Modified lithium manganese iron phosphate positive electrode material and its precursor and preparation method, battery

Abstract

The invention discloses a modified lithium manganese iron phosphate positive electrode material and its precursor, preparation method and battery, belonging to the technical field of positive electrode materials. The modified lithium manganese iron phosphate precursor is obtained by coating the surface of the iron manganese phosphate precursor with iron phosphate doped with Sb. The conductivity of the material can be improved by coating the iron phosphate, and the Mn can be suppressed by doping Sb in the iron phosphate coating layer. 2+ The modified lithium manganese iron phosphate positive electrode material prepared from the modified lithium manganese iron phosphate precursor has a lower resistivity and a higher capacity retention rate. The preparation methods of the modified lithium manganese iron phosphate positive electrode material and its precursor are relatively simple and easy to operate.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and in particular to a modified lithium manganese iron phosphate positive electrode material, a precursor thereof, a preparation method thereof, and a battery. Background Art

[0002] Lithium manganese iron phosphate (LMFP, LiMn 1-x Fe x Lithium iron phosphate (LFP, LiFePO4) is an upgraded version of lithium iron phosphate (LFP, LiFePO4), which is based on lithium iron phosphate and doped with a certain amount of manganese and adjusted to the ratio of its atomic number to iron (manganese iron ratio) to increase the voltage platform of the material. Compared with lithium iron phosphate, lithium manganese iron phosphate material has a higher voltage platform, the voltage can reach about 4.1V; under the same conditions, the theoretical energy density of lithium manganese iron phosphate is increased by 15-20%; in terms of cost, lithium manganese iron phosphate has better economy.

[0003] However, lithium manganese iron phosphate also has defects such as poor conductivity and rate performance, dual voltage platform increases the difficulty of BMS, and manganese ion dissolution affects battery cycle performance, which limits its large-scale application in the industry.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] One of the purposes of the present invention is to provide a modified lithium manganese iron phosphate precursor, which is beneficial to improving the capacity retention rate and conductivity of the positive electrode material prepared therefrom.

[0006] A second object of the present invention is to provide a method for preparing the modified lithium manganese iron phosphate precursor.

[0007] The third object of the present invention is to provide a modified lithium manganese iron phosphate positive electrode material using the above-mentioned modified lithium manganese iron phosphate precursor as a precursor.

[0008] A fourth object of the present invention is to provide a method for preparing the above-mentioned modified lithium manganese iron phosphate positive electrode material.

[0009] A fifth object of the present invention is to provide a battery whose preparation raw materials include the above-mentioned modified lithium manganese iron phosphate positive electrode material.

[0010] This application can be implemented as follows:

[0011] In a first aspect, the present application provides a modified lithium manganese iron phosphate precursor, which is obtained by coating the surface of the lithium manganese iron phosphate precursor with Sb-doped iron phosphate.

[0012] In an optional embodiment, the surface of every 100 g of ferromanganese phosphate precursor is coated with 1-5 g of ferrophosphate doped with Sb, and the doping amount of Sb in the ferrophosphate is 0.01-0.1 g.

[0013] In a second aspect, the present application provides a method for preparing the modified lithium manganese iron phosphate precursor, comprising the following steps:

[0014] The suspension of the ferromanganese phosphate precursor is reacted with an iron source solution, an antimony source solution and a phosphorus source solution under an oxidizing atmosphere to obtain a modified lithium ferromanganese phosphate precursor slurry; then, filter pressing, washing, drying and sintering are performed in sequence to obtain a modified lithium ferromanganese phosphate precursor.

[0015] In an optional embodiment, the suspension of the ferromanganese phosphate precursor is obtained by mixing the ferromanganese phosphate precursor with a first solvent;

[0016] Wherein, the first solvent includes at least one of anhydrous ethanol, propanol, isopropanol and butanol.

[0017] In an optional embodiment, the iron source solution is obtained by mixing the iron source with the second solvent;

[0018] and / or, the antimony source solution is obtained by mixing the antimony source with a second solvent;

[0019] and / or, the phosphorus source solution is obtained by mixing the phosphorus source with a third solvent;

[0020] Wherein, the second solvent includes ethylene glycol and water; and the third solvent includes water.

[0021] In an optional embodiment, the volume ratio of ethylene glycol to water in the second solvent is 1:3-5.

