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

Abstract

The invention provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof, a lithium ion battery and electric equipment, and relates to the technical field of new energy. According to the lithium manganese iron phosphate positive electrode material provided by the invention, the amorphous precursor and the high-crystallization precursor are used as raw materials, and the high-crystallization precursor causes a relatively high specific surface area of the material and affects the processability; the amorphous precursor can improve the compaction density and the specific surface area of the material, and the capacity and the cycle performance of the lithium manganese iron phosphate positive electrode material are ensured by combined use of the two precursors. The combination of elements with different valence states is used, so that the doping and coating effects are achieved at the same time, and the performance of the material is synergistically improved; elements with relatively low valence states are easily doped in a lithium manganese iron phosphate crystal structure, so that the capacity of the material is improved; and elements with relatively high valence states are distributed on the surfaces of lithium manganese iron phosphate particles, so that the stability of the surface structure of the material is improved.

Description

Technical Field

[0001] This application relates to the field of new energy technologies, and particularly to a lithium iron manganese phosphate cathode material, a preparation method thereof, a lithium ion battery, and an electricity-related device. Background Art

[0002] Lithium iron manganese phosphate and lithium iron phosphate have similar theoretical discharge specific capacities, but the voltage platform of the lithium iron manganese phosphate material is significantly higher than that of lithium iron phosphate, showing an advantage of high energy density in the power field. However, the lithium iron manganese phosphate has a low tap density and poor electrical conductivity, and the Jahn-Teller effect is likely to occur during charge and discharge, resulting in manganese dissolution and unstable crystal structure, making the cycle performance poor. Summary of the Invention

[0003] The purpose of this application is to provide a lithium iron manganese phosphate cathode material, a preparation method thereof, a lithium ion battery, and an electricity-related device, aiming to solve the problems of low tap density, poor electrical conductivity, and poor cycle performance of the existing lithium iron manganese phosphate.

[0004] To achieve the above purpose, this application provides a lithium iron manganese phosphate cathode material, including a matrix material and a composite coating layer; wherein, The matrix material includes a cathode material A prepared from a precursor A and a cathode material B prepared from a precursor B; The precursor A is an amorphous precursor with (Fe + Mn) / P = 0.960 - 0.975, and the precursor B is a highly crystalline precursor with (Fe + Mn) / P = 0.970 - 0.985; The chemical formulas of the cathode material A and the cathode material B are independently Li a [Fe x Mn 1-x 1-y M y PO4, where a is 1.01 - 1.05; 0.1 ≤ x ≤ 0.6, preferably 0.2 ≤ x ≤ 0.5; 0.01 ≤ y ≤ 0.08, preferably 0.015 ≤ y ≤ 0.07, more preferably 0.02 ≤ y ≤ 0.06, M includes at least one of Mg 2+ , Ni 2+ , Co 3+ , V 3+ , Ti 4+ ; preferably including at least one of Mg 2+ , Ti 4+ ; the chemical formulas of the cathode material A and the cathode material B can be the same or different; The composite coating layer includes carbon and an oxide of M', where M' includes Zr 4+ , Ti 4+ , Nb​5+ , W 6+ , Mo 6+ , at least one of them, preferably including Nb 5+ , Ti 4+ , at least one of them.

[0005] In some embodiments, the mass of the carbon is 1.0% - 2.0% of the total mass of the matrix material.

[0006] In some embodiments, the M includes divalent elements, trivalent elements, and tetravalent elements in lower valence states, and the M' includes tetravalent elements, pentavalent elements, and hexavalent elements in higher valence states.

[0007] Preferably, the M and M' are Mg 2+ and Nb 5+ , or Ti 4+ and Nb 5+ , or Mg 2+ and Ti 4+ , or Mg 2+ and Zr 4+ , or V 3+ and W 6+ , or Mg 2+ and Ti 4+ and Nb 5+ , or (Mg 2+ and Ti 4+ ) and (Nb 5+ and Ti 4+ ), more preferably, they are Mg 2+ and Nb 5+ .

[0008] In some embodiments, at least one of the following conditions is satisfied: A. In the X-ray diffraction pattern of the lithium iron manganese phosphate cathode material, the diffraction peak in the range of diffraction angle 2θ of 32.0° - 34.0° is the (131) diffraction peak, and the peak intensity I （131） of the (131) diffraction peak is 3300 - 4300, preferably 3400 - 3600; B. The specific surface area of the lithium iron manganese phosphate cathode material is 5 - 30 g / m 2 , preferably 10 - 20 g / m 2 , more preferably 11 - 17 g / m 2 ; C. The tap density of the lithium iron manganese phosphate cathode material is 2.3 - 2.55 g / cm 3 , preferably 2.35 - 2.5 g / cm 3 ; D. The resistivity of the lithium iron manganese phosphate cathode material is 5 - 50 Ω·cm, preferably 8 - 14 Ω·cm; E. The thickness of the composite coating layer is 1 - 50 nm, preferably 3 - 20 nm.

[0009] This application also provides a preparation method of a lithium iron manganese phosphate cathode material, including: (1) Mixing a precursor A, a precursor B, a lithium source, a carbon source, a dopant, a coating agent, and water uniformly to obtain a mixture, The chemical formula of the precursor A is (Fe x’ Mn (1-x’) ) 0.960-0.975 PO4, The chemical formula of the precursor B is (Fe x’’ Mn (1-x’’) ) 0.970~0.985 PO4, wherein, 0.1 ≤ x' ≤ 0.6, preferably 0.2 ≤ x' ≤ 0.5, 0.1 ≤ x'' ≤ 0.6, preferably 0.2 ≤ x'' ≤ 0.5, and x' and x'' can be the same or different; (2) Wet grinding the mixture to obtain a slurry, and spray drying to obtain a dried material; (3) Sintering the dried material once and pulverizing to obtain an intermediate material; (4) Sintering the intermediate material a second time in an atmosphere containing a gaseous carbon source to obtain the lithium iron manganese phosphate cathode material.

