Lithium iron manganese phosphate cathode material, its preparation method, battery and electrical equipment

Abstract

The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium iron manganese phosphate cathode material, a preparation method thereof, a battery and an electrical device. The lithium iron manganese phosphate cathode material has manganese element, iron element and a doped metal element, and the standard deviation of the molar proportion of the manganese element in the lithium iron manganese phosphate is less than or equal to 1%; the standard deviation of the molar proportion of the iron element is less than or equal to 1%; the standard deviation of the molar proportion of the doped metal element is less than or equal to 1%. Thereby, the uniform distribution of manganese, iron elements and the doped metal element in the lithium iron manganese phosphate cathode material can be realized, and the reduction of the battery discharge capacity caused by the uneven distribution of metal elements can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium iron manganese phosphate cathode material, a preparation method thereof, a battery and an electrical device. Background Art

[0002] As an important power system, lithium-ion batteries are widely used in 3C products such as computers, communication tools and electronic tools, as well as in the fields of electric vehicles such as EV and PHEV and energy storage systems. As a lithium-ion battery cathode material, lithium iron phosphate has the characteristics of good safety, good stability and low cost, which makes its market share continuously increase. However, the disadvantages of lithium iron phosphate, such as poor electronic conductivity, small lithium-ion diffusion coefficient and low energy density, limit its further development and application in the field of electric vehicles. As an upgraded product of lithium iron phosphate, lithium iron manganese phosphate has the same specific capacity as lithium iron phosphate (the theoretical capacity is 170 mAh / g), but the introduction of manganese gives it a higher redox potential, thereby increasing the energy density of the material.

[0003] At present, the synthesis methods of lithium iron manganese phosphate mainly include high-temperature solid-phase method, hydrothermal method and co-precipitation method, etc. Among them, the high-temperature solid-phase method has a simple process flow and is suitable for industrial production, but it is difficult to achieve atomic-level uniform mixing of manganese and iron, poor consistency and non-uniform particle morphology, thus affecting the tap density and discharge capacity. The main advantages of the co-precipitation method are that the particle components are uniform, the size structure can be regulated, and the operation is simple and can be industrially produced. Among them, the preparation of the lithium iron manganese phosphate precursor is the key to synthesizing high-performance materials.

[0004] At present, people have conducted extensive research on the lithium iron manganese phosphate precursor. The prior art discloses a preparation method of a lithium iron manganese phosphate precursor, and the chemical formula of the lithium iron manganese phosphate precursor is (NH4)Mn 1-x-y Fe x M yPO4·H2O / C, the elements in the precursor are evenly distributed, the doped elements enter the metal sites to form nanoparticles with a stable structure, and at the same time, the surface of the nanoparticles is coated with carbon to form a dense spherical aggregate. However, the samples prepared by this method have a low density, a low firing rate during the preparation of the cathode material, and a large amount of ammonia will be released. In addition, in the prior art, a mixed salt solution, a phosphate solution and an oxidant are added into a reaction kettle in a co-current manner for coprecipitation reaction, and the lithium iron phosphate precursor is obtained after filtration, washing and drying. The samples prepared by this method can well solve the problem of uniform distribution of manganese and iron, but have a high impurity content. At the same time, since the lithium iron phosphate precursor contains crystal water, there is a problem of unstable batching during the preparation of the cathode material, and the structure collapses during the sintering process, blocking the lithium ion diffusion channels, thereby affecting the electrochemical performance. Therefore, it is urgent to provide a lithium iron phosphate and its preparation method to achieve uniform coprecipitation of manganese and iron, low impurity content, high density, no crystal water, stable structure, simple synthesis process, environmentally friendly and pollution-free, and suitable for industrial production. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, the present invention provides a lithium iron phosphate cathode material and a preparation method thereof. The lithium iron phosphate prepared by the present invention can achieve uniform coprecipitation of manganese and iron, low impurity content, high density, no crystal water, and stable structure; at the same time, the synthesis process is simple, environmentally friendly and pollution-free, and is suitable for industrial production.

[0006] For this reason, in the first aspect of the present invention, a lithium iron phosphate cathode material is provided. The lithium iron phosphate cathode material has manganese element, iron element and doped metal element. The standard deviation of the molar ratio of manganese element in the lithium iron phosphate is less than or equal to 1%; the standard deviation of the molar ratio of iron element is less than or equal to 1%; the standard deviation of the molar ratio of doped metal element is less than or equal to 1%.

[0007] In the present invention, by controlling the standard deviation of the molar ratio of manganese element, iron element and doped metal element in the lithium iron phosphate cathode material, the uniform distribution of manganese, iron element and doped metal element in the lithium iron phosphate cathode material can be achieved, and the reduction of the battery discharge capacity caused by the uneven distribution of metal elements can be reduced.

[0008] According to an embodiment of the present invention, the standard deviation of the molar ratio of the manganese element is less than or equal to 0.5%.

[0009] According to an embodiment of the present invention, the standard deviation of the molar ratio of the iron element is less than or equal to 0.5%.

[0010] According to an embodiment of the present invention, the standard deviation of the molar ratio of the doped metal element is less than or equal to 0.5%.

[0011] According to an embodiment of the present invention, the molar content ratio of the total amount of metal elements other than lithium to phosphorus element in the lithium iron manganese phosphate is K, and K satisfies 0.97 < K < 1.03, preferably 0.98 < K < 1.02.

[0012] According to an embodiment of the present invention, the doped metal element is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, Ti, Ca, Sr, V, Cr, Y, Mo, Nb, B, W, La, and Sm.

[0013] According to an embodiment of the present invention, the lithium iron manganese phosphate cathode material has a secondary particle structure formed by primary particles.

[0014] According to an embodiment of the present invention, the average particle size of the secondary particles is 1 - 50 μm, preferably 7 - 15 μm.

[0015] According to an embodiment of the present invention, the average particle size of the primary particles is 10 - 500 nm, preferably 10 - 200 nm.

[0016] According to an embodiment of the present invention, the tap density of the lithium iron manganese phosphate cathode material is 2.0 - 3.0 g / cm 3 , preferably 2.5 - 3.0 g / cm 3 .

[0017] According to an embodiment of the present invention, the specific surface area of the lithium iron manganese phosphate cathode material is 10 - 25 m 2 / g.

[0018] According to an embodiment of the present invention, the manganese dissolution rate in the lithium iron manganese phosphate cathode material < 50 ppm, and the iron dissolution rate < 50 ppm; preferably, the manganese dissolution rate < 30 ppm and the iron dissolution rate < 20 ppm.

[0019] According to an embodiment of the present invention, the volume resistivity of the lithium iron manganese phosphate cathode material is 10 - 10 3 Ω·cm.

[0020] According to an embodiment of the present invention, the lithium iron manganese phosphate cathode material has a chemical formula shown in formula (1):

[0021] Li d Mn 1-a-b-c Fe a M b M' c PO4 / C(1)

[0022] wherein, 0.1 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.04, 0 ≤ c ≤ 0.04, 0.9 < d ≤ 1.2;

[0023] M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti;

[0024] M' is selected from at least one of Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La, and Sm.

[0025] According to an embodiment of the present invention, based on the total weight of the lithium iron manganese phosphate cathode material, the carbon content is 0.5 - 5 wt%.

[0026] The second aspect of the present invention provides a method for preparing a lithium iron manganese phosphate cathode material, and the preparation method includes the following steps:

[0027] (1) Prepare a mixed solution containing a manganese source, an iron source, and an M source, an alkaline solution, and a first oxidant solution respectively;

[0028] (2) Add the mixed solution, the alkaline solution, and the first oxidant solution to a reaction kettle in a co-current manner to carry out a coprecipitation reaction to obtain a first precipitate;

[0029] (3) Prepare a phosphorus source solution and a second oxidant solution;

[0030] (4) Mix the phosphorus source solution, the second oxidant solution, and the first precipitate to carry out a transformation reaction to obtain a second precipitate;

[0031] (5) Mix the second precipitate with a first carbon source and sinter in an inert reducing atmosphere to obtain the lithium iron manganese phosphate precursor;

[0032] (6) Mix the lithium iron manganese phosphate precursor with a lithium source, a second carbon source, and an M' source to obtain a mixture;

[0033] (7) Sinter the mixture in an inert atmosphere to obtain the lithium iron manganese phosphate cathode material;

[0034] Wherein, the M source is used to provide the M element, and the M element is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti;

[0035] The M' source is used to provide the M' element, and the M' element is selected from at least one of Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La, and Sm.

