Positive electrode material and preparation method and application thereof

Abstract

The invention relates to a positive electrode material and a preparation method and application thereof, the specific surface area y of the positive electrode material and the tap density x of the positive electrode material satisfy y = (26.67-1.6596 * 2-7.6236 x) * theta1, theta1 is a first error coefficient, 0.75 < = theta1 < = 1.2, the unit of the specific surface area y is m < 2 > / g, and the unit of the tap density x is g / cm < 3 >. According to the invention, the relationship between the specific surface area and the tap density of the positive electrode material is quantitatively regulated and controlled, so that the positive electrode material has high energy density and excellent cycling stability.

Description

TECHNICAL FIELD

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

[0002] Traditional lithium manganese iron phosphate positive electrode materials usually have limitations, for example: a lithium manganese iron phosphate positive electrode material with a dense structure and high energy density has poor cycle performance; although high porosity is beneficial to lithium ion transmission, making the lithium manganese iron phosphate positive electrode material have good cycle performance, the compaction density is low, resulting in small capacity. Therefore, the traditional lithium manganese iron iron phosphate positive electrode material is difficult to simultaneously improve the energy density and cycle stability. SUMMARY

[0003] Therefore, it is necessary to provide a positive electrode material and a preparation method and application thereof in view of the above problems; the present application quantitatively controls the relationship between the specific surface area and the tap density of the positive electrode material, so that the positive electrode material can have high energy density and excellent cycle stability.

[0004] A positive electrode material, wherein the specific surface area y of the positive electrode material and the tap density x of the positive electrode material satisfy: y=(26.67-1.6596x 2 -7.6236x) x θ1, θ1 is a first error coefficient, 0.75≤θ1≤1.2, the specific surface area y is in units of m 2 / g, and the tap density x is in units of g / cm 3 .

[0005] In one embodiment, the tap density x of the positive electrode material satisfies: x=1.986-5.3864n 2 +0.4177n+θ2, wherein n represents the mass fraction of NH4Mn a Fe 1-a PO4 precursor in a composite precursor for preparing the positive electrode material, 0.1≤n≤0.5, 0.2≤a≤0.8; θ2 is a second error coefficient, -0.2≤θ2≤0.2.

[0006] In one embodiment, the chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1- a PO4, 0.1≤n≤0.5, 0.2≤a≤0.8.

[0007] In one embodiment, the specific surface area y of the positive electrode material is 4.12 m 2 / g to 22.78 m 2 / g.

[0008] and / or, the tap density x of the positive electrode material is 0.65 g / cm 3 to 2.15 g / cm 3 .

[0009] In one embodiment, in the X-ray diffraction pattern of the positive electrode material, at least one of the following conditions is satisfied:

[0010] (1) the peak intensity of the characteristic peak in the range of 16.41° to 17.52° is less than 39.8, the peak intensity of the characteristic peak in the range of 21.83° to 22.93° is less than 49.2, the peak intensity of the characteristic peak in the range of 22.68° to 23.74° is less than 26.2, the peak intensity of the characteristic peak in the range of 33.46° to 34.71° is less than 16, and the peak intensity of the characteristic peak in the range of 35.49° to 36.96° is less than 25.2;

[0011] (2) the peak intensity of the characteristic peak in the range of 17.7° to 18.74° is less than 11, the peak intensity of the characteristic peak in the range of 42.54° to 43.04° is less than 3.6, and the peak intensity of the characteristic peak in the range of 61.58° to 62.85° is less than 17.5;

[0012] (3) the peak intensity of the characteristic peak in the range of 29.6° to 30.6° is less than 12.1, the peak intensity of the characteristic peak in the range of 42.51° to 43.55° is less than 6.9, the peak intensity of the characteristic peak in the range of 56.44° to 56.94° is less than 17.1, and the peak intensity of the characteristic peak in the range of 61.95° to 63° is less than 11.2.

[0013] In one embodiment, the positive electrode material is selected from the orthorhombic system, and the space group includes at least one of Pbnm, Pnma, and Pmnb.

[0014] In one embodiment, the positive electrode material is a secondary particle composed of primary particles, wherein the particle size of the primary particles is 20 nm to 100 nm, and the particle size of the secondary particles is 2 μm to 6 μm.

[0015] In one embodiment, the chemical formula of the positive electrode material is Li b Mn c Fe 1-c-d M d PO4 / C, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, and Sn, 1.0≤b≤1.1, 0.2≤c≤0.8, and 0≤d≤0.1.

[0016] A method for preparing a positive electrode material, comprising the following steps:

[0017] The iron source, the manganese source and the phosphorus source are prepared into a first mixed solution, a compound is prepared into a second mixed solution with part of the first mixed solution, the first mixed solution and the second mixed solution are parallelly flowed, and a composite precursor is prepared by first spray pyrolysis, or the iron source, the manganese source, the phosphorus source and the compound are prepared into a third mixed solution, and a composite precursor is prepared by first spray pyrolysis, wherein the compound is selected from ammonia water or an ammonium salt, and a chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1-a PO4, 0.1≤n≤0.5, 0.2≤a≤0.8;

[0018] The composite precursor is mixed with a lithium source and a carbon source to prepare a slurry, and a positive electrode material is prepared by second spray pyrolysis and sintering.

[0019] In one of the embodiments, the composite precursor is selected from an orthorhombic system, and a space group includes at least one of Pbnm and Pnma.