[0010] In some embodiments, the mass ratio of the precursor A to the precursor B is (10:90) - (40:60).

[0011] In some embodiments, at least one of the following conditions is satisfied: (1) The molar ratio of lithium in the lithium source to the total metal elements of the precursor A and the precursor B satisfies Li / (Fe + Mn) = 1.01 - 1.05, and / or the lithium source contains at least one of lithium carbonate and lithium hydroxide; (2) The carbon source is 9% - 15% of the total mass of the precursor A and the precursor B, and / or the carbon source includes at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; (3) The dopant contains at least one of magnesium oxide, magnesium hydroxide, magnesium nitrate, nickel oxide, nickel hydroxide, nickel nitrate, cobalt oxide, cobalt hydroxide, cobalt nitrate, vanadium pentoxide, ammonium metavanadate, titanium dioxide, and metatitanic acid, And / or, the molar amount of the doping element M of the dopant is 0.01 to 0.08, preferably 0.02 to 0.06, of the total molar amount of the metal elements of the precursor A and the precursor B and the molar amount of the doping element M; (4) The coating agent includes at least one of zirconia, titanium dioxide, metatitanic acid, niobium pentoxide, niobic acid, tungsten trioxide, and molybdenum trioxide; The molar amount of the coating element M' of the coating agent is 0.01 to 0.06 of the total molar amount of the metal elements of the precursor A and the precursor B and the molar amount of the coating element M'.

[0012] In some embodiments, the temperature of the first sintering is 550 to 850 °C, and the time is 4 to 10 h; And / or, the temperature of the second sintering is 500 to 800 °C, and the time is 2 to 6 h; And / or, in step (1), water is used to adjust the solid content to 30% to 45%; And / or, in the wet grinding, the grinding particle size D50 is controlled to be 0.2 to 0.5 μm, preferably 0.35 to 0.40 μm; And / or, the inlet air temperature of the spray drying is 220 to 280 °C, and the outlet air temperature is 90 to 120 °C; And / or, the pulverization is jet pulverization, and the final jet pulverization particle size satisfies: D10≥0.20um, D50 is 0.3 to 1.1um, preferably 0.4 to 0.6 um, D90≤10um, 1.0≤(D90-D10) / D50≤3.0; And / or, the gaseous carbon source includes at least one of methane, ethane, ethylene, and acetylene; And / or, the flow rate of the gaseous carbon source is 0.1 to 0.6 L / min, preferably 0.2 to 0.5 L / min.

[0013] This application also provides a lithium-ion battery, the raw materials of which include the above-mentioned lithium iron manganese phosphate cathode material, or the lithium iron manganese phosphate cathode material prepared by the above method.

[0014] This application also provides an electricity-related device, including the above-mentioned lithium-ion battery.

[0015] Compared with the prior art, the beneficial effects of this application include: The lithium iron manganese phosphate cathode material provided by this application uses two different types of lithium iron manganese phosphate precursors as raw materials. The amorphous precursor is a massive particle formed by the accumulation of massive primary particles. The amorphous precursor has a low dehydration sintering temperature, a small BET specific surface area, basically no pores, is difficult to grind, and has a low (Fe + Mn) / P ratio. The resulting lithium iron manganese phosphate cathode material has a large particle size, improving the processing performance.

[0016] The highly crystalline precursor is a massive particle formed by the accumulation of flaky primary particles. The highly crystalline precursor has a long aging time and a relatively high dehydration sintering temperature. It has characteristics of high crystallinity and high specific surface area, with obvious crystallization peaks, which is beneficial to the diffusion of doped elements and lithium ions in the finally formed lithium iron manganese phosphate cathode material, and is beneficial to improving the capacity. The highly crystalline precursor has a large BET specific surface area, large sectional pores, is easy to grind, and has a high (Fe + Mn) / P ratio. The resulting lithium iron manganese phosphate cathode material has a small particle size.

[0017] The highly crystalline precursor may lead to a relatively high specific surface area of the material, thus affecting the processing performance; the amorphous precursor can improve the compaction density and specific surface area of the material. By using these two precursors in combination, it is possible to not only ensure the capacity of the lithium iron manganese phosphate cathode material but also improve the cycle performance, and can exert a beneficial synergistic effect, enabling the lithium iron manganese phosphate cathode material to obtain both high electrochemical performance and good processing performance.

[0018] On the basis of using the above two different types of lithium iron manganese phosphate precursors as raw materials, the lithium iron manganese phosphate cathode material of this application further includes specific lower-valence elements in the doped elements and specific higher-valence elements in the coating elements, which can not only improve the capacity of the material but also improve the cycle performance, and ultimately play a significant synergistic role in improving the material performance.

[0019] Specifically, the doped elements with lower valence have higher reaction activity and are easily doped into the crystal structure of lithium iron manganese phosphate. While changing the crystal structure, they can improve the electrochemical performance of the material and increase the capacity of the material; the coating elements with higher valence have lower reaction activity, are difficult to be doped into the interior of lithium iron manganese phosphate particles, and are easily distributed on the surface of lithium iron manganese phosphate particles, which can improve the stability of the surface structure of the material, thereby improving the cycle performance. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of this application, and therefore should not be regarded as limiting the scope of this application.

