Lithium iron manganese phosphate positive electrode material, preparation method and application thereof

Abstract

The application relates to the field of lithium batteries, and discloses a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof. i (Fe x M y Mn z )PO4 / C; wherein 0.15<=x<=0.45, 0

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium batteries, in particular to a lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, lithium iron phosphate as a positive electrode material of lithium ion battery is widely used in the field of power batteries due to its high safety, low cost and good cycle performance. However, its low voltage platform (3.4V) makes its energy density too low to meet the market demand for high endurance power batteries.

[0003] Lithium manganese iron phosphate is a new type of phosphate lithium ion battery positive electrode material formed by replacing a certain proportion of iron in lithium iron phosphate with manganese. It has the same structure as lithium iron phosphate, but has a higher voltage platform (4.1V) and a higher energy density, which is theoretically 20% higher than lithium iron phosphate under the same conditions. Its production process can be largely compatible with lithium iron phosphate, and the production cost is close to that of lithium iron phosphate, so it has attracted widespread attention in the market.

[0004] At present, the preparation methods of lithium manganese iron phosphate mainly include solid phase method and hydrothermal method. The synthesis of lithium manganese iron phosphate by hydrothermal method needs to be carried out in a high temperature and high pressure environment, which requires high equipment and has high industrial application cost. At present, the synthesis of lithium manganese iron phosphate by solid phase method is mainly prepared by pre-mixing, sand milling, spray drying and sintering of manganese source, iron source, phosphorus source, lithium source and carbon source. However, this simple mixing cannot achieve uniform mixing of manganese and iron at the atomic level, and the prepared lithium manganese iron phosphate has poor charge and discharge capacity and constant voltage platform.

[0005] To improve the problem of uniform distribution of manganese and iron, the current solution is to obtain manganese iron salt such as manganese iron phosphate and manganese iron oxalate by co-precipitation. In the above process, due to the removal of oxalate and crystal water, the carbon coating property of lithium manganese iron phosphate is poor, and the lithium and phosphorus segregation causes the prepared lithium manganese iron phosphate to have poor electrical performance. SUMMARY

[0006] In order to overcome the problems of poor carbon coating property and lithium and phosphorus segregation of the existing lithium manganese iron phosphate positive electrode material, a lithium manganese iron phosphate positive electrode material and a preparation method and application thereof are provided. The carbon coating property of the lithium manganese iron phosphate positive electrode material is good, the distribution of phosphorus element is uniform, and the prepared battery has good electrical performance.

[0007] In order to achieve the above purpose, the first aspect of the present application provides a lithium manganese iron phosphate positive electrode material, the expression of the positive electrode material is Li i (Fe x M y Mn z )PO4 / C;

[0008] wherein 0.15≤x≤0.45, 0<y≤0.03, 0.52≤z≤0.85, 0.98≤i≤1.05;

[0009] M is selected from at least one of Mg, Ti, V, Ni, Zn, Cu, Zr and Nb;

[0010] The coefficient of variation of the content of phosphorus element in the positive electrode material is ≤0.045.

[0011] The second aspect of the present application provides a method for preparing the positive electrode material provided in the first aspect of the present application, and the method comprises the following steps:

[0012] (1) obtaining a mixed solution by mixing a manganese source, an iron source and a M source in the presence of a first solvent, and then mixing with oxalic acid and / or oxalate, and separating a precipitate;

[0013] (2) performing a first heat treatment on the precipitate under a protective atmosphere to obtain a manganese-iron oxide doped with M element;

[0014] (3) mixing the manganese-iron oxide with a lithium source, a phosphorus source and a carbon source in the presence of a second non-aqueous solvent to obtain a slurry, and then grinding and drying to obtain a positive electrode material precursor;

[0015] (4) performing a second heat treatment on the positive electrode material precursor under a protective atmosphere to obtain a manganese iron lithium phosphate positive electrode material.

[0016] The third aspect of the present application provides an application of the positive electrode material provided in the first aspect of the present application or the positive electrode material prepared by the method provided in the second aspect of the present application in a battery.

[0017] The beneficial technical effects of the present application are as follows:

[0018] (1) The positive electrode material provided in the present application has a uniform distribution of each element, especially lithium and phosphorus element, and good carbon coating property, and the battery prepared therefrom has excellent charge-discharge performance and voltage platform.

[0019] (2) The method for preparing the manganese iron lithium phosphate positive electrode material provided in the present application uses oxalic acid (salt) as a precipitant, co-precipitates the manganese source, the iron source and the M source, and performs a heat treatment on the precipitate to obtain a manganese-iron oxide with a uniform distribution of metal elements; then the manganese-iron oxide is mixed with a lithium source, a phosphorus source and a carbon source in a non-aqueous solvent by grinding, to obtain a positive electrode material precursor, and a heat treatment is performed on the precursor, which can avoid gas production of oxalic acid and segregation of the lithium source and the phosphorus source, so that each element, especially lithium and phosphorus element, is uniformly distributed, and the carbon coating property is good.