[0020] And / or, a phase of the composite precursor includes at least one of NH4MnPO4·H2O, NH4FePO4·H2O, NH4MnFePO4·H2O, NH4MnPO4, NH4FePO4, NH4MnFePO4, MnPO4·H2O, FePO4·H2O, MnFePO4·H2O, MnPO4, FePO4, MnFePO4, FePO4·2H2O, Mn3(PO4)2·7H2O, Fe3(PO4)2, (MnFe)3(PO4)2·4H2O, (MnFe)3(PO4)2, Mn3(PO4)2.

[0021] In one of the embodiments, the ammonium salt includes at least one of monobasic ammonium phosphate, dibasic ammonium phosphate, tribasic ammonium phosphate, dihydrogen ammonium pyrophosphate, tetraammonium pyrophosphate, manganese ammonium phosphate, ammonium iron phosphate, diammonium iron phosphate.

[0022] And / or, a total concentration of all solutes in the third mixed solution is 120g / L to 200g / L.

[0023] And / or, the first mixed solution, the second mixed solution and the third mixed solution respectively and independently include a salt containing an element M, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W and Sn.

[0024] And / or, the feed flow rate of the first spray pyrolysis is 0.1 L / h to 0.7 L / h, the cyclone gas flow rate is 10 L / min to 50 L / min, the temperature is 450℃ to 950℃, and the time is 0.2 min to 3 min.

[0025] In one of the embodiments, the lithium source comprises at least one of lithium carbonate, lithium chloride, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium nitrite, and lithium sulfate.

[0026] And / or, the solid content of the slurry is 30% to 60%;

[0027] And / or, the feed flow rate of the second spray pyrolysis is 0.5 L / h to 1 L / h, the cyclone gas flow rate is 20 L / min to 40 L / min, the temperature is 450℃ to 750℃, and the time is 0.5 min to 5 min.

[0028] And / or, the sintering temperature is 450℃ to 850℃, and the time is 3 h to 6 h.

[0029] A positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material as described above.

[0030] A secondary battery comprises the positive electrode sheet as described above.

[0031] The positive electrode material as described in the present application quantitatively controls the quantitative relationship between the specific surface area y and the tap density x of the positive electrode material, realizes a synergistic balance, and makes the positive electrode material have high specific surface area and high tap density at the same time, that is, a certain porosity is introduced into the positive electrode material with a relatively dense structure, which is beneficial to improve the diffusion rate of lithium ions, so that the positive electrode material can improve the cycle stability while maintaining high energy density. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0033] Figure 1 X-ray diffraction (XRD) pattern of the composite precursor prepared for Example 1;

[0034] Figure 2 XRD pattern of the positive electrode material prepared for Example 1;

[0035] Figure 3A scanning electron microscope (SEM) image of the cathode material prepared for Example 1;

[0036] Figure 4 An XRD pattern of the precursor prepared for Comparative Example 1;

[0037] Figure 5 An XRD pattern of the cathode material prepared for Comparative Example 1;

[0038] Figure 6 An SEM image of the cathode material prepared for Comparative Example 1;

[0039] Figure 7 An XRD pattern of the precursor prepared for Comparative Example 2;

[0040] Figure 8 An XRD pattern of the cathode material prepared for Comparative Example 2;

[0041] Figure 9 An SEM image of the cathode material prepared for Comparative Example 2;

[0042] Figure 10 An XRD pattern of the cathode material prepared for Comparative Example 3;

[0043] Figure 11 An SEM image of the cathode material prepared for Comparative Example 3. DETAILED DESCRIPTION

[0044] In order to facilitate the understanding of the present application, the present application will be described in more detail below. It should be understood, however, that the present application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing specific embodiments or examples only and is not intended to be limiting. As used in this patent, the term "and / or" includes any and all combinations of one or more of the associated listed items. In this application, expressions such as "between," "among," and "ranging from" are used to indicate an inclusive range, unless specifically indicated otherwise. Further, when a range is provided, it is intended to include every integer within the range, unless specifically indicated otherwise. Additionally, when a plurality of ranges is provided, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. The above summary of the application is not intended to describe each illustrated embodiment or every implementation of the present application. The details of one or more embodiments of the application are also set forth in the description below. Other features, objects, and advantages of the application will be apparent from the description and from the claims.

[0046] The present application provides a positive electrode material, a specific surface area y of the positive electrode material and a tap density x of the positive electrode material satisfy: y = (26.67 - 1.6596x 2 -7.6236x) x θ1, θ1 is a first error coefficient, 0.75 ≤ θ1 ≤ 1.2, the specific surface area y is in units of m 2 / g, and the tap density x is in units of g / cm 3 .

[0047] It should be noted that the above relationship is only a quantitative conversion and does not involve unit conversion.

[0048] The positive electrode material provided by the present application quantitatively controls the quantitative relationship between the specific surface area y and the tap density x of the positive electrode material, realizes a synergistic balance, and makes the positive electrode material have high specific surface area and high tap density at the same time, that is, a certain porosity is introduced into the positive electrode material with a relatively dense structure, which is beneficial to improving the diffusion rate of lithium ions, so that the positive electrode material can improve the cycle stability while maintaining a high energy density.

