Lithium manganese iron phosphate material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention discloses a lithium manganese iron phosphate material and a preparation method thereof, an electrochemical device and electronic equipment. The preparation method of the lithium iron manganese phosphate material comprises the following steps: S1, carrying out first hydrothermal reaction on an iron manganese phosphate precursor to obtain a first mixture; s2, performing a second hydrothermal reaction on the second mixture under a supercritical condition to obtain an intermediate; the second mixture comprises the first mixture and a lithium source; and S3, sintering the third mixture, wherein the third mixture comprises the intermediate and the carbon source. The lithium manganese iron phosphate material prepared by the preparation method is low in impurity ion content, and the electrochemical device prepared from the lithium manganese iron phosphate material has excellent electrical properties.

Description

Technical Field

[0001] This invention provides a lithium manganese iron phosphate material, its preparation method, an electrochemical device, and an electronic device. Background Technology

[0002] Lithium iron manganese phosphate (LMP) is a phosphate-based cathode material. Compared to traditional lithium cobalt oxide and lithium manganese oxide, LMP offers higher safety, lower cost, and better environmental friendliness, making it a highly sought-after material. In the context of the rapid development of the electric vehicle market, LMP, as a high-performance, low-cost cathode material, has been widely adopted. It not only provides higher energy and power densities, extending battery range, but also meets the requirements for fast charging and high-temperature stability. Furthermore, LMP does not contain the rare metal cobalt, reducing dependence on cobalt resources and thus lowering battery manufacturing costs. Therefore, LMP has broad application prospects.

[0003] However, since its inception, the large-scale production process of lithium iron phosphate has not yet been fully mature. Industrial production often employs a simple, stable, and high-yield co-precipitation synthesis method for large-scale production. However, the biggest problem with co-precipitation synthesis lies in the impurities introduced during the precipitation process (such as Na+ introduced by precipitants, oxidants, etc.). + K + With NH4 + The difficulty in removing impurity ions (such as iron phosphate and manganese phosphate) is that the precipitates formed by the sedimentation of impurities are not easily removed in subsequent processes. Common impurity removal methods include simple multiple water washing or crushing. However, these methods often fail to remove the large number of impurity ions and some impurity by-product particles carried by the rapid formation and precipitation of particles. Therefore, there are problems such as incomplete impurity removal or ineffectiveness. Moreover, the most common water washing method in industry requires repeated washing, which is not only ineffective but can only remove impurity ions attached to the surface of iron phosphate and manganese phosphate particles. At the same time, the huge amount of water used is obviously contrary to the current domestic green and economical concept.

[0004] In addition, the conventional liquid-phase coprecipitation synthesis method in the existing technology results in non-uniform composition of lithium manganese iron phosphate, which leads to a significant reduction in the electrical performance of lithium manganese iron phosphate when it is used in batteries. Summary of the Invention

[0005] To address the aforementioned problems with lithium manganese iron phosphate in existing technologies, this invention provides a lithium manganese iron phosphate material, its preparation method, an electrochemical device, and an electronic device. The electrochemical device prepared using this lithium manganese iron phosphate material as the active material exhibits high reversible discharge specific capacity, initial discharge specific capacity, and capacity retention.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] In a first aspect, the present invention provides a lithium manganese iron phosphate material, wherein the lithium manganese iron phosphate material satisfies the following:

[0008] S 2 (C) Fe / C Mn =10~500ppm; and C 杂质离子 ≤500ppm;

[0009] Among them, C Fe / C Mn S represents the molar ratio of iron to manganese in the lithium manganese iron phosphate particles of the lithium manganese iron phosphate material. 2 (C) Fe / C Mn () represents the sample variance of the molar ratio of iron and manganese in different lithium manganese phosphate particles;

[0010] C 杂质离子 This indicates that the impurity ion Na in the lithium manganese iron phosphate material + NH4 + and K + Total molar content.

[0011] Secondly, the present invention provides a method for preparing lithium manganese iron phosphate material, which includes the following steps:

[0012] S1. The iron-manganese phosphate precursor is subjected to a first hydrothermal reaction to obtain a first mixture;

[0013] S2. The second mixture is subjected to a second hydrothermal reaction under supercritical conditions to obtain an intermediate;

[0014] The second mixture includes the first mixture and a lithium source;

[0015] S3. The third mixture is sintered to obtain the lithium manganese iron phosphate material;

[0016] The third mixture includes the intermediate and the carbon source.

[0017] Thirdly, the present invention provides a lithium manganese iron phosphate material prepared by the preparation method of lithium manganese iron phosphate as described above.

[0018] Fourthly, the present invention provides an electrochemical device, wherein the positive electrode of the electrochemical device comprises the lithium manganese iron phosphate material as described above.

[0019] Fifthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0020] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0021] The reagents and raw materials used in this invention are all commercially available.

[0022] The positive and progressive effects of this invention are as follows:

[0023] The lithium manganese iron phosphate material provided by this invention includes lithium manganese iron phosphate particles. The sample variance of the molar ratio of iron and manganese elements in different lithium manganese iron phosphate particles is small, indicating that its composition is more uniform. Furthermore, the lithium manganese iron phosphate material contains impurity ions such as Na+. + NH4 + and K + With a total content of less than 500 ppm, lithium manganese iron phosphate materials can exhibit excellent electrical performance when applied to batteries.

[0024] This invention addresses a series of problems existing in liquid phase coprecipitation methods by providing a method for preparing lithium manganese iron phosphate materials. This method achieves efficient impurity removal, effectively controls particle morphology in the precursor stage, and significantly shortens the material synthesis time under supercritical conditions. It greatly reduces the difficulty of production and impurity removal and does not generate a large amount of washing wastewater. Attached Figure Description

[0025] Figure 1 This is a SEM image of the iron-manganese phosphate precursor from Example 1.

[0026] Figure 2 The image shows the SEM image of the intermediate obtained in step S2 of Example 1.

[0027] Figure 3 The image shows a SEM image of the material after spray drying in step S3 of Example 1.

[0028] Figure 4 This is a SEM image of the lithium manganese iron phosphate material from Example 1, magnified 1000 times.

[0029] Figure 5 This is a SEM image of the lithium manganese iron phosphate material from Example 1, magnified 3000 times.

[0030] Figure 6 This is a SEM image of the lithium manganese iron phosphate material from Example 1, magnified 30,000 times.

[0031] Figure 7 The image shows the SEM image of the manganese iron phosphate precursor of Comparative Example 1.

[0032] Figure 8 The image shows the SEM image of lithium manganese iron phosphate material in Comparative Example 1.

[0033] Figure 9 The image shows the XRD pattern of the manganese iron phosphate precursor from Example 1.

[0034] Figure 10 The image shows the XRD pattern of the intermediate obtained in step S2 of Example 1.

[0035] Figure 11 The image shows the XRD pattern of the lithium manganese iron phosphate material in Example 1. Detailed Implementation

[0036] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0037] lithium manganese iron phosphate materials

[0038] In the lithium manganese iron phosphate material provided in the first aspect of the present invention, the lithium manganese iron phosphate material satisfies the following:

[0039] S 2 (C) Fe / C Mn =10~500ppm; and C 杂质离子 ≤500ppm;

[0040] Among them, C Fe / C Mn S represents the molar ratio of iron to manganese in the lithium manganese iron phosphate particles of the lithium manganese iron phosphate material. 2 (C) Fe / C Mn () represents the sample variance of the molar ratio of iron and manganese in different lithium manganese phosphate particles;

[0041] C 杂质离子 This indicates that the impurity ion Na in the lithium manganese iron phosphate material + NH4 + and K + Total molar content.