[0021] Figure 1XRD patterns of the amorphous precursor and highly crystalline precursor used in this application; Figure 2 SEM image of the amorphous precursor used in this application; Figure 3 SEM image of the highly crystalline precursor used in this application; Figure 4 SEM image of the lithium iron manganese phosphate cathode material of Example 1; Figure 5 XPS spectrum of the surface of the lithium iron manganese phosphate cathode material of Example 1; Figure 6 XRD pattern of the lithium iron manganese phosphate cathode material of Example 1; Figure 7 Charge-discharge curve of the lithium iron manganese phosphate cathode material of Example 1; Figure 8 Charge-discharge curve of the lithium iron manganese phosphate cathode material of Comparative Example 1. Detailed implementation manners

[0022] As used herein, the terms: "prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing" or any other variation thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises the recited elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0023] The connecting phrase "consisting of" excludes any unrecited element, step, or component. If used in a claim, this phrase will render the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0024] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0025] In these embodiments, unless otherwise specified, the parts and percentages are by mass.

[0026] "Part by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. If we say that the mass part of component A is a parts and the mass part of component B is b parts, it means the mass ratio of component A to component B is a:b. Or, it means the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of mass parts, the sum of the mass parts of all components is not limited to 131 parts.

[0027] "And / or" is used to indicate that one or both of the described situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0028] The present application provides a lithium iron manganese phosphate cathode material, comprising a matrix material and a composite coating layer; wherein, the matrix material includes a cathode material A prepared from a precursor A and a cathode material B prepared from a precursor B; the precursor A is an amorphous precursor with (Fe + Mn) / P = 0.960 - 0.975, and the precursor B is a highly crystalline precursor with (Fe + Mn) / P = 0.970 - 0.985; the chemical formulas of the cathode material A and the cathode material B are independently Li a [Fe x Mn 1-x 1-y M y PO4, where a is 1.01 - 1.05; 0.1 ≤ x ≤ 0.6, preferably 0.2 ≤ x ≤ 0.5; 0.01 ≤ y ≤ 0.08, preferably 0.015 ≤ y ≤ 0.07, more preferably 0.02 ≤ y ≤ 0.06, and M includes at least one of Mg 2+ , Ni 2+ , Co 3+ , V 3+ , Ti 4+ , and preferably includes at least one of Mg 2+ , Ti 4+ , and more preferably includes Mg 2+ . The chemical formulas of the cathode material A and the cathode material B may be the same or different; the composite coating layer includes carbon and an oxide of M', where M' includes Zr 4+ , Ti 4+ , Nb 5+ , W​6+ and at least one of Mo 6+ , preferably including Nb 5+ and at least one of Ti 4+ , more preferably including Nb 5+ .

[0029] Among them, the amorphous precursor is a massive particle formed by the accumulation of massive primary particles, with a relatively small BET specific surface area of 3 - 7 m 2 / g, having basically no pores, being relatively difficult to grind, and having a relatively low (Fe + Mn) / P ratio, with relatively large particles and a D50 of 6 - 9 μm. The dehydration sintering temperature of the amorphous precursor is low, having the characteristics of low crystallinity, and there is no obvious crystallization peak in XRD.

[0030] The highly crystalline precursor is a massive particle formed by the accumulation of flaky primary particles, with a relatively large BET specific surface area of 6 - 12 m 2 / g, having large sectional pores, being easy to grind, and having a relatively high (Fe + Mn) / P ratio, with relatively small particles and a D50 of 3 - 8 μm. Most of the small particles in the finished product come from the highly crystalline precursor; the highly crystalline precursor has a long aging time, a relatively high dehydration sintering temperature, forming characteristics of high crystallinity and high specific surface area, having obvious crystallization peaks, being more conducive to the diffusion of doping elements and lithium ions, and facilitating the capacity to play.

[0031] The (Fe + Mn) / P ratio of the amorphous precursor can be, for example, 0.960, 0.965, 0.970, 0.975, or any value between 0.960 and 0.975. The (Fe + Mn) / P ratio of the highly crystalline precursor can be, for example, 0.970, 0.975, 0.980, 0.985, or any value between 0.970 and 0.985.

[0032] In some embodiments, the mass of the carbon is 1.0% - 2.0% of the total mass of the matrix material, and can be, for example, 1.0%, 1.5%, 2.0%, or any value between 1.0% and 2.0%.

[0033] In some embodiments, M includes divalent elements, trivalent elements, and tetravalent elements with lower valence states, and M' includes tetravalent elements, pentavalent elements, and hexavalent elements with higher valence states; Preferably, M and M' are Mg 2+ and Nb 5+ , or Ti 4+ and Nb 5+ , or Mg 2+ and Ti 4+ , or Mg 2+ and Zr 4+ , or V 3+ and W 6+ , or Mg 2+ and Ti4+ and Nb 5+ 、or (Mg 2+ and Ti 4+ ) and (Nb 5+ and Ti 4+ ), more preferably, Mg 2+ and Nb 5+ .

[0034] M includes elements with lower valence states, and M' includes elements with higher valence states; by including specific elements with lower valence states in the doping elements and specific elements with higher valence states in the coating elements, a synergistic effect is achieved.

[0035] Among them, the valence states of the elements with lower valence states are divalent, trivalent, and tetravalent, and the valence states of the elements with higher valence states are tetravalent, pentavalent, and hexavalent.

[0036] Ti 4+ can be used as both a doping element and a coating element, mainly determined by its dosage. When the doping molar amount of Ti 4+ is less than or equal to 0.02, the XPS results show that there are no characteristic peaks of Ti elements on the surface of the material, indicating that Ti 4+ is completely doped into the internal grains of the material. When the doping molar amount of Ti 4+ is greater than or equal to 0.03, the XPS results show that a Ti peak appears on the surface of the material. At this time, Ti 4+ enters the interior of the material as part of the doping element and coats the surface of the material as part of the coating element.