[0020] Further, by adding the antioxidant, the change of valence of manganese and iron can be avoided in the preparation of the positive electrode material, the generation of trivalent manganese and iron is reduced, and the charge-discharge performance of the battery made of the positive electrode material is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 XRD spectrum of the manganese-iron oxide obtained in Example 1 of the present application;

[0022] Figure 2 SEM image of the manganese-iron oxide obtained in Example 1 of the present application;

[0023] Figure 3 XRD spectrum of the lithium manganese iron phosphate positive electrode material obtained in Example 1 of the present application;

[0024] Figure 4 SEM image of the lithium manganese iron phosphate positive electrode material obtained in Example 1 of the present application;

[0025] Figure 5 SEM image of the lithium manganese iron phosphate positive electrode material obtained in Comparative Example 1 of the present application;

[0026] Figure 6 EDS line scan spectrum of the phosphorus element of the lithium manganese iron phosphate positive electrode material obtained in Example 1 of the present application;

[0027] Figure 7 EDS line scan spectrum of the phosphorus element of the lithium manganese iron phosphate positive electrode material obtained in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values claimed herein are not to be understood as being limited to the exact values recited as implicitly included within the range. Ranges can be expressed as from about one particular value to about another; however, when such a range is recited, it is to be understood that the end points of the range are included in the range, just as if the range were expressed as from the one particular value to the other particular value. It is also to be understood that each individual value within a range is included as if it were individually recited.

[0029] The first aspect of the present application provides a lithium manganese iron phosphate positive electrode material, the expression of the positive electrode material is Li i (Fe x M y Mn z )PO4 / C;

[0030] wherein 0.15≤x≤0.45, 0<y≤0.03, 0.52≤z≤0.85, 0.98≤i≤1.05;

[0031] M is selected from at least one of Mg, Ti, V, Ni, Zn, Cu, Zr and Nb;

[0032] The coefficient of variation of the content of phosphorus element in the positive electrode material is less than or equal to 0.045.

[0033] In the present application, the values of x, y, z and i can be determined by inductively coupled plasma elemental analysis (ICP).

[0034] The X-ray energy spectrum analysis (EDS) signal intensity of the phosphorus element at different positions in the positive electrode material is X i , X i The average value of the EDS signal intensity of the phosphorus element is μ, and the standard deviation is σ, the coefficient of variation CV of the EDS signal intensity of the phosphorus element in the positive electrode material is σ / μ, and the coefficient of variation of the content of phosphorus element is represented by the coefficient of variation of the EDS signal intensity of the phosphorus element.

[0035] The present application provides a lithium iron manganese phosphate positive electrode material, wherein each element, especially the phosphorus element, is uniformly distributed, and the carbon coating is good, so that the prepared battery has excellent charge-discharge performance and voltage platform.

[0036] According to a preferred embodiment of the present application, 0.15≤x≤0.35, 0<y≤0.02, 0.63≤z≤0.85, and 1≤i≤1.02.

[0037] In the present application, when the composition of the positive electrode material is within the above range, the charge-discharge performance and voltage platform of the prepared battery can be further improved.

[0038] According to the present application, preferably, M is selected from at least one of Mg, Ti, Ni and Zn.

[0039] In the present application, the above-mentioned M element can further improve the charge-discharge performance of the battery made of the positive electrode material.

[0040] According to the present application, preferably, the coefficient of variation of the content of phosphorus element in the positive electrode material is less than or equal to 0.035%.

[0041] In the present application, when the coefficient of variation of the content of phosphorus element is within the above range, the charge-discharge performance of the positive electrode material can be further improved.

[0042] According to a preferred embodiment of the present application, the content of carbon element in the positive electrode material is 1.4-2.5wt%.

[0043] In the present application, when the content of carbon element in the positive electrode material is within the above range, the conductivity of the material can be further improved.

[0044] More preferably, the content of carbon element is 1.5-1.9wt%.

[0045] According to the application, preferably, the median particle size of the positive electrode material is 50-600 nm.

[0046] In the application, when the median particle size of the positive electrode material is within the above range, the compaction density of the positive electrode material can be further improved, and the conductivity is improved.

[0047] More preferably, the median particle size of the positive electrode material is 50-250 nm.

[0048] The second aspect of the application provides a method for preparing the positive electrode material provided by the first aspect of the application, and the method comprises the following steps:

[0049] (1) obtaining a mixed solution by mixing a manganese source, an iron source and an M source in the presence of a first solvent, and then mixing with oxalic acid and / or oxalate, and separating the precipitate;

[0050] (2) performing first heat treatment on the precipitate in a protective atmosphere to obtain manganese-iron oxide doped with M elements;

[0051] (3) obtaining a slurry by mixing the manganese-iron oxide with a lithium source, a phosphorus source and a carbon source in the presence of a second non-aqueous solvent, and obtaining a positive electrode material precursor after grinding and drying;

[0052] (4) performing second heat treatment on the positive electrode material precursor in a protective atmosphere to obtain a manganese-iron lithium phosphate positive electrode material.

[0053] The method for preparing the manganese-iron lithium phosphate positive electrode material provided by the application uses oxalic acid (salt) as a precipitant, co-precipitates the manganese source, the iron source and the M source, and performs heat treatment on the precipitate to obtain manganese-iron oxide doped with M elements with uniform distribution of metal elements; then the manganese-iron oxide is mixed with a lithium source, a phosphorus source and a carbon source in a non-aqueous solvent by grinding to obtain a positive electrode material precursor, and heat treatment is performed on the precursor, which can avoid gas production of oxalic acid and segregation of the lithium source and the phosphorus source, and the positive electrode material obtained has uniform distribution of elements, especially lithium and phosphorus, good carbon coating, and the battery prepared has excellent charge-discharge performance and voltage platform.

[0054] The protective atmosphere is not particularly limited in the application, and the protective atmosphere can be nitrogen and / or argon.

[0055] The manganese source, the iron source and the M source are not particularly limited in the application, and can be routinely selected by those skilled in the art. According to one specific embodiment of the application, the manganese source is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride and manganese acetate.