[0042] In this invention, the sample variance S of the iron and manganese content ratio in the different lithium manganese iron phosphate particles is... 2 (C) Fe / C Mn The testing can be performed using conventional methods in the field, such as the following method: SEM-EDS testing is performed on the lithium manganese iron phosphate material. First, an SEM image at 5000x magnification is obtained. Then, 10 lithium manganese iron phosphate particles are randomly selected from this image, and the electron microscope is magnified to 10000x. The molar content of iron and manganese in each lithium manganese iron phosphate particle is obtained using EDS, and the molar ratio of iron to manganese (C) is calculated.Fe / C Mn The variance of the molar ratio of iron to manganese in these 10 lithium manganese iron phosphate particles was calculated and used as the sample variance S. 2 (C) Fe / C Mn The conditions for SEM-EDS testing are as follows: operating voltage of 20 kV, electron microscope magnification of ×5000 / 10000, and elemental screening for EDS of Li, Mn, Fe, P and O (doped elements and impurity elements are present in very small amounts and cannot be accurately qualitatively analyzed by EDS, therefore they are not included in the EDS elemental screening range).

[0043] In some alternative implementations, the sample variance S of the molar ratio of iron to manganese in different lithium manganese iron phosphate particles 2 (C) Fe / C Mn ) is 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm or 210 ppm.

[0044] In this invention, the "impurity ion" is Na introduced during the preparation process. + NH4 + and K + Within a certain content range, these impurity ions can negatively impact the electrical performance of lithium manganese iron phosphate materials. These "impurity ions" are distinct from the "doping elements" that may also be included in the lithium manganese iron phosphate materials; the doping elements generally promote the electrical performance of lithium manganese iron phosphate materials.

[0045] In some optional embodiments of the present invention, the molar content of the impurity ions is 80 to 500 ppm.

[0046] In some optional embodiments of the present invention, the molar content of the impurity ions is less than 200 ppm.

[0047] In some alternative embodiments, the lithium manganese iron phosphate particles include a first particle and a second particle, with at least a portion of the first particle adhering to the surface of the second particle to form secondary particles; the particle size of the first particle is smaller than the particle size of the second particle.

[0048] In some embodiments of the present invention, the particle size D1 of the first particle is (0.9~1.1)Dn50, where Dn50 is the Dn50 of the lithium manganese iron phosphate material. The particle size of the first particle refers to the longest distance between any two points on the surface of the first particle in a SEM image.

[0049] In some embodiments of the present invention, the particle size D2 of the second particle is (0.5~1.0)Dn99, where Dn99 is the Dn99 of the lithium manganese iron phosphate material. The particle size of the second particle refers to the longest distance between any two points on the surface of the second particle in a SEM image.

[0050] In some specific embodiments, the Dn50 of the lithium manganese iron phosphate material is 5~10μm.

[0051] In some specific embodiments, the Dn50 of the lithium manganese iron phosphate material is 4~11 μm.

[0052] In some specific embodiments, the Dn50 of the lithium manganese iron phosphate material is 4.4μm, 4.65μm, 5.1μm, 5.2μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6μm, 6.1μm, 7.7μm, 8.9μm, 9.5μm, 9.8μm, or 10.9μm.

[0053] In some specific embodiments, the Dn99 of the lithium manganese iron phosphate material is 100~200μm.

[0054] In some specific embodiments, the Dn99 of the lithium manganese iron phosphate material is 131μm, 133μm, 137μm, 138μm, 139μm, 141μm, 143μm, 147μm, 150μm, 153μm, 158μm, 160μm, 164μm, 165μm, 167μm, 176μm, 181μm, 183μm, 184μm, 191μm, or 193μm.

[0055] In this invention, Dn50 refers to the number of particles smaller than this diameter accounting for 50% of the total number of particles in the cumulative particle size distribution; Dn99 refers to the number of particles smaller than this diameter accounting for 99% of the total number of particles in the cumulative particle size distribution. Dn50 and Dn99 can be determined using a conventional laser particle size analyzer (e.g., DIF 500) in the art.

[0056] In some embodiments of the present invention, the volume ratio of the second particle to the total volume of the first particle in the secondary particles is 1:(8~10).

[0057] In some specific embodiments, the volume ratio of the second particle to the total volume of the first particle in the secondary particles is 1:8.03, 1:8.11, 1:8.22, 1:8.29, 1:8.3, 1:8.35, 1:8.38, 1:8.48, 1:8.5, 1:8.51, 1:8.65, 1:8.7, 1:8.71, 1:8.75, 1:8.77, 1:8.82, 1:8.84, 1:8.85, 1:8.94, 1:8.96, 1:9.02, 1:9.12, 1:9.32, 1:9.49, or 1:9.54.

[0058] In this invention, the ratio of the volume of the second particle to the total volume of the first particle in the secondary particles is obtained in the following manner:

[0059] (1) The lithium manganese iron phosphate material was subjected to SEM testing to obtain a 3000x SEM image. Five regions were randomly selected for observation. All secondary particles in the selected regions were identified. The criteria for identifying "secondary particles" were as follows: First, the first particle and the second particle were identified. The first particle was a primary particle with a particle size of D1 = (0.9~1.1)Dn50 and the second particle was a primary particle with a particle size of D2 = (0.5~1.0)Dn99. Second particles with several first particles attached to their surface were identified as "secondary particles".

[0060] (2) For each identified secondary particle, measure the radius R1 of the second particle and the radius R2 of the second particle in the secondary particle respectively; where the radius of the particle is half of the longest distance between any two points on the particle surface. For the first particle in the secondary particle, randomly select 3 first particles attached to the surface of the second particle, measure the radius and take the average value as the radius R1 of the first particle.

[0061] (3) Calculate the ratio of the volume of the second particle to the total volume of the first particle in the secondary particles. Since the prepared particles have a spherical morphology, their volume can be approximately calculated using the spherical volume formula V=4 / 3·π·R. 3 Where R is the radius of the particle, and the ratio of the volume of the second particle to the total volume of the first particle is R² (simplified). 3 mR2 3 , where m is the number of first particles attached to the surface of the second particle in the secondary particle.

[0062] In some embodiments of the present invention, the secondary particles account for 5% to 16% of the volume percentage of the lithium manganese iron phosphate material.

[0063] In some specific embodiments, the secondary particles account for 6.64%, 6.98%, 7.44%, 9.15%, 9.27%, 9.46%, 9.53%, 9.63%, 9.67%, 9.81%, 9.93%, 9.98%, 10%, 10.01%, 10.27%, 10.31%, 10.61%, 10.77%, 10.89%, 11.01%, 11.26%, 11.35%, 11.70%, 11.79%, 13.12%, 13.90%, 14.60%, or 15.20% of the volume of the lithium manganese iron phosphate material.