[0049] In an embodiment, the tap density x of the positive electrode material satisfies: x = 1.986 - 5.3864n 2 + 0.4177n + θ2, wherein n represents the mass fraction of NH4Mn a Fe 1-a PO4 precursor in the composite precursor for preparing the positive electrode material, 0.1 ≤ n ≤ 0.5, 0.2 ≤ a ≤ 0.8; θ2 is a second error coefficient, -0.2 ≤ θ2 ≤ 0.2, and by using a specific mass ratio of NH4Mn aFe 1-a The precursor of PO4 is conducive to further regulating the tap density x of the positive electrode material.

[0050] It should be noted that the above relationship is only a quantitative conversion and does not involve unit conversion, the value of n includes but is not limited to any one value or a range value between any two values in 0.1, 0.2, 0.3, 0.4, 0.5, and is preferably 0.2 to 0.45; the value of a includes but is not limited to any one value or a range value between any two values in 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and is preferably 0.4 to 0.7.

[0051] In an embodiment, the chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1-a PO4, 0.1≤n≤0.5, 0.2≤a≤0.8.

[0052] In an embodiment, the specific surface area y of the positive electrode material is preferably 4.12m 2 / g to 22.78m 2 / g, including but not limited to any one value or a range value between any two values in 4.12m 2 / g, 5.5m 2 / g, 10m 2 / g, 12m 2 / g, 15m 2 / g, 18m 2 / g, 19m 2 / g, 20m 2 / g, 22.78m 2 / g, and is further preferably 6m 2 / g to 15m 2 / g.

[0053] In an embodiment, the tap density x of the positive electrode material is preferably 0.65g / cm 3 to 2.15g / cm 3 , including but not limited to any one value or a range value between any two values in 0.65g / cm 3 , 0.85g / cm 3 , 1g / cm 3 , 1.2g / cm 3 , 1.5g / cm 3 , 1.95g / cm 3 , 2.15g / cm 3 , and is further preferably 0.9g / cm 3 to 1.5g / cm3 .

[0054] In an embodiment, the phase of the positive electrode material includes at least one of LiFeMnPO4, LiFePO4, and LiMnPO4. It can be understood that, since the three phase peaks of LiFePO4, LiMnPO4, and LiFeMnPO4 are basically the same, as long as the lithium manganese iron phosphate satisfies any one of the three phases, it can be proved that the lithium manganese iron phosphate is synthesized.

[0055] It should be noted that the material phase is generally analyzed by X-ray diffraction pattern, but in the actual analysis process, a small amount of impurity phase cannot be avoided in the X-ray diffraction pattern. Generally, when the peak intensity of the characteristic peak of the impurity phase is lower than a certain range, it is considered that the impurity phase can be ignored.

[0056] In an embodiment, in the X-ray diffraction pattern of the positive electrode material, the peak intensity of the characteristic peak in the range of 16.41° to 17.52° is less than 39.8, the peak intensity of the characteristic peak in the range of 21.83° to 22.93° is less than 49.2, the peak intensity of the characteristic peak in the range of 22.68° to 23.74° is less than 26.2, the peak intensity of the characteristic peak in the range of 33.46° to 34.71° is less than 16, and the peak intensity of the characteristic peak in the range of 35.49° to 36.96° is less than 25.2.

[0057] It should be noted that, in the X-ray diffraction pattern of the positive electrode material, there are characteristic peaks in the ranges of 16.41° to 17.52°, 21.83° to 22.93°, 22.68° to 23.74°, 33.46° to 34.71°, and 35.49° to 36.96°, which indicates that there is an impurity phase Li3PO4 in the X-ray diffraction pattern. Among them, the characteristic peak in the range of 16.41° to 17.52° corresponds to the (020) crystal face, the characteristic peak in the range of 21.83° to 22.93° corresponds to the (120) crystal face, the characteristic peak in the range of 22.68° to 23.74° corresponds to the (101) crystal face, the characteristic peak in the range of 33.46° to 34.71° corresponds to the (040) crystal face, and the characteristic peak in the range of 35.49° to 36.96° corresponds to the (002) crystal face. It can be understood that the peak intensity of each characteristic peak in the X-ray diffraction pattern of the positive electrode material is less than a certain value, in other words, the impurity phase Li3PO4 in the X-ray diffraction pattern of the positive electrode material can be ignored, which indicates that the positive electrode material has a highly oriented pure phase, which is beneficial to further improve the energy density and cycle stability of the positive electrode material.

[0058] In an embodiment, the peak intensity of the characteristic peak in the range of 17.7° to 18.74° in the X-ray diffraction pattern of the positive electrode material is less than 11, the peak intensity of the characteristic peak in the range of 42.54° to 43.04° is less than 3.6, and the peak intensity of the characteristic peak in the range of 61.58° to 62.85° is less than 17.5.

[0059] It should be noted that the presence of the characteristic peaks in the ranges of 17.7° to 18.74°, 42.54° to 43.04°, and 61.58° to 62.85° in the X-ray diffraction pattern of the positive electrode material indicates the presence of the impurity phase Mn3O4 in the X-ray diffraction pattern, wherein the characteristic peak in the range of 17.7° to 18.74° corresponds to the (111) crystal plane, the characteristic peak in the range of 42.54° to 43.04° corresponds to the (400) crystal plane, and the characteristic peak in the range of 61.58° to 62.85° corresponds to the (440) crystal plane. It can be understood that the peak intensity of each characteristic peak in the X-ray diffraction pattern of the positive electrode material is less than a certain value, in other words, the impurity phase Mn3O4 in the X-ray diffraction pattern of the positive electrode material can be ignored, which indicates that the positive electrode material has a highly oriented pure phase, which is beneficial to further improve the energy density and cycle stability of the positive electrode material.