[0056] The iron source is selected from at least one of ferrous sulfate, ferrous chloride and ferrous acetate.

[0057] The M source is selected from soluble salts of M, such as soluble nitrate, sulfate and acetate.

[0058] The present application does not particularly limit the specific type of oxalate, and preferably is ammonium oxalate.

[0059] The present application does not particularly limit the specific amount of oxalic acid and / or oxalate, and the person skilled in the art can make a routine selection, as long as the metal ions can be sufficiently precipitated. According to one specific embodiment of the present application, the molar ratio of the total amount of metal elements in the manganese source, the iron source and the M source to oxalic acid (salt) in terms of oxalate is 1:1-1.05.

[0060] According to the present application, preferably, the total concentration of metal ions in the mixed solution is 0.2-2 mol / L.

[0061] In the present application, when the total concentration of metal ions in the mixed solution is within the above range, the metal ions can be more uniformly precipitated.

[0062] More preferably, the total concentration of metal ions in the mixed solution is 0.2-1 mol / L.

[0063] According to the present application, preferably, the mixed solution further comprises an antioxidant.

[0064] In the present application, by adding an antioxidant, the conversion of the valence of manganese and iron can be avoided during the preparation of the positive electrode material, and the generation of trivalent manganese and iron is reduced, thereby further improving the charge-discharge performance of the battery made of the positive electrode material.

[0065] The present application does not particularly limit the specific type and amount of the antioxidant, and the person skilled in the art can make a routine selection.

[0066] According to one specific embodiment of the present application, the antioxidant is selected from at least one of ascorbic acid, citric acid and tartaric acid.

[0067] The amount of the antioxidant is 0.1-0.4% of the total mass of the manganese source and the iron source.

[0068] In the present application, the manganese iron oxalate can be subjected to a first drying before the first heat treatment. According to one specific embodiment of the present application, the first drying is performed by heating to 90-120℃ under a protective atmosphere for 2-4h.

[0069] According to one preferred embodiment of the present application, the temperature of the first heat treatment is 500-700℃, and the time is 5-12h.

[0070] In the present application, when the conditions of the first heat treatment are within the above range, the manganese iron oxalate can be fully converted into manganese iron oxide, while avoiding the performance decline of the positive electrode material due to particle aggregation.

[0071] More preferably, the temperature of the first heat treatment is 550-600℃, and the time is 8-10h.

[0072] The present application does not particularly limit the specific types of the lithium source, the phosphorus source and the carbon source, which can be routinely selected by those skilled in the art. According to one specific embodiment of the present application, the lithium source is selected from at least one of lithium oxalate, lithium hydroxide, lithium carbonate, lithium acetate and lithium dihydrogen phosphate.

[0073] The phosphorus source is selected from at least one of ammonium dihydrogen phosphate, phosphoric acid and lithium dihydrogen phosphate.

[0074] The carbon source is selected from at least one of glucose, galactose, lactose, sucrose, caramel, phenolic resin, polyethylene glycol and polyvinyl alcohol.

[0075] The present application does not particularly limit the specific types of the solvent, which can be routinely selected by those skilled in the art. According to one specific embodiment of the present application, the first solvent is water.

[0076] The second non-aqueous solvent is N-methyl pyrrolidone and / or anhydrous ethanol.

[0077] According to one preferred embodiment of the present application, in step (1), the molar ratio of the manganese source, the iron source and the M source, in terms of metal elements, satisfies n(Mn):n(Fe):n(M)=1-1.2:0.4-1:0.015-0.045.

[0078] In the present application, when the molar ratio of the manganese source, the iron source and the M source satisfies the above range, the electrical performance of the battery can be further improved.

[0079] More preferably, the molar ratio of the manganese source, the iron source and the M source satisfies n(Mn):n(Fe):n(M)=1.05-1.15:0.5-0.9:0.02-0.03.

[0080] According to the present application, preferably, in step (3), the molar ratio of the manganese iron oxide, the lithium source, the phosphorus source and the carbon source, in terms of metal elements and phosphorus elements and carbon elements, satisfies n(Li):n(Mn+Fe):n(P):n(C)=0.98-1.05:0.96-1:0.98-1.05:0.7-1.3.

[0081] In the present application, when the molar ratio of the manganese iron oxide, the lithium source, the phosphorus source and the carbon source satisfies the above range, the electrical performance of the battery can be further improved.

[0082] More preferably, the molar ratio of the manganese iron oxide, the lithium source, the phosphorus source and the carbon source satisfies n(Li):n(Mn+Fe):n(P):n(C)=1-1.02:0.98-1:1-1.05:0.8-1.

[0083] The present application does not particularly limit the solid content of the slurry, which can be routinely selected by those skilled in the art. According to one embodiment of the present application, the solid content of the slurry is 20-70wt%, more specifically 37-50wt%.

[0084] The present application does not particularly limit the specific way of the grinding, which can be routinely selected by those skilled in the art, for example, it can be ball milling or rod milling.

[0085] According to the present application, preferably, the median particle size of the positive electrode material precursor is 100-200nm.

[0086] In the present application, when the median particle size of the positive electrode material precursor is within the above range, the uniformity of the slurry and the crystallinity of the positive electrode material can be further improved.

[0087] More preferably, the median particle size of the positive electrode material precursor is 120-180nm.

[0088] According to one preferred embodiment of the present application, the temperature of the second heat treatment is 220-800℃, and the time is 4-12h.