[0064] In this invention, the volume percentage of the secondary particles in the lithium manganese iron phosphate material can be obtained in the following manner:

[0065] (1) Take 10 portions of lithium manganese iron phosphate material powder of the same weight, take a sample of each portion of lithium manganese iron phosphate material powder for SEM testing, obtain 1000x SEM image, randomly select 5 areas for observation, and identify all secondary particles in the selected areas.

[0066] (2) Obtain the equivalent average volume and equivalent diameter of the secondary particles.

[0067] Since both the first and second particles are spherical, the volume V of the secondary particle is... 二次颗粒 =V 第一颗粒 +ΣV 第二颗粒 The volumes of the first and second particles can be approximated using the formula for the volume of a sphere: V = 4 / 3 · π · R 3 Where R is the radius of the particle, and the volume of all n secondary particles identified in each region is measured and calculated, V 二次颗粒1 V 二次颗粒2 ... V 二次颗粒n Then, all secondary particles in each region are averaged using the following weighted average formula:

[0068] V 加权平均 = (V 2 二次颗粒1 / V 平均 + V 2 二次颗粒2 / V 平均 +……+ V 2 二次颗粒n / V 平均 ) / n;

[0069] V 平均 = (V 二次颗粒1 +V 二次颗粒2 +……+ V 二次颗粒n ) / n;

[0070] The weighted average volume of the obtained 50 secondary particles (10 samples, 5 regions randomly selected from each sample) is averaged to obtain the equivalent average volume of the secondary particles, and the equivalent diameter d of the secondary particles under the equivalent average volume is calculated according to the spherical volume formula.

[0071] (3) Measure the volume percentage of secondary particles in the lithium manganese iron phosphate material.

[0072] Ten portions of the remaining powder sample of lithium manganese iron phosphate were mixed evenly, and the particle size distribution curve of the material was obtained using a laser particle size analyzer (model: DIF500). The volume cumulative distribution percentage corresponding to the equivalent diameter d was obtained from the particle size distribution curve and calculated according to the following formula:

[0073] The volume percentage of secondary particles in the total lithium manganese iron phosphate material = 100% - the cumulative volume distribution percentage corresponding to the equivalent diameter d.

[0074] In some alternative embodiments, the molar ratio of iron to manganese in the lithium manganese iron phosphate material is x:(1-x), where 0<x<1.

[0075] In some specific implementations, x is 0.7.

[0076] In some alternative embodiments, the molar ratio of the sum of the molar amounts of iron and manganese to that of lithium in the lithium manganese phosphate material is 1:(1~2).

[0077] In one specific embodiment, the molar ratio of the sum of the molar amounts of iron and manganese elements to that of lithium in the lithium manganese phosphate material is 1:1.8.

[0078] In some specific embodiments, the molar ratio of the sum of the molar amounts of iron and manganese elements to that of lithium in the lithium manganese phosphate material is 1:1.

[0079] In some alternative embodiments, the lithium manganese iron phosphate material further includes a doping element, which is a transition metal, including one or more of Ti, V, Nb and Zr.

[0080] In some specific implementations, the transition metal is Ti.

[0081] In some specific implementations, the transition metal is Nb.

[0082] In some specific embodiments, the molar content of the dopant element is 20~100ppm.

[0083] In some specific embodiments, the molar content of the dopant element is 0 ppm, 24 ppm, 33 ppm, 34 ppm, 35 ppm, 36 ppm, 37 ppm, 38 ppm, 39 ppm, 40 ppm, 41 ppm, 42 ppm or 348 ppm.

[0084] In some alternative embodiments, the compaction density of the lithium manganese iron phosphate material is 2.45~2.55 g / cm³. 3 .

[0085] In some specific embodiments, the compaction density of the lithium manganese iron phosphate material is 2.48 g / cm³. 3 2.49 g / cm 3 2.5 g / cm 3 2.51 g / cm 3 2.52 g / cm 3 Or 2.53 g / cm 3 .

[0086] Preparation method of lithium manganese iron phosphate material

[0087] The method for preparing lithium manganese iron phosphate material provided in the second aspect of the present invention includes the following steps:

[0088] S1. The iron-manganese phosphate precursor is subjected to a first hydrothermal reaction to obtain a first mixture;

[0089] S2. The second mixture is subjected to a second hydrothermal reaction under supercritical conditions to obtain an intermediate;

[0090] The second mixture includes the first mixture and a lithium source;

[0091] S3. The third mixture is sintered to obtain the lithium manganese iron phosphate material;

[0092] The third mixture includes the intermediate and the carbon source.

[0093] In some alternative embodiments, the temperature of the first hydrothermal reaction is 100~200°C.

[0094] In some specific implementations, the temperature of the first hydrothermal reaction is 100°C, 120°C, 200°C, or 300°C.

[0095] In some alternative embodiments, the first hydrothermal reaction takes 5 to 32 hours.

[0096] In one specific implementation, the first hydrothermal reaction takes 24 hours.

[0097] In some specific implementations, the duration of the first hydrothermal reaction is 5 hours, 16 hours, 20 hours, or 32 hours.

[0098] In some alternative embodiments, the iron manganese phosphate precursor includes impurity ions.

[0099] Optionally, the impurity ions include Na. + NH4 + and K + One or more of them.

[0100] Optionally, the molar content of the impurity ions is 5000~10000ppm.

[0101] In some specific embodiments, the molar content of the impurity ions is 5400 ppm, 6100 ppm, 6278 ppm, 6320 ppm, 6683 ppm, 7020 ppm, 7100 ppm, 7105 ppm, 7122 ppm, 7152 ppm, 7227 ppm, 7233 ppm, 7284 ppm, 7294 ppm, 7298 ppm, 7300 ppm, 7360 ppm, 7306 ppm, 7450 ppm, 7522 ppm, 7552 ppm, 7600 ppm, 7698 ppm, 7729 ppm, 7861 ppm, or 8596 ppm.

[0102] In some alternative embodiments, the solid content of the first mixture is 20-70 g / L.

[0103] In some specific embodiments, the solid content of the first mixture is 30 g / L.

[0104] In some alternative embodiments, the temperature of the second hydrothermal reaction is 364~390°C.

[0105] In some alternative embodiments, the temperature of the second hydrothermal reaction is 360~400°C.

[0106] In some specific embodiments, the temperature of the second hydrothermal reaction is 360°C, 364°C, 374°C, 390°C, or 400°C.

[0107] In some alternative embodiments, the pressure of the second hydrothermal reaction is 22.1~23.0 MPa.

[0108] In some alternative embodiments, the second hydrothermal reaction takes 3 to 12 hours.

[0109] In some specific implementations, the second hydrothermal reaction takes 6 hours.

[0110] In some alternative embodiments, the molar content of impurity ions in the intermediate is below 200 ppm, wherein the impurity ions include Na. + NH4 + and K + One or more of them.

[0111] In some specific embodiments, the molar content of the impurity ions in the intermediate is 51 ppm, 53 ppm, 54 ppm, 56 ppm, 57 ppm, 59 ppm, 64 ppm, 73 ppm, 78 ppm, 79 ppm, 80 ppm, 81 ppm, 82 ppm, 83 ppm, 85 ppm, 86 ppm, 87 ppm, 88 ppm, 91 ppm, 100 ppm, or 149 ppm.

