997 B 0.003 O 3.99 8F 0.002 / C:

[0092] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and add 130.65 kg of the magnesium-doped ferromanganese phosphate precursor prepared above, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 146.15 g of titanium dioxide, 160.87 g of boron oxide and 76.83 g of sodium fluoride in sequence, and sand grind to a particle size D50 of slurry ≤ 0.4 μm;

[0093] 6) Drying with a sprayer, setting the inlet air temperature of the sprayer to 240°C and the outlet air temperature to 110°C, spray drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0094] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-titanium-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0095] Example 5

[0096] This embodiment provides a magnesium-doped ferromanganese phosphate and uses it to prepare lithium ferromanganese phosphate. The magnesium-doped ferromanganese phosphate is the same as that in Example 1.

[0097] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028 K 0.002 Mn 0.595 Mg 0.005 Fe 0.399 V 0.001 P 0.997 B 0.003 O 3.998 Br 0.002 / C:

[0098] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and add 131.04 kg of magnesium-doped ferromanganese phosphate precursor, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 141.78 g of vanadyl oxalate, 160.87 g of boron oxide, 96.52 g of boron oxide and 188.28 g of potassium bromide in sequence, and sand grind until the particle size of the slurry is ≤ 0.4 μm;

[0099] 6) Using a spray machine to dry, setting the air inlet temperature to 240°C and the air outlet temperature to 110°C, spray-drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0100] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining nano-lithium manganese iron phosphate co-doped with magnesium, vanadium, boron and bromine.

[0101] Comparative Example 1

[0102] This comparative example provides a magnesium-doped ferromanganese phosphate and the use thereof to prepare lithium ferromanganese phosphate, and the preparation process is as follows (basically the same as Example 1, the only difference is: the addition of magnesium oxide from step 1) is replaced by step 4), and the amount remains unchanged). In the magnesium-doped ferromanganese phosphate, the molar amount of Mg is 0.005 times the total molar amount of Mg, Mn and Fe, and Mg partially occupies the Mn position and partially occupies the Fe position.

[0103] 1) Weigh the raw materials: 184.66 kg of ammonium monohydrogen phosphate and 135.66 kg of manganese sulfate monohydrate, dissolve and filter them respectively with 200.0 kg of pure water, and add 18.50 kg of concentrated phosphoric acid (mass percentage is 10%) to the ammonium monohydrogen phosphate solution;

[0104] 2) Put the mixed solution of ammonium dihydrogen phosphate and concentrated phosphoric acid into the feeding tank of the sand mill, set the speed of the sand mill, start the circulation, add the aforementioned manganese sulfate solution and 69.79 kg of manganese dioxide into the sand mill in sequence, and sand grind until the particle size D50 of the slurry is ≤0.3 μm;

[0105] 3) The sand-milled slurry is put into a plate-and-frame filter press for filter pressing and water washing, and then the byproduct ammonium sulfate is recovered, and the filter cake is continuously washed with water until the conductivity of the washing liquid is ≤500 μS / cm, and the filter cake is removed;

[0106] 4) According to the Mn / Fe molar ratio of 6 / 4, the filter cake, dihydrate iron phosphate, 543.72 kg of magnesium oxide and pure water were dispersed and mixed, and the filter cake was washed with a phosphoric acid aqueous solution with a mass concentration of about 1%, and then dried and calcined in a rotary kiln with the furnace temperature controlled at 600° C. to finally obtain a magnesium-doped manganese iron phosphate precursor.

[0107] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028 Na 0.002 Mn 0.6-f Mg 0.005 Fe 0.399-g Co 0.001 P 0.995 B 0.00 5O 3.998 F 0.002 / C: wherein 0≤f≤0.005, 0≤g≤0.005, and f+g=0.005, that is, the molar amount of Mg is 0.005 times the total molar amount of Mg, Mn, Fe and Co, and Mg partially occupies the Mn position and partially occupies the Fe position.