[0060] In an embodiment, the peak intensity of the characteristic peak in the range of 29.6° to 30.6° in the X-ray diffraction pattern of the positive electrode material is less than 12.1, the peak intensity of the characteristic peak in the range of 42.51° to 43.55° is less than 6.9, the peak intensity of the characteristic peak in the range of 56.44° to 56.94° is less than 17.1, and the peak intensity of the characteristic peak in the range of 61.95° to 63° is less than 11.2.

[0061] It should be noted that the presence of the characteristic peaks in the ranges of 29.6° to 30.6°, 42.51° to 43.55°, 56.44° to 56.94°, and 61.95° to 63° in the X-ray diffraction pattern of the positive electrode material indicates the presence of the impurity phase Fe3O4 in the X-ray diffraction pattern, wherein the characteristic peak in the range of 29.6° to 30.6° corresponds to the (220) crystal plane, the characteristic peak in the range of 42.51° to 43.55° corresponds to the (400) crystal plane, the characteristic peak in the range of 56.44° to 56.94° corresponds to the (511) crystal plane, and the characteristic peak in the range of 61.95° to 63° corresponds to the (440) crystal plane. It can be understood that the peak intensity of each characteristic peak in the X-ray diffraction pattern of the positive electrode material is less than a certain value, in other words, the impurity phase Fe3O4 in the X-ray diffraction pattern of the positive electrode material can be ignored, which indicates that the positive electrode material has a highly oriented pure phase, which is beneficial to further improve the energy density and cycle stability of the positive electrode material.

[0062] In an embodiment, the positive electrode material is selected from at least one of orthorhombic system, space group including Pbnm, Pnma, Pmnb, and further, space group number is 62.

[0063] In an embodiment, the positive electrode material is a secondary particle composed of primary particles, wherein the primary particles and the secondary particles are both selected from a spherical structure.

[0064] Preferably, the particle size of the primary particles is 20nm to 100nm, including but not limited to any one value or a range value between any two values of 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, and further preferably 40nm to 80nm; the particle size of the secondary particles is 2μm to 6μm, including but not limited to any one value or a range value between any two values of 2μm, 3μm, 4μm, 5μm, 6μm, and further preferably 3μm to 5μm.

[0065] In an embodiment, the chemical formula of the positive electrode material is Li b Mn c Fe 1-c-d M d PO4 / C, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, Sn, 1.0≤b≤1.1, 0.2≤c≤0.8, 0≤d≤0.1, preferably 1.02≤b≤1.06, 0.4≤c≤0.7, 0.03≤d≤0.09.

[0066] The traditional lithium manganese iron phosphate positive electrode material is generally prepared by first preparing a precursor through solvothermal or co-precipitation, then mixing lithium with the precursor, and then ball milling and high-temperature solid-phase sintering. However, this traditional method has high sintering temperature, long sintering time, high energy consumption, poor sintering uniformity, and large particle size caused by long-time sintering, which is not conducive to capacity improvement. In addition, under the condition of long-time high temperature, due to the high activity of lithium ions, it is easy to react with phosphate ions to increase the Li3PO4 impurity phase, and it is also easy to cause partial oxidation or decomposition of Mn and Fe elements, resulting in element segregation and the generation of Mn3O4 and Fe2O3 impurity phases, thereby reducing the energy density and cycle stability of the positive electrode material.

[0067] Based on this, the application provides a preparation method of a positive electrode material, comprising the following steps:

[0068] S1, the iron source, the manganese source and the phosphorus source are prepared into a first mixed solution, a compound is prepared into a second mixed solution with part of the first mixed solution, the first mixed solution and the second mixed solution are parallelly flowed, and a composite precursor is prepared through first spray pyrolysis, or the iron source, the manganese source, the phosphorus source and the compound are prepared into a third mixed solution, and the composite precursor is prepared through first spray pyrolysis, wherein the compound is selected from ammonia water or ammonium salt, and the chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1- a PO4, 0.1<=n<=0.5, 0.2<=a<=0.8;

[0069] S2, the composite precursor is mixed with a lithium source and a carbon source to prepare a slurry, and a positive electrode material is prepared through second spray pyrolysis and sintering.

[0070] The present application prepares a positive electrode material by first preparing a composite precursor with a chemical formula of nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1-a PO4 through spray pyrolysis, and then preparing lithium, on the one hand, short-time high-temperature calcination promotes the crystallization and stabilization of the LFMP (lithium manganese iron phosphate) phase; on the other hand, NH 4+ 3 in the composite precursor overflows in the form of NH3 and leaves a gap in the spray pyrolysis process, thereby introducing a certain porosity into the positive electrode material with a relatively dense structure, so that the positive electrode material can improve the cycle stability while maintaining a high energy density.

[0071] In addition, the preparation method of the present application is also helpful to improve the energy efficiency, so that the elements in the positive electrode material are uniformly distributed, which can not only avoid overfiring and oversized primary particles caused by long-time high-temperature calcination, thereby realizing higher specific capacity at high charge and discharge rate, but also avoid the generation of Li3PO4, Mn3O4, Fe2O3 and other impurity phases, which is beneficial to obtain a single phase, thereby further improving the energy density and cycle stability of the positive electrode material.