[0036] The present invention first uses a manganese source, an iron source, an M source, an alkaline solution, and a first oxidant as raw materials to uniformly co-precipitate manganese and iron under alkaline conditions. At the same time, the oxidation of divalent manganese is more favorable under alkaline conditions, and the prepared first precipitate can achieve uniform co-precipitation of manganese and iron with a stable metal stoichiometric ratio. At the same time, the second precipitate is calcined to obtain a lithium iron manganese phosphate precursor. Generally, the second precipitate contains crystal water, and the content of crystal water is not easy to control. By calcining the second precipitate in an inert reducing atmosphere, a pure-phase pyrophosphate is obtained, which is beneficial to maintaining the uniform distribution state of manganese and iron and also reduces the impact on the electrochemical performance of the prepared cathode material. The entire preparation process is non-toxic and harmless, with a simple process, easily available raw materials, low equipment requirements, easy to promote and apply, and can be widely used in the industrial production of lithium iron manganese phosphate cathode materials.

[0037] According to an embodiment of the present invention, in step (1), the total concentration of the manganese source, the iron source, and the M source in the mixed solution is 0.1 - 4 mol / L, preferably 0.2 - 2 mol / L.

[0038] According to an embodiment of the present invention, the manganese source includes a divalent manganese salt selected from at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0039] According to an embodiment of the present invention, the iron source includes a divalent iron salt selected from at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0040] According to an embodiment of the present invention, the concentration of the alkaline solution is 0.1 - 8 mol / L, preferably 0.2 - 4 mol / L.

[0041] According to an embodiment of the present invention, the oxidant in the first oxidant solution includes a peroxide selected from hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate.

[0042] According to an embodiment of the present invention, in step (2), the reaction temperature T1 of the co-precipitation reaction is 30 - 60 °C, preferably T1 is 40 - 60 °C.

[0043] According to an embodiment of the present invention, the co-precipitation reaction is carried out under stirring conditions, and the stirring speed is 200 - 800 r / min, preferably 400 - 800 r / min.

[0044] According to an embodiment of the present invention, the pH value of the co-precipitation reaction is 7 - 11, preferably 8 - 10.

[0045] According to an embodiment of the present invention, in step (3), the phosphorus source in the phosphorus source solution includes a phosphorus source selected from at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0046] According to an embodiment of the present invention, the oxidant in the second oxidant solution includes at least one selected from hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate.

[0047] According to an embodiment of the present invention, in step (4), the molar amount of phosphorus in the phosphorus source solution to the total molar amount of metal elements in the iron source and the manganese source is (1-5):1, preferably (1-3):1.

[0048] According to an embodiment of the present invention, the reaction temperature T2 of the transformation reaction is 50-90 °C, preferably 70-90 °C.

[0049] According to an embodiment of the present invention, the reaction time of the transformation reaction is 1-10 h, preferably 3-6 h.

[0050] According to an embodiment of the present invention, the transformation reaction is carried out under stirring conditions, and the stirring speed is 200-800 r / min, preferably 400-800 r / min.

[0051] According to an embodiment of the present invention, the pH value of the transformation reaction is 0.5-3, preferably 0.5-2.0.

[0052] According to an embodiment of the present invention, in step (5), the first carbon source includes at least one selected from glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0053] According to an embodiment of the present invention, the inert reducing atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0054] According to an embodiment of the present invention, the sintering temperature is 400-800 °C, preferably 500-700 °C; the sintering time is 1-10 h, preferably 3-6 h.

[0055] According to an embodiment of the present invention, the weight loss rate of the lithium iron manganese phosphate precursor at 900 °C is 2.0% or less.

[0056] According to an embodiment of the present invention, in step (6), the lithium source includes at least one selected from lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium nitrate, and lithium acetate.

[0057] According to an embodiment of the present invention, the second carbon source includes at least one selected from glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0058] According to an embodiment of the present invention, in step (7), the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0059] According to an embodiment of the present invention, the sintering temperature is 500 - 1000 °C, preferably 600 - 800 °C; the sintering time is 4 - 20 h, preferably 6 - 12 h.

[0060] The third aspect of the present invention provides a battery, which includes the lithium iron manganese phosphate cathode material described in the first aspect or the lithium iron manganese phosphate cathode material obtained by the preparation method described in the second aspect.

[0061] The fourth aspect of the present invention provides an electrical device, which includes the battery described in the third aspect.

[0062] The additional aspects and advantages of the present invention will be partly given in the following description, partly become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0063] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0064] Figure 1 Shows the XRD pattern of the lithium iron manganese phosphate precursor prepared in Example 1 of the present invention;

[0065] Figure 2 Shows the SEM image of the lithium iron manganese phosphate precursor prepared in Example 1 of the present invention;

[0066] Figure 3 Shows the XRD pattern of the lithium iron manganese phosphate cathode material prepared in Example 1 of the present invention;

[0067] Figure 4 Shows the SEM image of the lithium iron manganese phosphate cathode material prepared in Example 1 of the present invention;

[0068] Figure 5 Shows the sampling position map when performing EDS analysis on the lithium iron manganese phosphate cathode materials prepared in the example and comparative example of the present invention. Detailed Embodiments

[0069] The embodiments of the technical solutions of the present invention will be described in detail below. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0070] Reference to "embodiments" in this document means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present invention. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment each time, nor are they independent or alternative embodiments mutually exclusive of other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0071] The "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present invention, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] If there is no special instruction, all embodiments and alternative embodiments of the present invention can be combined with each other to form new technical solutions.

[0073] If there is no special instruction, all technical features and alternative technical features of the present invention can be combined with each other to form new technical solutions.

[0074] If there is no special instruction, all steps of the present invention can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0075] The first aspect of the present invention provides a lithium iron manganese phosphate cathode material, which has manganese element, iron element and doped metal element, and the standard deviation of the molar proportion of manganese element in the lithium iron manganese phosphate is less than or equal to 1%; the standard deviation of the molar proportion of iron element is less than or equal to 1%; the standard deviation of the molar proportion of doped metal element is less than or equal to 1%.

[0076] The inventors found that by controlling the standard deviation of the molar proportions of manganese, iron and doped metal elements in the lithium iron manganese phosphate cathode material, the distribution of metal elements in the lithium iron manganese phosphate cathode material can be made uniform, the reduction of the battery discharge capacity caused by the uneven distribution of metal elements such as manganese and iron can be reduced, and at the same time, the cycle life of the battery containing it is also improved.

[0077] According to specific embodiments of the present invention, the standard deviation of the molar proportion of manganese element can be 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0%, etc., and the standard deviation of the molar proportion of iron element can be 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0%, etc., and the standard deviation of the molar proportion of doped metal element can be 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0%, etc. When the standard deviations of the molar proportions of manganese, iron and doped metal elements in the lithium iron manganese phosphate are within the above ranges, the reduction of the battery discharge capacity caused by the uneven distribution of metal elements such as manganese and iron can be reduced, and at the same time, the cycle life of the battery containing it is improved.

[0078] According to a preferred embodiment of the present invention, the standard deviation of the molar proportion of manganese element is less than or equal to 0.5%; the standard deviation of the molar proportion of iron element is less than or equal to 0.5%; the standard deviation of the molar proportion of doped metal element is less than or equal to 0.5%.

[0079] Specifically, the standard deviation, also known as the standard deviation of a sample, is a measure of the degree to which a set of values (in the present invention, referring to the molar proportion of metal elements) are dispersed from the average value. A larger standard deviation represents a larger difference between most of the values and their average value; a smaller standard deviation represents that these values are closer to the average value. In the present invention, the smaller the standard deviation of the molar proportion of the target metal element, the more uniform the distribution of the metal element.

