Lithium iron manganese phosphate positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a lithium iron manganese phosphate positive electrode material, a preparation method thereof and a lithium ion battery, and relates to the field of lithium ion batteries. The preparation method of the lithium iron manganese phosphate positive electrode material comprises the following steps: mixing a combined precursor, a lithium source, a sugar compound, a dispersing agent, a dopant containing a doping element M2 and water to obtain a slurry; performing spray drying on the slurry to obtain an intermediate powder; and performing sintering and crushing on the intermediate powder to obtain the lithium iron manganese phosphate positive electrode material; the combined precursor comprises a first precursor and a second precursor; the first precursor comprises at least one of manganese iron hydrogen phosphate, amorphous manganese iron phosphate and ammonium manganese iron phosphate, and a doping element M1 of the first precursor comprises at least one of Ti, V, Mg and Zr; the second precursor comprises at least one of hydrated manganese iron phosphate, manganese iron pyrophosphate and crystalline manganese iron phosphate; and the metal phosphorus ratio of the first precursor is less than or equal to the metal phosphorus ratio of the second precursor. The positive electrode material prepared by the application has a high compaction density.

Description

TECHNICAL FIELD

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

[0002] As one of the key factors affecting the performance of lithium ion batteries, the performance of the positive electrode material directly affects the energy density, safety, cycle stability and cost-effectiveness of the battery.

[0003] Lithium manganese iron phosphate, as a potential positive electrode material, has attracted widespread attention in recent years due to its abundant raw materials, low cost, environmental friendliness and high theoretical specific capacity. Lithium manganese iron phosphate combines the high energy density of lithium manganese phosphate and the stability of lithium iron phosphate, and theoretically can provide higher energy output, making it an ideal choice for improving the performance of lithium ion batteries.

[0004] However, despite the many advantages of lithium manganese iron phosphate, its commercial application still faces a series of challenges: first, safety risks and insufficient compaction density. The inherent properties of manganese elements cause structural instability problems in lithium manganese iron phosphate materials during charging and discharging, which not only increases the safety risk of the battery, but also limits the improvement of the compaction density of the battery, thereby affecting the energy density of the battery. Second, the problem of resistance conductivity. The resistance conductivity of lithium manganese iron phosphate is relatively low, and the kinetic performance of lithium manganese iron phosphate at large particle size is significantly deteriorated, affecting the charging and discharging rate and efficiency of the battery.

[0005] To improve the above problems, researchers try to improve the performance of lithium manganese iron phosphate through complex surface coating technology and battery structure design. However, these methods have the defect of high cost, and the operation is complex, it is difficult to ensure the stability of the process, further increasing the production cost and quality control difficulty, the improvement effect is not good in practical application, it is difficult to popularize on a large scale.

[0006] In summary, although lithium manganese iron phosphate positive electrode material has great potential to improve the performance of lithium ion batteries in theory, it faces safety risks, insufficient compaction density, low cost-effectiveness, poor resistance conductivity and unstable process in practical application, which seriously hinders its commercialization process. Therefore, developing a preparation method that can not only improve the above defects, but also maintain the advantages of lithium manganese iron phosphate material, is of great significance to the further development of lithium ion battery technology. SUMMARY

[0007] The purpose of the present application is to provide a lithium manganese iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery to solve the above problems.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0010] (1) mixing a combined precursor, a lithium source, a saccharide compound, a dispersing agent, a dopant containing a doping element M2, and water, and performing sand milling to obtain a slurry;

[0011] The doping element M2 includes at least one of Nb, Ti, W, Ni, and Bi, and preferably includes at least one of Nb and Ti;

[0012] (2) performing spray drying on the slurry to obtain an intermediate powder;

[0013] (3) performing sintering and crushing on the intermediate powder to obtain the lithium manganese iron phosphate positive electrode material;

[0014] The combined precursor includes a first precursor and a second precursor.

[0015] The first precursor includes at least one of manganese iron hydrogen phosphate, amorphous manganese iron phosphate, and ammonium manganese iron phosphate, and preferably includes amorphous manganese iron phosphate.

[0016] The first precursor further includes a doping element M1, and the doping element M1 includes at least one of Ti, V, Mg, and Zr, and preferably includes at least one of Mg and Zr.

[0017] The second precursor includes at least one of hydrated manganese iron phosphate, manganese iron pyrophosphate, and crystalline manganese iron phosphate, and preferably includes manganese iron pyrophosphate.

[0018] The metal phosphorus ratio of the first precursor is less than or equal to the metal phosphorus ratio of the second precursor, and the metal phosphorus ratio refers to the ratio of the molar amount of metal elements (metal elements other than Mn and Fe) to the molar amount of phosphorus elements.