[0072] In step S1, it can be understood that the present application does not limit the specific proportion of the mixed solution, which can be prepared according to the proportion of each element in the chemical formula of the composite precursor. The parallel flow means that the first mixed solution and the second mixed solution are respectively transported to the pyrolysis furnace along the same direction through independent spray rods, and each spray rod is equipped with a precision atomizing nozzle to ensure that the two mixed solutions are simultaneously atomized into fine and uniform droplets.

[0073] In an embodiment, the total concentration of all solutes in the third mixed solution is 120 g / L to 200 g / L, including but not limited to any one of 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 180 g / L, 200 g / L or a range between any two of them, preferably 150 g / L to 190 g / L. It can be understood that all solutes include iron source, manganese source, phosphorus source and compounds.

[0074] Specifically, the iron source includes but is not limited to at least one of ferric nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric acetate; the manganese source includes but is not limited to at least one of manganese nitrate, manganese sulfate, manganese chloride, manganese acetate; the phosphorus source includes but is not limited to at least one of phosphoric acid, pyrophosphoric acid; the ammonium salt includes but is not limited to at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, dihydrogen ammonium pyrophosphate, tetraammonium pyrophosphate, ammonium manganese phosphate, ammonium iron phosphate, diammonium iron phosphate, preferably at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, dihydrogen ammonium pyrophosphate, tetraammonium pyrophosphate.

[0075] In an embodiment, the first mixed solution, the second mixed solution and the third mixed solution each independently comprises a salt containing element M, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, Sn.

[0076] In an embodiment, the composite precursor is selected from at least one of orthorhombic system, space group including Pbnm, Pnma.

[0077] In an embodiment, the phase of the composite precursor includes at least one of NH4MnPO4·H2O, NH4FePO4·H2O, NH4MnFePO4·H2O, NH4MnPO4, NH4FePO4, NH4MnFePO4, MnPO4·H2O, FePO4·H2O, MnFePO4·H2O, MnPO4, FePO4, MnFePO4, FePO4·2H2O, Mn3(PO4)2·7H2O, Fe3(PO4)2, (MnFe)3(PO4)2·4H2O, (MnFe)3(PO4)2, Mn3(PO4)2.

[0078] In an embodiment, the feeding flow rate of the first spray pyrolysis is 0.1 L / h to 0.7 L / h, the cyclone gas flow rate is 10 L / min to 50 L / min, the temperature is 450°C to 950°C, and the time is 0.2 min to 3 min. It can be understood that the temperature of the first spray pyrolysis refers to the working temperature of the reaction device.

[0079] In step S2, it can be understood that the present application does not limit the specific proportion of the slurry, which can be prepared according to the proportion of each element in the chemical formula of the prepared positive electrode material. Preferably, the chemical formula of the positive electrode material is Li b Mn c Fe 1-c- d M d PO4 / C, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, Sn, 1.0≤b≤1.1, 0.2≤c≤0.8, 0≤d≤0.1.

[0080] In an embodiment, the lithium source includes, but is not limited to, at least one of lithium carbonate, lithium chloride, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium nitrite, lithium sulfate; the carbon source includes, but is not limited to, at least one of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl alcohol, graphite, carbon nanotubes.

[0081] In an embodiment, the solid content of the slurry is 30% to 60%, including but not limited to any one value or a range value between any two values of 30%, 40%, 50%, 60%, preferably 30% to 50%.

[0082] In an embodiment, the feeding flow rate of the second spray pyrolysis is 0.5L / h to 1L / h, including but not limited to any one value or a range value between any two values of 0.5L / h, 0.6L / h, 0.7L / h, 0.8L / h, 0.9L / h, 1L / h, preferably 0.6L / h to 0.8L / h; the cyclone gas flow rate is 20L / min to 40L / min, including but not limited to any one value or a range value between any two values of 20L / min, 25L / min, 30L / min, 35L / min, 40L / min, preferably 25L / min to 35L / min.

[0083] In an embodiment, the temperature of the second spray pyrolysis is 450℃ to 750℃, and the time is 0.5min to 5min. It can be understood that the temperature of the second spray pyrolysis refers to the working temperature of the reaction device.

[0084] In an embodiment, the first spray pyrolysis and the second spray pyrolysis are both carried out in an atmosphere of inert gas and / or reducing gas, wherein the inert gas includes but is not limited to nitrogen, argon, and the reducing gas includes but is not limited to hydrogen. Preferably, the sum of the mass fractions of nitrogen and argon in the gas is 90% to 100%, and the mass fraction of hydrogen is 0% to 10%.

[0085] In one embodiment, the sintering temperature is 450° C. to 850° C., and the sintering time is 3 to 6 hours. It is understood that the sintering temperature refers to the operating temperature of the reaction device.

[0086] The present invention also provides a positive electrode sheet and a secondary battery comprising the positive electrode material, wherein the positive electrode material comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, and the positive electrode material layer comprises the positive electrode material as described above.

[0087] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector, for example, aluminum foil is used as the metal foil; the composite current collector may be formed by forming a metal material on a polymer material substrate.

[0088] It can be understood that the positive electrode material layer also includes a binder and a conductive agent, wherein the binder can be any commercially available binder for positive electrode sheets, or any binder prepared by existing technology, and the present invention does not limit this; the conductive agent can be any commercially available conductive agent for secondary batteries.