[0080] Specifically, the calculation formula for the standard deviation σ of the molar proportion of the target metal element is: σ = [Σ(m i -m0) 2 / n] 1 / 2 ,

[0081] where i = 1, 2... n, mi represents the molar proportion of the target metal element in the \(i\)-th region among \(n\) regions. \(m_0\) represents the average molar proportion of the target metal element in the lithium iron phosphate manganese cathode material, that is, based on the total molar amount of metal elements other than lithium in the lithium iron phosphate manganese cathode material, the molar proportion of the target metal element. In addition, \(\sum\) represents summation. For example, when \(n = 4\), \(\sigma=\left[\sum((m_1 - m_0)\right. 2 +(m_2 - m_0) 2 +(m_3 - m_0) 2 +(m_4 - m_0) 2 ) / 4] 1 / 2 .

[0082] Specifically, the region for calculating the standard deviation is the cross-section of the lithium iron phosphate manganese cathode material particles. The cross-section is the cross-section obtained by conventional ion beam cross-section scanning electron microscopy testing. A single particle is randomly selected. The cross-section of the selected particle may pass through the center of the particle or may not pass through the center of the particle, both of which are within the protection scope of the present invention.

[0083] Specifically, the "standard deviation of the molar proportion of manganese element", the "standard deviation of the molar proportion of iron element", and the "standard deviation of the molar proportion of doped metal element" are obtained by performing ion beam cross-section scanning electron microscopy testing on the lithium iron phosphate manganese cathode material. A single particle is randomly selected from the cross-section SEM image and equally divided into six parts along any diameter. EDS analysis is performed at the five equally divided point positions, and the concentration shown by the molar ratio when the total molar amount of metal elements other than lithium is set to 1 is analyzed. Finally, the average result is statistically calculated.

[0084] According to a specific embodiment of the present invention, the molar content ratio of the total amount of metal elements other than lithium to the phosphorus element in the lithium iron phosphate manganese is \(K\), and \(K\) satisfies \(0.97\lt K\lt1.03\), preferably \(0.98\lt K\lt1.02\). This indicates that the phosphate radical forms a stable framework system and there is no other impurity phase, enabling the lithium iron phosphate manganese cathode material to have excellent electrochemical performance.

[0085] According to a specific embodiment of the present invention, the doped metal element includes but is not limited to at least one selected from Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti. Thus, the addition of the doping element can change its electronic structure and crystal structure, effectively improving the electrochemical performance.

[0086] According to a specific embodiment of the present invention, the lithium iron manganese phosphate cathode material has a secondary particle structure formed by primary particles. The average particle size of the secondary particles is 1-50 μm. For example, the average particle size of the secondary particles can be 1 μm, 3 μm, 7 μm, 10 μm, 13 μm, 15 μm, 17 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc., and is preferably 7-15 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc. The average particle size of the primary particles is 10-500 nm. For example, the average particle size of the primary particles can be 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., and is preferably 10-200 nm, such as 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, etc.

[0087] Specifically, the average particle size of the secondary particles can be measured by a Malvern laser particle size analyzer Mastersizer2000. The average particle size of the primary particles can be obtained by measuring the scanning electron microscope images.

[0088] According to a specific embodiment of the present invention, the tap density of the lithium iron manganese phosphate cathode material is 2.0-3.0 g / cm 3 , for example, the tap density of the lithium iron manganese phosphate cathode material is 2.0 g / cm 3 , 2.5 g / cm 3 , 3.0 g / cm 3 , and is preferably 2.5-3.0 g / cm 3 , such as 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3.0 g / cm 3 etc.

[0089] According to a specific embodiment of the present invention, the specific surface area of the lithium iron manganese phosphate cathode material is 10-25 m 2 / g. For example, the specific surface area of the lithium iron manganese phosphate cathode material is 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 25 m 2 / g, etc.

[0090] According to specific embodiments of the present invention, the manganese dissolution rate in the lithium iron manganese phosphate cathode material is < 50 ppm, preferably < 30 ppm; the iron dissolution rate is < 50 ppm, preferably < 20 ppm. This indicates that during charge and discharge, the cathode material maintains a stable structure and has good cycling performance.

[0091] Specifically, the dissolution rate refers to the metal content in the filtrate measured after dispersing the lithium iron manganese phosphate cathode material in a solvent and allowing it to stand for a certain period of time.

[0092] According to specific embodiments of the present invention, the volume resistivity of the lithium iron manganese phosphate cathode material is 10 - 10 3 Ω·cm. For example, the volume resistivity of the lithium iron manganese phosphate cathode material is 10 Ω·cm, 10 2 Ω·cm, 10 3 Ω·cm, etc.

[0093] According to specific embodiments of the present invention, the lithium iron manganese phosphate cathode material has the chemical formula shown in formula (1):

[0094] Li d Mn 1-a-b-c Fe a M b M' c PO4 / C(1)

[0095] Where 0.1 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.04, 0 ≤ c ≤ 0.04, 0.9 < d ≤ 1.2;

[0096] M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti;

[0097] M' is selected from at least one of Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La, and Sm.

[0098] Specifically, the doping metal element M can be the element doped during the preparation of the lithium iron manganese phosphate precursor, and M' can be the element doped during the preparation of lithium iron manganese phosphate based on the lithium iron manganese phosphate precursor. They can be the same or different, and there is no particular limitation.

[0099] According to specific embodiments of the present invention, based on the total weight of the lithium iron manganese phosphate cathode material, the carbon content is 0.5 - 5 wt%, such as 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, etc.

[0100] The second aspect of the present invention provides a method for preparing a lithium iron manganese phosphate cathode material, and the preparation method includes the following steps:

[0101] (1) Prepare a mixed solution, an alkaline solution, and a first oxidant solution containing a manganese source, an iron source, and an M source respectively.

[0102] According to specific embodiments of the present invention, the specific type of the manganese source is not particularly limited, and those skilled in the art can select according to actual situations. For example, divalent manganese salts, preferably at least one of manganese sulfate, manganese chloride, manganese nitrate, and manganese acetate.

[0103] According to specific embodiments of the present invention, the specific type of the iron source is not particularly limited, and those skilled in the art can select according to actual situations. For example, divalent iron salts, preferably at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0104] According to specific embodiments of the present invention, the M source is used to provide the M element, and the M element is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti. The specific type of the M source is not particularly limited, and those skilled in the art can select according to actual situations. For example, aluminum sulfate, titanium oxysulfate, etc.

[0105] According to specific embodiments of the present invention, the total concentration of the manganese source, the iron source, and the M source in the mixed solution is 0.1 - 4 mol / L. For example, the total concentration of the manganese source, the iron source, and the M source in the mixed solution is 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, etc., preferably 0.2 - 2 mol / L.

[0106] According to specific embodiments of the present invention, the specific type of the alkaline solution is not particularly limited, and those skilled in the art can select according to actual situations. For example, sodium hydroxide solution. Its concentration is also not particularly limited, and those skilled in the art can select according to actual situations. For example, the concentration of the alkaline solution is 0.1 - 8 mol / L, preferably 0.2 - 4 mol / L.

[0107] According to specific embodiments of the present invention, the specific type of the oxidant in the first oxidant solution is not particularly limited, and those skilled in the art can select according to actual situations. For example, at least one of hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate, preferably hydrogen peroxide, potassium permanganate, and sodium persulfate.

[0108] (2) Add the mixed solution, the alkaline solution, and the first oxidant solution into the reaction kettle in a co-current manner to carry out a coprecipitation reaction to obtain a first precipitate.

[0109] The present invention uses a manganese source, an iron source, an M source, an alkaline solution, and a first oxidant as raw materials to uniformly coprecipitate manganese and iron under alkaline conditions; at the same time, it is more conducive to the oxidation of divalent manganese under alkaline conditions, and the prepared first precipitate can achieve uniform coprecipitation of manganese and iron, and the metal stoichiometric ratio is stable.