[0037] In some embodiments, in the X-ray diffraction pattern of the lithium iron manganese phosphate cathode material, the diffraction peak in the range of diffraction angle 2θ of 32.0° - 34.0° is the (131) diffraction peak, and the peak intensity I （131） of the (131) diffraction peak is 3300 - 4300. For example, it can be 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300 or any value between 3300 - 4300, preferably 3400 - 3600.

[0038] In some embodiments, the specific surface area of the lithium iron manganese phosphate cathode material is 5 - 30 g / m 2 , for example, it can be 5 g / m 2 , 10 g / m 2 , 15 g / m 2 , 20 g / m 2 , 25 g / m 2 , 30 g / m 2 or 5 - 30 g / m 2Any value between, preferably 10 - 20 g / m 2 , more preferably 11 - 17 g / m 2 .

[0039] In some embodiments, the tap density of the lithium iron manganese phosphate cathode material is 2.3 - 2.55 g / cm 3 , for example, it can be 2.3 g / cm 3 , 2.35 g / cm 3 , 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.55 g / cm 3 or any value between 2.3 - 2.55 g / cm 3 , preferably 2.35 - 2.5 g / cm 3 .

[0040] In some embodiments, the resistivity of the lithium iron manganese phosphate cathode material is 5 - 50 Ω·cm, for example, it can be 5 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm or any value between 5 - 50 Ω·cm, preferably 8 - 14 Ω·cm.

[0041] In some embodiments, the thickness of the composite coating layer is 1 - 50 nm, for example, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm or any value between 1 - 50 nm, preferably 3 - 20 nm.

[0042] This application also provides a method for preparing a lithium iron manganese phosphate cathode material, comprising: (1) Mixing a precursor A, a precursor B, a lithium source, a carbon source, a dopant, a coating agent and water uniformly to obtain a mixture, The chemical formula of the precursor A is (Fe x’ Mn (1-x’) ) 0.960-0.975 PO4, The chemical formula of the precursor B is (Fe x’’ Mn (1-x’’) ) 0.970~0.985 PO4, wherein, 0.1 ≤ x’ ≤ 0.6, preferably 0.2 ≤ x’ ≤ 0.5, 0.1 ≤ x’’ ≤ 0.6, preferably 0.2 ≤ x’’ ≤ 0.5, and x’ and x’’ can be the same or different; (2) Wet-mill the mixture to obtain a slurry, and then obtain a dried material through spray drying; (3) Sinter the dried material once and then crush it to obtain an intermediate material; (4) Sinter the intermediate material a second time in an atmosphere containing a gaseous carbon source to obtain the lithium iron manganese phosphate cathode material.

[0043] Among them, the carbon source in step (1) is for reduction and coating, and the gaseous carbon source in step (4) is for further coating.

[0044] In some embodiments, the mass ratio of the precursor A to the precursor B is (10:90) to (40:60), and for example, it can be 10:90, 20:80, 30:70, or 40:60.

[0045] In some embodiments, the molar ratio of lithium in the lithium source to the total metal elements of the precursor A and the precursor B satisfies Li / (Fe + Mn) = 1.01 to 1.05. For example, it can be 1.01, 1.02, 1.03, 1.04, 1.05, or any value between 1.01 and 1.05, and / or the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0046] In some embodiments, the carbon source is 9% - 15% of the total mass of the precursor A and the precursor B. For example, it can be 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value between 9% and 15%, and / or the carbon source includes at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol.

[0047] In some embodiments, the dopant includes at least one of magnesium oxide, magnesium hydroxide, magnesium nitrate, nickel oxide, nickel hydroxide, nickel nitrate, cobalt oxide, cobalt hydroxide, cobalt nitrate, vanadium pentoxide, ammonium metavanadate, titanium dioxide, and metatitanic acid. and / or the molar amount of the doping element M in the dopant is 0.01 to 0.08 of the total molar amount of the metal elements of the precursor A and the precursor B and the molar amount of the doping element M. For example, it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, or any value between 0.01 and 0.08, and preferably 0.02 to 0.06.

[0048] In some embodiments, the coating agent includes at least one of zirconium oxide, titanium dioxide, metatitanic acid, niobium pentoxide, niobic acid, tungsten trioxide, and molybdenum trioxide; The molar amount of the coating element M' of the coating agent is 0.01 to 0.06 of the total molar amount of the metal elements of the precursors A and B and the molar amount of the coating element M', and for example, it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 or any value between 0.01 and 0.06.

[0049] In some embodiments, the temperature of the first sintering is 550 to 850 °C, and for example, it can be 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C or any value between 550 and 850 °C, and the time is 4 to 10 h, and for example, it can be 4 h, 6 h, 8 h, 10 h or any value between 4 and 10 h.

[0050] In some embodiments, the temperature of the second sintering is 500 to 800 °C, and for example, it can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C or any value between 500 and 800 °C, and the time is 2 to 6 h, and for example, it can be 2 h, 4 h, 6 h or any value between 2 and 6 h.

[0051] In some embodiments, in step (1), water is used to adjust the solid content to 30% to 45%, and for example, it can be 30%, 35%, 40%, 45% or any value between 30% and 45%.

[0052] In some embodiments, in the wet grinding, the grinding particle size D50 is controlled to be 0.2 to 0.5 μm, and for example, it can be 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or any value between 0.2 and 0.5 μm, and preferably it is 0.35 - 0.4 μm.

[0053] In some embodiments, the inlet air temperature of the spray drying is 220 to 280 °C, and for example, it can be 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C or any value between 220 and 280 °C, and the outlet air temperature is 90 to 120 °C, and for example, it can be 90 °C, 100 °C, 110 °C, 120 °C or any value between 90 and 120 °C.

[0054] In some embodiments, the pulverization is jet pulverization, and the final gas - powder particle size satisfies: D10≥0.20 um, D50 is 0.3 to 1.1 um, preferably 0.4 to 0.6 um, D90≤10 um, 1.0≤(D90 - D10) / D50≤3.0.