[0022] In an optional embodiment, the iron source includes at least one of ferrous sulfate and ferrous nitrate, and / or the antimony source includes at least one of antimony trichloride and antimony nitrate; and / or the phosphorus source includes at least one of diammonium phosphate and ammonium phosphate.

[0023] In an optional embodiment, the volume ratio of the ferromanganese phosphate precursor to the iron source solution, the antimony source solution, and the phosphorus source solution is 100 g: 80-120 mL: 80-120 mL: 80-120 mL;

[0024] Among them, the concentration of the iron source solution is 0.066-0.33 mol / L, the concentration of the antimony source is 0.00044-0.0044 mol / L, and the concentration of the phosphorus source solution is 0.066-0.33 mol / L.

[0025] In an alternative embodiment, the oxidizing atmosphere is provided by ozone and / or oxygen.

[0026] In an optional embodiment, the suspension of the ferromanganese phosphate precursor is reacted with the iron source solution, the antimony source solution and the phosphorus source solution at a pH of 1.8-2.2 and a temperature of 45-55° C. for 8-12 hours;

[0027] and / or, drying is carried out at 90-110° C.;

[0028] And / or, the sintering is performed in an oxygen atmosphere at 480-520° C. for 5-7 hours.

[0029] In a third aspect, the present application provides a modified lithium iron manganese phosphate positive electrode material, whose precursor is the above-mentioned modified lithium iron manganese phosphate precursor.

[0030] In a fourth aspect, the present application provides a method for preparing the above-mentioned modified lithium manganese iron phosphate positive electrode material, which comprises the following steps:

[0031] The mixture of the modified lithium iron manganese phosphate precursor, the lithium source and the carbon source is sintered.

[0032] In an alternative embodiment, the lithium source comprises at least one of lithium carbonate and lithium hydroxide.

[0033] In an optional embodiment, the molar ratio of the metal element in the modified lithium manganese iron phosphate precursor to the lithium element in the lithium source is 1:1.15-1.25.

[0034] In an optional embodiment, the carbon source is a high molecular carbon-containing organic matter, preferably including at least one of glucose, sucrose and alcohol.

[0035] In an optional embodiment, the mass of the carbon source is 4-6% of the modified lithium manganese iron phosphate precursor.

[0036] In an optional embodiment, the modified lithium manganese iron phosphate precursor, the lithium source and the carbon source are mixed by ball milling.

[0037] In an optional embodiment, the mixture of the modified lithium manganese iron phosphate precursor, the lithium source and the carbon source is sintered in a nitrogen atmosphere at 580-620° C. for 6-10 h.

[0038] In a fifth aspect, the present application provides a battery, the raw materials for preparing the battery include the above-mentioned modified lithium manganese iron phosphate positive electrode material.

[0039] The beneficial effects of this application include:

[0040] The present invention can improve the conductivity of the material by coating iron phosphate on the surface of the manganese iron phosphate precursor, and by doping Sb in the iron phosphate coating layer, Sb 3+ The ionic radius is larger than that of Mn 2+ , in the long-term cycle process, it can effectively block Mn2+ Pass through the coating layer to reduce Mn 2+ The amount of dissolution is reduced, thereby improving the structural stability and electrochemical stability of the material. The modified lithium manganese iron phosphate positive electrode material prepared from the modified lithium manganese iron phosphate precursor has a lower resistivity and a higher capacity retention rate. The corresponding battery has a higher conductivity and capacity retention rate.

[0041] The preparation methods of the modified lithium manganese iron phosphate positive electrode material and its precursor are relatively simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 This is the SEM image of the modified lithium manganese iron phosphate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0045] The modified manganese iron phosphate precursor lithium positive electrode material and its precursor, preparation method, and battery provided in this application are described in detail below.

[0046] The present application provides a modified manganese ferrophosphate precursor lithium precursor, which is obtained by coating the surface of the manganese ferrophosphate precursor with Sb-doped iron phosphate.

[0047] The conductivity of lithium manganese iron phosphate material can be improved by coating iron phosphate on the surface of the iron manganese phosphate precursor; by doping Sb in the iron phosphate coating layer, Sb 3+ The ionic radius is larger than that of Mn 2+ , in the long-term cycle process, it can effectively block Mn 2+ Pass through the coating layer to reduce Mn 2+ The dissolution amount is increased to improve the structural stability and electrochemical stability of lithium manganese iron phosphate materials.