[0112] In some alternative embodiments, the second mixture further includes a dopant source, wherein the dopant source includes transition metal elements.

[0113] Optionally, the transition metal is one or more of Ti, V, Nb, and Zr.

[0114] Optionally, the dopant element source is TiO2.

[0115] Optionally, the dopant element source is Nb2O5.

[0116] Optionally, the amount of the dopant element source added is 0.1% to 2% of the theoretical mass of lithium manganese iron phosphate material, preferably 0.5% to 1%; the theoretical mass of lithium manganese iron phosphate material is calculated based on the chemical reaction formula of each material.

[0117] Optionally, the amount of the dopant source added is 0.5% or 5% of the theoretical mass of lithium manganese iron phosphate material.

[0118] In some alternative embodiments, the holding temperature of the sintering process is 600~1000℃.

[0119] In some alternative embodiments, the holding temperature of the sintering process is 700~1000℃.

[0120] In some specific embodiments, the holding temperature of the sintering process is 600°C, 700°C, 750°C, 1000°C, or 1100°C.

[0121] In some alternative embodiments, the holding period of the sintering process is 5 to 12 hours.

[0122] In some specific implementations, the holding period of the sintering treatment is 5 hours, 8 hours, or 12 hours.

[0123] In some alternative embodiments, the heating rate of the heating stage of the sintering process is 4~8°C / min.

[0124] In one specific embodiment, the heating rate of the heating stage of the sintering process is 5°C / min.

[0125] In some specific embodiments, the heating rate of the heating stage of the sintering process is 4°C / min, 5°C / min, or 8°C / min.

[0126] In some alternative embodiments, the sintering process is performed in an inert gas atmosphere.

[0127] Optionally, the inert gas is nitrogen and / or argon.

[0128] In some alternative embodiments, the third mixture is further dried and ground prior to the sintering process.

[0129] In some specific implementations, the drying is spray drying.

[0130] In some alternative embodiments, prior to the sintering process, the third mixture is further subjected to pre-sintering, wherein the temperature of the pre-sintering holding stage is 300-450°C.

[0131] In some specific implementations, the temperature of the pre-sintering holding stage is 400°C.

[0132] The preferred duration of the heat preservation stage during pre-sintering is 8 to 10 hours.

[0133] In some specific implementations, the heat preservation stage of the pre-sintering is 9 hours.

[0134] The heating rate of the pre-sintering heating stage is preferably 1~5℃ / min, for example 1.5℃ / min.

[0135] In some specific implementations, the heating rate of the pre-sintering heating stage is 3°C / min.

[0136] In some alternative embodiments, the lithium source includes one or more of lithium nitrate, lithium carbonate, lithium acetate, lithium oxalate, lithium hydroxide, lithium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate.

[0137] In some alternative embodiments, the molar ratio of the lithium source to the iron manganese phosphate precursor is (4~15):1.

[0138] In some specific implementations, the molar ratio of the lithium source to the iron-manganese phosphate precursor is 5:1.

[0139] In some alternative embodiments, the carbon source includes one or more of sucrose, glucose, fructose, oxalic acid, citric acid, ascorbic acid, graphene, graphyne, polyethylene glycol ether, polyethylene glycol, polyethylene glycol sulfate, and polyoxyethylene ethyl ether.

[0140] In one specific implementation, the carbon source is glucose, ascorbic acid, and polyethylene glycol.

[0141] Optionally, the mass ratio of the glucose, the ascorbic acid, and the polyethylene glycol is 80:19.5:0.5.

[0142] In some alternative embodiments, the carbon source is 5% to 15% of the theoretical mass of lithium manganese iron phosphate material, wherein the theoretical mass of lithium manganese iron phosphate material is calculated based on the chemical reaction formula of each material.

[0143] In some specific implementations, the carbon source is 8% of the mass of the theoretical lithium manganese iron phosphate material.

[0144] In some alternative embodiments, the iron-manganese phosphate precursor is prepared by a co-precipitation method, comprising the following steps: first reacting the mixture with an oxidant for oxidation, and then reacting it with a precipitant for precipitation; wherein the mixture comprises an iron source, a manganese source, and a phosphorus source.

[0145] In some specific embodiments, the iron source is a soluble iron salt; the soluble iron salt is selected from one or more of ferric nitrate, ferric chloride, ferric acetate, ferric chloride, ferrous nitrate, ferrous sulfate, and ferric citrate.

[0146] In some specific embodiments, the manganese source is selected from one or more of manganese nitrate, manganese oxalate, manganese acetate, and manganese sulfate.

[0147] In some specific implementations, the iron source and manganese source may be conventional hydrates of the aforementioned substances.

[0148] In some specific embodiments, the phosphorus source is an aqueous solution containing phosphate ions, which may be selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0149] In some specific embodiments, the oxidant is selected from one or more of potassium permanganate, hydrogen peroxide, and nitric acid.

[0150] Optionally, the oxidant is a potassium permanganate solution, and the concentration of the potassium permanganate solution can be 1 mol / L.

[0151] In some specific embodiments, the ratio of the number of moles of the oxidant to the total number of moles of the iron source and manganese source is (0.5~2):1.

[0152] In some specific embodiments, the precipitant is selected from one or more of sodium phosphate, sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and ammonia water.

[0153] In some specific embodiments, the preparation of the mixture includes the following steps: first, mixing the iron source and the manganese source, and then adding the phosphorus source.

[0154] Optionally, the first mixing is stirring.

[0155] Optionally, the stirring speed is 100 r / min.

[0156] Optionally, the stirring temperature is 30°C.

[0157] Optionally, the addition rate is 20 mL / min.

[0158] In some specific embodiments, the solvent of the mixture is water.

[0159] In some specific embodiments, the oxidation reaction is carried out at a temperature of 20~90°C.

[0160] In some specific embodiments, the oxidation reaction takes 1 to 5 hours, for example, 2 hours.

[0161] In some specific embodiments, the precipitation reaction is carried out at a temperature of 20-90°C, for example, 40°C.

[0162] In some specific implementations, the precipitation reaction takes 1 to 5 hours, for example, 2 hours.

[0163] In some specific embodiments, the pH of the solution in the precipitation reaction process is 2.5 to 7, for example, 6 or 7.

[0164] In some specific embodiments, after the precipitation reaction, a precipitate is obtained through solid-liquid separation. The precipitate is then filtered, washed with water, and dried to obtain the iron-manganese phosphate precursor. The drying temperature is, for example, 120°C.

[0165] In some alternative embodiments, the molar ratio of the sum of the molar amounts of iron and manganese in the iron-manganese phosphate precursor to the molar ratio of phosphorus is (0.98~1):1.

[0166] In some specific implementations, the molar ratio of the sum of the molar amounts of iron and manganese in the iron-manganese phosphate precursor to the molar ratio of phosphorus is 0.9842:1, 0.9847:1, 0.9955:1, 0.9963:1, 0.9971:1, 0.9974:1, 0.9977:1, 0.9981:1, 0.9982:1, 0.9983:1, 0.9984:1, 0.9985:1, 0.9989:1, 0.999:1, or 0.9991:1.

[0167] In some alternative embodiments, the preparation method of the second mixture includes: ball milling or sand milling the first mixture and the lithium source.