[0108] 5) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and sequentially add 130.78 kg of the magnesium-doped ferromanganese phosphate precursor prepared above, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 227.89 g of cobalt acetate tetrahydrate, 160.87 g of boron oxide and 76.83 g of sodium fluoride, and sand grind until the particle size D50 of the slurry is ≤0.4 μm;

[0109] 6) Drying with a sprayer, setting the inlet air temperature of the sprayer to 240°C and the outlet air temperature to 110°C, spray drying the sand-milled slurry into a powder, and sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0110] 7) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0111] Comparative Example 2

[0112] The present comparative example provides a magnesium-doped ferromanganese phosphate and the use thereof to prepare lithium ferromanganese phosphate, and the preparation process is as follows (without performing the redox reaction of manganese, manganese (III) phosphate monohydrate prepared by reacting manganese trioxide with phosphoric acid, and magnesium oxide and ferric phosphate dihydrate are reacted to prepare a magnesium-doped ferromanganese phosphate precursor), in which the molar amount of Mg in the magnesium-doped ferromanganese phosphate is 0.005 times the total molar amount of Mg, Mn and Fe, and Mg partially occupies the Mn position and partially occupies the Fe position.

[0113] 1) According to the Mn / Fe molar ratio of 6 / 4, 269.61 kg of manganese (III) phosphate monohydrate, 543.72 g of magnesium oxide and 201.41 kg of ferric phosphate dihydrate were dispersed and mixed with pure water, filtered, and the filter cake was washed with a phosphoric acid aqueous solution with a mass concentration of about 1%. After drying, it was calcined in a rotary kiln with the furnace temperature controlled at 600° C. to obtain a magnesium-doped manganese iron phosphate precursor.

[0114] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028 Na 0.002 Mn 0.6-h Mg 0.005 Fe 0.399-i Co 0.001 P 0.995 B 0.00 5O 3.998 F0.002 / C: wherein 0≤h≤0.005, 0≤i≤0.005, and h+i=0.005, that is, the molar amount of Mg is 0.005 times the total molar amount of Mg, Mn, Fe and Co, and Mg partially occupies the Mn position and partially occupies the Fe position.

[0115] 2) Add 380 kg of deionized water to the sand mill tank, turn on the sand mill, and add 130.78 kg of the magnesium-doped ferromanganese phosphate precursor prepared above, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 227.89 g of cobalt acetate tetrahydrate, 160.87 g of boron oxide and 76.83 g of sodium fluoride in sequence, and sand grind to a particle size D50 of the slurry ≤ 0.4 μm;

[0116] 3) Drying with a sprayer, setting the inlet air temperature of the sprayer to 240°C and the outlet air temperature to 110°C, spray drying the sand-milled slurry into powder, sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0117] 4) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0118] Comparative Example 3

[0119] This comparative example provides a magnesium-doped ferromanganese phosphate and the use thereof to prepare lithium ferromanganese phosphate, and the preparation process is as follows (without performing a redox reaction of manganese, and without first preparing a magnesium-doped ferromanganese phosphate precursor, but directly reacting a magnesium source, a lithium source and ferromanganese phosphate to synthesize lithium ferromanganese phosphate):

[0120] Preparation of lithium manganese iron phosphate, whose chemical formula is Li 1.028-j Na 0.002 Mn 0.6-k Mg 0.005 Fe 0.399-l Co 0.001 P 0.995 B 0.00 5O 3.998 F 0.002 / C: wherein 0≤j≤0.005, 0≤k≤0.005, 0≤l≤0.005, and j+k+l=0.005, that is, the molar amount of Mg is 0.005 times the total molar amount of Mg, Mn, Fe and Co, and Mg partially occupies the Mn position, partially occupies the Fe position, and partially occupies the Li position.

[0121] 1) Add 380 kg of deionized water to a sand mill tank, turn on the sand mill, and add 89.91 g of manganese (III) phosphate monohydrate, 67.81 kg of iron phosphate dihydrate, 34.43 kg of lithium carbonate, 12.48 kg of glucose monohydrate, 1.47 kg of polyethylene glycol, 543.72 g of magnesium oxide, 227.89 g of cobalt acetate tetrahydrate, 160.87 g of boron oxide and 76.83 g of sodium fluoride in sequence, and sand grind until the particle size D50 of the slurry is ≤0.4 μm;

[0122] 2) Drying with a sprayer, setting the inlet air temperature of the sprayer to 240°C and the outlet air temperature to 110°C, spray drying the sand-milled slurry into powder, sintering the powder in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0123] 3) The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining sodium-magnesium-cobalt-boron-fluorine co-doped nano-lithium manganese iron phosphate.