[0055] In some embodiments, the gaseous carbon source includes at least one of methane, ethane, ethylene, and acetylene.

[0056] In some embodiments, the flow rate of the gaseous carbon source is 0.1~0.6 L / min, for example, it can be 0.1 L / min, 0.2 L / min, 0.3 L / min, 0.4 L / min, 0.5 L / min, 0.6 L / min or any value between 0.1~0.6 L / min, and preferably 0.2~0.5 L / min.

[0057] This application also provides a lithium-ion battery, the raw materials of which include the above-mentioned lithium iron manganese phosphate cathode material or the lithium iron manganese phosphate cathode material prepared by the above method.

[0058] This application also provides an electricity-related device, including the above-mentioned lithium-ion battery.

[0059] The following will describe the implementation scheme of this application in detail with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0060] The amorphous precursor A (Fe 0.4 Mn 0.6 ) 0.965 PO4 and the highly crystalline precursor B (Fe 0.4 Mn 0.6 ) 0.975 PO4 used in the following examples and comparative examples have XRD as Figure 1 shown. It can be seen that the crystallization degrees of the characteristic peaks are significantly different. The SEM diagram of the amorphous precursor is as Figure 2 shown, and the SEM diagram of the highly crystalline precursor is as Figure 3 shown. They are all purchased from Hubei Gaobo Technology Co., Ltd.

[0061] Example 1 This example provides a lithium iron manganese phosphate cathode material, and its preparation method includes the following steps: (1) Mix the amorphous precursor A (Fe 0.4 Mn 0.6 ) 0.965 PO4, the highly crystalline precursor B (Fe 0.4 Mn 0.6 ) 0.975 PO4, lithium carbonate as the lithium source, glucose as the carbon source, magnesium oxide as the dopant, niobate as the coating agent and pure water evenly to obtain a mixture; Among them, the mass ratio of the precursor A to the precursor B is 20:80, and the specific surface area of the precursor A is 5 m 2 / g, the D50 particle size is 7 μm; the specific surface area of the precursor B is 9 m 2 / g, the D50 particle size is 5 μm; the molar ratio of lithium element in lithium carbonate to the total metal elements of precursor A and precursor B satisfies Li / (Fe + Mn)=1.02; the mass ratio of glucose to the total mass of the precursors is 12%; the molar amount of Mg in magnesium oxide is 0.04 of (the total molar amount of precursor metal elements + the molar amount of Mg), and the molar amount of Nb in the coating agent niobate is 0.03 of (the total molar amount of precursor metal elements + the molar amount of Nb); the solid content of the mixture is 40%; (2) Wet grinding the mixture to obtain a slurry, and spray drying to obtain a dried material; Among them, the final particle size D50 of the grinding is 0.37 μm; the inlet air temperature of the spray drying is 240 °C, and the outlet air temperature is 110 °C; (3) Sintering the dried material at 600 °C for 8 h, and performing air flow crushing. The final D50 is 0.5 μm, (D90 - D10) / D50 = 2.0, to obtain an intermediate material; (4) Sintering the intermediate material in an atmosphere containing methane at 700 °C for 3 h, and the gas flow rate is 0.4 L / min, to obtain a lithium iron manganese phosphate cathode material, which includes a matrix material and a composite coating layer. The chemical composition of the matrix material is Li 1.02 (Fe 0 .4 Mn 0.6 ) 0.96 Mg 0.04 PO4.

[0062] The lithium iron manganese phosphate cathode material prepared in Example 1 was characterized by SEM, and the results are as Figure 4 shown. It can be seen from the figure that the material contains large and small particles, and the particle surface is relatively smooth and the carbon coating is relatively uniform. Figure 5 It is the XPS characterization of the surface of the material obtained in Example 1. Obvious characteristic peaks of Nb are shown on the material surface, indicating that Nb is coated on the material surface. Figure 6 It is the XRD of the material obtained in Example 1, showing the characteristic peaks of a conventional lithium iron manganese phosphate material; the diffraction peak at a diffraction angle 2θ of 33.2° is the (131) diffraction peak, and the peak intensity of the (131) diffraction peak is 3500.

[0063] The particle size D50 of the lithium iron manganese phosphate cathode material prepared in Example 1 is 0.5 μm, the carbon content is 1.6 wt% of the total mass of the matrix material, the thickness of the composite coating layer is 7 nm, and the specific surface area is 12.5 g / m 2 ; the strongest peak value I （131） in the XRD is 3500 (the unit is atomic units), and the tap density is 2.45 g / cm3 , the resistivity is 9.8 Ω·cm; the discharge specific capacity at 0.1C is 155.4 mAh / g, the discharge specific capacity at 1C is 147.4 mAh / g, the initial efficiency is 97.6%, and the capacity after 50 cycles at 1C is 146.6 mAh / g.

[0064] Example 2 This example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 lies in: (1) The mass ratio of precursor A to precursor B is 40:60, and the molar ratio of lithium element in lithium carbonate to the total metal elements of precursor A and precursor B satisfies Li / (Fe + Mn)=1.05; the mass ratio of glucose to the total mass of the precursors is 15%; the molar amount of Mg in magnesium oxide is 0.06 of (the molar amount of the total metal elements of the precursors + the molar amount of Mg), and the molar amount of Nb in the coating agent niobate is 0.06 of (the molar amount of the total metal elements of the precursors + the molar amount of Nb); the solid content is 40%; (2) The final particle size D50 of sanding is 0.40 μm; the inlet air temperature of spray drying is 280 °C, and the outlet air temperature is 120 °C; (3) The dried material is sintered at 850 °C for 4 h for the first time, and then air flow pulverization is carried out. The final D50 is 1.1 μm, (D90 - D10) / D50 = 2.2, to obtain an intermediate material; (4) The intermediate material is sintered at 800 °C for 2 h in an atmosphere containing methane, and the gas flow rate is 0.5 L / min to obtain a lithium iron manganese phosphate cathode material, which includes a matrix material and a composite coating layer. The chemical composition of the matrix material is Li 1.05 (Fe 0 .4 Mn 0.6 ) 0.94 Mg 0.06 PO4.