[0089] More preferably, the second heat treatment adopts the programmed temperature rising method:

[0090] (1) rising the temperature to 220-350℃ at a rate of 1-5℃ / min, and keeping the temperature for 2-3h;

[0091] (2) continuing to rise the temperature to 450-650℃ at a rate of 1.5-2.5℃ / min, and keeping the temperature for 4-5h;

[0092] (3) continuing to rise the temperature to 650-800℃ at a rate of 1-1.5℃ / min, and keeping the temperature for 7-12h.

[0093] In the present application, the second heat treatment adopts the programmed temperature rising method, which can further improve the crystallinity of the positive electrode material.

[0094] In the present application, the slurry can be subjected to a second drying before the second heat treatment. Preferably, the way of the second drying is spray drying, the inlet temperature is 300-400℃, and the outlet temperature is 180-220℃.

[0095] The third aspect of the present application provides application of the positive electrode material provided by the first aspect of the present application or the positive electrode material prepared by the method provided by the second aspect of the present application in a battery.

[0096] The present application will be described in detail below through examples.

[0097] In the following examples, the content of each element (except for the carbon element) in the manganese iron oxalate, manganese iron oxide and positive electrode material is determined by inductively coupled plasma elemental analysis (ICP);

[0098] The valence of manganese and iron is determined by X-ray diffraction (XRD);

[0099] The number of water molecules of the manganese iron oxalate is determined by thermal gravimetric analysis;

[0100] The carbon content in the positive electrode material is determined by a carbon-sulfur tester.

[0101] The particle size is tested by a laser particle size analyzer according to GB / T 19077-2016;

[0102] The content of phosphorus element at different positions of the positive electrode material is determined by X-ray energy spectrum analysis (EDS) line scanning.

[0103] Unless otherwise specified, all reagents and raw materials are commercially available.

[0104] Example 1

[0105] (1) MnSO4·H2O 19.601 kg (purity 99.4 wt%, same below), battery grade FeSO4·7H2O 11.716 kg (purity 99.2 wt%, same below), magnesium sulfate 180.19 g, titania sulfate 165.31 g, zinc sulfate 71.86 g, pure water 300 kg, ascorbic acid 95.07 g were weighed, heated and the temperature was maintained at 40℃, nitrogen was introduced as protective gas, and a mixed solution was obtained by stirring. Battery grade ammonium oxalate 18.945 kg and pure water 200 kg were mixed, then added to the above mixed solution, and a co-precipitation reaction was carried out at 40℃, and after washing and drying, a manganese iron oxalate with doped elements was obtained.

[0106] The chemical composition of the above manganese iron oxalate is Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 C2O4·2H2O.

[0107] (2) Put the above manganese iron oxalate into a graphite box and transfer into a nitrogen gas box furnace, first heat up to 150℃ at a speed of 5℃ / min, keep for 3h to remove crystal water, then heat up to 550℃ at a speed of 3℃ / min, keep for 10h to obtain manganese iron oxide with doped elements.

[0108] The chemical composition of the above manganese iron oxide is (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )O.

[0109] (3) Take 237.639g of the above manganese iron oxide powder, add N-methyl pyrrolidone 615.867g, under stirring add battery grade lithium dihydrogen phosphate 310.052g, lithium carbonate 2.222g, polyethylene glycol 65.954g to obtain a positive electrode material precursor slurry, and the solid content of the slurry is 50wt% calculated by the amount of feed.

[0110] Use an organic sand mill to sand the slurry, and the median particle size of the particles in the sanded slurry is 136nm measured by a laser particle size analyzer.

[0111] Spray dry the above slurry at an inlet temperature of 380℃ and an outlet temperature of 200℃ to obtain a positive electrode material precursor.

[0112] (4) Transfer the above positive electrode material precursor into a gas furnace, first heat up to 350℃ at a speed of 2℃ / min under nitrogen protection atmosphere, keep for 3h, then heat up to 600℃ at a speed of 1.5℃ / min, keep for 4h, then heat up to 700℃ at a speed of 1℃ / min, keep for 10h, and then naturally cool and gasify to obtain a lithium manganese iron phosphate positive electrode material.

[0113] The chemical composition of the above positive electrode material is Li 1.01 (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )PO4 / C, wherein the carbon content is 1.85wt%.

[0114] Example 2

[0115] (1) Take battery-grade manganese manganous sulfate 14.844 kg, battery-grade ferrous sulfate heptahydrate 11.009 kg, magnesium sulfate 145.99 g, titanyl sulfate 133.94 g, zinc sulfate 58.22 g, pure water 300 kg, ascorbic acid 76.750 g, heat and maintain the temperature at 40℃, and pass in nitrogen as protective gas, and stir to obtain a mixed solution. Take battery-grade ammonium oxalate 15.350 kg and pure water 200 kg, mix, and then add to the above mixed solution to carry out co-precipitation reaction, and after washing and drying, manganese iron oxalate with doped elements is obtained.

[0116] The chemical composition of the above manganese iron oxalate is Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.33 Mn 0.65 C2O4·2H2O.

[0117] (2) Put the above manganese iron oxalate into a graphite box and transfer into a nitrogen-passing box furnace, first heat to 150℃ at a rate of 5℃ / min and maintain for 3h to remove crystal water, and then heat to 550℃ at a rate of 3℃ / min and maintain for 10h to obtain manganese iron oxide with doped elements.

[0118] The chemical composition of the above manganese iron oxide is (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.33 Mn 0.65 )O.