[0124] The doped lithium manganese iron phosphate positive electrode material (LMFP / C) prepared in the above embodiments and comparative examples is configured with conductive carbon nanotubes, conductive carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone to form a positive electrode slurry, wherein the mass ratio of LMFP / C positive electrode material to conductive carbon nanotubes, conductive carbon black and binder polyvinylidene fluoride is 91.5:1.5:1.0:6; the positive electrode slurry is coated on aluminum foil, followed by vacuum baking, punching, and finally making LMFP / C positive electrode sheet. LMFP / C is used as the positive electrode, lithium sheet as the negative electrode, 1mol / L LiPF6 EC / DMC / EMC solution as the electrolyte, and button batteries are assembled, and the battery is charged and discharged (the charge and discharge window is 2.5V~4.3V), and the electrical properties of lithium manganese iron phosphate can be obtained. The results are shown in Table 1 below.

[0125] Table 1 Performance of each embodiment and comparative example

[0126]

[0127]

[0128] As can be seen from Table 1, compared with the case where each raw material such as magnesium source, phosphorus source, manganese source, iron source and lithium source are fed together (Comparative Example 3), the magnesium doping position in the final magnesium-doped lithium iron manganese phosphate product is uncertain, and the doped magnesium ions do not necessarily occupy the manganese position. In the lithium iron manganese phosphate product of Example 1 of the present invention, the doped magnesium ions occupy the manganese position, which can improve the cycle performance of the product and inhibit manganese dissolution. Compared with not doping magnesium when high-valent manganese and low-valent manganese are oxidized and reduced (for example, although an oxidization-reduction reaction is performed in Comparative Example 1, magnesium is not added during the oxidization-reduction reaction, or no oxidization-reduction reaction is performed in Comparative Example 2), the lithium iron manganese phosphate product of Example 1 of the present invention has higher cycle performance and lower manganese dissolution.

[0129] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0130] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A method for preparing magnesium-doped ferromanganese phosphate, characterized in that: The preparation method comprises the following steps: 1) mixing a phosphorus source, a divalent manganese salt, manganese dioxide and a magnesium source to obtain a reaction mixture, wherein the phosphorus source is selected from one or both of phosphate and phosphoric acid; 2) grinding the reaction mixture to cause an oxidation-reduction reaction in the reaction mixture to generate magnesium-doped manganese phosphate, thereby obtaining a slurry containing magnesium-doped manganese phosphate; 3) separating the slurry to obtain magnesium-doped manganese phosphate particles; and 4) reacting the magnesium-doped manganese phosphate particles with an iron source to obtain the magnesium-doped manganese iron phosphate.

2. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The phosphate is selected from one or two of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate and potassium dihydrogen phosphate; and / or, based on the stoichiometric ratio of the divalent manganese salt, the molar amount of the phosphorus source is 5%-15% excess.

3. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The phosphorus source is a mixture of phosphate and phosphoric acid; preferably, based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.05-0.15 equivalents.

4. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The divalent manganese salt is selected from a combination of one or more of manganese sulfate, manganese chloride, and manganese nitrate; and / or the magnesium source is selected from a combination of one or more of magnesium oxide, magnesium phosphate, magnesium carbonate, magnesium sulfate, magnesium oxalate, magnesium nitrate, and magnesium chloride; and / or the iron source is selected from a combination of one or more of ferrous oxalate, ferrous acetate, ferric phosphate dihydrate, ferric phosphate, ferric oxide, and ferrous sulfate.

5. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The molar amount of magnesium in the magnesium source accounts for 0.1%-5% of the total molar amount of manganese in the divalent manganese salt and manganese dioxide; and / or, in the slurry, the D50 particle size of the magnesium-doped manganese phosphate is below 0.3 μm.

6. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The phosphoric acid is present in the form of a phosphoric acid aqueous solution, the mass concentration of the phosphoric acid aqueous solution is 10% to 70%; and / or the phosphate is present in the form of a phosphate aqueous solution; And / or, the divalent manganese salt exists in the form of a divalent manganese salt aqueous solution.

7. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The step 4) specifically comprises dispersing and mixing the magnesium-doped manganese phosphate particles and the iron source in water, filtering, washing, drying and sintering to obtain the magnesium-doped manganese phosphate iron; preferably, the washing is performed with an aqueous phosphoric acid solution; more preferably, the mass concentration of the aqueous phosphoric acid solution used for washing is 0.5%-2%.

8. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: In step 1), the mixing temperature is set at 20-40°C; and / or, in step 2), the grinding is carried out in a sand mill at a temperature of 20-60°C; and / or, in step 4), the drying temperature is 100-120°C; and / or, in step 4), the sintering temperature is 500-800°C; and / or, step 3) includes filtering and washing the slurry.

9. The method for preparing magnesium-doped ferromanganese phosphate according to claim 1, characterized in that: The ratio of the molar amount of manganese in the magnesium-doped manganese phosphate particles to the molar amount of iron in the iron source is 5-8:5-2.

10. A magnesium-doped ferromanganese phosphate, characterized in that: The magnesium-doped ferromanganese phosphate is prepared by the method for preparing magnesium-doped ferromanganese phosphate according to any one of claims 1 to 8, and its general chemical formula is Mn 1-a-b Fe a Mg b PO4, and 0.2≤a≤0.5, 0.001≤b≤0.

04.

11. A manganese iron phosphate battery positive electrode material, characterized in that: The manganese iron phosphate battery positive electrode material is prepared by high temperature sintering reaction of raw materials including the magnesium-doped manganese iron phosphate according to claim 10 and a compound of a lithium source compound, an optional organic carbon source and optional other dopants.

12. The manganese iron phosphate battery positive electrode material according to claim 11, characterized in that: The chemical formula of the manganese iron phosphate battery positive electrode material is Li 1.03-x M x Mn 1-a-b Mg b Fe a-c X c P 1-d Y d O 4-e Z e , wherein M is a lithium dopant, X is an iron dopant, Y is a phosphorus dopant, Z is an oxygen dopant, and 0.001≤x≤0.03, 0.2≤a≤0.5, 0.001≤b≤0.04, 0.001≤c<0.5, 0.001≤d<1, and 0.001≤e<4.

13. The manganese iron phosphate battery positive electrode material according to claim 12, characterized in that: The lithium dopant M is selected from a combination of one or more of sodium, potassium and niobium; and / or, the iron dopant X is selected from a combination of one or more of vanadium, cobalt and titanium; and / or, the phosphorus dopant Y is selected from one or both of boron and silicon; And / or, the oxygen dopant Z is selected from one or both of fluorine and bromine.

14. The method for preparing magnesium-doped ferromanganese phosphate according to claim 13, characterized in that: The compound of M is selected from a combination of one or more of sodium carbonate, sodium hydroxide, sodium fluoride, potassium hydroxide, potassium bromide, potassium carbonate, niobium fluoride, niobium oxalate, niobium hydroxide, and niobium oxide; and / or, the compound of X is selected from a combination of one or more of vanadium oxide, ammonium metavanadate, vanadium oxalate, cobalt oxide, cobalt acetate tetrahydrate, cobalt oxalate, cobalt carbonate, titanium dioxide, and titanium hydroxide; and / or, the compound of Y is selected from a combination of one or more of boric acid, boron oxide, boron tribromide, silicic acid, and silicon dioxide; and / or, the compound of Z is selected from a combination of one or more of lithium fluoride, sodium fluoride, magnesium fluoride, lithium bromide, potassium bromide, bromic acid, and sodium bromide.

15. The manganese iron phosphate battery positive electrode material according to claim 11, characterized in that: The lithium source compound is selected from a combination of one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium acetate; and / or the organic carbon source is selected from a combination of one or more of glucose, sucrose, fructose, citric acid, polyethylene glycol, polyvinyl pyrrolidone, ethylenediaminetetraacetic acid and ascorbic acid.

16. A lithium ion battery comprising a positive electrode material, characterized in that: The positive electrode material comprises the manganese iron phosphate positive electrode material according to any one of claims 11 to 15.

17. The lithium ion battery according to claim 26, characterized in that: The lithium ion battery has a discharge specific capacity of more than 155 mAh / g at 0.1C, a discharge specific capacity of more than 145 mAh / g at 1C, a capacity retention rate of more than 98% after 200 cycles of charge and discharge at a 1C rate, and a manganese dissolution amount of less than 0.03 ppm after 200 cycles of charge and discharge at a 1C rate.

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