[0065] Example 3 This example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 lies in: (1) The mass ratio of precursor A to precursor B is 10:90; the molar ratio of lithium element in lithium carbonate to the total metal elements of precursor A and precursor B satisfies Li / (Fe + Mn)=1.01; the mass ratio of glucose to the total mass of the precursors is 9%; the molar amount of Mg in magnesium oxide is 0.02 of (the molar amount of the total metal elements of the precursors + the molar amount of Mg), and the molar amount of Nb in the coating agent niobate is 0.01 of (the molar amount of the total metal elements of the precursors + the molar amount of Nb); (2) The final particle size D50 of sanding is 0.35 μm; the inlet air temperature of spray drying is 220 °C, and the outlet air temperature is 90 °C; (3)Subject the dried material to primary sintering at 550 °C for 10 h, perform air jet milling, and finally obtain an intermediate material with D50 being 0.3 μm and (D90 - D10) / D50 = 1.5. (4)Subject the intermediate material to secondary sintering in an atmosphere containing methane at 500 °C for 6 h with a gas flow rate of 0.2 L / min to obtain a lithium iron manganese phosphate cathode material, which comprises a matrix material and a composite coating layer. The chemical composition of the matrix material is Li 1.01 (Fe 0 .4 Mn 0.6 ) 0.98 Mg 0.02 PO4.

[0066] Example 4 This example provides a lithium iron manganese phosphate cathode material. The difference in its preparation method from that of Example 1 lies in: The chemical formula of the amorphous precursor A is (Fe 0.5 Mn 0.5 ) 0.960 PO4 (purchased from Hubei Gaobo Technology Co., Ltd.), and the chemical formula of the highly crystalline precursor B is (Fe 0.5 Mn 0.5 ) 0.970 PO4 (purchased from Hubei Gaobo Technology Co., Ltd.). Other steps are the same as those in Example 1.

[0067] Example 5 This example provides a lithium iron manganese phosphate cathode material. The difference in its preparation method from that of Example 1 lies in: The chemical formula of the amorphous precursor A is (Fe 0.2 Mn 0.8 ) 0.975 PO4 (purchased from Hubei Gaobo Technology Co., Ltd.), and the chemical formula of the highly crystalline precursor B is (Fe 0.2 Mn 0.8 ) 0.985 PO4 (purchased from Hubei Gaobo Technology Co., Ltd.). Other steps are the same as those in Example 1.

[0068] Example 6 This example provides a lithium iron manganese phosphate cathode material. The difference in its preparation method from that of Example 1 lies in: The dopant is titanium dioxide, and the molar amount of Ti is 0.04 of (the total molar amount of metal elements in the precursor + the molar amount of Ti). Other than this, it is the same as Example 1.

[0069] After detection, when the molar amount of the dopant titanium dioxide is 0.04, the main part of the titanium element is doped in the matrix material, and a small part of the titanium element will be coated on the surface of the material, so that the coating layer contains Ti and Nb.

[0070] Example 7 This example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 is as follows: The dopants are magnesium oxide and titanium dioxide, the molar amounts of Mg and Ti are 0.04 of (the total molar amount of precursor metal elements + the molar amounts of Mg and Ti), the molar ratio of Mg to Ti is 1:1, and in other respects, it is the same as Example 1.

[0071] Comparative Example 1 This comparative example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 is as follows: The amorphous precursor A (Fe 0.4 Mn 0.6 ) 0.965 PO4 is changed to the correspondingly dosed highly crystalline precursor B (Fe 0.4 Mn 0.6 ) 0.975 PO4, and in other respects, it is the same as Example 1.

[0072] Comparative Example 2 This comparative example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 is as follows: The highly crystalline precursor B (Fe 0.4 Mn 0.6 ) 0.975 PO4 is changed to the correspondingly dosed amorphous precursor A (Fe 0.4 Mn 0.6 ) 0.965 PO4, and in other respects, it is the same as Example 1.

[0073] Comparative Example 3 This comparative example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 is as follows: Magnesium oxide as the dopant is changed to tungsten oxide as the coating agent, the molar amount of W is 0.04 of (the total molar amount of precursor metal elements + the molar amounts of W and Nb), and in other respects, it is the same as Example 1.

[0074] Comparative Example 4 This comparative example provides a lithium iron manganese phosphate cathode material, and the difference in its preparation method from that of Example 1 is as follows: The niobic acid as a coating agent was changed to aluminum oxide as a doping agent, and the molar amount of Al in the aluminum oxide was 0.03 of (the molar amount of the total metal elements of the precursor + the molar amounts of Mg and Al). Others were the same as in Example 1.

[0075] The physical indicators of the lithium manganese iron phosphate positive electrode materials of each embodiment and comparative example are shown in Table 1. The compaction density is tested using a Sansi Zongheng battery powder compaction density meter, and the resistivity is tested using an instrument prepared by Yuanneng Technology Co., Ltd.

[0076] Table 1 Physical indicators of lithium manganese iron phosphate positive electrode materials of various embodiments and comparative examples

[0077] Power-off test process The positive electrode materials prepared in the examples and comparative examples were mixed with PVDF and NMP at a ratio of 90:5:5 to prepare positive electrode slurry, which was coated on aluminum foil, dried, punched and sheared to obtain positive electrode plates. Button cells were assembled in a glove box, and the positive electrode plates were assembled with lithium sheets, diaphragms, and electrolytes to form button cells. The assembled button cells were placed in the mold groove of a hydraulic sealing machine, locked, pressed, and then unlocked to take out the sealed button cells. The diaphragm was a Celgard polypropylene film, and the electrolyte was purchased from Xinya Shanshan New Materials Technology Co., Ltd.