[0019] According to an embodiment of the present application, in step (1), the mass of the first precursor accounts for 20-50% of the mass of the combined precursor, and preferably accounts for 30-40%, and the mass of the second precursor accounts for 50-80% of the mass of the combined precursor, and preferably accounts for 60-70%.

[0020] And / or, the metal phosphorus ratio of the first precursor is 0.950-0.970, and the metal phosphorus ratio of the second precursor is 0.970-0.990.

[0021] And / or, the D50 particle size of the first precursor is 5-15 μm, and preferably is 8-12 μm, and the D50 particle size of the second precursor is 0.2-6.0 μm, and preferably is 0.5-4.0 μm.

[0022] According to the embodiment of the present application, in step (1), the ratio of the molar amount of the doping element M1 to the total molar amount of manganese and iron in the first precursor is M1 / (Mn+Fe) = 0.002-0.02:1, preferably 0.004-0.015:1.

[0023] According to the embodiment of the present application, in step (1), the molar ratio of the phosphorus element in the combined precursor to the lithium element in the lithium source is 1:(0.98-1.12).

[0024] And / or, the mass ratio of the combined precursor to the saccharide compound, the dispersant, the dopant is 1:(3-10)%:(1-9)%:(0.2-1)%.

[0025] And / or, the dispersant comprises at least one of PEG, PVP.

[0026] And / or, the lithium source comprises at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide.

[0027] And / or, the saccharide compound comprises at least one of glucose, sucrose, maltose.

[0028] According to the embodiment of the present application, in step (1), the solid content of the slurry is 25-65%.

[0029] And / or, the particle size Dv50 of the slurry is 0.15-0.65 μm.

[0030] And / or, the particle size Dv50 of the intermediate powder is 5-50 μm.

[0031] According to the embodiment of the present application, in step (3), the sintering is carried out in a nitrogen atmosphere.

[0032] And / or, the sintering temperature is 600-800°C, and the sintering time is 4-15 h.

[0033] And / or, the crushing method comprises air flow crushing, and the particle size Dv50 of the material obtained after crushing is 0.3-2.5 μm.

[0034] The present application also provides a lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method of the lithium iron manganese phosphate positive electrode material described above.

[0035] The lithium iron manganese phosphate positive electrode material comprises a first lithium iron manganese phosphate material and a second lithium iron manganese phosphate material, the first lithium iron manganese phosphate material is prepared from a first precursor, the second lithium iron manganese phosphate material is prepared from a second precursor, and the particle size of the first lithium iron manganese phosphate material is larger than that of the second lithium iron manganese phosphate material.

[0036] According to the embodiments of the present application, the primary particle size of the first lithium manganese iron phosphate material is 100-500 nm;

[0037] The primary particle size of the second lithium manganese iron phosphate material is 20-200 nm.

[0038] According to the embodiments of the present application, the mass of the first lithium manganese iron phosphate material accounts for 20%-50% of the total mass of the lithium manganese iron phosphate cathode material;

[0039] And / or, the powder compaction density of the lithium manganese iron phosphate cathode material under a 4t pressure is 2.35-2.50 g / cm 3 ;

[0040] And / or, the powder resistivity of the lithium manganese iron phosphate cathode material is 5-182 Ω·cm, preferably 5-100 Ω·cm.

[0041] The present application also provides a lithium ion battery comprising the lithium manganese iron phosphate cathode material prepared by the preparation method of the lithium manganese iron phosphate cathode material described above or comprising the lithium manganese iron phosphate cathode material described above.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] The first precursor of the present application has a lower metal-phosphorus ratio, and is easy to form large particles after sintering. The second precursor has a higher metal-phosphorus ratio, and is easy to form small particles after sintering. The large particles and the small particles cooperate with each other, which can effectively improve the compaction density of the cathode material.

[0044] The present application selects at least one of manganese hydrogen phosphate iron, amorphous manganese iron phosphate, and ammonium manganese iron phosphate as the first precursor, which has high sintering reactivity and can form uniform and dense spherical large particle lithium manganese iron phosphate. Such large particle lithium manganese iron phosphate can provide better structural stability and optimize the coating performance of the cathode material.

[0045] The present application selects at least one of hydrated manganese iron phosphate, manganese iron pyrophosphate, and crystalline manganese iron phosphate as the second precursor, which has a stable crystalline material structure and can provide a good crystalline template as small particles, helping the surrounding area (including the surface of the large particles in contact with it) to form a structured lithium manganese iron phosphate, reducing the generation of impurities, improving the structural uniformity and crystallinity of the product, and such small particle lithium manganese iron phosphate maintains high reactivity, improves the lithium ion diffusion rate, and the small particles as high-activity units contribute mainly to the capacity output in the fast-charging scenario.