[0048] For reference, the surface of every 100 g of the manganese iron phosphate precursor can be coated with 1-5 g of iron phosphate doped with Sb, and the doping amount of Sb in the iron phosphate is 0.01-0.1 g.

[0049] Illustratively, the coating amount of iron phosphate per 100 g of ferromanganese phosphate precursor can be 1 g, 1.5 g, 2 g, 2.5 g, 3 g, 3.5 g, 4 g, 4.5 g or 5 g, etc., or any other value within the range of 1-5 g.

[0050] Illustratively, the doping amount of Sb in iron phosphate can be 0.01g, 0.02g, 0.03g, 0.04g, 0.05g, 0.06g, 0.07g, 0.08g, 0.09g or 0.1g, etc., or any other value within the range of 0.01-0.1g.

[0051] It should be noted that if the amount of iron phosphate coating is too much, it will easily lead to a decrease in gram capacity, that is, a decrease in the voltage platform; if the amount of Sb doping is too much, it will cause antimony to expand in volume during the cycle process and will also reduce the proportion of active substances.

[0052] Accordingly, the present application provides a method for preparing the modified lithium manganese iron phosphate precursor, comprising the following steps:

[0053] The suspension of the ferromanganese phosphate precursor is reacted with an iron source solution, an antimony source solution and a phosphorus source solution under an oxidizing atmosphere to obtain a modified lithium ferromanganese phosphate precursor slurry; then, filter pressing, washing, drying and sintering are performed in sequence to obtain a modified lithium ferromanganese phosphate precursor.

[0054] For reference, the suspension of ferromanganese phosphate precursor can be obtained by mixing the ferromanganese phosphate precursor with a first solvent; the iron source solution can be obtained by mixing an iron source with a second solvent; the antimony source solution can be obtained by mixing an antimony source with a second solvent; and the phosphorus source solution can be obtained by mixing a phosphorus source with a third solvent.

[0055] It should be noted that the ferromanganese phosphate precursor in the present application can be prepared by referring to the relevant existing technology, and no further details will be given here.

[0056] The first solvent may include (be) at least one of anhydrous ethanol, propanol, isopropanol, and butanol.

[0057] The usage ratio of the ferromanganese phosphate precursor to the first solvent may be 100 g: 50-100 mL.

[0058] The second solvent may include ethylene glycol and water. For example, the volume ratio of ethylene glycol to water may be 1:3-5, such as 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, or any other value within the range of 1:3-5.

[0059] The third solvent includes (is) water.

[0060] The volume ratio of the ferromanganese phosphate precursor to the iron source solution, the antimony source solution and the phosphorus source solution can be 100 g: 80-120 mL: 80-120 mL: 80-120 mL, preferably 100 g: 100 mL: 100 mL: 100 mL.

[0061] The concentration of the iron source solution may be 0.066-0.33 mol / L, such as 0.066 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L or 0.33 mol / L, or any other value within the range of 0.066-0.33 mol / L.

[0062] The concentration of the antimony source can be 0.00044-0.0044 mol / L, such as 0.00044 mol / L, 0.001 mol / L, 0.0015 mol / L, 0.002 mol / L, 0.0025 mol / L, 0.003 mol / L, 0.0035 mol / L, 0.004 mol / L or 0.0044 mol / L, etc., or it can be any other value within the range of 0.00044-0.0044 mol / L.

[0063] The concentration of the phosphorus source solution can be 0.066-0.33 mol / L, such as 0.066 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L or 0.33 mol / L, or any other value within the range of 0.066-0.33 mol / L.

[0064] The above-mentioned iron source may exemplarily include (be) at least one of ferrous sulfate and ferrous nitrate, the antimony source may exemplarily include (be) at least one of antimony trichloride and antimony nitrate, and the phosphorus source may exemplarily include (be) at least one of diammonium phosphate and ammonium phosphate.

[0065] The iron source is mainly used to provide iron in the iron phosphate coating layer; the phosphorus source is used to provide phosphate ions to precipitate iron ions on the one hand, and can adjust the pH value of the reaction system on the other hand; the antimony source is used to provide the doping element Sb.