[0110] According to a specific embodiment of the present invention, the reaction temperature of the coprecipitation reaction is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the reaction temperature T1 is 30-60°C, specifically 30°C, 40°C, 50°C, 60°C, etc., and preferably 40-60°C.

[0111] According to a specific embodiment of the present invention, the coprecipitation reaction can be carried out under stirring, and the selection of the stirring speed is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the stirring speed is 200-800 r / min, specifically 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, etc., and preferably 400-800 r / min.

[0112] According to a specific embodiment of the present invention, the pH value of the coprecipitation reaction is controlled at 7-11. For example, the pH value of the coprecipitation reaction is 7, 8, 9, 10, 11, etc., and preferably 8-10, thereby achieving a better coprecipitation effect.

[0113] According to a specific embodiment of the present invention, the speed at which the mixed solution, the alkaline solution, and the first oxidant solution flow into the reaction kettle in this step is not particularly limited, and those skilled in the art can select it according to the actual situation, so as to enable uniform coprecipitation of manganese and iron.

[0114] According to a specific embodiment of the present invention, step (2) may further include filtering and washing after the coprecipitation reaction to obtain a first precipitate. By filtering and washing, it is beneficial to remove sulfate radicals in the mother liquor (because common manganese sources, iron sources, and M sources are mostly sulfates), and avoid excessive sulfate radicals being wrapped during the subsequent transformation to generate phosphates, resulting in too high sulfur content in the finished product.

[0115] Specifically, the type of the washing liquid used for washing is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, pure water at 20-90°C, and preferably pure water at 60-90°C.

[0116] (3) Prepare a phosphorus source solution and a second oxidant solution.

[0117] According to specific embodiments of the present invention, the specific type of the phosphorus source is not particularly limited, and those skilled in the art can select according to the actual situation. For example, it can be at least one of phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium hydrogen phosphate. Preferably, it is at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0118] According to specific embodiments of the present invention, the specific type of the second oxidant is not particularly limited, and those skilled in the art can select according to the actual situation. For example, it can be at least one of hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate. Preferably, it is at least one of hydrogen peroxide, potassium permanganate, sodium persulfate, and ammonium persulfate.

[0119] (4) Mix the phosphorus source solution, the second oxidant solution, and the first precipitate, and carry out a transformation reaction to obtain a second precipitate.

[0120] According to specific embodiments of the present invention, the ratio of the molar amount of phosphorus in the phosphorus source solution to the total molar amount of metal elements in the iron source and the manganese source is (1 - 5):1, such as 1:1, 2:1, 3:1, 4:1, 5:1, etc. Preferably, it is (1 - 3):1.

[0121] According to specific embodiments of the present invention, the reaction temperature of the transformation reaction is not particularly limited, and those skilled in the art can select according to the actual situation. For example, the reaction temperature T2 is 50 - 90°C, specifically it can be 50°C, 60°C, 70°C, 80°C, 90°C, etc. Preferably, it is 70 - 90°C.

[0122] According to specific embodiments of the present invention, the reaction time of the transformation reaction is not particularly limited, and those skilled in the art can select according to the actual situation. For example, the reaction time is 1 - 10 h, specifically it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc. Preferably, it is 3 - 6 h.

[0123] According to specific embodiments of the present invention, the pH value of the transformation reaction is controlled at 0.5 - 3. For example, the pH value of the coprecipitation reaction is 0.5, 1, 1.5, 2, 2.5, 3, etc. Preferably, it is 0.5 - 2.0, thereby achieving a better coprecipitation effect.

[0124] According to specific embodiments of the present invention, the transformation reaction can be carried out under stirring, and the selection of the stirring speed is not particularly limited. Those skilled in the art can select according to the actual situation. For example, the stirring speed is 200 - 800 r / min, specifically it can be 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, etc. Preferably, it is 400 - 800 r / min.

[0125] According to a specific embodiment of the present invention, step (4) may further include performing a transformation reaction, followed by filtration and washing to obtain a second precipitate. The type of the washing liquid used for washing is not particularly limited, and those skilled in the art can select according to the actual situation. For example, pure water at 20-90 °C, preferably pure water at 60-90 °C.

[0126] (5) Mix the second precipitate with a first carbon source and sinter in an inert reducing atmosphere to obtain the lithium iron manganese phosphate precursor.

[0127] The present invention calcines the second precipitate to obtain a lithium iron manganese phosphate precursor. The second precipitate usually contains crystal water, and the content of crystal water is not easy to control, which may lead to deviation in the batching process. At the same time, due to the presence of crystal water, structural collapse is likely to occur during the calcination process, blocking the lithium ion diffusion channels. The weight loss rate of the lithium iron manganese phosphate precursor obtained by the present invention is below 2.0% at 900 °C, indicating that the lithium iron manganese phosphate precursor basically does not contain crystal water. Therefore, the problem of unstable batching in the subsequent preparation process of the cathode material is avoided, as well as its impact on the electrochemical performance of the battery.

[0128] According to a specific embodiment of the present invention, the specific type of the first carbon source is not particularly limited, and those skilled in the art can select according to the actual situation. For example, at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine, preferably at least one of glucose, sucrose, starch, and cellulose.

[0129] According to a specific embodiment of the present invention, the sintering of the second precipitate is carried out in an inert reducing atmosphere to obtain a pure-phase pyrophosphate, which is beneficial to maintaining the uniform distribution state of manganese and iron. If the second precipitate is sintered in air or an inert atmosphere, a mixture phase of pyrophosphate and phosphate will appear, resulting in phase separation of manganese and iron and affecting the uniform distribution of manganese and iron. The specific type of the inert reducing atmosphere is not particularly limited, and those skilled in the art can select according to the actual situation. For example, a nitrogen atmosphere and / or an argon atmosphere.

[0130] According to a specific embodiment of the present invention, the sintering temperature is not particularly limited, and those skilled in the art can select according to the actual situation. For example, the reaction temperature T2 is 400-800 °C, specifically 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, etc., preferably 500-700 °C.

[0131] According to specific embodiments of the present invention, the sintering time is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the reaction time is 1-10 h, specifically 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc., and preferably 3-6 h.

[0132] According to specific embodiments of the present invention, the sulfur content of impurities in the lithium iron manganese phosphate precursor is ≤200 ppm. This indicates that the impurity content in the lithium iron manganese phosphate precursor is relatively low, further reducing the adverse effects on the battery capacity and cycle performance.

[0133] According to specific embodiments of the present invention, the tap density of the lithium iron manganese phosphate precursor is 0.80-1.50 g / cm 3 , for example, the tap density of the lithium iron manganese phosphate precursor is 0.80 g / cm 3 , 0.90 g / cm 3 , 1.00 g / cm 3 , 1.10 g / cm 3 , 1.20 g / cm 3 , 1.30 g / cm 3 , 1.40 g / cm 3 , 1.50 g / cm 3 etc.

[0134] According to specific embodiments of the present invention, the specific surface area of the lithium iron manganese phosphate precursor is 10-40 m 2 / g. For example, the specific surface area of the lithium iron manganese phosphate cathode material is 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 25 m 2 / g, 30 m 2 / g, 35 m 2 / g, 40 m 2 / g, etc.

[0135] According to specific embodiments of the present invention, the lithium iron manganese phosphate precursor has a secondary particle structure formed by primary particles. The primary particle size of the lithium iron manganese phosphate precursor is 20-200 nm. For example, the primary particle size of the lithium iron manganese phosphate precursor is 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, etc.

[0136] According to specific embodiments of the present invention, the median particle size D of the lithium iron manganese phosphate precursor50 is 0.5 - 5 μm. For example, the median particle size D of the lithium iron manganese phosphate precursor 50 is 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, etc.

[0137] According to a specific embodiment of the present invention, the lithium iron manganese phosphate precursor has the chemical formula shown in formula (2):

[0138] (Mn 1-x-y Fe x M y )2P2O7 / C(2)

[0139] where 0.1 ≤ x ≤ 0.5 and 0 ≤ y ≤ 0.04;

[0140] M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti.