[0046] The positive electrode material prepared by the method of the present application includes large-particle-size particles (first lithium manganese iron phosphate material) and small-particle-size particles (second lithium manganese iron phosphate material). The large-particle-size particles support the electrode structure as a framework, and the small-particle-size particles fill the gaps. The gaps between the particles can be effectively filled, thereby improving the compaction density of the positive electrode material, forming a dense and stable electrode layer, and reducing the lithium ion transmission resistance.

[0047] The first precursor of the present application includes a doping element M1. This pre-doping method can uniformly dope elements with relatively large ion diameters, effectively overcoming the problem of uneven doping caused by differences in thermodynamic conditions of large particles in the subsequent sintering process. Through this pre-doping method, the structural stability of the material can be significantly improved, the dissolution of iron and manganese can be inhibited, and the electrical conductivity of large particles can be improved.

[0048] The dopant of the present application contains a doping element M2, which can effectively improve the overall electrochemical performance of the positive electrode material.

[0049] By controlling the amount and ratio of the first precursor and the second precursor, the present application can make the size ratio of the lithium manganese iron phosphate particles moderate, which is conducive to obtaining the optimal compaction.

[0050] In summary, the above effects can be achieved by a simple process to prepare a high-capacity, long-cycle, high-compaction lithium manganese iron phosphate material. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.

[0052] Figure 1 SEM image of the lithium manganese iron phosphate material prepared for Example 1;

[0053] Figure 2 SEM image of the lithium manganese iron phosphate material prepared for Comparative Example 2;

[0054] Figure 3 SEM image of the lithium manganese iron phosphate material prepared for Comparative Example 3. DETAILED DESCRIPTION

[0055] As used herein:

[0056] "comprising," "having," "including," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises, has, includes, or contains one or more elements possesses those one or more elements but is not limited to only those elements.

[0057] The conjunctive term "consisting of" excludes any element, step, or ingredient not specified. If used in the claims, this phrase shall not be construed to mean that the noted elements or steps are essential to the practice of the claims. The phrase "consisting of" shall not be interpreted to mean that any reference to a step or element not specified in the claim is excluded from the claim.

[0058] When equivalent, concentration, or other values or parameters are expressed in ranges, preferred ranges, or a series of upper preferred values and lower preferred values, it is to be understood that all ranges formed by any pair of any upper or lower preferred value, whether or not the range is expressly stated, is specifically disclosed. For example, where a range "1-5" is disclosed, the disclosure is to be interpreted to include ranges "1-4," "1-3," "1-2," "1-2 and 4-5," "1-3 and 5," etc. When numerical ranges are disclosed, unless otherwise stated, the range is intended to include both the upper and lower values and all intervening values, including integers and fractions, unless the context clearly indicates otherwise.

[0059] In these embodiments, the parts and percentages described are by mass, unless otherwise indicated.

[0060] "Mass parts" refers to a basic unit of measurement that represents the proportional relationship of the mass of multiple components, 1 part can represent any unit mass, such as 1 g, 2.689 g, etc. If we say that the mass parts of component A is a parts, and the mass parts of component B is b parts, it means that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK, and the mass of component B is bK (K is an arbitrary number, representing a multiple factor). It must not be misunderstood that, unlike mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0061] "and / or" is used to indicate that one or both of the stated conditions can occur, for example, A and / or B includes (A and B) and (A or B).

[0062] In order to better illustrate the technical solutions provided in the present application, before the embodiments, the technical solutions are stated as a whole, as follows:

[0063] A preparation method of a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0064] (1) mixing a combined precursor, a lithium source, a saccharide compound, a dispersing agent, a dopant containing a doping element M2, and water, and performing sand milling to obtain a slurry;

[0065] The doping element M2 includes at least one of Nb, Ti, W, Ni, and Bi, and preferably includes at least one of Nb and Ti;

[0066] (2) performing spray drying on the slurry to obtain an intermediate powder;

[0067] (3) performing sintering and crushing on the intermediate powder to obtain the lithium manganese iron phosphate positive electrode material;

[0068] The combined precursor includes a first precursor and a second precursor.

[0069] The first precursor includes at least one of manganese iron hydrogen phosphate, amorphous manganese iron phosphate, and ammonium manganese iron phosphate, and preferably includes amorphous manganese iron phosphate.

[0070] The first precursor further includes a doping element M1, and the doping element M1 includes at least one of Ti, V, Mg, and Zr, and preferably includes at least one of Mg and Zr.