[0066] The present application allows a suspension of a ferromanganese phosphate precursor to react with an iron source solution, an antimony source solution, and a phosphorus source solution in an oxidizing atmosphere. On the one hand, the ferrous ions can be oxidized to form ferric phosphate precipitates; on the other hand, the antimony source can be oxidized (for example, antimony trichloride is converted into antimony trioxide), thereby better precipitating antimony.

[0067] As a reference, the oxidizing atmosphere may be provided by ozone and / or oxygen, preferably by ozone, to ensure that Fe 2+ Can be completely oxidized to Fe 3+ , so that it forms iron phosphate precipitation.

[0068] Specifically, the suspension of ferromanganese phosphate precursor, iron source solution, antimony source solution and phosphorus source solution can be added into the reaction tank at the same time, and ozone gas is continuously introduced into the bottom of the mixed solution, and the mixture is continuously stirred vigorously.

[0069] In the present application, the suspension of the ferromanganese phosphate precursor and the iron source solution, the antimony source solution and the phosphorus source solution can be reacted together for 8-12h (such as 8h, 9h, 10h, 11h or 12h, etc., preferably 10h) at a pH of 1.8-2.2 (such as 1.8, 1.9, 2.0, 2.1 or 2.2, etc., preferably 2.0) and a temperature of 45-55°C (such as 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C or 55°C, etc., preferably 50°C).

[0070] It should be noted that if the pH value during the reaction is lower than 1.8, iron phosphate may not precipitate easily; if it is higher than 2.2, iron hydroxide may be produced easily.

[0071] After the modified lithium manganese iron phosphate precursor slurry is obtained, the slurry is subjected to conventional filter pressing and washing.

[0072] The subsequent drying can be carried out at 90-110° C. (such as 90° C., 95° C., 100° C., 105° C. or 110° C., etc., preferably 100° C.) to obtain a dried filter cake.

[0073] Further, the dried filter cake is sintered in an oxygen atmosphere at 480-520°C (such as 480°C, 485°C, 490°C, 495°C, 500°C, 505°C, 510°C, 515°C or 520°C, etc., preferably 500°C) for 5-7h (such as 5h, 5.5h, 6h, 6.5h or 7h, etc., preferably 6h) to obtain a modified lithium manganese iron phosphate precursor.

[0074] In addition, the present application also provides a modified lithium iron manganese phosphate positive electrode material, whose precursor is the above-mentioned modified lithium iron manganese phosphate precursor.

[0075] Accordingly, the present application also provides a method for preparing the modified lithium manganese iron phosphate positive electrode material, which may include the following steps:

[0076] The mixture of the modified lithium iron manganese phosphate precursor, the lithium source and the carbon source is sintered.

[0077] The lithium source may include at least one of lithium carbonate and lithium hydroxide.

[0078] The molar ratio of the metal element in the modified lithium iron manganese phosphate precursor to the lithium element in the lithium source can be 1:1.15-1.25, such as 1:1.15, 1:1.18, 1:1.2, 1:1.22 or 1:1.25, or any other value within the range of 1:1.15-1.25, preferably 1:1.2.

[0079] The carbon source may be a high molecular weight carbon-containing organic matter, for example, may include at least one of glucose, sucrose and alcohol.

[0080] The mass of the carbon source may be 4-6% of the modified lithium manganese iron phosphate precursor, such as 4%, 4.5%, 5%, 5.5% or 6%, etc., or any other value within the range of 4-6%.

[0081] The above-mentioned carbon source is mainly used to reduce ferromanganese phosphate to form lithium ferromanganese phosphate during the preparation process of the positive electrode material.

[0082] For reference, the modified lithium manganese iron phosphate precursor, the lithium source and the carbon source can be mixed by ball milling, and an appropriate amount of ethanol is added during the ball milling process. The ball milling time can be 4-6 hours (such as 5 hours).

[0083] For reference, a mixture of a modified lithium manganese iron phosphate precursor, a lithium source and a carbon source can be sintered in a nitrogen atmosphere at 580-620°C (such as 580°C, 585°C, 590°C, 595°C, 600°C, 605°C, 610°C, 615°C or 620°C, etc., preferably 600°C) for 6-10h (such as 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, etc., preferably 8h).

[0084] In addition, the present application also provides a battery, the raw materials for preparing the battery include the above-mentioned modified lithium manganese iron phosphate positive electrode material.