[0119] (3) Take 253.482g of the above manganese iron oxide powder, add N-methyl pyrrolidone 659.258g, and under stirring, add battery-grade lithium dihydrogen phosphate 333.055g, lithium carbonate 2.37g, and polyethylene glycol 70.351g to obtain a positive electrode material precursor slurry, and by calculation of the feeding amount, the solid content of the slurry is 50wt%.

[0120] Use an organic sand mill to sand mill the slurry, and by a laser particle size instrument, the median particle size of the particles in the sand-milled slurry is 169 nm.

[0121] Spray dry the above slurry at an inlet temperature of 380℃ and an outlet temperature of 200℃ to obtain a positive electrode material precursor.

[0122] (4) Transfer the above positive electrode material precursor into a gas atmosphere furnace, first heat from room temperature to 350℃ at a rate of 2℃ / min and maintain for 3h, then heat to 600℃ at a rate of 1.5℃ / min and maintain for 4h, and then heat to 700℃ at a rate of 1℃ / min and maintain for 10h, and then naturally cool and gas crush to obtain a lithium manganese iron phosphate positive electrode material.

[0123] The chemical composition of the above positive electrode material is Li 1.01 (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.33 Mn 0.65 )PO4 / C, wherein the carbon content is 1.79wt%.

[0124] Example 3

[0125] (1) Take 18.650 kg of battery-grade manganese molybdate, 11.120 kg of battery-grade ferrous sulfate heptahydrate, 253.55 g of magnesium sulfate, 114.20 g of zinc sulfate, 300 kg of pure water, and 90.858 g of ascorbic acid, heat and maintain the temperature at 40℃, and pass nitrogen as a protective gas, and stir to obtain a mixed solution. Take 18.013 kg of battery-grade ammonium oxalate and 200 kg of pure water, mix them, and then add them to the above mixed solution to carry out a co-precipitation reaction, and after washing and drying, manganese iron oxalate with doped elements is obtained.

[0126] The chemical composition of the above manganese iron oxalate is Mg 0.015 Zn 0.005 Fe 0.28 Mn 0.7 C2O4·2H2O.

[0127] (2) Put the above manganese iron oxalate into a graphite box and transfer it into a nitrogen-passing box furnace, first heat it to 150℃ at a rate of 5℃ / min and keep it for 3h to remove the crystal water, and then heat it to 550℃ at a rate of 3℃ / min and keep it for 10h to obtain manganese iron oxide with doped elements.

[0128] The chemical composition of the above manganese iron oxide is (Mg 0.015 Zn 0.005 Fe 0.28 Mn 0.7 )O.

[0129] (3) Take 238.809 g of the above manganese iron oxide powder, add 743.013 g of N-methyl pyrrolidone, and under stirring, add 318.123 g of battery-grade lithium dihydrogen phosphate, 2.222 g of lithium carbonate, and 66.218 g of polyethylene glycol to obtain a positive electrode material precursor slurry. The solid content of the slurry is 50wt% as calculated by the amount of feed.

[0130] The slurry is sand milled using an organic sand mill, and the median particle size of the particles in the sand milled slurry is 179 nm as measured by a laser particle size analyzer.

[0131] The slurry is spray dried at an inlet temperature of 380℃ and an outlet temperature of 200℃ to obtain the positive electrode material precursor.

[0132] (4) The positive electrode material precursor is transferred into a gas atmosphere furnace, and is first heated at a rate of 2℃ / min from room temperature to 350℃ under nitrogen protection, and then heated at a rate of 1.5℃ / min to 600℃ for 4h, and then heated at a rate of 1℃ / min to 700℃ for 10h, and then naturally cooled and air-crushed to obtain the lithium manganese iron phosphate positive electrode material.

[0133] The chemical composition of the positive electrode material is Li 1.01 (Mg 0.015 Zn 0.005 Fe 0.28 Mn 0.7 )PO4 / C, wherein the carbon content is 1.81wt%.

[0134] Example 4

[0135] (1) Battery-grade manganese molybdate dihydrate 19.410kg, battery-grade ferrous sulfate heptahydrate 11.597kg, titanyl sulfate 350.75g, zinc sulfate 118.93g, pure water 300kg, and ascorbic acid 95.937g are weighed, heated and maintained at a temperature of 40℃, nitrogen gas is introduced as a protective gas, and stirring is performed to obtain a mixed solution. Battery-grade ammonium oxalate 19.187kg and pure water 200kg are mixed, and then added to the above mixed solution to perform a co-precipitation reaction, and after washing and drying, manganese iron oxalate with doped elements is obtained.

[0136] The chemical composition of the manganese iron oxalate is Ti 0.015 Zn 0.005 Fe 0.28 Mn 0.7 C2O4·2H2O.

[0137] (2) The manganese iron oxalate is placed in a graphite box and transferred into a nitrogen gas passing box furnace, and first heated at a rate of 5℃ / min to 150℃ for 3h to remove crystal water, and then heated at a rate of 3℃ / min to 550℃ for 10h to obtain manganese iron oxide with doped elements.

[0138] The chemical composition of the manganese iron oxide is (Ti 0.015 Zn 0.005 Fe 0.28 Mn 0.7 )O.

[0139] (3) Take 316.492 g of the above manganese iron oxide powder, add N-methyl pyrrolidone 818.646 g, under stirring, add battery grade lithium dihydrogen phosphate 411.823 g, lithium carbonate 2.933 g, polyethylene glycol 87.398 g, to obtain a positive electrode material precursor slurry, and the solid content of the slurry is 50 wt% by calculation of the amount of feed.