[0078] The test was conducted using a battery test cabinet from Lanhe (model: CT3002A) with a test voltage range of 2.0V to 4.5V. Specifically, the battery was charged to 4.5V at a constant current of 0.1C, charged to 50μA at a constant voltage, and discharged to 2.0V at 0.1C. The above was considered the first cycle, and the discharge capacity after the first cycle was recorded as the 0.1C discharge capacity (mAh / g). Again, charge to 4.5V at 1C constant current, charge to 50μA at constant voltage, and discharge to 2.0V at 1C. Record the discharge capacity after the second cycle as 1C discharge capacity (mAh / g). Again, continue to charge at 1C constant current to 4.5V, charge at constant voltage to 50μA, and discharge at 1C to 2.0V. Repeat the above operations and record the discharge capacity after the 51st cycle as the 1C discharge capacity (mAh / g) after 50 cycles.

[0079] The charge and discharge curve of the lithium manganese iron phosphate positive electrode material of Example 1 is as follows: Figure 7 As shown, the charge and discharge curve of the lithium manganese iron phosphate positive electrode material of Comparative Example 1 is as follows Figure 8 The electrochemical properties of the lithium manganese iron phosphate positive electrode materials of the embodiments and comparative examples are shown in Table 2.

[0080] Table 2 Electrochemical Performance of Lithium Iron Manganese Phosphate Cathode Materials in Each Example and Comparative Example

[0081] It can be seen from the data tables obtained in Examples 1-7 and Comparative Examples 1-4 that the capacity and initial efficiency of the lithium iron manganese phosphate cathode materials obtained by the solution of this application are superior to those of the materials obtained by the comparative example solutions. Among them, the lithium iron manganese phosphate cathode material obtained in Example 1 has the best electrochemical performance. Compared with Examples 1-7, Comparative Examples 1-4 all show poor performance. Among them, in Comparative Example 1, only the highly crystalline precursor B was used, and the specific surface area of the obtained cathode material was relatively high. Although the capacity was not much different from that of the example, the cycling performance was poor; in Comparative Example 2, only the amorphous precursor A was used, and the specific surface area of the obtained cathode material was small and the capacity was low; in Comparative Example 3, magnesium oxide as a dopant was changed to tungsten oxide as a coating agent. Since the high-valence element W 6+ could not enter the crystal grains of the cathode material and could not dope the inside of the material, the lithium iron manganese phosphate cathode material obtained in Comparative Example 3 only had coating elements and did not dope the specific lower-valence elements of the present invention, affecting the electrochemical performance such as the discharge capacity of the cathode material; in Comparative Example 4, niobic acid as a coating agent was changed to aluminum oxide as a dopant. Since Al 3+ is a low-valence element and easily enters the material for doping, the specific high-valence elements of the present invention are not included in the coating layer, resulting in poor stability of the surface structure of the material and unable to play a synergistic role in improving the material performance.

[0082] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of this application and are not intended to limit them; although this application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of each example of this application.

[0083] In addition, those skilled in the art can understand that although some of the examples herein include certain features included in other examples but not other features, the combination of the features of different examples means that it is within the scope of this application and forms different examples. For example, in the above claims, any one of the claimed examples can be used in any combination. The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of this application and should not be regarded as an admission or any form of suggestion that this information constitutes prior art known to those skilled in the art.

Claims

1. A lithium iron manganese phosphate cathode material, characterized in that, It includes a matrix material and a composite coating layer, wherein, the matrix material contains a cathode material A prepared from a precursor A and a cathode material B prepared from a precursor B; the precursor A is an amorphous precursor with (Fe + Mn) / P = 0.960 - 0.975, and the precursor B is a highly crystalline precursor with (Fe + Mn) / P = 0.970 - 0.985; The chemical formulas of the positive electrode material A and the positive electrode material B are independently Li a [Fe x Mn 1-x 1-y M y PO4, where a is 1.01 to 1.05; 0.1 ≤ x ≤ 0.6; 0.01 ≤ y ≤ 0.08, M includes Mg 2+ , Ni 2+ , Co 3+ , V 3+ , Ti 4+ and at least one of them. The chemical formulas of the positive electrode material A and the positive electrode material B may be the same or different;​ The composite coating layer includes carbon and an oxide of M', where M' includes Zr 4+ , Ti 4+ , Nb 5+ , W 6+ , Mo 6+ and at least one of them.

2. The lithium iron manganese phosphate cathode material according to claim 1, characterized in that at least one of the following conditions is satisfied: A. The mass of the carbon is 1.0% - 2.0% of the total mass of the matrix material; B. In the chemical formulas of the cathode material A and the cathode material B, 0.2 ≤ x ≤ 0.5; C. In the chemical formulas of the cathode material A and the cathode material B, 0.015 ≤ y ≤ 0.07; D. The M includes at least one of Mg 2+ , Ti 4+ ; E. The M' includes at least one of Nb 5+ , Ti 4+ .

3. The lithium iron manganese phosphate cathode material according to claim 1, wherein the M includes divalent elements, trivalent elements and tetravalent elements in lower valence states, and the M' includes tetravalent elements, pentavalent elements and hexavalent elements in higher valence states; The M and the M' are Mg respectively 2+ and Nb 5+ or Ti 4+ and Nb 5+ or Mg 2+ and Ti 4+ or Mg 2+ and Zr 4+ or V 3+ and W 6+ or Mg 2+ and Ti 4+ and Nb 5+ .