[0168] In some specific implementations, the first mixture and the lithium source are first ball-milled at 500 r / min for 2 hours, and then sand-milled for 1 hour after being mixed evenly.

[0169] In the third aspect of the present invention, a lithium manganese iron phosphate material is provided, which is prepared by the method for preparing lithium manganese iron phosphate material as described above.

[0170] The composition and properties of the lithium manganese iron phosphate material prepared by the aforementioned method are as described in the first aspect of this invention.

[0171] In the fourth aspect of the present invention, a lithium manganese iron phosphate material is provided, wherein the positive electrode of the electrochemical device comprises the lithium manganese iron phosphate material as described above.

[0172] In this invention, the electrochemical device is preferably a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0173] Positive electrode film

[0174] In this invention, the positive electrode sheet may include a positive current collector and a positive electrode material layer, wherein the positive electrode material layer is disposed on at least one surface of the positive current collector; the positive electrode material layer includes a positive electrode material, wherein the positive electrode material includes lithium manganese iron phosphate material as described above.

[0175] In some embodiments, the positive electrode material layer further includes a conductive agent. The conductive agent is a reagent used to ensure that the electrode has good charge-discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide, for example, conductive carbon black.

[0176] In some embodiments, the positive electrode material layer further includes a binder. The binder may be a component that facilitates bonding between the positive electrode material and the conductive agent, and also facilitates bonding between the positive electrode material and the positive electrode current collector. It can typically be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0177] In some embodiments, the positive electrode material layer includes a positive electrode material, polyvinylidene fluoride, and conductive carbon black.

[0178] In some specific implementations, the mass ratio of the positive electrode material, polyvinylidene fluoride, and conductive carbon black is 8:1:1.

[0179] In some implementations, the positive electrode material layer includes a positive electrode material, polytetrafluoroethylene, and acetylene black.

[0180] In some specific implementations, the mass ratio of the positive electrode material, acetylene black, and polytetrafluoroethylene is 8:1:1.

[0181] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation. For example, commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0182] In some alternative implementations, the positive current collector is aluminum foil.

[0183] In some alternative embodiments, the thickness of the positive current collector can be 8 to 16 μm, for example 15 μm.

[0184] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0185] In some alternative embodiments, the method for preparing the positive electrode includes the following steps:

[0186] A positive electrode material, binder, and conductive agent are mixed in a certain mass ratio, and then a solvent is added and mixed evenly to obtain a positive electrode slurry. The positive electrode material includes lithium manganese iron phosphate as described above. The positive electrode slurry is then uniformly coated on at least one surface of the positive electrode current collector. After drying, rolling, slitting, and other processes, a positive electrode sheet is prepared.

[0187] negative electrode sheet

[0188] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, the negative electrode material layer being disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode material.

[0189] In this invention, the negative electrode material in the negative electrode material layer can be a negative electrode material conventionally used in the art, preferably including one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide and silicon carbide materials, such as artificial graphite.

[0190] In some implementations, the negative electrode material layer further includes a conductive agent.

[0191] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0192] In some specific implementations, the conductive agent in the negative electrode material layer is acetylene black.

[0193] In some implementations, the negative electrode material layer further includes a binder.

[0194] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as SBR.

[0195] In some implementations, the negative electrode material layer also includes a thickener.

[0196] The addition of the thickener can increase the viscosity of the system of each component in the negative electrode slurry. It can be a thickener commonly used in the art to prepare negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0197] In this invention, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector, serving as the substrate supporting the negative electrode material layer, is typically a metal foil with a thickness of 3-500 μm. There are no particular limitations on the material, as long as it has high conductivity and does not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the negative electrode material layer and the current collector. Besides foil, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0198] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating the negative electrode slurry obtained by thoroughly mixing the components of the negative electrode material layer in a solvent onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the final product.

[0199] diaphragm

[0200] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0201] In one specific embodiment, the diaphragm is a polypropylene membrane; the thickness of the diaphragm is 11 μm.

[0202] electrolyte

[0203] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries, typically including non-aqueous solvents and lithium salts.

[0204] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0205] In some embodiments, the non-aqueous solvent preferably includes ester solvents, more preferably carbonate solvents. The carbonate solvent may optionally be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0206] In this invention, the lithium salt can be a conventional lithium salt in the art, such as LiPF6.

[0207] In some embodiments, the electrolyte includes LiPF6, ethyl methyl carbonate, and ethylene carbonate.

[0208] The volume ratio of ethylene carbonate to methyl ethyl carbonate is, for example, 7:3.

[0209] The concentration of the lithium salt is, for example, 1 mol / L.

[0210] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: mixing the various non-aqueous solvents in proportion in an argon atmosphere glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing evenly to obtain the electrolyte.

[0211] In this invention, the method for preparing the lithium-ion battery can be a conventional method in the art, which can be to wind a positive electrode sheet, a separator, and a negative electrode sheet to obtain a battery cell, then package it in a packaging shell and inject the electrolyte; or it can be to stack a negative electrode sheet, a separator, a positive electrode sheet, and a separator in sequence to obtain a battery cell, then package it in a packaging shell and inject the electrolyte.

[0212] electronic devices

[0213] The electronic device provided in the fifth aspect of the present invention includes the electrochemical device as described above.

[0214] For example, the electronic devices described in this invention may be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0215] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention. The present invention is further illustrated below by way of embodiments, but this does not limit the present invention to the scope of the described embodiments. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or according to the product instructions. Unless otherwise specified, all reagents and raw materials used in the present invention are commercially available.

[0216] Example 1

[0217] The iron-manganese phosphate precursor was prepared by a co-precipitation method, which included the following steps:

[0218] After mixing the iron source (214.1g ferrous nitrate heptahydrate) and the manganese source (66.91g manganese sulfate tetrahydrate), add 2L of water and mix thoroughly in a 5L reactor. Heat to 30℃ and dissolve all materials by stirring at 100 r / min. Add the phosphorus source (85 wt% phosphoric acid) to the reactor at a feed rate of 20mL / min. Keep stirring (3min) to ensure uniform mixing.

[0219] Add 550 mL of 1 mol / L oxidant (potassium permanganate solution) quickly to carry out the oxidation reaction for 2 h at 30 °C;

[0220] After the oxidation reaction is complete, the temperature is raised to 40°C, and a precipitant (sodium hydroxide) is added to carry out the precipitation reaction for 2 hours, controlling the pH of the solution during the precipitation reaction process to be 7.0.

[0221] After the precipitation reaction was completed, the precipitate was obtained by solid-liquid separation. The precipitate was then filtered and washed twice with water, and dried at 120°C to obtain 148.44 g of iron-manganese phosphate precursor (impurity ions included Na). + NH4 + and K + The content of impurity ions was 7284 ppm.

[0222] ICP analysis of the iron-manganese phosphate precursor revealed a molar ratio of iron to manganese of 2.37:1, and a molar ratio of the sum of the molar amounts of iron and manganese to that of phosphorus of 0.9981:1.

[0223] The preparation method of lithium manganese iron phosphate material includes the following steps:

[0224] S1. The above-mentioned iron manganese phosphate precursor is subjected to a first hydrothermal reaction (temperature 120℃, time 5h) to obtain a first mixture (solid content 30g / L).