[0140] The slurry is sand milled by using an organic sand mill, and the median particle size of the particles in the sand milled slurry is 147 nm measured by a laser particle size analyzer.

[0141] The above slurry is spray dried with an inlet temperature of 380℃ and an outlet temperature of 200℃ to obtain a positive electrode material precursor.

[0142] (4) The above positive electrode material precursor is transferred into a gas atmosphere furnace, and under the protection of nitrogen atmosphere, first heated from room temperature to 350℃ at a rate of 2℃ / min, and then heated to 600℃ at a rate of 1.5℃ / min, and then heated to 700℃ at a rate of 1℃ / min, and then naturally cooled and air crushed to obtain a lithium manganese iron phosphate positive electrode material.

[0143] The chemical composition of the above positive electrode material is Li 1.01 (Ti 0.015 Zn 0.005 Fe 0.28 Mn 0.7 )PO4 / C, wherein the carbon content is 1.93 wt%.

[0144] Comparative Example 1

[0145] (1) Take battery grade manganese sulfate monohydrate 19.791 kg, battery grade ferrous sulfate heptahydrate 11.835 kg, magnesium sulfate 181.96 g, titanyl sulfate 166.94 g, zinc sulfate 72.57 g, pure water 300 kg, ascorbic acid 96.963 g, heat and maintain the temperature at 40℃, and pass in nitrogen as a protective gas, and stir to obtain a mixed solution. Take battery grade ammonium oxalate 19.132 kg and pure water 200 kg, mix, and then add to the above mixed solution to carry out co-precipitation reaction, and after washing and drying, manganese iron oxalate is obtained.

[0146] The chemical composition of the above manganese iron oxalate is Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 C2O4·2H2O.

[0147] (2) Put the above manganese iron oxalate into a graphite box, and transfer into a nitrogen gas box furnace, first heat up to 150℃ at a speed of 5℃ / min, and keep for 3h to remove the crystal water, then heat up to 550℃ at a speed of 3℃ / min, and keep for 10h to obtain manganese iron oxide with doped elements.

[0148] The chemical composition of the above manganese iron oxide is (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )O.

[0149] (3) Take 1792.507g of the above manganese iron oxalate, add water 2866.091g, under stirring, add battery grade lithium dihydrogen phosphate 1042.925g, lithium carbonate 11.851g, and polyethylene glycol 341.674g to obtain a positive electrode material precursor slurry, and the solid content of the slurry is 50wt% calculated by the amount of the feed.

[0150] Use an organic sand mill to sand the slurry, and the median particle size of the particles in the sanded slurry is 208nm measured by a laser particle size analyzer.

[0151] Spray dry the above slurry at an inlet temperature of 210℃ and an outlet temperature of 95℃ to obtain a positive electrode material precursor.

[0152] (4) Transfer the above positive electrode material precursor into a gas atmosphere furnace, first heat up to 350℃ at a speed of 2℃ / min from room temperature, keep for 3h, then heat up to 600℃ at a speed of 1.5℃ / min, keep for 4h, then heat up to 700℃ at a speed of 1℃ / min, keep for 10h, and then naturally cool and gas crush to obtain a lithium manganese iron phosphate positive electrode material.

[0153] The chemical composition of the above positive electrode material is Li 1.01 (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )PO4 / C, wherein the carbon content is 1.76wt%.

[0154] Comparative Example 2

[0155] (1) Take 18.840 kg of battery-grade manganese molybdate, 11.796 kg of battery-grade ferrous sulfate heptahydrate, 300 kg of pure water, and 91.473 g of ascorbic acid, heat and maintain the temperature at 40°C, and pass nitrogen as a protective gas while stirring to obtain a mixed solution. Take 18.460 kg of ammonium oxalate and 200 kg of pure water, mix them, and then add them to the above mixed solution to perform a co-precipitation reaction. After washing and drying, manganese iron oxalate is obtained.

[0156] The chemical composition of the above manganese iron oxalate is Fe 0.3 Mn 0.7 C2O4·2H2O.

[0157] (2) Put the above manganese iron oxalate into a graphite box and transfer it into a nitrogen-passing box furnace. First, heat it to 150°C at a rate of 5°C / min and maintain the temperature for 3 h to remove the crystal water. Then, heat it to 550°C at a rate of 3°C / min and maintain the temperature for 10 h to obtain manganese iron oxide.

[0158] The chemical composition of the above manganese iron oxide is (Fe 0.3 Mn 0.7 )O.

[0159] (3) Take 316.840 g of the above manganese iron oxide powder, add 823.726 g of N-methyl pyrrolidone, and under stirring, add 415.983 g of battery-grade lithium dihydrogen phosphate, 2.963 g of lithium carbonate, and 87.94 g of polyethylene glycol to obtain a positive electrode material precursor slurry. The solid content of the slurry is 50 wt% as calculated by the amount of feed.

[0160] Use an organic sand mill to sand the slurry. The median particle size of the particles in the sanded slurry is 195 nm as measured by a laser particle size analyzer.

[0161] Spray dry the above slurry at an inlet temperature of 380°C and an outlet temperature of 200°C to obtain a positive electrode material precursor.

[0162] (4) Transfer the above positive electrode material precursor into a gas atmosphere furnace and first heat it from room temperature to 350°C at a rate of 2°C / min and maintain the temperature for 3 h. Then, heat it to 600°C at a rate of 1.5°C / min and maintain the temperature for 4 h. Then, heat it to 700°C at a rate of 1°C / min and maintain the temperature for 10 h. Then, naturally cool and gasify it to obtain a lithium manganese iron phosphate positive electrode material.