[0085] The battery has high conductivity and capacity retention rate.

[0086] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0087] Example 1

[0088] This embodiment provides a modified lithium manganese iron phosphate positive electrode material, which is prepared by the following method:

[0089] S1: preparing a manganese iron phosphate precursor whose surface is coated with Sb-doped iron phosphate.

[0090] S11: Add 100 g of ferromanganese phosphate precursor to an appropriate amount (100 mL) of the first solvent (anhydrous ethanol), and stir evenly to obtain a suspension A;

[0091] S12: Weigh a sufficient amount of FeSO4 and dissolve it in a second solvent (mixed with 20 mL of ethylene glycol and 80 mL of deionized water) at room temperature to prepare 100 mL of 0.2 mol / L solution B;

[0092] Weigh a sufficient amount of SbCl3 powder and dissolve it in a second solvent (mixed with 20 mL of ethylene glycol and 80 mL of deionized water) at room temperature to prepare 100 mL of 0.002 mol / L solution C;

[0093] Prepare 0.2 mol / L diammonium phosphate solution D in 100 mL of deionized water.

[0094] S13: The suspension A, solution B, solution C and solution D are added into a reaction tank at the same time, and ozone gas is continuously introduced into the bottom of the mixed solution, and the mixture is continuously stirred vigorously. The pH value of the reaction is controlled to be 2.0, and the mixture is reacted at 50° C. for 10 hours to obtain a ferromanganese phosphate precursor slurry with Sb-doped ferrophosphate coated on the surface;

[0095] S14: The above-mentioned ferromanganese phosphate precursor slurry is filtered and washed, and the filter cake is dried at 100° C., and then calcined at 500° C. for 6 hours under an oxygen atmosphere to obtain a ferromanganese phosphate precursor material with Sb-doped iron phosphate coated on the surface.

[0096] S2: Prepare a lithium manganese iron phosphate positive electrode material with a surface coated with Sb-doped iron phosphate.

[0097] After the metal elements in the modified lithium iron manganese phosphate precursor and the lithium elements in the lithium source (lithium carbonate) are mixed evenly at a molar ratio of 1:1.2, 5% of the mass of the modified lithium iron manganese phosphate precursor is added as a carbon source, and an appropriate amount of ethanol is added for ball milling for 5 hours; then placed in a nitrogen atmosphere, calcined at 600°C for 8 hours, and a lithium iron manganese phosphate positive electrode material with a surface coated with Sb-doped lithium iron phosphate coating is obtained. The mass of lithium iron phosphate in the coating layer is 1g, and the mass of Sb is 0.01g.

[0098] The SEM image of the lithium manganese iron phosphate positive electrode material with the Sb-doped lithium iron phosphate coating film on the surface is as follows: Figure 1 shown.

[0099] Example 2

[0100] This embodiment provides a modified lithium manganese iron phosphate positive electrode material, which is prepared by the following method:

[0101] S1: preparing a manganese iron phosphate precursor whose surface is coated with Sb-doped iron phosphate.

[0102] S11: Add 100 g of ferromanganese phosphate precursor to an appropriate amount (80 mL) of the first solvent (anhydrous ethanol), and stir evenly to obtain a suspension A;

[0103] S12: Weigh a sufficient amount of Fe(NO3)2 and dissolve it in a second solvent (mixed with 25 mL of ethylene glycol and 75 mL of deionized water) at room temperature to prepare 100 mL of 0.066 mol / L solution B;

[0104] Weigh a sufficient amount of Sb(NO3)3 powder and dissolve it in a second solvent (mixed with 25 mL of ethylene glycol and 75 mL of deionized water) at room temperature to prepare 100 mL of 0.00044 mol / L solution C;

[0105] Prepare 0.0.066 mol / L ammonium phosphate solution D in 100 mL of deionized water.

[0106] S13: The suspension A, solution B, solution C and solution D are added to a reaction tank at the same time, and ozone gas is continuously introduced into the bottom of the mixed solution, and the mixture is continuously stirred vigorously. The pH value of the reaction is controlled to be 1.8, and the mixture is reacted at 45° C. for 12 hours to obtain a ferromanganese phosphate precursor slurry with Sb-doped iron phosphate coated on the surface;

[0107] S14: The above-mentioned ferromanganese phosphate precursor slurry is filtered and washed, and the filter cake is dried at 90° C., and then calcined at 480° C. for 7 hours under an oxygen atmosphere to obtain a ferromanganese phosphate precursor material with Sb-doped iron phosphate coated on the surface.