[0141] According to a specific embodiment of the present invention, based on the total weight of the lithium iron manganese phosphate precursor, the carbon content is 0.5 - 5 wt%, for example, based on the total weight of the lithium iron manganese phosphate precursor, the carbon content is 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%.

[0142] (6) Mix the lithium iron manganese phosphate precursor with a lithium source, a second carbon source, and an M' source to obtain a mixture.

[0143] According to a specific embodiment of the present invention, the type of the lithium source is not particularly limited, and those skilled in the art can select according to the actual situation. For example, at least one of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium nitrate, and lithium acetate, preferably at least one of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0144] According to a specific embodiment of the present invention, the type of the second carbon source is not particularly limited, and those skilled in the art can select according to the actual situation. For example, at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine, preferably at least one of glucose, sucrose, starch, and cellulose.

[0145] According to a specific embodiment of the present invention, the M' source is used to provide M' elements, and the M' elements are selected from at least one of Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La, and Sm. The type of the M' source is not particularly limited, and those skilled in the art can select according to the actual situation, such as magnesium carbonate, etc.

[0146] According to a specific embodiment of the present invention, step (6) may further include: in the presence of a solvent, mixing and homogenizing the lithium iron manganese phosphate precursor with a lithium source, a second carbon source, and an M' source to obtain a slurry.

[0147] Specifically, the type of the solvent is not particularly limited as long as a uniform slurry can be formed. Those skilled in the art can select according to the actual situation, such as water, ethanol, etc., and water is preferred.

[0148] Specifically, the dosage of the solvent is not particularly limited, and it is also based on the ability to form a uniform slurry.

[0149] (7) Sintering the mixture under an inert atmosphere to obtain the lithium iron manganese phosphate cathode material.

[0150] According to a specific embodiment of the present invention, the type of the inert atmosphere is not particularly limited, and those skilled in the art can select according to the actual situation, such as a nitrogen atmosphere and / or an argon atmosphere.

[0151] According to a specific embodiment of the present invention, the sintering temperature is not particularly limited, and those skilled in the art can select according to the actual situation. For example, the sintering temperature is 500 - 1000 °C, specifically 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, etc., and preferably 600 - 800 °C.

[0152] According to a specific embodiment of the present invention, the sintering time is not particularly limited, and those skilled in the art can select according to the actual situation. For example, the reaction time is 4 - 20 h, specifically 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, etc., and preferably 6 - 12 h.

[0153] According to a specific embodiment of the present invention, step (7) may further include: removing the solvent in the slurry to obtain a dry material, and then calcining the dry material under the protection of an inert atmosphere to obtain the lithium iron manganese phosphate cathode material.

[0154] Specifically, the solvent in the slurry can be removed by direct evaporation. The evaporation temperature and process are not particularly limited, and those skilled in the art can select according to the actual situation. For example, static drying or spray drying can be used to remove the solvent in the slurry.

[0155] The third aspect of the present invention provides a battery, which includes the lithium iron manganese phosphate cathode material described in the first aspect of the present invention or the lithium iron manganese phosphate cathode material obtained according to the preparation method described in the second aspect.

[0156] A battery refers to a battery that can be activated by charging after discharging and can be used continuously.

[0157] It can be understood that the battery proposed by the present invention is a lithium-ion battery.

[0158] Generally, a battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate to play a role of isolation. The electrolyte plays a role of conducting ions between the positive electrode plate and the negative electrode plate.

[0159] [Positive electrode plate]

[0160] In some embodiments of the present invention, the positive electrode plate includes a positive current collector, and the positive current collector can be a metal foil, a foam metal, or a composite current collector. For example, as the metal foil, aluminum or stainless steel with a silver surface treatment, stainless steel, copper, aluminum, a carbon electrode, carbon, nickel, or titanium, etc. can be used. The composite current collector can include a polymer material substrate layer and a metal layer. The foam metal can be foam nickel, foam copper, foam aluminum, foam alloy, or foam carbon, etc. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0161] In some embodiments of the present invention, the positive electrode plate may further include a positive active material layer, and the positive active material layer includes a positive active material. The specific type of the positive active material is not limited, and active materials known in the art that can be used for the positive electrode of a battery can be used, and those skilled in the art can select according to actual needs.

[0162] The positive active material layer generally also optionally includes a binder, a conductive agent, and other optional additives.

[0163] As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, SuperP (SP), graphene, and carbon nanofibers.

[0164] As an example, the adhesive may include at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0165] [Negative electrode plate]

[0166] In a battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0167] The negative electrode current collector is generally a structure or component for collecting current. The negative electrode current collector can be various materials in the art suitable for use as the negative electrode current collector of a lithium secondary battery, and can be a conventional metal foil or a composite current collector (for example, a composite current collector can be formed by disposing a metal material on a polymer substrate). As an example, the negative electrode current collector can be a copper foil or a lithium sheet.

[0168] The specific type of the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of a battery can be used, and those skilled in the art can select according to actual needs. As an example, the negative electrode active material can be a combination of one or more of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form an alloy with lithium. Among them, the graphite can be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials can be selected from a combination of one or more of elemental tin, tin oxides, and tin alloys. These materials can all be obtained through commercial channels.

[0169] In some embodiments, in order to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0170] The negative electrode active material layer generally also optionally includes a binder, a conductive agent, and other optional additives.

[0171] As an example, the conductive agent can include one or several of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0172] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0173] As an example, other optional additives may include thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials.

[0174] [Electrolyte solution]

[0175] The electrolyte solution may include an electrolyte salt and a solvent.

[0176] As an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro bis(oxalato)phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0177] As an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0178] In some embodiments, the electrolyte solution further includes additives. For example, the additives may include negative electrode film-forming additives, may also include positive electrode film-forming additives, and may further include additives that can improve certain battery performances, such as additives for improving battery overcharge performance, additives for improving battery high-temperature performance, and additives for improving battery low-temperature performance.

[0179] [Separator]

[0180] As the separator membrane described above, the present invention is not particularly limited, and any publicly known porous structure separator membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it may include a combination of at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0181] The fourth aspect of the present invention provides an electrical device, which includes the battery described in the third aspect. Specifically, the battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0182] The solution of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0183] In the following embodiments,

[0184] Morphology test: Measured by a scanning electron microscope of model S-4800 from Hitachi, Japan;

[0185] Phase test: Tested by an X-ray powder diffractometer of model XRD-6000 from Shimadzu, Japan;

[0186] Specific surface area test: Measured by a specific surface area analyzer of model Tristar II 3020 from Micromertics, USA;

[0187] Tap density test: Measured by a tap density tester of model BT-30 from Baxter;

[0188] Compacted density test: Measured by a compacted density meter of model MCP-PD51 from Mitsubishi Chemical, Japan;

[0189] Impurity sulfur content test: Measured by an ICP-OES spectrometer of model 5800 from Agilent, USA;

[0190] Carbon content test: The carbon content in the positive electrode material was measured by a CS-i carbon and sulfur analyzer from Eltra, Germany;

[0191] The molar contents of Mn, Fe, doping elements, and P at any position of the positive electrode material are measured by EDS test of the 50mm model from Oxford Energy Spectroscopy manufacturer. 2 The EDS test of the 50mm model from Oxford Energy Spectroscopy manufacturer is used for measurement.

[0192] Example 1

[0193] (1) According to the molar ratio of Mn:Fe:Ti = 65:34:1, a certain mass of manganese sulfate, ferrous sulfate, and titanyl sulfate are weighed and dissolved in deionized water to prepare a 2mol / L mixed solution S1; a certain mass of sodium hydroxide is weighed and dissolved in deionized water to prepare a 4mol / L alkaline solution S2; a certain mass of 30% hydrogen peroxide aqueous solution is weighed as the first oxidant solution S3.

[0194] (2) The mixed solution S1, alkaline solution S2, and the first oxidant solution S3 are added into the reaction kettle in parallel flow for synthesis reaction. The synthesis reaction temperature is 60°C, the stirring speed is 500r / min, and the pH of the reaction slurry is controlled to be 9.6 by regulating the inlet flow rate of the alkaline solution S2. After the synthesis reaction is completed, filtration and washing are carried out to obtain the first precipitate W1.