[0163] The chemical composition of the above positive electrode material is Li 1.01 (Fe 0.3 Mn 0.7 )PO4 / C, wherein the carbon content is 1.71 wt%.

[0164] Comparative Example 3

[0165] (1) Take battery grade manganese manganous sulfate 13.321 kg, battery grade ferrous sulfate heptahydrate 7.784 kg, magnesium sulfate 121.66 g, titanyl sulfate 112.55 g, zinc sulfate 48.52 g, and pure water 300 kg, heat and maintain the temperature at 40℃, and stir to obtain a mixed solution. Take 17.2wt% ammonia water 9.884 kg, and then add it into the above mixed solution to carry out co-precipitation reaction, and after washing and drying, manganese iron oxyhydroxide with doped elements is obtained.

[0166] The chemical composition of the above manganese iron oxyhydroxide is (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )OOH.

[0167] (2) Put the above manganese iron hydroxide into a graphite box, and transfer into a nitrogen gas box furnace, first heat to 150℃ at a speed of 5℃ / min, and maintain for 3h to remove crystal water, and then heat to 550℃ at a speed of 3℃ / min, and maintain for 10h to obtain manganese iron oxide with doped elements.

[0168] The chemical composition of the above manganese iron oxide is (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )O.

[0169] (3) Take 237.639g of the above manganese iron oxide powder, add N-methyl pyrrolidone 659.046g, under stirring, add battery grade lithium dihydrogen phosphate 310.052g, lithium carbonate 2.222g, and polyethylene glycol 65.94g to obtain a positive electrode material precursor slurry, and through feeding amount calculation, the solid content of the slurry is 50wt%.

[0170] Use an organic sand mill to sand mill the slurry, and through a laser particle size instrument, the median particle size of the particles in the sand milled slurry is 187 nm.

[0171] Spray dry the above slurry at an inlet temperature of 380℃ and an outlet temperature of 200℃ to obtain a positive electrode material precursor.

[0172] (4) Transfer the above positive electrode material precursor into a gas furnace, and under nitrogen protection atmosphere, first heat from room temperature to 350℃ at a speed of 2℃ / min, maintain for 3h, then heat to 600℃ at a speed of 1.5℃ / min, maintain for 4h, then heat to 700℃ at a speed of 1℃ / min, maintain for 10h, and then naturally cool and gas crush to obtain a manganese iron lithium phosphate positive electrode material.

[0173] The chemical composition of the above-mentioned cathode material is Li 1.01 (Mg 0.01 Ti 0.007 Zn 0.003 Fe 0.28 Mn 0.7 )PO4 / C, of ​​which the carbon content is 1.87wt%.

[0174] Test Example 1

[0175] The manganese iron oxide and cathode material obtained in Example 1 and Comparative Example 1 were characterized using XRD and SEM.

[0176] Figure 1 , Figure 2 The images shown are the XRD and SEM images of the manganese iron oxide obtained in Example 1.

[0177] pass Figure 1 It can be seen that in the manganese-iron oxide obtained in Example 1, manganese and iron elements are mainly in the divalent state. Figure 2 It can be seen that the manganese iron oxide obtained in Example 1 is in an agglomerated state, and the diameter of the primary particles is about 200-300 nm.

[0178] Figure 3 , Figure 4 The images shown are the XRD and SEM images of the lithium manganese iron phosphate cathode material obtained in Example 1.

[0179] Figure 3 Compared to the lithium manganese iron phosphate standard card, fewer impurity peaks were observed, indicating that the cathode material obtained in Example 1 had fewer impurities. Figure 4 It can be seen that the cathode material obtained in Example 1 has uniform particles, with a primary particle size of approximately 50 nm.

[0180] Figure 5 The image shows the SEM image of the lithium manganese iron phosphate cathode material obtained in Comparative Example 1. It can be seen that the cathode material obtained in Comparative Example 1 has uneven particle size and poor sphericity, with a primary particle size of about 200-300 nm.

[0181] Test Example 2

[0182] The phosphorus signal intensity at different locations in the lithium manganese iron phosphate cathode materials obtained by EDS line scanning in the above embodiments and comparative examples was obtained. The average value, standard deviation and coefficient of variation of the phosphorus signal intensity were calculated, as shown in Table 1.

[0183] Figure 6 The image shows an EDS line scan of phosphorus in the lithium iron phosphate cathode material obtained in Example 1, which indicates that the phosphorus is distributed relatively evenly.

[0184] Figure 7 The EDS line scanning of the phosphorus element in the lithium manganese iron phosphate positive electrode material obtained in Comparative Example 1 shows that the uniformity of the phosphorus element distribution is poor.

[0185] Table 1

[0186]

[0187] As can be seen from the results in Table 1, the phosphorus element in the lithium manganese iron phosphate positive electrode material provided by the present application is more uniformly distributed.

[0188] Test Example 3

[0189] The positive electrode materials obtained in the above examples and comparative examples were mixed with polyvinylidene fluoride and conductive carbon black in a mass ratio of 95:5:5, coated on an aluminum foil as a positive electrode; a lithium sheet was used as a counter electrode, 1.2 mol / L LiPF6 (lithium hexafluorophosphate) was dissolved in EC (ethylene carbonate): PC (propylene carbonate): EMC (methyl ethyl carbonate) in a volume ratio of 1:1:1 as an electrolyte, and a CR2016 button cell was prepared.