4. The lithium iron manganese phosphate cathode material according to any one of claims 1 to 3, characterized in that, at least one of the following conditions is satisfied: A. In the X-ray diffraction pattern of the lithium iron manganese phosphate cathode material, the diffraction peak in the range of diffraction angle 2θ from 32.0° to 34.0° is the (131) diffraction peak, and the peak intensity I （131） of the (131) diffraction peak is 3300 - 4300; B. The specific surface area of the lithium iron manganese phosphate cathode material is 5-30 g / m 2 ; C. The tap density of the lithium iron manganese phosphate cathode material is 2.3 - 2.55 g / cm 3 ; D. The resistivity of the lithium iron manganese phosphate cathode material is 5 - 50 Ω·cm; E. The D50 of the lithium iron manganese phosphate cathode material is 0.3 - 1.1 um; F. The thickness of the composite coating layer is 1 - 50 nm.

5. The lithium iron manganese phosphate cathode material according to claim 4, wherein at least one of the following conditions is satisfied: A. The peak intensity I of the diffraction peak (131) （131） is 3400 - 3600; B. The specific surface area of the lithium iron manganese phosphate cathode material is 10 - 20 g / m 2 ; C. The tap density of the lithium iron manganese phosphate cathode material is 2.35 - 2.5 g / cm 3 ; D. The resistivity of the lithium iron manganese phosphate cathode material is 8 - 14 Ω·cm; E. The D50 of the lithium iron manganese phosphate cathode material is 0.4 - 0.6 um; F. The thickness of the composite coating layer is 3 - 20 nm.

6. A preparation method of a lithium iron manganese phosphate cathode material, characterized in that, It includes: (1) Mix the precursor A, precursor B, lithium source, carbon source, dopant, coating agent and water evenly to obtain a mixture, The chemical formula of the precursor A is (Fe x’ Mn (1-x’) ) 0.960-0.975 PO4 The chemical formula of the precursor B is (Fe x’’ Mn (1-x’’) ) 0.970~0.985 PO4 wherein, 0.1 ≤ x' ≤ 0.6, 0.1 ≤ x'' ≤ 0.6, and x' and x'' can be the same or different; (2) Wet-mill the mixture to obtain a slurry, and spray-dry it to obtain a dried material; (3) Sinter the dried material once, and crush it to obtain an intermediate material; (4) Sinter the intermediate material twice in an atmosphere containing a gaseous carbon source to obtain the lithium iron manganese phosphate cathode material.

7. The preparation method of the lithium iron manganese phosphate cathode material according to claim 6, wherein The mass ratio of the precursor A to the precursor B is (10:90) - (40:60).

8. The preparation method of the lithium iron manganese phosphate cathode material according to claim 6 or 7, characterized in that, at least one of the following conditions is satisfied: (1) The molar ratio of lithium in the lithium source to the total metal elements of the precursor A and the precursor B satisfies Li / (Fe + Mn) = 1.01 - 1.05, and / or, the lithium source contains at least one of lithium carbonate and lithium hydroxide; (2) The carbon source is 9% - 15% of the total mass of the precursor A and the precursor B, and / or, the carbon source includes at least one of glucose, sucrose, polyethylene glycol and polyvinyl alcohol; (3) The dopant contains at least one of magnesium oxide, magnesium hydroxide, magnesium nitrate, nickel oxide, nickel hydroxide, nickel nitrate, cobalt oxide, cobalt hydroxide, cobalt nitrate, vanadium pentoxide, ammonium metavanadate, titanium dioxide and metatitanic acid, And / or, the molar amount of the doping element M of the dopant is 0.01 to 0.08 of the total molar amount of the metal elements of the precursor A and the precursor B and the molar amount of the doping element M; (4) The coating agent includes at least one of zirconia, titanium dioxide, metatitanic acid, niobium pentoxide, niobic acid, tungsten trioxide, and molybdenum trioxide; The molar amount of the coating element M' of the coating agent is 0.01 to 0.06 of the total molar amount of the metal elements of the precursor A and the precursor B and the molar amount of the coating element M'; 9. The method for preparing the lithium iron manganese phosphate cathode material according to claim 6, wherein The temperature of the first sintering is 550 to 850 °C, and the time is 4 to 10 h; And / or, the temperature of the second sintering is 500 to 800 °C, and the time is 2 to 6 h; And / or, in step (1), water is used to adjust the solid content to 30% to 45%; And / or, in the wet grinding, the grinding particle size D50 is controlled to be 0.2 to 0.5 μm; And / or, the inlet air temperature of the spray drying is 220 to 280 °C, and the outlet air temperature is 90 to 120 °C; And / or, the pulverization is jet milling, and the final jet-milled particle size satisfies: D10≥0.20um, D50 is 0.3 to 1.1 um, D90≤10um, 1.0≤(D90-D10) / D50≤3.0; And / or, the gaseous carbon source includes at least one of methane, ethane, ethylene, and acetylene; And / or, the flow rate of the gaseous carbon source is 0.1 to 0.6 L / min.

10. The preparation method of the lithium iron manganese phosphate cathode material according to claim 9, wherein, In the wet grinding, the grinding particle size D50 is controlled to be 0.35 - 0.40 μm; And / or, the pulverization is jet milling, and the final jet-milled particle size satisfies: D50 is 0.4 to 0.6 um; And / or, the flow rate of the gaseous carbon source is 0.2 to 0.5 L / min.

11. A lithium-ion battery, characterized in that, Its raw materials include the lithium iron manganese phosphate cathode material described in any one of claims 1 to 5, or the lithium iron manganese phosphate cathode material prepared by the method described in any one of claims 6 - 10.

12. An electric-related device, characterized in that, It includes the lithium ion battery described in claim 11.

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