[0108] S2: Prepare a lithium manganese iron phosphate positive electrode material with a surface coated with Sb-doped iron phosphate.

[0109] After the metal elements in the modified lithium iron phosphate precursor and the lithium elements in the lithium source (lithium carbonate) are mixed evenly in a molar ratio of 1:1.15, 4% sucrose of the modified lithium iron phosphate precursor is added as a carbon source, and an appropriate amount of ethanol is added for ball milling for 5 hours; then, it is placed in a nitrogen atmosphere and calcined at 580°C for 10 hours to obtain a lithium iron phosphate positive electrode material with a Sb-doped lithium iron phosphate coating on the surface.

[0110] Example 3

[0111] This embodiment provides a modified lithium manganese iron phosphate positive electrode material, which is prepared by the following method:

[0112] S1: preparing a manganese iron phosphate precursor whose surface is coated with Sb-doped iron phosphate.

[0113] S11: Add 100 g of ferromanganese phosphate precursor to an appropriate amount (50 mL) of the first solvent (anhydrous ethanol), and stir evenly to obtain a suspension A;

[0114] S12: Weigh a sufficient amount of FeSO4 and dissolve it in a second solvent (mixed with 18 mL of ethylene glycol and 82 mL of deionized water) at room temperature to prepare 100 mL of 0.33 mol / L solution B;

[0115] Weigh a sufficient amount of SbCl3 powder and dissolve it in a second solvent (mixed with 18 mL of ethylene glycol and 82 mL of deionized water) at room temperature to prepare 100 mL of 0.0044 mol / L solution C;

[0116] Prepare 0.33 mol / L diammonium phosphate solution D in 100 mL of deionized water.

[0117] S13: The suspension A, solution B, solution C and solution D are added to a reaction tank at the same time, and ozone gas is continuously introduced into the bottom of the mixed solution, and the mixture is continuously stirred vigorously. The pH value of the reaction is controlled to be 2.2, and the mixture is reacted at 55° C. for 8 hours to obtain a ferromanganese phosphate precursor slurry with Sb-doped iron phosphate coated on the surface;

[0118] S14: filter the above-mentioned ferromanganese phosphate precursor slurry, wash it, dry the filter cake at 110° C., and then calcine it at 520° C. for 5 hours in an oxygen atmosphere to obtain a ferromanganese phosphate precursor material with Sb-doped lithium iron phosphate coated on the surface.

[0119] S2: Prepare a lithium manganese iron phosphate positive electrode material with a surface coated with Sb-doped iron phosphate.

[0120] After the metal elements in the modified lithium iron manganese phosphate precursor and the lithium elements in the lithium source (lithium carbonate) are mixed evenly in a molar ratio of 1:1.25, 6% glucose of the mass of the modified lithium iron manganese phosphate precursor is added as a carbon source, and an appropriate amount of ethanol is added for ball milling for 5 hours; then, it is placed in a nitrogen atmosphere and calcined at 620°C for 6 hours to obtain a lithium iron manganese phosphate positive electrode material with a surface coated with an Sb-doped iron phosphate coating.

[0121] Example 4

[0122] The difference between this embodiment and embodiment 1 is that in S13, oxygen is used instead of ozone.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is:

[0125] In S13, only suspension A, solution B and solution D are added to the reaction tank at the same time, and ozone gas is continuously introduced into the bottom of the mixed solution. Vigorous stirring is continuously continued, and the reaction pH value is controlled to be 2.2. The reaction is carried out at 55°C for 8 hours to obtain a manganese iron phosphate precursor slurry with surface coated with iron phosphate.

[0126] That is, the coating layer of the modified lithium manganese iron phosphate precursor is not doped with Sb.

[0127] Comparative Example 2

[0128] The difference between this comparative example and Example 1 is:

[0129] Directly use the manganese iron phosphate precursor to prepare manganese iron phosphate lithium positive electrode material according to the process and conditions of S2.

[0130] That is, the manganese iron phosphate precursor is not modified, and its surface is not coated with Sb-doped iron phosphate.