[0089] The cathode material, its preparation method, and its application will be further described below through the following specific examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, for which the manufacturer is not specified, are all commercially available conventional products.

[0090] Example 1

[0091] Ferric sulfate, manganese sulfate, phosphoric acid and ammonium dihydrogen phosphate were prepared into a mixed solution, the cyclone gas flow rate was set to 40 L / min, the feed flow rate was 0.3 L / h, and the first spray pyrolysis was carried out at 650 ° C for 2 min to obtain a composite precursor. The prepared composite precursor was subjected to XRD test, and the results are as follows: Figure 1 As shown, according to Figure 1 It can be seen that the chemical formula of the composite precursor is 0.3NH4Mn 0.6 Fe 0.4 PO4 / 0.7Mn 0.6 Fe 0.4 PO4, the physical phases are NH4FePO4·H2O and FePO4·2H2O.

[0092] The prepared composite precursor is mixed with lithium carbonate and glucose to prepare a slurry, the rotational flow gas flow is set to 30 L / min, the feeding flow is set to 0.6 L / h, the second spray pyrolysis is carried out at 680 ℃ for 3 min in a nitrogen and hydrogen (mass ratio 95:5) atmosphere, and then sintering is carried out at 750 ℃ for 4 h to prepare the positive electrode material. The XRD and SEM tests are carried out on the prepared positive electrode material, and the results are shown in Figs. 2 and 3, respectively. Figure 2 and Figure 3 According to Figure 2 , the chemical formula of the positive electrode material is Li 1.02 Mn 0.6 Fe 0.4 PO4 / C; according to Figure 3 , the positive electrode material is a polycrystalline structure with a spherical shape, the primary particles have a spherical structure, the particles are closely arranged, the particle size is small and uniform, the average particle size of the primary particles is 67.8 nm, and the average particle size of the secondary particles is 2.8 μm.

[0093] Example 2

[0094] The iron nitrate, manganese nitrate, pyrophosphoric acid and ammonium manganese phosphate are prepared into a mixed solution, the rotational flow gas flow is set to 50 L / min, the feeding flow is set to 0.1 L / h, the first spray pyrolysis is carried out at 450 ℃ for 3 min to prepare the composite precursor, and the XRD test shows that the chemical formula of the composite precursor is 0.5NH4Mn 0.8 Fe 0.2 PO4 / 0.5Mn 0.8 Fe 0.2 O4, and the phases are NH4FePO4·H2O and MnPO4·2H2O.

[0095] The prepared composite precursor is mixed with lithium nitrate and sucrose to prepare a slurry, the rotational flow gas flow is set to 40 L / min, the feeding flow is set to 0.5 L / h, the second spray pyrolysis is carried out at 450 ℃ for 3 min in an argon atmosphere, and then sintering is carried out at 850 ℃ for 3 h to prepare the positive electrode material. The XRD and SEM tests show that the chemical formula of the positive electrode material is Li 1.05 Mn 0.8 Fe 0.2 PO4 / C; the primary particles and the secondary particles in the positive electrode material have a spherical structure, the average particle size of the primary particles is 32.4 nm, and the average particle size of the secondary particles is 2.1 μm.

[0096] Example 3

[0097] The ferrous chloride, manganese chloride, phosphoric acid and ammonium iron phosphate are prepared into a mixed solution, the cyclone gas flow is set to 10 L / min, the feeding flow is set to 0.7 L / h, the first spray pyrolysis is carried out at 930 ℃ for 0.2 min to obtain a composite precursor, and the chemical formula of the composite precursor is 0.05NH4Mn 0.25 Fe 0.75 PO4 / 0.95Mn 0.25 Fe 0.75 O4.

[0098] The composite precursor prepared above is mixed with lithium hydroxide and citric acid to prepare a slurry, the cyclone gas flow is set to 40 L / min, the feeding flow is set to 0.8 L / h, the second spray pyrolysis is carried out at 750 ℃ for 0.5 min in an atmosphere of argon and hydrogen (mass ratio of 9:1), and then sintering is carried out at 460 ℃ for 6 h to obtain a positive electrode material, and the chemical formula of the positive electrode material is Li 1.05 Mn 0.25 Fe 0.7 Mg 0.05 PO4 / C, the phase is LiMnFePO4; the positive electrode material has a spherical polycrystalline structure, the average particle size of the primary particles is 97.5 nm, and the average particle size of the secondary particles is 5.2 μm.

[0099] Example 4

[0100] The ferrous acetate, manganese acetate, phosphoric acid and triammonium phosphate are prepared into a mixed solution, the cyclone gas flow is set to 20 L / min, the feeding flow is set to 0.55 L / h, the first spray pyrolysis is carried out at 800 ℃ for 1 min to obtain a composite precursor, and the chemical formula of the composite precursor is 0.1NH4Mn 0.65 Fe 0.35 PO4 / 0.9Mn 0.65 Fe 0.35 O4.

[0101] The composite precursor prepared above is mixed with lithium sulfate and graphite to prepare a slurry, the cyclone gas flow is set to 25 L / min, the feeding flow is set to 0.35 L / h, the second spray pyrolysis is carried out at 700 ℃ for 2 min in argon, and then sintering is carried out at 780 ℃ for 3.5 h to obtain a positive electrode material, and the chemical formula of the positive electrode material is Li 1.03 Mn 0.65 Fe 0.35 PO4 / C, the phase is LiMnFePO4; the positive electrode material has a spherical polycrystalline structure, the average particle size of the primary particles is 53.5 nm, and the average particle size of the secondary particles is 4.6 μm.