[0071] The second precursor includes at least one of hydrated manganese iron phosphate, manganese iron pyrophosphate, and crystalline manganese iron phosphate, and preferably includes manganese iron pyrophosphate.

[0072] The metal phosphorus ratio of the first precursor is less than or equal to the metal phosphorus ratio of the second precursor, and the metal phosphorus ratio refers to the ratio of the molar amount of metal elements to the molar amount of phosphorus elements.

[0073] In the case of high metal phosphorus ratio, the surface proportion of phosphorus oxygen tetrahedron constituting the particle skeleton is low, and the particles are not easy to grow and fuse. On the contrary, the components with low metal phosphorus ratio are easy to form large particles. The first precursor of the present application has the property of easy growth, and the second precursor has the property of not easy growth. The first precursor with low metal phosphorus ratio and the second precursor with high metal phosphorus ratio in the present application are mutually matched, which is beneficial to the uniform distribution of interstitial spaces in space. Specifically, the first precursor also has a low metal phosphorus ratio, and the precursor with a low metal phosphorus ratio is easy to form large particles after sintering. The second precursor has a high metal phosphorus ratio, and the precursor with a high metal phosphorus ratio is easy to form small particles after sintering. After sintering, the positive electrode material can include large particles and small particles, and the large particles and the small particles are matched with each other, which can effectively improve the compaction density of the positive electrode material. Moreover, the first precursor has pores in the interior, which is beneficial to the more sufficient contact with the electrolyte and the migration of lithium ions.

[0074] According to the embodiments of the present application, the first precursor further comprises a doping element M1, and the doping element M1 comprises at least one of Ti, V, Mg and Zr. These elements can control the phosphate crystal structure, expand the lithium ion transmission channel and adjust the energy band structure. By introducing the doping element M1 into the first precursor, the problems of insufficient ion conductivity and electronic conductivity of large particles can be compensated.

[0075] Further, the first precursor can be prepared by a coprecipitation method, and the M1 element can be introduced in the preparation process, so that the first precursor contains the doping element M1.

[0076] The introduction of the doping element M2 can form a fast ion conductor on the surface of the material, improve the lithium ion transfer capacity on the interface of the material, and improve the kinetic performance. Small particles can optimize the kinetics by doping M2, and large particles can further optimize the kinetics.

[0077] According to some embodiments of the present application, the dopant can be an oxide of the doping element M2, for example, the dopant can be niobium oxide and / or titanium oxide.

[0078] According to the embodiments of the present application, in step (1), the mass of the first precursor accounts for 20-50% of the mass of the combined precursor, preferably 30-40%, and the mass of the second precursor accounts for 50-80% of the mass of the combined precursor, preferably 60-70%. If the content of the first precursor is too low, the electrical performance defects of the manganese lithium material will be amplified, which is easy to cause capacity and kinetic defects.

[0079] For example, the mass of the first precursor can account for 20%, 25%, 30%, 35%, 40%, 45%, 50% or any value between 20% and 50% of the mass of the combined precursor, and the mass of the second precursor can account for 50%, 55%, 60%, 65%, 70%, 75%, 80% or any value between 50% and 80% of the mass of the combined precursor.

[0080] For example, the metal-phosphor ratio of the first precursor can be 0.950, 0.955, 0.960, 0.965, 0.970 or any value between 0.950 and 0.970, and the metal-phosphor ratio of the second precursor can be 0.970, 0.975, 0.980, 0.985, 0.990 or any value between 0.970 and 0.990.

[0081] For example, the metal-phosphor ratio of the first precursor can be 0.950, 0.955, 0.960, 0.965, 0.970 or any value between 0.950 and 0.970, and the metal-phosphor ratio of the second precursor can be 0.970, 0.975, 0.980, 0.985, 0.990 or any value between 0.970 and 0.990.

[0082] For example, the D50 particle size of the first precursor can be 5-15 μm, preferably 8-12 μm, and the D50 particle size of the second precursor can be 0.2-6.0 μm, preferably 0.5-4.0 μm.

[0083] According to an embodiment of the present application, in step (1), the ratio of the molar amount of the doping element M1 to the total molar amount of manganese and iron in the first precursor M1 / (Mn+Fe) is 0.002-0.02:1, preferably 0.004-0.015:1. When the content of the doping element M1 is within the above range, the kinetic performance of the positive electrode material is improved. If the content of the doping element M1 is too high, the first precursor cannot achieve the required metal-phosphor ratio, and the morphology is also damaged.

[0084] For example, the ratio of the molar amount of the doping element M1 to the total molar amount of manganese and iron in the first precursor M1 / (Mn+Fe) can be 0.002:1, 0.004:1, 0.006:1, 0.008:1, 0.01:1, 0.012:1, 0.014:1, 0.015:1, 0.016:1, 0.018:1, 0.02:1 or any value between 0.002 and 0.02:1.