[0225] S2. The second mixture is placed in a stainless steel reactor and subjected to a second hydrothermal reaction under supercritical conditions (temperature 374℃, pressure 22.1 MPa, time 6 h) to obtain an intermediate.

[0226] The preparation of the second mixture involves: ball milling the first mixture, lithium source (lithium nitrate trihydrate), and dopant source (transition metal oxide TiO2, with the amount of TiO2 added being 0.5% of the theoretical mass of lithium manganese iron phosphate material, the mass of which is calculated based on the chemical reaction formula of each material) at 500 r / min for 2 h, mixing them evenly, and then sand milling them for 1 h to obtain the second mixture.

[0227] The molar ratio of lithium source to manganese iron phosphate precursor is 5:1.

[0228] S3. Spray dry and grind the third mixture, and sinter the third mixture under an argon atmosphere (the temperature of the holding stage is 750℃, the holding time is 8h, and the heating rate of the heating stage is 5℃ / min) to obtain lithium manganese iron phosphate material.

[0229] The third mixture is a mixture of the above intermediate and a carbon source (glucose + ascorbic acid + PEG, wherein the mass ratio of glucose:ascorbic acid:PEG is 80:19.5:0.5); wherein the amount of carbon source is 8% of the theoretical mass of lithium manganese iron phosphate material, and the theoretical mass of lithium manganese iron phosphate material is calculated based on the chemical reaction formula of each material.

[0230] Examples 2-28

[0231] The parameters that differ from those in Example 1 in the preparation methods of the iron-manganese phosphate precursors in Examples 2-28 are listed in Table 1, while the other conditions are the same as in Example 1.

[0232] The parameters that differ from those in Example 1 in the preparation methods of lithium manganese iron phosphate materials in Examples 2-15 and 17-25 are listed in Table 1, while the other conditions are the same as in Example 1.

[0233] In the preparation method of lithium manganese iron phosphate material in Example 16, step S3 includes pre-sintering the third mixture before sintering treatment. The temperature of the pre-sintering holding stage is 400°C, the holding time of the pre-sintering stage is 9 hours, and the heating rate of the pre-sintering heating stage is 3°C / min.

[0234] In the preparation method of lithium manganese iron phosphate material in Example 26, the doping element source in step S2 is transition metal oxide TiO2, and the amount of TiO2 added is 5% of the theoretical mass of lithium manganese iron phosphate material.

[0235] In the preparation method of lithium manganese iron phosphate material in Example 27, the doping element source in step S2 is transition metal oxide Nb2O5, and the amount of Nb2O5 added is 0.5% of the theoretical mass of lithium manganese iron phosphate material.

[0236] In the preparation method of lithium manganese iron phosphate material in Example 28, no transition metal oxides are doped in step S2.

[0237] Comparative Examples 1-2

[0238] The parameters that differ from those in Example 1 in the preparation methods of the iron-manganese phosphate precursors in Comparative Examples 1 and 2 are listed in Table 1, while the other conditions are the same as in Example 1.

[0239] The preparation methods of lithium manganese iron phosphate materials in Comparative Examples 1 and 2 do not involve a second hydrothermal reaction, and specifically include the following steps:

[0240] S1. The iron manganese phosphate precursor is subjected to a first hydrothermal reaction (temperature 120℃, time 5h) to obtain a first mixture (solid content 30g / L).

[0241] S2. The first mixture, lithium source (lithium nitrate trihydrate), and dopant source (transition metal oxide TiO2, the amount of TiO2 added is 0.5% of the theoretical mass of lithium manganese iron phosphate material, the mass of the theoretical lithium manganese iron phosphate material is calculated according to the chemical reaction formula of each material) are ball-milled at 500 r / min for 2 h. After being mixed evenly, the mixture is sand-milled for 1 h to obtain the second mixture. The molar ratio of lithium source to manganese iron phosphate precursor is 5:1.

[0242] S3. Spray dry and grind the third mixture, and sinter the third mixture under an argon atmosphere (the temperature of the holding stage is 750℃, the holding time is 8h, and the heating rate of the heating stage is 5℃ / min) to obtain lithium manganese iron phosphate material.

[0243] The third mixture is a mixture of the second mixture and a carbon source (glucose + ascorbic acid + PEG, wherein the mass ratio of glucose:ascorbic acid:PEG is 80:19.5:0.5); wherein the amount of carbon source is 8% of the theoretical mass of lithium manganese iron phosphate material, and the theoretical mass of lithium manganese iron phosphate material is calculated based on the chemical reaction formula of each material.

[0244] Table 1

[0245] serial number Types of precipitants pH value of the solution during the precipitation reaction process The temperature of the first hydrothermal reaction The time of the first hydrothermal reaction The temperature of the second hydrothermal reaction The pressure of the second hydrothermal reaction The time of the second hydrothermal reaction Temperature during the holding stage of sintering treatment Time of heat preservation during sintering Heating rate (°C / min) during the heating stage of sintering treatment Example 1 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 2 Sodium hydroxide 6 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 3 ammonia 6 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 4 Sodium hydroxide 7 100℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 5 Sodium hydroxide 7 200℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 6 Sodium hydroxide 7 120℃ 16h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 7 Sodium hydroxide 7 120℃ 32h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 8 Sodium hydroxide 7 120℃ 20h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 9 Sodium hydroxide 7 120℃ 5h 364℃ 22.1 MPa 6h 750℃ 8h 5 Example 10 Sodium hydroxide 7 120℃ 5h 390℃ 22.1 MPa 6h 750℃ 8h 5 Example 11 Sodium hydroxide 7 120℃ 5h 374℃ 23.0 MPa 6h 750℃ 8h 5 Example 12 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 3h 750℃ 8h 5 Example 13 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 12h 750℃ 8h 5 Example 14 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 8 Example 15 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 4 Example 16 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 17 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 1000℃ 8h 5 Example 18 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 700℃ 8h 5 Example 19 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 5h 5 Example 20 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 12h 5 Example 21 Sodium hydroxide 7 300℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 22 Sodium hydroxide 7 120℃ 5h 360℃ 22.1 MPa 6h 750℃ 8h 5 Example 23 Sodium hydroxide 7 120℃ 5h 400℃ 22.1 MPa 6h 750℃ 8h 5 Example 24 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 1100℃ 8h 5 Example 25 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 600℃ 8h 5 Example 26 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 27 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Example 28 Sodium hydroxide 7 120℃ 5h 374℃ 22.1 MPa 6h 750℃ 8h 5 Comparative Example 1 ammonia 6 120℃ 5h / / / 750℃ 8h 5 Comparative Example 2 ammonia 7 120℃ 5h / / / 750℃ 8h 5

[0246] Example 1: Ion emission spectrometry (ICP) test

[0247] Under heating conditions, the sample was completely dissolved in concentrated hydrochloric acid, and then sufficient deionized water was added to prepare the test solution. The content of the test elements in the obtained solution was analyzed using an inductively coupled plasma atomic emission spectrometer (ICP, instrument model: ICPA7400radial).

[0248] (1) The molar ratio of iron to manganese in the iron-manganese phosphate precursor, the molar ratio of the sum of the molar amounts of iron and manganese to that of lithium, and the content of impurity ions.