[0102] Comparative Example 1

[0103] Mn 0.6 Fe 0.4 The PO4 precursor was mixed with lithium carbonate and polyethylene glycol to prepare a slurry. The cyclone gas flow rate was set to 40 L / min and the feed flow rate was set to 0.9 L / h. Spray pyrolysis was carried out at 860°C for 10 minutes and then sintered at 880°C for 10 hours to obtain the positive electrode material.

[0104] like Figure 4 As shown, Mn 0.6 Fe 0.4 The XRD pattern of PO4 precursor is as follows: Figure 5 and Figure 6 The following are the XRD and SEM images of the positive electrode material. According to the XRD image, the chemical formula of the positive electrode material is LiMn 0.6 Fe 0.4 PO4 / C, the physical phase includes LiMnPO4 main phase and Li3PO4 and Fe3O4 impurity phases; according to the SEM image, the positive electrode material is a spherical polycrystalline structure, the primary particles are in close contact, and there are basically no pores. Due to the high pyrolysis temperature and long pyrolysis time, the particles grow excessively, and melting is found between the primary particles, which is not conducive to lithium ion transmission. The average particle size of the primary particles is 198.5nm, and the average particle size of the secondary particles is 6.4μm.

[0105] Comparative Example 2

[0106] NH4Mn 0.7 Fe 0.3 The PO4 precursor was mixed with lithium acetate and carbon nanotubes to prepare a slurry. The cyclone gas flow rate was set to 30 L / min, the feed flow rate was set to 0.7 L / h, spray pyrolysis was carried out at 400°C for 5 minutes, and then sintered at 700°C for 12 hours to obtain the positive electrode material.

[0107] like Figure 7 As shown, it is NH4Mn 0.6 Fe 0.4 From the XRD pattern of PO4 precursor, we can see that the precursor phases are NH4MnPO4·H2O and NH4FePO4·H2O; Figure 8 and Figure 9 As shown in the figure, it is the XRD pattern and SEM pattern of the positive electrode material. According to the XRD pattern, the chemical formula of the positive electrode material is Li 1.05 Mn 0.7 Fe 0.3 PO4 / C, the physical phases include LiMnPO4, LiMnFePO4 main phases and Li3PO4 impurity phase; according to the SEM image, the positive electrode material is a spherical polycrystalline structure, the primary particles are also spherical and have a large number of pores, the average particle size of the primary particles is 20.3nm, and the average particle size of the secondary particles is 1.8μm.

[0108] Comparative Example 3

[0109] Mn 0.8 Fe 0.2 PO4 precursor was mixed with lithium carbonate and sucrose to prepare a slurry, and the slurry was calcined at 750 DEG C for 12 hours under nitrogen in an atmosphere furnace to obtain the positive electrode material.

[0110] According to Figure 10 It can be seen that the chemical formula of the positive electrode material is Li 1.02 Mn 0.8 Fe 0.2 PO4 / C, and the phases include Li3PO4 and Mn3O4 impurities; according to Figure 11 It can be seen that the positive electrode material is a single crystal structure, and the primary particles are spherical structures. Due to the excessively high pyrolysis temperature and excessively long pyrolysis time, the particles are excessively grown, and the particles are in close contact due to the serious melting phenomenon, which is not conducive to the transmission of lithium ions. The average particle size of the primary particles is 327.4 nm.

[0111] The positive electrode materials prepared in all the examples and all the comparative examples were tested, and the results are shown in Table 1.

[0112] Table 1

[0113]

[0114] The positive electrode materials prepared in all the examples and all the comparative examples were prepared into lithium ion button batteries, and the specific capacity of 0.1C was tested under the condition of 2.5-4.25V voltage, and the capacity retention rate after 50 cycles was tested under the same voltage condition, and the test results are shown in Table 2.

[0115] Table 2

[0116]

[0117] According to Table 2, the positive electrode material provided by the application can have high energy density and excellent cycle stability, the specific capacity of 0.1C is as high as 158.2 mAh / g, and the capacity retention rate after 50 cycles is as high as 96.5%. The specific capacity of 0.1C of the comparative examples is less than 150 mAh / g, and the capacity retention rate after 50 cycles is less than 85%.

[0118] The technical features of the above-described examples can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-described examples are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the description.

[0119] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A positive electrode material, characterized in that The specific surface area y of the positive electrode material and the tap density x of the positive electrode material satisfy: y=(26.67-1.6596x 2 -7.6236x)×θ1, θ1 is the first error coefficient, 0.75≤θ1≤1.2, the specific surface area y is in m 2 / g, tap density x is in g / cm 3 .

2. The positive electrode material according to claim 1, characterized in that The tap density x of the positive electrode material satisfies: x=1.986-5.3864n 2 +0.4177n+θ2, wherein n represents the NH4Mn in the composite precursor for preparing the positive electrode material a Fe 1-a The mass fraction of the PO4 precursor is 0.1≤n≤0.5, 0.2≤a≤0.8; θ2 is the second error coefficient, -0.2≤θ2≤0.

2.

3. The positive electrode material according to claim 2, characterized in that The chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1-a PO4, 0.1≤n≤0.5, 0.2≤a≤0.

8.