[0085] According to an embodiment of the present application, in step (1), the molar ratio of phosphorus in the combined precursor to lithium in the lithium source is 1:(0.98-1.12).

[0086] For example, the molar ratio of phosphorus element in the combined precursor to lithium element in the lithium source can be 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.10, 1:1.12, or any value between 1:(0.98-1.12).

[0087] For example, the mass ratio of the combined precursor to the saccharide compound, the dispersant, and the dopant can be 1:3%:1%:0.2%, 1:5%, 5%, 0.5%, 1:10%:9%:1%, or any value between 1:(3-10)%:(1-9)%:(0.2-1%).

[0088] For example, the mass ratio of the combined precursor to the saccharide compound, the dispersant, and the dopant can be 1:3%:1%:0.2%, 1:5%, 5%, 0.5%, 1:10%:9%:1%, or any value between 1:(3-10)%:(1-9)%:(0.2-1%).

[0089] The saccharide compound has a reducing and carbon-coating effect. If the content of the saccharide compound is too low, the conductivity of the positive electrode material will be insufficient, and if the content of the saccharide compound is too high, the processing performance will be affected.

[0090] If the content of the dispersant is too low, the morphology and conductivity of the positive electrode material will be poor, and if the content of the dispersant is too high, the viscosity will be too large, which is not conducive to the process.

[0091] The main function of the dopant is doping, and it also has a coating effect. If the content of the dopant is too low, the kinetic performance of the positive electrode material will be insufficient, and if the content of the dopant is too high, the particle growth will be abnormal, reducing the tap density.

[0092] For example, the molar ratio of phosphorus element in the combined precursor to lithium element in the lithium source can be 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.10, 1:1.12, or any value between 1:(0.98-1.12).

[0093] For example, the molar ratio of phosphorus element in the combined precursor to lithium element in the lithium source can be 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.10, 1:1.12, or any value between 1:(0.98-1.12).

[0094] For example, the molar ratio of phosphorus element in the combined precursor to lithium element in the lithium source can be 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.10, 1:1.12, or any value between 1:(0.98-1.12).

[0095] According to an embodiment of the present application, in step (1), the solid content of the slurry is 25-65%.

[0096] And / or, the particle size Dv50 of the slurry is 0.15-0.65 μm; if the particle size Dv50 of the slurry is too low, the energy consumption of sanding is high, the growth rate is too fast in the sintering process, leading to uneven microstructure of the positive electrode material, affecting the electrochemical performance of the positive electrode material. If the particle size Dv50 of the slurry is too high, the material uniformity is poor, leading to poor electrochemical performance of the positive electrode material.

[0097] Further, the sanding includes coarse sanding and fine sanding. Through coarse sanding, large particles in the slurry can be rapidly broken, reducing the particle size. Fine sanding is a more fine grinding after coarse sanding. Fine sanding can grind the slurry more finely, making the particle size more uniform and the fineness higher.

[0098] And / or, the particle size Dv50 of the intermediate powder is 5-50 μm.

[0099] In some embodiments, in step (2), the temperature of spray drying is 250℃, 260℃, 270℃ or any value between 250-270℃.

[0100] According to the embodiments of the present application, in step (3), the sintering is performed under a nitrogen atmosphere;

[0101] And / or, the temperature of sintering is 600-800℃, and the time of sintering is 4-15 h.

[0102] For example, the temperature of sintering can be 600℃, 650℃, 700℃, 750℃, 800℃ or any value between 600-800℃, and the time of sintering can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or any value between 4-15 h.

[0103] If the temperature of sintering is too low, it will lead to insufficient particle growth, affecting the electrochemical performance and mechanical performance of the material. If the temperature of sintering is too high, it will lead to excessive particle growth, leading to poor charge-discharge performance.

[0104] And / or, the pulverization method includes air flow pulverization, and the particle size Dv50 of the material obtained after pulverization is 0.3-2.5 μm, preferably 0.3-0.8 μm.

[0105] The present application also provides a lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method of the lithium iron manganese phosphate positive electrode material described above.

[0106] The lithium manganese iron phosphate positive electrode material comprises a first lithium manganese iron phosphate material and a second lithium manganese iron phosphate material, the first lithium manganese iron phosphate material is prepared from a first precursor, the second lithium manganese iron phosphate material is prepared from a second precursor, and the particle size of the first lithium manganese iron phosphate material is larger than the particle size of the second lithium manganese iron phosphate material.

[0107] According to an embodiment of the present application, the primary particle size of the first lithium manganese iron phosphate material is 100-500 nm;

[0108] The primary particle size of the second lithium manganese iron phosphate material is 20-200 nm.