[0249] The above method was used to perform ICP testing on the iron-manganese phosphate precursor to detect iron ions, manganese ions, and phosphorus (Na). + NH4 + and K +The content of [the element]. Based on n=m / M, where m is the ion content and M is the relative atomic mass of the element, the molar concentrations of iron, manganese, and phosphorus are calculated, and then the molar ratio of iron to manganese, and the molar ratio of the sum of the molar amounts of iron and manganese to phosphorus are obtained. Calculate Na. + NH4 + and K + The sum of their contents is recorded as the content of impurity ions.

[0250] (2) Content of impurity ions in the intermediate

[0251] The intermediates obtained in step S2 of each embodiment were subjected to ICP testing using the method described above to detect Na. + NH4 + and K + The content of Na is calculated. + NH4 + and K + The sum of the contents is recorded as the content of impurity ions. For Comparative Examples 1 and 2, the second mixture obtained in step S2 of each embodiment was tested using the above method.

[0252] (3) The molar ratio of iron to manganese in lithium manganese iron phosphate materials, the molar ratio of the sum of the molar amounts of iron and manganese to that of lithium, and the content of impurity ions.

[0253] The above method was used to perform ICP testing on lithium manganese iron phosphate materials to detect iron ions, manganese ions, lithium ions, and sodium ions. + NH4 + and K + The content of [the element]. Based on n=m / M, where m is the ion content and M is the relative atomic mass of the element, the molar concentrations of iron, manganese, and lithium are calculated, and then the molar ratio of iron to manganese, and the molar ratio of the sum of the molar amounts of iron and manganese to lithium are obtained. Calculate Na. + NH4 + and K + The sum of their contents is recorded as the content of impurity ions.

[0254] (4) Content of doping elements in lithium manganese iron phosphate materials

[0255] The above method was used to perform ICP testing on lithium manganese iron phosphate materials to detect the content of doping elements Ti or Nb.

[0256] The test results are shown in Table 2.

[0257] Table 2

[0258]

[0259] Example 2: Particle Size Test

[0260] The Dn50 and Dn99 of the lithium manganese iron phosphate materials prepared in each example and comparative example were tested using a laser particle size analyzer (model: DIF 500). The test results are shown in Table 3.

[0261] Example 3: Scanning Electron Microscopy (SEM) Test

[0262] 1. SEM observation of morphology

[0263] SEM tests were performed on the iron-manganese phosphate precursor of Example 1, the intermediate obtained in step S2, the material after spray drying in step S3, the final lithium manganese phosphate material, and the iron manganese phosphate precursor and lithium manganese phosphate material of Comparative Example 1.

[0264] Figure 1 The image shows a SEM image (1000x magnification) of the iron-manganese phosphate precursor from Example 1. Figure 2 The image shows the SEM image (9000x magnification) of the intermediate obtained in step S2 of Example 1. Figure 3 SEM image (3000x magnification) of the material after spray drying in step S3 of Example 1. Figures 4-6 The images shown are SEM images of lithium manganese iron phosphate material at magnifications of 1000, 3000, and 30000. Figure 1 and Figure 2 The results show that the material after the second hydrothermal reaction has a basically complete morphology, with uniform spherical granular morphology, more uniform composition, and no longer obvious blocky particles. According to... Figure 3 It can be seen that the spray-dried material particles still maintain a distinct and well-formed spherical shape, and the particle distribution is uniform.

[0265] according to Figures 4-6 The SEM images show that the lithium manganese iron phosphate material obtained in Example 1 has a spherical morphology, complete particle structure, and good microstructure. In the lithium manganese iron phosphate material obtained in Example 1, there are relatively obvious small particles (first particles) and large particles (second particles), and some small particles are attached to the surface of large particles to form secondary particles.

[0266] Figure 7 SEM image (3000x magnification) of the manganese iron phosphate precursor of Comparative Example 1. Figure 8 The image shows a SEM image (1000x magnification) of the lithium manganese iron phosphate material in Comparative Example 1. According to... Figure 7 and Figure 8 It is known that the manganese iron phosphate precursor contains a large number of blocky structures. If the second hydrothermal reaction is not carried out, the resulting lithium iron manganese phosphate material still contains blocky components, and its morphology is significantly worse than that of the lithium iron manganese phosphate material after the second hydrothermal reaction (see...). Figure 4 ).

[0267] 2. Sample variance S of the iron and manganese content ratio in different lithium manganese iron phosphate particles determined by SEM-EDS. 2 (C) Fe / C Mn )

[0268] SEM-EDS testing was performed on lithium manganese iron phosphate (LFP) materials: First, SEM images at 5000x magnification were obtained. Ten LFP particles were randomly selected from these images, and the SEM magnification was increased to 10000x. EDS analysis was then used to determine the molar content of iron and manganese in each LFP particle, and the molar ratio of iron to manganese (C) was calculated. Fe / C Mn The variance of the molar ratio of iron to manganese in these 10 lithium manganese iron phosphate particles was calculated and used as the sample variance S. 2 (C) Fe / C Mn The conditions for SEM-EDS testing are as follows: operating voltage of 20 kV, electron microscope magnification of 5000 / 10000x, and elemental screening for EDS of Li, Mn, Fe, P and O (doped elements and impurity elements are present in very small amounts and cannot be accurately qualitatively analyzed by EDS, therefore they are not included in the EDS elemental screening range).

[0269] 3. Test the ratio of the volume of the second particle to the total volume of the first particle in the secondary particle test.

[0270] (1) SEM testing was performed on the lithium manganese iron phosphate material to obtain a 3000x SEM image. Five regions were randomly selected for observation, and all secondary particles in the selected regions were identified. The criteria for identifying "secondary particles" were as follows: first, the first particle and the second particle were identified. The first particle was a primary particle with a particle size of D1 = (0.9~1.1)Dn50, and the second particle was a primary particle with a particle size of D2 = (0.5~1.0)Dn99. The second particle with several first particles attached to its surface was identified as a "secondary particle". Among them, Dn50 and Dn99 are the Dn50 and Dn99 of the lithium manganese iron phosphate material obtained in Example 2, respectively. "Particle size" is the longest distance between any two points on the particle surface.

[0271] (2) For each identified secondary particle, measure the radius R1 of the second particle and the radius R2 of the second particle in the secondary particle. The radius of a particle is half of the longest distance between any two points on the particle surface. For the first particle in the secondary particle, randomly select 3 first particles attached to the surface of the second particle, measure their radii, and take the average value as the radius R1 of the first particle.

[0272] (3) Calculate the ratio of the volume of the second particle to the total volume of the first particle in the secondary particles. Since the prepared particles have a spherical morphology, their volume can be approximately calculated using the spherical volume formula V=4 / 3·π·R. 3 Where R is the radius of the particle. The ratio of the volume of the second particle to the total volume of the first particle is simplified to R². 3 mR2 3 , where m is the number of first particles attached to the surface of the second particle in the secondary particle.

[0273] For all secondary particles within the selected area, calculate the ratio of the volume of the second particle to the total volume of the first particle, and take the average value as the final ratio of the volume of the second particle to the total volume of the first particle in the secondary particles.

[0274] 4. Test the volume percentage of secondary particles in the lithium manganese iron phosphate material.

[0275] Take 10 portions of lithium manganese iron phosphate material powder of equal weight and prepare for testing.