[0190] The charge specific capacity and discharge specific capacity of the battery at 0.2C and 0.5C were determined by a constant current-constant voltage charging and constant current discharging method, the constant current was based on the selected rate, the constant current charging cutoff voltage was 4.4V, the constant voltage charging cutoff current was 1 / 10 of the constant current, and the discharge cutoff voltage was 2.5V. The results are shown in Table 2.

[0191] Table 2

[0192]

[0193] As can be seen from the results in Table 2, the battery prepared from the lithium manganese iron phosphate positive electrode material provided by the present application has higher charge specific capacity and discharge specific capacity.

[0194] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A lithium iron manganese phosphate cathode material, characterized in that, The positive electrode material has a formula of Li i (Fe x M y Mn z )PO4 / C; wherein 0.15≤x≤0.45, 0<y≤0.03, 0.52≤z≤0.85, 0.98≤i≤1.05; M is selected from at least one of Mg, Ti, V, Ni, Zn, Cu, Zr and Nb; the coefficient of variation of the content of phosphorus element in the positive electrode material is ≤0.029; The X-ray energy spectrum analysis (EDS) signal intensity of the phosphorus element in the positive electrode material at different positions is X i , X i The average value is μ, the standard deviation is σ, the coefficient of variation CV = σ / μ of the phosphorus element EDS signal intensity in the positive electrode material, and the coefficient of variation of the phosphorus element content is represented by the coefficient of variation of the phosphorus element EDS signal intensity.

2. The positive electrode material of claim 1, wherein, 0.15≤x≤0.35, 0<y≤0.01, 0.64≤z≤0.85, 1≤i≤1.

02.

3. The cathode material of claim 1, wherein, M in the expression of the positive electrode material is selected from at least one of Mg, Ti, Ni and Zn.

4. The positive electrode material according to claim 1 or 2, characterized in that, the content of carbon element in the positive electrode material is 1.4-2.5wt%.

5. The positive electrode material according to claim 1 or 2, characterized in that, the median particle size of the positive electrode material is 50-600nm.

6. A method for producing the positive electrode material according to any one of claims 1 to 5, characterized by, the method comprises the following steps: (1) obtaining a mixed solution by mixing a manganese source, an iron source and a M source in the presence of a first solvent, and then mixing with oxalic acid and / or oxalate, and separating a precipitate; (2) performing first heat treatment on the precipitate under a protective atmosphere to obtain manganese-iron oxide doped with M element; (3) mixing the manganese-iron oxide with a lithium source, a phosphorus source and a carbon source in the presence of a second non-aqueous solvent to obtain a slurry, and grinding and drying to obtain a positive electrode material precursor; (4) performing second heat treatment on the positive electrode material precursor under a protective atmosphere to obtain a manganese-iron lithium phosphate positive electrode material.

7. The method of claim 6, wherein, the manganese source is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride and manganese acetate.

8. The method of claim 6, wherein, the iron source is selected from at least one of ferrous sulfate, ferrous chloride and ferrous acetate.

9. The method of claim 6, wherein, the M source is selected from a soluble salt of M.

10. The method of claim 6, wherein, the total concentration of metal ions in the mixed solution is 0.2-2 mol / L.

11. The method of claim 6, wherein, the mixed solution further comprises an antioxidant.

12. The method according to any one of claims 6-11, characterized in that, the temperature of the first heat treatment is 500-700℃, and the time is 5-12h.

13. The method according to any one of claims 6-11, characterized in that, the lithium source is selected from at least one of lithium oxalate, lithium hydroxide, lithium carbonate, lithium acetate and lithium dihydrogen phosphate.

14. The method according to any one of claims 6-11, characterized in that, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, phosphoric acid and lithium dihydrogen phosphate.

15. The method of any of claims 6-11, wherein, the carbon source is selected from at least one of glucose, galactose, lactose, sucrose, caramel, phenolic resin, polyethylene glycol and polyvinyl alcohol.

16. The method of any of claims 6-11, wherein, the first solvent is water.

17. The method of any of claims 6-11, wherein, the second non-aqueous solvent is N-methyl pyrrolidone and / or anhydrous ethanol.

18. The method of any of claims 6-11, wherein, in step (1), the molar ratio of the manganese source, the iron source and the M source, calculated based on metal elements, satisfies n(Mn):n(Fe):n(M)=1-1.2:0.4-1:0.015-0.045; and / or, in step (3), the molar ratio of the manganese-iron oxide, the lithium source, the phosphorus source and the carbon source, calculated based on metal elements and phosphorus element and carbon element, satisfies n(Li):n(Mn+Fe):n(P):n(C)=0.98-1.05:0.96-1:0.98-1.05:0.7-1.

3.

19. The method of any of claims 6-11, wherein, the solid content of the slurry is 20-70wt%.

20. The method of any of claims 6-11, wherein, the median particle size of the positive electrode material precursor is 100-200nm.

21. The method of any of claims 6-11, wherein, the second heat treatment adopts a programmed temperature rising method: (1) rising the temperature to 220-350℃ at a rate of 1-5℃ / min, and keeping the temperature for 2-3h; (2) continue to increase the temperature to 450-650 °C at a rate of 1.5-2.5 °C / min, and keep the temperature for 4-5 h; (3) continue to increase the temperature to 650-800 °C at a rate of 1-1.5 °C / min, and keep the temperature for 7-12 h.

22. Use of the cathode material of any one of claims 1-5 or the cathode material prepared by the method of any one of claims 6-21 in a battery.

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