[0109] According to an embodiment of the present application, the mass of the first lithium manganese iron phosphate material accounts for 20%-50% of the total mass of the lithium manganese iron phosphate positive electrode material;

[0110] And / or, the powder compaction density of the lithium manganese iron phosphate positive electrode material under a pressure of 4 t is 2.35-2.50 g / cm 3 ;

[0111] And / or, the powder resistivity of the lithium manganese iron phosphate positive electrode material is 5-182 Ω·cm.

[0112] According to some embodiments of the present application, the 1C discharge gram capacity of the lithium manganese iron phosphate positive electrode material is 144 mAh / g or more, and the 0.1C discharge gram capacity of the lithium manganese iron phosphate positive electrode material is 155 mAh / g or more.

[0113] The present application also provides a lithium ion battery comprising the lithium manganese iron phosphate positive electrode material prepared by the preparation method of the lithium manganese iron phosphate positive electrode material described above or comprising the lithium manganese iron phosphate positive electrode material described above.

[0114] The embodiments of the present application will be described in detail below with reference to specific examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0115] Example 1

[0116] S1: weigh the combined precursor, lithium source, sugar compound, dispersant, and dopant.

[0117] The combined precursor is composed of a first precursor and a second precursor. The first precursor is amorphous manganese iron phosphate with a metal-phosphorus ratio (Mn+Fe) / P of 0.9625, and the first precursor further comprises a doping element Mg. The molar ratio of the doping element Mg to the metal elements of the first precursor is 0.01:1, and the D50 particle size of the first precursor is 10 μm. The second precursor is manganese iron pyrophosphate with a metal-phosphorus ratio (Mn+Fe) / P of 0.975, and the D50 particle size of the second precursor is 3 μm. The mass of the first precursor accounts for 35% of the mass of the combined precursor, and the mass of the second precursor accounts for 65% of the mass of the combined precursor.

[0118] The lithium source is lithium carbonate, and the molar ratio of the phosphorus element in the combined precursor to the lithium element in the lithium source is 1:1.08.

[0119] The saccharide compound is sucrose, the dispersant is polyethylene glycol (PEG), and the dopant comprises niobium oxide and titanium oxide, wherein the mass ratio of the niobium oxide to the titanium oxide is 2:1.

[0120] The mass ratio of the combined precursor to the saccharide compound, the dispersant, and the dopant is 1:5%:5%:0.5%.

[0121] The weighed combined precursor, lithium source, saccharide compound, dispersant, and dopant are dispersed in pure water to obtain a slurry mixture, and the solid content of the slurry mixture is 30%.

[0122] S2: The slurry is coarsely ground until the particle size Dv50 is 1.0-2.0 μm. Then, the slurry is transferred to fine grinding, and sand grinding is performed until the particle size Dv50 is 0.35-0.40 μm.

[0123] S3: The slurry treated in S2 is spray dried at 260°C to obtain a spray powder, and an intermediate powder is obtained, wherein the Dv50 of the intermediate powder is 20-50 μm.

[0124] S4: The intermediate powder obtained in S3 is sintered in a nitrogen atmosphere, the sintering temperature is controlled at 720±5°C, and the sintering time is 8 h, to obtain lithium manganese iron phosphate agglomerates. The lithium manganese iron phosphate agglomerates are subjected to jet milling to obtain a lithium manganese iron phosphate positive electrode material, and the particle size Dv50 of the lithium manganese iron phosphate positive electrode material is controlled to be 0.4±0.1 μm.

[0125] The SEM image of the lithium manganese iron phosphate material prepared in Example 1 is as shown in FIG. 1. Figure 1The lithium manganese iron phosphate positive electrode material includes a first lithium manganese iron phosphate material and a second lithium manganese iron phosphate material, the first lithium manganese iron phosphate material is prepared from a first precursor, the second lithium manganese iron phosphate material is prepared from a second precursor, and the particle size of the first lithium manganese iron phosphate material is larger than that of the second lithium manganese iron phosphate material. The primary particle size of the first lithium manganese iron phosphate material is 100-500 nm, and the primary particle size of the second lithium manganese iron phosphate material is 20-200 nm.

[0126] The mass of the first lithium manganese iron phosphate material accounts for 20%-50% of the total mass of the lithium manganese iron phosphate positive electrode material.

[0127] Example 2

[0128] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the mass of the first precursor accounts for 30% of the mass of the combined precursor, and the mass of the second precursor accounts for 70% of the mass of the combined precursor.

[0129] Example 3

[0130] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the mass of the first precursor accounts for 40% of the mass of the combined precursor, and the mass of the second precursor accounts for 60% of the mass of the combined precursor.