[0195] (3) A certain mass of 85% concentrated phosphoric acid is weighed as the phosphorus source solution S4; a certain mass of sodium persulfate is weighed and dissolved in deionized water to prepare a 2mol / L second oxidant solution S5.

[0196] (4) The first precipitate W1 is slurried and then returned to the reaction kettle, and the phosphorus source solution S4 and the second oxidant solution S5 are added for transformation reaction; the transformation reaction temperature is 90°C, the stirring speed is 500r / min, and the pH of the transformation reaction slurry is 1.0. After the transformation reaction is completed, filtration and washing are carried out to obtain the second precipitate W2.

[0197] (5) After the second precipitate is dried at 120°C for 6h, it is uniformly mixed with a certain mass of glucose; the mixture is calcined at 500°C for 3h in a nitrogen atmosphere to obtain the lithium iron manganese phosphate precursor.

[0198] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.34 Ti 0.01 )2P2O7 / C, where the median diameter D 50 is 3.36μm, the primary particle size is 100nm, the tap density is 1.27g / cm 3 , the specific surface area is 18.8m 2 / g, the impurity sulfur content is 52ppm, and the carbon content is 1.25wt%. Figure 1 is the XRD pattern of the lithium iron manganese phosphate precursor, Figure 2As its SEM image shows, it can be seen that the primary particles of the lithium iron manganese phosphate precursor prepared by the present invention are relatively small, and when it is used to prepare the lithium iron manganese phosphate cathode material, it is more conducive to the uniform mixing with the lithium source and the carbon source.

[0199] (6) Mix the prepared lithium iron manganese phosphate precursor, lithium carbonate, magnesium carbonate and glucose with pure water according to a molar ratio of 1:0.52:0.01:0.7, and mix them evenly by mechanical stirring to obtain a slurry;

[0200] (7) Evaporate the slurry in the heating furnace tray, then put it into a vacuum oven at 85 °C and dry it for 4 h to obtain dry material; calcine the dry material in a nitrogen atmosphere at 650 °C for 10 h, and after sieving, obtain the lithium iron manganese phosphate cathode material.

[0201] The chemical formula of the lithium iron manganese phosphate cathode material prepared in the above example is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 80 nm, and the tap density is 2.42 g / cm 3 , and the specific surface area is 14.3 m 2 / g, and the carbon content is 1.85 wt%. Figure 3 As the XRD pattern of the lithium iron manganese phosphate cathode material, it can be seen that manganese and iron do not form a phase separation in the structure, and no other impurities are generated. Figure 4 As its SEM image, the primary particles of this lithium iron manganese phosphate cathode material are small and uniform, and there is no carbon agglomeration on the surface, indicating that carbon is uniformly coated on the surface of the cathode material.

[0202] Example 2

[0203] Compared with Example 1, the difference lies in:

[0204] In step (1), the doping element is Al.

[0205] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.34 Al 0.01 )2P2O7 / C, and its median diameter D 50 is 3.05 μm, the primary particle size is 95 nm, the tapped density is 1.28 g / cm 3 , and the specific surface area is 18.5 m 2 / g, the impurity sulfur content is 55 ppm, and the carbon content is 1.22 wt%.

[0206] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn0.642 Fe 0.339 Al 0.01 Mg 0.01 PO4 / C, with an average particle size of the primary particles of 83 nm and a tap density of 2.42 g / cm 3 , and a specific surface area of 14.3 m 2 / g and a carbon content of 1.79 wt%.

[0207] Example 3

[0208] Compared with Example 1, the differences are as follows:

[0209] In step (1), the molar ratio of Mn, Fe, and Ti is 79:20:1;

[0210] In step (6), the M' source is tungsten oxide.

[0211] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.79 Fe 0.20 Ti 0.01 )2P2O7 / C, where the median particle size D 50 is 3.12 μm, the primary particle size is 100 nm, the tapped density is 1.26 g / cm 3 , and the specific surface area is 18.6 m 2 / g, the impurity sulfur content is 50 ppm, and the carbon content is 1.25 wt%.

[0212] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.782 Fe 0.198 Ti 0.01 W 0.01 PO4 / C, with an average particle size of the primary particles of 85 nm and a tap density of 2.42 g / cm 3 , and the specific surface area is 14.5 m 2 / g, and the carbon content is 1.80 wt%.

[0213] Example 4

[0214] Compared with Example 1, the differences are as follows:

[0215] There is no doping element M in step (1).

[0216] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.35 )2P2O7 / C, where the median particle size D 50 is 3.35 μm, the primary particle size is 105 nm, the tapped density is 1.25 g / cm 3 , and the specific surface area is 18.8 m2 / g, the impurity sulfur content is 63 ppm, and the carbon content is 1.25 wt%.

[0217] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.644 Fe 0.346 Mg 0.01 PO4 / C, the average particle size of its primary particles is 80 nm, and the tap density is 2.40 g / cm 3 , and the specific surface area is 14.0 m 2 / g, and the carbon content is 1.80 wt%.

[0218] Example 5

[0219] Compared with Example 1, the difference is that:

[0220] In step (2), the pH of the reaction slurry is 10.6.

[0221] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.34 Ti 0.01 )2P2O7 / C, the median particle size D 50 is 2.68 μm, the primary particle size is 105 nm, the tapped density is 1.22 g / cm 3 , and the specific surface area is 20.6 m 2 / g, the impurity sulfur content is 66 ppm, and the carbon content is 1.24 wt%.

[0222] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 85 nm, and the tap density is 2.35 g / cm 3 , and the specific surface area is 15.3 m 2 / g, and the carbon content is 1.92 wt%.

[0223] Example 6

[0224] Compared with Example 1, the difference is that:

[0225] In step (4), the pH of the transformation reaction slurry is 1.5.

[0226] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.34 Ti 0.01 )2P2O7 / C, the median particle size D 50is 3.25 μm, the primary particle size is 140 nm, the tapped density is 1.32 g / cm 3 , and the specific surface area is 16.6 m 2 / g, the impurity sulfur content is 45 ppm, and the carbon content is 1.23 wt%.

[0227] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 100 nm, the tap density is 2.33 g / cm 3 , and the specific surface area is 14.8 m 2 / g, and the carbon content is 1.88 wt%.

[0228] Example 7

[0229] Compared with Example 1, the difference is that:

[0230] In step (5), the calcination temperature is 600 °C.

[0231] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above example is (Mn 0.65 Fe 0.34 Ti 0.01 )2P2O7 / C, and its median diameter D 50 is 3.65 μm, the primary particle size is 150 nm, the tapped density is 1.30 g / cm 3 , and the specific surface area is 17.6 m 2 / g, the impurity sulfur content is 36 ppm, and the carbon content is 1.06 wt%.

[0232] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 70 nm, the tap density is 2.34 g / cm 3 , and the specific surface area is 14.4 m 2 / g, and the carbon content is 1.86 wt%.

[0233] Comparative Example 1

[0234] Compared with Example 1, the difference is that:

[0235] Step (5): After drying the second precipitate at 120 °C for 6 h, a lithium iron manganese phosphate precursor is obtained.

[0236] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above comparative example is (Mn 0.65 Fe 0.34 Ti 0.01 )PO4·H2O, where the median particle size D 50 is 3.05 μm, the primary particle size is 200 nm, the tapped density is 1.02 g / cm 3 , the specific surface area is 22.1 m 2 / g, the impurity sulfur content is 256 ppm, and the carbon content is 0 wt%.

[0237] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 180 nm, the tap density is 2.12 g / cm 3 , the specific surface area is 22.6 m 2 / g, and the carbon content is 1.86 wt%.

[0238] Comparative Example 2

[0239] Compared with Example 1, the difference is that:

[0240] Step (5): After drying the second precipitate at 120 °C for 6 h, the second precipitate is calcined at 500 °C for 3 h in a nitrogen atmosphere to obtain a lithium iron manganese phosphate precursor.