4. The positive electrode material according to claim 1 or 2, characterized in that The specific surface area y of the positive electrode material is 4.12 m 2 / g to 22.78m 2 / g; And / or, the tap density x of the positive electrode material is 0.65 g / cm 3 Up to 2.15g / cm 3 .

5. The positive electrode material according to claim 1, characterized in that In the X-ray diffraction pattern of the positive electrode material, at least one of the following conditions is met: (1) The peak intensity of the characteristic peak in the range of 16.41° to 17.52° is less than 39.8, the peak intensity of the characteristic peak in the range of 21.83° to 22.93° is less than 49.2, the peak intensity of the characteristic peak in the range of 22.68° to 23.74° is less than 26.2, the peak intensity of the characteristic peak in the range of 33.46° to 34.71° is less than 16, and the peak intensity of the characteristic peak in the range of 35.49° to 36.96° is less than 25.2; (2) The peak intensity of the characteristic peak in the range of 17.7° to 18.74° is less than 11, the peak intensity of the characteristic peak in the range of 42.54° to 43.04° is less than 3.6, and the peak intensity of the characteristic peak in the range of 61.58° to 62.85° is less than 17.5; (3) The peak intensity of the characteristic peak in the range of 29.6° to 30.6° is less than 12.1, the peak intensity of the characteristic peak in the range of 42.51° to 43.55° is less than 6.9, the peak intensity of the characteristic peak in the range of 56.44° to 56.94° is less than 17.1, and the peak intensity of the characteristic peak in the range of 61.95° to 63° is less than 11.

2.

6. The positive electrode material according to claim 1, characterized in that The positive electrode material is selected from an orthorhombic system, and the space group includes at least one of Pbnm, Pnma, and Pmnb.

7. The positive electrode material according to claim 1, characterized in that The positive electrode material is a secondary particle composed of primary particles, wherein the particle size of the primary particles is 20 nm to 100 nm, and the particle size of the secondary particles is 2 μm to 6 μm.

8. The positive electrode material according to claim 1, characterized in that The chemical formula of the positive electrode material is Li b Mn c Fe 1-c- d M d PO4 / C, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, and Sn, 1.0≤b≤1.1, 0.2≤c≤0.8, and 0≤d≤0.

1.

9. A method for preparing a positive electrode material, characterized in that: The steps include: An iron source, a manganese source, and a phosphorus source are prepared into a first mixed liquid, a compound and a portion of the first mixed liquid are prepared into a second mixed liquid, the first mixed liquid and the second mixed liquid are flowed in parallel, and a composite precursor is obtained by a first spray pyrolysis. Alternatively, an iron source, a manganese source, a phosphorus source, and a compound are prepared into a third mixed liquid, and a composite precursor is obtained by a first spray pyrolysis. The compound is selected from ammonia water or an ammonium salt, and the chemical formula of the composite precursor is nNH4Mn a Fe 1-a PO4 / (1-n)Mn a Fe 1-a PO4, 0.1≤n≤0.5, 0.2≤a≤0.8; The composite precursor is mixed with a lithium source and a carbon source to prepare a slurry, and the positive electrode material is prepared by a second spray pyrolysis and sintering.

10. The method for preparing the positive electrode material according to claim 9, wherein: The composite precursor is selected from the orthorhombic system, and the space group includes at least one of Pbnm and Pnma; And / or, the physical phase of the composite precursor includes at least one of NH4MnPO4·H2O, NH4FePO4·H2O, NH4MnFePO4·H2O, NH4MnPO4, NH4FePO4, NH4MnFePO4, MnPO4·H2O, FePO4·H2O, MnFePO4·H2O, MnPO4, FePO4, MnFePO4, FePO4·2H2O, Mn3(PO4)2·7H2O, Fe3(PO4)2, (MnFe)3(PO4)2·4H2O, (MnFe)3(PO4)2, and Mn3(PO4)2.

11. The method for preparing the positive electrode material according to claim 9, wherein: The ammonium salt includes at least one of diammonium phosphate, diammonium hydrogen phosphate, triammonium phosphate, diammonium pyrophosphate, tetraammonium pyrophosphate, manganese ammonium phosphate, ferric ammonium phosphate, and diammonium ferric phosphate; and / or, the total concentration of all solutes in the third mixed solution is 120 g / L to 200 g / L; And / or, the first mixed solution, the second mixed solution, and the third mixed solution each independently include a salt containing an element M, wherein M is selected from at least one of Cu, Zn, Li, Ti, Al, Mg, Ca, Na, W, and Sn; And / or, the feed flow rate of the first spray pyrolysis is 0.1 L / h to 0.7 L / h, the cyclone gas flow rate is 10 L / min to 50 L / min, the temperature is 450° C. to 950° C., and the time is 0.2 min to 3 min.

12. The method for preparing the positive electrode material according to claim 9, wherein: The lithium source includes at least one of lithium carbonate, lithium chloride, lithium nitrate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium nitrite, and lithium sulfate; and / or, the solid content of the slurry is 30% to 60%; and / or, the feed flow rate of the second spray pyrolysis is 0.5 L / h to 1 L / h, the cyclone gas flow rate is 20 L / min to 40 L / min, the temperature is 450° C. to 750° C., and the time is 0.5 min to 5 min; And / or, the sintering temperature is 450° C. to 850° C., and the sintering time is 3 h to 6 h.

13. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode material according to any one of claims 1 to 8.

14. A secondary battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 13.

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