[0131] Example 4

[0132] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the mass ratio of the combined precursor, the saccharide compound, the dispersing agent, and the dopant is 1:5%:5%:0.2%.

[0133] Example 5

[0134] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the mass ratio of the combined precursor, the saccharide compound, the dispersing agent, and the dopant is 1:5%:5%:1%.

[0135] Example 6

[0136] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the dopant only includes niobium oxide.

[0137] Example 7

[0138] The lithium manganese iron phosphate positive electrode material is prepared according to the method of Reference Example 1, and other parameters are the same as those of Example 1, except that the dopant only includes titanium oxide.

[0139] Example 8

[0140] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that the first precursor was ammonium manganese iron phosphate with a metal phosphorus ratio (Mn+Fe) / P of 0.9625, and the second precursor was crystalline manganese iron phosphate with a metal phosphorus ratio (Mn+Fe) / P of 0.975.

[0141] Comparative Example 1

[0142] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that the second precursor was manganese iron pyrophosphate with a metal phosphorus ratio (Mn+Fe) / P of 0.945.

[0143] Comparative Example 2

[0144] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that no first precursor was added.

[0145] The SEM image of the lithium manganese iron phosphate material prepared in Comparative Example 2 is shown in FIG. 2. Figure 2

[0146] Comparative Example 3

[0147] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that no second precursor was added.

[0148] The SEM image of the lithium manganese iron phosphate material prepared in Comparative Example 3 is shown in FIG. 3. Figure 3

[0149] Comparative Example 4

[0150] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that the first precursor did not include the doping element Mg.

[0151] Comparative Example 5

[0152] The lithium manganese iron phosphate positive electrode material was prepared according to the method of Reference Example 1, and other parameters were the same as those of Example 1, except that no dopant was added.

[0153] Test process of discharging

[0154] ​​The positive electrode material prepared in the examples and comparative examples was mixed with PVDF and NMP in a ratio of 90:5:5 to prepare a positive electrode slurry, which was coated on an aluminum foil, dried, punched and cut to obtain a positive electrode sheet. The assembly of a button cell was carried out in a glove box, and the positive electrode sheet, lithium sheet, separator and electrolyte were assembled into a button cell. The assembled button cell was placed in the mold groove of a hydraulic sealing machine, locked, pressed, and then unlocked to take out the sealed button cell. The separator was a Celgard polypropylene film, and the electrolyte was purchased from Xinyashengsheng New Material Technology Co., Ltd.

[0155] The test was carried out using a blue and (model: CT3002A) battery test cabinet, and the test voltage range was 2.0 V-4.5 V. Specifically, 0.1C constant current charging to 4.5 V, constant voltage charging to 50 μA, 0.1C discharging to 2.0 V, which was regarded as the first cycle, and the discharge capacity after the first cycle was recorded as the 0.1C discharge capacity (mAh / g); again, 1C constant current charging to 4.5 V, constant voltage charging to 50 μA, 1C discharging to 2.0 V, and the discharge capacity after the second cycle was recorded as the 1C discharge capacity (mAh / g); again, 1C constant current charging to 4.5 V, constant voltage charging to 50 μA, 1C discharging to 2.0 V, and the above operation was repeated, and the discharge capacity after the fifty-first cycle was recorded as the 1C discharge capacity after 50 cycles (mAh / g).

[0156] The performance data of examples 1-8 and comparative examples 1-5 are shown in Table 1.

[0157] Table 1 Performance comparison table of examples 1-8 and comparative examples 1-5

[0158]

[0159] In Table 1, the "powder compaction density" refers to the powder compaction density of the lithium manganese iron phosphate positive electrode material under a pressure of 4t.

[0160] As can be seen from Table 1, the powder compaction density of the lithium manganese iron phosphate positive electrode material of examples 1-8 is 2.36-2.46 g / cm 3 , the resistivity is 30-82 Ω·cm, and the particle size Dv50 is 0.37-0.47 μm.

[0161] Compared with comparative examples 1-5, examples 1-8 have higher 0.1C discharge capacity, 1C discharge capacity, initial efficiency and 1C discharge capacity after 50 cycles, which indicates that the examples have more excellent comprehensive electrochemical performance.

[0162] Specifically, the comprehensive electrochemical performance of Comparative Example 1 is poor, which can be caused by the fact that the metal-phosphor ratio of the first precursor in Comparative Example 1 is greater than that of the second precursor.

[0163] The comprehensive electrochemical performance of Comparative Example 2 is poor, which can be caused by the fact that no combined precursor is added.