[0241] The lithium iron manganese phosphate precursor prepared in the above comparative example is a mixed phase of Mn2P2O7 and FePO4, where the median particle size D 50 is 3.48 μm, the primary particle size is 97 nm, the tapped density is 1.27 g / cm 3 , the specific surface area is 21.5 m 2 / g, the impurity sulfur content is 50 ppm, and the carbon content is 0 wt%.

[0242] The chemical formula of the prepared lithium iron manganese phosphate cathode material is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C, the average particle size of its primary particles is 90 nm, the tap density is 2.15 g / cm 3 , the specific surface area is 18.7 m 2 / g, and the carbon content is 1.88 wt%.

[0243] Comparative Example 3

[0244] (1) Weigh a certain mass of manganese sulfate, ferrous sulfate, and titanium oxysulfate according to the molar ratio of Mn:Fe:Ti = 65:34:1, and dissolve them in deionized water to prepare a 2 mol / L mixed solution S1; weigh a certain mass of sodium hydroxide and dissolve it in deionized water to prepare a 4 mol / L alkaline solution S2; weigh a certain mass of 30% hydrogen peroxide solution as the first oxidant solution S3;

[0245] (2) Add the mixed solution S1, the alkaline solution S2, and the first oxidant solution S3 into the reaction kettle in parallel for a synthesis reaction. The synthesis reaction temperature is 60 °C, the stirring speed is 500 r / min, and the pH of the reaction slurry is controlled at 9.6 by regulating the inlet flow rate of the alkaline solution S2;

[0246] (3) Weigh a certain mass of 85% concentrated phosphoric acid as the phosphorus source solution S4; weigh a certain mass of sodium persulfate and dissolve it in deionized water to prepare a 2 mol / L second oxidant solution S5;

[0247] (4) Directly add the phosphorus source solution S4 and the second oxidant solution S5 into the reaction kettle for a transformation reaction; the transformation reaction temperature is 90 °C, the stirring speed is 500 r / min, and the pH of the transformation reaction slurry is 1.0. After the transformation reaction is completed, filter and wash to obtain a precipitate W;

[0248] (5) After drying the precipitate at 120 °C for 6 h, uniformly mix it with a certain mass of glucose; calcine the mixture in a nitrogen atmosphere at 500 °C for 3 h to obtain a lithium iron manganese phosphate precursor;

[0249] The chemical formula of the lithium iron manganese phosphate precursor prepared in the above comparative example is (Mn 0.65 Fe 0.34 Ti 0.01 )2P2O7 / C, where the median diameter D 50 is 3.33 μm, the primary particle size is 98 nm, the tapped density is 1.26 g / cm 3 , the specific surface area is 18.6 m 2 / g, the impurity sulfur content is 650 ppm, and the carbon content is 1.25 wt%.

[0250] (6) Mix the prepared lithium iron manganese phosphate precursor, lithium carbonate, magnesium carbonate, and glucose with pure water according to the molar ratio of 1:0.52:0.01:0.7, and mix them evenly by mechanical stirring to obtain a slurry;

[0251] (7) Evaporate the slurry to dryness in the heating furnace tray, and then dry it in a vacuum oven at 85 °C for 4 h to obtain a dry material; calcine the dry material in a nitrogen atmosphere at 650 °C for 10 h, and after screening, obtain a lithium iron manganese phosphate cathode material.

[0252] The chemical formula of the lithium iron manganese phosphate cathode material prepared in the above comparative example is Li 1.04 Mn 0.642 Fe 0.339 Ti 0.01 Mg 0.01 PO4 / C. The average particle size of its primary particles is 75 nm, and the tap density is 2.44 g / cm 3 , and the specific surface area is 13.8 m 2 / g, and the carbon content is 1.78 wt%.

[0253] The median particle size D 50 of the lithium iron manganese phosphate precursors prepared in the examples and comparative examples, the primary particle size, the tapped density, the specific surface area, the impurity sulfur content, and the carbon content were tested, and the results are shown in Table 1.

[0254] Table 1

[0255]

[0256]

[0257] The average particle size, tap density, specific surface area, and carbon content of the primary particles of the lithium iron manganese phosphate cathode material were tested, and the results are shown in Table 2.

[0258] Table 2

[0259] Average particle size of primary particles (nm) <![CDATA[Compaction density (g / cm 3 )]]> <![CDATA[Specific surface area (m 2 / g)]]> Carbon content (%) Example 1 80 2.42 14.3 1.85 Example 2 83 2.42 14.3 1.79 Example 3 85 2.42 14.5 1.80 Example 4 80 2.40 14.0 1.80 Example 5 85 2.35 15.3 1.92 Example 6 100 2.33 14.8 1.88 Example 7 70 2.34 14.4 1.86 Comparative Example 1 180 2.12 22.6 1.86 Comparative Example 2 90 2.15 18.7 1.88 Comparative Example 3 75 2.44 13.8 1.78

[0260] The compositions of the lithium iron manganese phosphate precursors and the lithium iron manganese phosphate cathode materials prepared in the examples and comparative examples are as Figure 3 shown.

[0261] Table 3

[0262]

[0263]

[0264] By randomly selecting a single particle of the above-prepared lithium iron manganese phosphate cathode material in the sample ion beam profile SEM, dividing it into six equal parts along any diameter, and performing EDS analysis at the positions of 5 equal points, the molar content ratios of Mn, Fe, and the doped metal element M at the selected points were obtained, and the corresponding standard deviation N and the molar content ratio K of the total amount of metal elements Me other than lithium to phosphorus element were calculated. The EDS sampling positions are shown in Figure 5 , and the analysis results are shown in Tables 4-5.

[0265] Table 4

[0266]

[0267]

[0268]

[0269] Table 5

[0270]

[0271]

[0272] Test Example

[0273] This test example is used to illustrate the electrode material, electrode, lithium-ion battery and its preparation method.

[0274] (1) Preparation of the positive electrode sheet: The lithium iron phosphate manganese positive electrode material, conductive agent carbon nanotubes, and NMP solution of binder PVDF prepared in the above-mentioned examples and comparative examples were mixed at a mass ratio of 90:5:5. The specific method is as follows: Grind the dried positive electrode material and conductive agent in a mortar for 15 minutes. After grinding evenly, add the PVDF solution (mass fraction 5%) according to the ratio and stir on a magnetic stirrer for 6 hours; coat the obtained paste-like slurry evenly on the current collector aluminum foil, then dry it in a vacuum drying oven at 60°C for 20 hours, and then press it into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa. Put the positive electrode sheet into a vacuum drying oven at 120°C and dry it for 12 h.

[0275] (2) Battery assembly: Use a metal lithium sheet with a diameter of 17 mm and a thickness of 1 mm as the negative electrode, use a polyethylene porous membrane with an alumina ceramic layer coated on the surface and a thickness of 25 μm as the separator, select an equal-volume mixture of 1 mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte, and assemble the positive electrode sheet, separator, negative electrode sheet and electrolyte into a 2025-type button battery in an Ar gas glove box with a water content and oxygen content both less than 5 ppm.

[0276] (3) Electrochemical performance test: Use the LAND CT2001A charge and discharge tester of Wuhan Lanbo Electronics Co., Ltd. to perform charge and discharge tests on the battery. The charge and discharge voltage range is 2.5 to 4.4 V. Perform specific capacity tests on the assembled lithium-ion battery at rates of 0.1C and 1C respectively, and perform cycle performance tests at a rate of 1C. The test results are shown in Table 6.

[0277] Table 6

[0278]

[0279] As can be seen from Table 6, the positive electrode material prepared by the present invention has good capacity performance, rate performance and cycle stability. This is because the manganese and iron in the positive electrode material prepared by the present invention are evenly distributed, the impurity content in the precursor is low, the density is high, there is no crystal water, and the structure is stable. The positive electrode material of the present invention has the characteristics of small primary particles and low volume resistivity, which is more conducive to the insertion and extraction of lithium ions, thereby making it have excellent electrochemical performance. Combining Table 6, it can be seen that the 0.2C discharge specific capacity of the positive electrode material of the present invention is greater than 150 mAh / g, the 1C discharge specific capacity is greater than 140 mAh / g, and the 80-week cycle retention rate is greater than 95%. When the precursor has doping elements, the 80-week cycle retention rate is basically greater than 98%.