[0131] Comparative Example 3

[0132] The difference between this comparative example and Example 1 is:

[0133] The metal elements in the precursor and the lithium elements in the lithium source (lithium carbonate) are directly mixed in a molar ratio of 1:1.2, and then 5% of the precursor mass of glucose is added as a carbon source, and 1.2g of boron oxide is added, and an appropriate amount of ethanol is added for ball milling for 5h; then it is placed in a nitrogen atmosphere and calcined at 600°C for 8h to obtain a lithium manganese iron phosphate positive electrode material with a surface coated with boron oxide.

[0134] Comparative Example 4

[0135] The difference between this embodiment and embodiment 1 is that the mass of lithium iron phosphate in the coating layer is 10 g, and the mass of Sb is 0.01 g.

[0136] Comparative Example 5

[0137] The difference between this comparative example and Example 1 is that the mass of Sb in the coating layer is 1 g.

[0138] Test example

[0139] The lithium manganese iron phosphate positive electrode material particles provided in the above examples 1-4 and comparative examples 1-5 are used to assemble a battery in the following manner:

[0140] Preparation of positive electrode sheet: The positive electrode material, conductive black and polyvinylidene fluoride prepared above were weighed respectively in a mass ratio of 8:1:1 and mixed with an appropriate amount of N-methylpyrrolidone; homogenized with an ultrafine homogenizer for 25 minutes to obtain a mixed positive electrode material slurry; the positive electrode material slurry was evenly coated on an aluminum foil (thickness of 170 μm) with an automatic coating and drying machine; the coated aluminum foil was placed in a vacuum oven and dried for 10 hours; taken out and sliced ​​to obtain a positive electrode material electrode sheet, and then the electrode sheet was pressed with an electric tablet press.

[0141] Assemble the battery: Use metal lithium sheet as the counter electrode, polyethylene microporous membrane as the diaphragm, lithium hexafluorophosphate as the electrolyte, and the synthesized and pressed material electrode sheet as the positive electrode sheet. The battery is assembled in an argon-filled glove box in the same way as CR2025 button battery to complete the battery production.

[0142] The resistivity test of the prepared positive electrode material was carried out using a semiconductor powder resistivity tester. First, a certain amount of the powder to be tested was placed in the silo of the resistivity tester until it was full, and the pressure was adjusted to 20.0kg to test its 20kg resistivity; and the cycle performance of the positive electrode material was tested at 25℃ (1C / 1C, 2.0~4.3V), and the results are shown in Table 1.

[0143] Table 1 Test results

[0144]

[0145] As can be seen from Table 1, the doping and coating methods in Examples 1-4, in which antimony ions are doped into the iron phosphate coating layer, have better conductivity and higher capacity retention and cycle performance than the undoped and uncoated positive electrode materials and the undoped and uncoated positive electrode materials in the comparative examples and the positive electrode materials after the preparation conditions are changed. Among Examples 1-4, Example 1 has the best effect.

[0146] In summary, the present invention can improve the conductivity of the material by coating with iron phosphate, and can inhibit the Mn 2+ The modified lithium manganese iron phosphate positive electrode material prepared from the modified lithium manganese iron phosphate precursor has a lower resistivity and a higher capacity retention rate. The preparation methods of the modified lithium manganese iron phosphate positive electrode material and its precursor are relatively simple and easy to operate.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modified lithium iron manganese phosphate precursor, characterized in that: The modified lithium iron manganese phosphate precursor is obtained by coating the surface of the iron manganese phosphate precursor with iron phosphate doped with Sb; The preparation of the modified lithium iron manganese phosphate precursor comprises the following steps: The suspension of the ferromanganese phosphate precursor is reacted with an iron source solution, an antimony source solution and a phosphorus source solution under an oxidizing atmosphere to obtain a modified lithium ferromanganese phosphate precursor slurry; and then pressure filtering, washing, drying and sintering are performed in sequence to obtain a modified lithium ferromanganese phosphate precursor; The suspension of the ferromanganese phosphate precursor is reacted with the iron source solution, the antimony source solution and the phosphorus source solution at a pH of 1.8-2.2 and a temperature of 45-55° C. for 8-12 hours; The volume ratio of the ferromanganese phosphate precursor to the iron source solution, the antimony source solution and the phosphorus source solution is 100g:80-120mL:80-120mL:80-120mL; wherein the concentration of the iron source solution is 0.066-0.33mol / L, the concentration of the antimony source is 0.00044-0.0044mol / L, and the concentration of the phosphorus source solution is 0.066-0.33mol / L.