[0164] The comprehensive electrochemical performance of Comparative Example 3 is poor, which can be caused by the fact that no combined precursor is added in the preparation method.

[0165] The comprehensive electrochemical performance of Comparative Example 4 is poor, which can be caused by the fact that no doping element is included in the first precursor.

[0166] The comprehensive electrochemical performance of Comparative Example 5 is poor, which can be caused by the fact that no dopant is added in the preparation method.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some or all of the technical features; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0168] In addition, those skilled in the art can understand that although some embodiments herein include certain features rather than others included in other embodiments, the combination of features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the BACKGROUND section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: (1) The combined precursor, lithium source, sugar compound, dispersant, dopant containing dopant element M2 are mixed with water and milled to obtain slurry; The doping element M2 includes at least one of Nb, Ti, W, Ni, and Bi; (2) The slurry is spray-dried to obtain intermediate powder; (3) The intermediate powder is sintered and pulverized to obtain the lithium manganese iron phosphate cathode material; The combined precursor includes a first precursor and a second precursor. The first precursor includes at least one of manganese ferric phosphate, amorphous manganese ferric phosphate, and manganese ferric ammonium phosphate; The first precursor further includes a doping element M1, wherein the doping element M1 includes at least one of Ti, V, Mg, and Zr; The second precursor includes at least one of hydrated ferromanganese phosphate, ferromanganese pyrophosphate, and crystalline ferromanganese phosphate; The metal-to-phosphorus ratio of the first precursor is less than or equal to that of the second precursor, wherein the metal-to-phosphorus ratio refers to the ratio of the molar amount of metal element to the molar amount of phosphorus element; In step (1), the ratio of the molar amount of the dopant element M1 to the total molar amount of manganese and iron in the first precursor, M1 / (Mn+Fe), is 0.002~0.02:1; In step (1), the mass of the first precursor accounts for 20-50% of the mass of the combined precursor, and the mass of the second precursor accounts for 50-80% of the mass of the combined precursor. The mass ratio of the combined precursor to the carbohydrate compound, the dispersant, and the dopant is 1:(3~10)%:(1~9)%:(0.2~1)%.

2. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The metal-to-phosphorus ratio of the first precursor is 0.950~0.970, and the metal-to-phosphorus ratio of the second precursor is 0.970~0.990; And / or, the D50 particle size of the first precursor is 5~15μm, and the D50 particle size of the second precursor is 0.2~6.0μm.

3. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (1), the molar ratio of phosphorus in the combined precursor to lithium in the lithium source is 1:(0.98~1.12). And / or, the dispersant includes at least one of PEG and PVP; And / or, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide; And / or, the carbohydrate compound includes at least one of glucose, sucrose, and maltose.

4. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (1), the solid content of the slurry is 25-65%; And / or, the particle size Dv50 of the slurry is 0.15~0.65μm; And / or, the particle size Dv50 of the intermediate powder is 5~50μm.

5. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (3), the sintering is carried out under a nitrogen atmosphere; And / or, the sintering temperature is 600~800℃, and the sintering time is 4~15 h; And / or, the pulverization method includes air jet milling, and the particle size Dv50 of the material obtained after pulverization is 0.3~2.5μm.

6. A lithium iron phosphate cathode material, characterized in that, The lithium manganese iron phosphate cathode material is prepared by the preparation method of lithium manganese iron phosphate cathode material according to any one of claims 1-5; The lithium manganese iron phosphate cathode material includes a first lithium manganese iron phosphate material and a second lithium manganese iron phosphate material. The first lithium manganese iron phosphate material is prepared from a first precursor, and the second lithium manganese iron phosphate material is prepared from a second precursor. The particle size of the first lithium manganese iron phosphate material is larger than that of the second lithium manganese iron phosphate material.

7. The lithium iron phosphate cathode material according to claim 6, characterized in that, The primary particle size of the first lithium manganese iron phosphate material is 100~500 nm; The primary particle size of the second lithium manganese iron phosphate material is 20~200nm.

8. The lithium iron phosphate cathode material according to claim 6 or 7, characterized in that, The mass of the first lithium manganese iron phosphate material accounts for 20% to 50% of the total mass of the lithium manganese iron phosphate cathode material; And / or, the powder compaction density of the lithium manganese iron phosphate cathode material under a pressure of 4t is 2.35~2.50 g / cm³. 3 ; And / or, the resistivity of the lithium manganese iron phosphate cathode material is 5~182 Ω·cm.

9. A lithium-ion battery, characterized in that, It includes lithium manganese iron phosphate cathode materials prepared by the method for preparing lithium manganese iron phosphate cathode materials according to any one of claims 1-5, or lithium manganese iron phosphate cathode materials according to any one of claims 6-8.

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