[0280] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0281] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium manganese iron phosphate positive electrode material, characterized in that: The lithium manganese iron phosphate positive electrode material contains manganese, iron and doped metal elements, wherein the standard deviation of the molar ratio of the manganese element in the lithium manganese iron phosphate is less than or equal to 1%; the standard deviation of the molar ratio of the iron element is less than or equal to 1%; and the standard deviation of the molar ratio of the doped metal element is less than or equal to 1%; The lithium manganese iron phosphate positive electrode material has a chemical formula shown in formula (1): Li d Mn 1-a-b-c Fe a M b M' c PO4 / C(1) Among them, 0.1≤a≤0.5, 0≤b≤0.04, 0 <c≤0.04,0.9<d≤1.2; M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr and Ti; M' is at least one selected from Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm; The method for preparing the lithium manganese iron phosphate positive electrode material comprises the following steps: (1) preparing a mixed solution containing a manganese source, an iron source and an M source, an alkaline solution and a first oxidant solution respectively; (2) adding the mixed solution, the alkaline solution and the first oxidant solution into a reactor in parallel to carry out a co-precipitation reaction to obtain a first precipitate; (3) preparing a phosphorus source solution and a second oxidant solution; (4) mixing the phosphorus source solution, the second oxidant solution and the first precipitate to perform a transformation reaction to obtain a second precipitate; (5) mixing the second precipitate with the first carbon source and sintering them in an inert reducing atmosphere to obtain the lithium manganese iron phosphate precursor; (6) mixing the lithium manganese iron phosphate precursor with a lithium source, a second carbon source, and an M' source to obtain a mixture; (7) sintering the mixture under an inert atmosphere to obtain the lithium manganese iron phosphate positive electrode material; The M source is used to provide the M element, and the M' source is used to provide the M' element.

2. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The standard deviation of the molar percentage of the manganese element is less than or equal to 0.5%.

3. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The standard deviation of the molar percentage of the iron element is less than or equal to 0.5%.

4. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The standard deviation of the molar ratio of the doped metal element is less than or equal to 0.5%.

5. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The molar content ratio of the total amount of metal elements other than lithium in the lithium manganese iron phosphate to the phosphorus element is K, and K satisfies 0.97<K<1.

03.

6. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The molar content ratio of the total amount of metal elements other than lithium in the lithium manganese iron phosphate to the phosphorus element is K, and K satisfies 0.98<K<1.

02.

7. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The lithium iron manganese phosphate positive electrode material has a secondary particle structure formed by primary particles.

8. The lithium iron manganese phosphate positive electrode material according to claim 7, characterized in that: The average particle size of the secondary particles is 1-50 μm.

9. The lithium iron manganese phosphate positive electrode material according to claim 7, characterized in that: The average particle size of the primary particles is 10-500 nm.

10. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The compaction density of the lithium manganese iron phosphate positive electrode material is 2.0-3.0 g / cm 3 .

11. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The specific surface area of ​​the lithium manganese iron phosphate positive electrode material is 10-25m 2 / g.

12. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The manganese dissolution rate of the lithium manganese iron phosphate positive electrode material is less than 50 ppm, and the iron dissolution rate is less than 50 ppm.

13. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The volume resistivity of the lithium manganese iron phosphate positive electrode material is 10-10 3 Ω·cm.

14. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: Based on the total weight of the lithium manganese iron phosphate positive electrode material, the carbon content is 0.5-5wt%.

15. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: The preparation method comprises the following steps: (1) preparing a mixed solution containing a manganese source, an iron source and an M source, an alkaline solution and a first oxidant solution respectively; (2) adding the mixed solution, the alkaline solution and the first oxidant solution into a reactor in parallel to carry out a co-precipitation reaction to obtain a first precipitate; (3) preparing a phosphorus source solution and a second oxidant solution; (4) mixing the phosphorus source solution, the second oxidant solution and the first precipitate to perform a transformation reaction to obtain a second precipitate; (5) mixing the second precipitate with the first carbon source and sintering them in an inert reducing atmosphere to obtain the lithium manganese iron phosphate precursor; (6) mixing the lithium manganese iron phosphate precursor with a lithium source, a second carbon source, and an M' source to obtain a mixture; (7) sintering the mixture under an inert atmosphere to obtain the lithium manganese iron phosphate positive electrode material; Wherein, the M source is used to provide the M element, and the M element is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr and Ti; The M' source is used to provide an M' element, and the M' element is selected from at least one of Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm.

16. The preparation method according to claim 15, characterized in that: In step (1), the total concentration of the manganese source, the iron source and the M source in the mixed solution is 0.1-4 mol / L.

17. The preparation method according to claim 15, characterized in that: In step (1), the manganese source is selected from divalent manganese salts.

18. The preparation method according to claim 15, characterized in that: In step (1), the iron source is selected from divalent iron salts.

19. The preparation method according to claim 15, characterized in that: In step (1), the concentration of the alkaline solution is 0.1-8 mol / L.

20. The preparation method according to claim 15, characterized in that: In step (1), the oxidant in the first oxidant solution includes at least one selected from hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate.

21. The preparation method according to claim 15, characterized in that: In step (2), the reaction temperature T1 of the coprecipitation reaction is 30-60°C.

22. The preparation method according to claim 15, characterized in that: In step (2), the pH value of the coprecipitation reaction is 7-11.

23. The preparation method according to claim 15, characterized in that: In step (3), the phosphorus source in the phosphorus source solution includes at least one selected from phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate.

24. The preparation method according to claim 15, characterized in that: In step (3), the oxidant in the second oxidant solution includes at least one selected from hydrogen peroxide, potassium permanganate, sodium persulfate, ammonium persulfate, sodium hypochlorite, and sodium ferrate.

25. The preparation method according to claim 15, characterized in that: In step (4), the ratio of the molar amount of phosphorus in the phosphorus source solution to the total molar amount of metal elements in the iron source and the manganese source is (1-5):

1.

26. The preparation method according to claim 15, characterized in that: In step (4), the reaction temperature T2 of the transformation reaction is 50-90°C.

27. The preparation method according to claim 15, characterized in that: In step (4), the reaction time of the transformation reaction is 1-10h.

28. The preparation method according to claim 15, characterized in that: In step (4), the pH value of the transformation reaction is 0.5-3.

29. The preparation method according to claim 15, characterized in that: In step (5), the first carbon source includes at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol and dopamine.

30. The preparation method according to claim 15, characterized in that: In step (5), the inert reducing atmosphere is selected from a nitrogen atmosphere and / or an argon atmosphere.

31. The preparation method according to claim 15, characterized in that: In step (5), the sintering temperature is 400-800°C.

32. The preparation method according to claim 15, characterized in that: In step (5), the sintering time is 1-10 hours.

33. The preparation method according to claim 15, characterized in that: In step (5), the weight loss rate of the lithium iron manganese phosphate precursor at 900° C. is less than 2.0%.

34. The preparation method according to claim 15, characterized in that: In step (6), the lithium source includes at least one selected from lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium nitrate, and lithium acetate.

35. The preparation method according to claim 15, characterized in that: In step (6), the second carbon source includes at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol and dopamine.

36. The preparation method according to claim 15, characterized in that: In step (7), the inert atmosphere includes nitrogen atmosphere and / or argon atmosphere.

37. The preparation method according to claim 15, characterized in that: In step (7), the sintering temperature is 500-1000°C.

38. The preparation method according to claim 15, characterized in that: In step (7), the sintering time is 4-20 hours.

39. A battery, characterized in that: The battery comprises the lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 14 or the lithium iron manganese phosphate positive electrode material obtained by the preparation method according to any one of claims 15 to 38.

40. An electrical device, characterized in that: Comprising the battery of claim 39.

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