2. The modified lithium iron manganese phosphate precursor according to claim 1, characterized in that: The surface of every 100g of the ferromanganese phosphate precursor is coated with 1-5g of ferrophosphate doped with Sb, and the doping amount of Sb in the ferrophosphate is 0.01-0.1g.

3. The method for preparing the modified lithium iron manganese phosphate precursor according to claim 1 or 2, characterized in that: The following steps are involved: The suspension of the ferromanganese phosphate precursor is reacted with an iron source solution, an antimony source solution and a phosphorus source solution under an oxidizing atmosphere to obtain a modified lithium ferromanganese phosphate precursor slurry; and then pressure filtering, washing, drying and sintering are performed in sequence to obtain a modified lithium ferromanganese phosphate precursor; The suspension of the ferromanganese phosphate precursor reacts with the iron source solution, the antimony source solution and the phosphorus source solution at a pH of 1.8-2.2 and a temperature of 45-55° C. for 8-12 hours.

4. The preparation method according to claim 3, characterized in that: The suspension of the ferromanganese phosphate precursor is obtained by mixing the ferromanganese phosphate precursor with a first solvent; Wherein, the first solvent includes at least one of anhydrous ethanol, propanol, isopropanol and butanol.

5. The preparation method according to claim 4, characterized in that: The iron source solution is obtained by mixing an iron source and a second solvent; And / or, the antimony source solution is obtained by mixing an antimony source with a second solvent; And / or, the phosphorus source solution is obtained by mixing a phosphorus source and a third solvent; Wherein, the second solvent includes ethylene glycol and water; and the third solvent includes water.

6. The preparation method according to claim 5, characterized in that: The volume ratio of ethylene glycol to water in the second solvent is 1:3-5.

7. The preparation method according to claim 5, characterized in that: The iron source includes at least one of ferrous sulfate and ferrous nitrate, and / or the antimony source includes at least one of antimony trichloride and antimony nitrate; and / or the phosphorus source includes at least one of ammonium dihydrogen phosphate and ammonium phosphate.

8. The preparation method according to claim 3, characterized in that: The oxidizing atmosphere is provided by ozone and / or oxygen.

9. The preparation method according to claim 3, characterized in that: Drying is carried out at 90-110°C; And / or, the sintering is performed in an oxygen atmosphere at 480-520° C. for 5-7 hours.

10. A modified lithium manganese iron phosphate positive electrode material, characterized in that: The precursor of the modified lithium iron manganese phosphate positive electrode material is the modified lithium iron manganese phosphate precursor according to claim 1 or 2.

11. The method for preparing the modified lithium manganese iron phosphate positive electrode material according to claim 10, characterized in that: The following steps are involved: The mixture of the modified lithium manganese iron phosphate precursor, the lithium source and the carbon source is sintered.

12. The preparation method according to claim 11, characterized in that: The lithium source includes at least one of lithium carbonate and lithium hydroxide.

13. The preparation method according to claim 11, characterized in that: The molar ratio of the metal element in the modified lithium manganese iron phosphate precursor to the lithium element in the lithium source is 1:1.15-1.

25.

14. The preparation method according to claim 11, characterized in that: The carbon source is high molecular carbon-containing organic matter.

15. The preparation method according to claim 11, characterized in that: The carbon source includes at least one of glucose, sucrose and alcohol.

16. The preparation method according to claim 11, characterized in that: The mass of the carbon source is 4-6% of the modified lithium manganese iron phosphate precursor.

17. The preparation method according to claim 11, characterized in that: The modified lithium manganese iron phosphate precursor, the lithium source and the carbon source are mixed by ball milling.

18. The preparation method according to claim 11, characterized in that: The mixture of the modified lithium manganese iron phosphate precursor, the lithium source and the carbon source is sintered in a nitrogen atmosphere at 580-620° C. for 6-10 hours.

19. A battery, characterized in that: The raw materials for preparing the battery include the modified lithium manganese iron phosphate positive electrode material as described in claim 10.

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