[0276] (1) SEM tests were performed on each sample of lithium manganese iron phosphate material powder to obtain a 1000x SEM image. Five regions were randomly selected for observation, and all secondary particles in the selected regions were identified. The criteria for identifying "secondary particles" are given in section "3. The ratio of the volume of the second particle to the total volume of the first particle in the test of secondary particles".

[0277] (2) Obtain the equivalent average volume and equivalent diameter of the secondary particles.

[0278] Since both the first and second particles are spherical, the volume V of the secondary particle is... 二次颗粒 =V 第一颗粒 +ΣV 第二颗粒 The volumes of the first and second particles can be approximated using the formula for the volume of a sphere: V = 4 / 3 · π · R 3 Where R is the radius of the particle, and the measurement method for the radii R1 and R2 of the second particle in the secondary particles is described in section "3. Testing the ratio of the volume of the second particle to the total volume of the first particle in the secondary particles". The volume of all (n) secondary particles identified in each region is measured and calculated, V. 二次颗粒1 V 二次颗粒2 ... V 二次颗粒n .

[0279] Then, all secondary particles in each region are averaged using the following formula to obtain a weighted average:

[0280] V 加权平均 = (V 2 二次颗粒1 / V 平均+ V 2 二次颗粒2 / V 平均 +……+ V 2 二次颗粒n / V 平均 ) / n;

[0281] V 平均 = (V 二次颗粒1 +V 二次颗粒2 +……+ V 二次颗粒n ) / n.

[0282] The weighted average volume of the obtained 50 secondary particles (10 samples, 5 regions randomly selected from each sample) is averaged to obtain the equivalent average volume of the secondary particles, and the equivalent diameter d of the secondary particles under the equivalent average volume is calculated according to the spherical volume formula.

[0283] (3) Measure the volume percentage of secondary particles in the lithium manganese iron phosphate material.

[0284] Ten portions of the remaining powder sample of lithium manganese iron phosphate were mixed evenly, and the particle size distribution curve of the material was obtained using a laser particle size analyzer (model: DIF500). The volumetric cumulative distribution percentage corresponding to the equivalent diameter d was obtained from the particle size distribution curve and calculated according to the following formula:

[0285] Secondary particles as a percentage of the total volume of lithium manganese iron phosphate material = 100% - the cumulative volume distribution percentage corresponding to the equivalent diameter d

[0286] For example, the equivalent average volume is 170 μm. 3 Then the equivalent diameter d is (3 / 4 * 170 / π). 1 / 3 Then, the volume cumulative distribution percentage corresponding to this d can be obtained from the particle size distribution curve. For example, if it is 80%, then the corresponding secondary particles account for 20% of the total volume percentage of the lithium manganese iron phosphate material.

[0287] Example 4: Compacted Density Test

[0288] The compaction density of the prepared lithium manganese iron phosphate material was tested using a powder compaction tester. The powder material was subjected to five repeated compaction tests at a pressure of 100 mPa, and the compaction density of the powder obtained from the five tests was recorded. The average value was calculated and recorded as the compaction density of the lithium manganese iron phosphate material.

[0289] The test results are listed in Table 3.

[0290] Example 5: X-ray diffraction (XRD) test

[0291] XRD tests were performed on the iron-manganese phosphate precursor, intermediate, and lithium manganese iron phosphate material of Example 1, and the results are as follows: Figures 9-11 As shown. Among them, Figure 9 The image shows the XRD pattern of the manganese iron phosphate precursor from Example 1. Figure 10 The image shows the XRD pattern of the intermediate from Example 1. Figure 11 The image shows the XRD pattern of the lithium manganese iron phosphate material in Example 1.

[0292] As can be seen from the above XRD pattern, each diffraction peak is clear and complete, and matches well with the standard PDF card #83-1304. No impurity peaks are observed. Carbon is coated in an amorphous form, so no carbon-related diffraction peaks are seen in the diffraction pattern.

[0293] Table 3

[0294]

[0295] The lithium manganese iron phosphate material obtained in the above embodiments can be referred to as LiFe. 0.7 Mn 0.3 PO4 / C, where " / C" indicates the presence of a carbon coating layer. In lithium manganese iron phosphate material, the molar ratio of iron to manganese is 7:3, and the sum of the molar amounts of iron and manganese is 1:1 with the molar ratio of lithium. The actual molar ratio of iron to manganese in lithium manganese iron phosphate material is consistent with that in the iron-manganese iron phosphate precursor.

[0296] According to Tables 2 and 3, the sample variance of the molar ratio of iron to manganese in different lithium manganese iron phosphate particles prepared in Examples 1-26 ranges from 10 to 500 ppm, indicating better uniformity. The molar content of impurity ions in the lithium manganese iron phosphate materials is below 500 ppm, indicating low impurity content. Furthermore, it also exhibits a molecular weight distribution of 2.45-2.55 g / cm³. 3 The compaction density.

[0297] According to the results of Comparative Examples 1 and 2, since the second hydrothermal reaction under supercritical conditions was not carried out in Comparative Examples 1 and 2, the sample variance of the molar ratio of iron and manganese in different lithium manganese iron phosphate particles in the lithium manganese iron phosphate material was higher than 7500 ppm, indicating poor uniformity; the molar content of impurity ions in the lithium manganese iron phosphate material was below 4975 ppm, indicating high impurity content.

[0298] Example 6

[0299] The lithium manganese iron phosphate material obtained in the above examples and comparative examples was used as the positive electrode active material, acetylene black as the conductive agent, polytetrafluoroethylene as the binder, and mixed at a mass ratio of 80:10:10. N-methylpyrrolidone was used as the dispersant to form an electrode sheet. The lithium sheet was used as the negative electrode, and the electrolyte was 1.0M LiPF6 with EC:DMC:EMC (VOL%) = 1:1:1. The electrodes were then assembled into CR2032 coin cells.

[0300] The above-mentioned batteries were subjected to the following tests:

[0301] 1. 0.1C and 1C reversible discharge capacity test: The batteries prepared above were tested for electrical performance in an electrochemical workstation using a Blue Electric M340A precision battery tester according to the test procedure. At room temperature of 25℃, the batteries were charged at 0.1C and 1C within a voltage range of 2.5~4.3V for 3 cycles of constant current and constant voltage charging (cutoff current of 0.05A) and constant current discharging (cutoff voltage of 2.5V). After 50 cycles at 0.33C, the batteries were charged at 0.1C and 1C within a voltage range of 2.5~4.3V for 3 cycles of constant current and constant voltage charging (cutoff current of 0.05A) and constant current discharging (cutoff voltage of 2.5V) for 3 cycles. The average discharge capacity of the last 3 cycles at 0.1C and 1C was recorded as the reversible discharge capacity at 0.1C and 1C.

[0302] 2. 5C First Discharge Specific Capacity Test: The battery prepared above was subjected to electrical performance testing in an electrochemical workstation device, model M340A precision battery tester, according to the test procedure. At room temperature of 25℃, constant current discharge was performed at 5C within a voltage range of 2.5~4.3V (cutoff voltage of 2.5V) to obtain the 5C first discharge specific capacity.

[0303] 3. Capacity retention test after 200 cycles at 45℃:

[0304] The newly assembled battery was activated by charging and discharging at a low rate (0.2C) for two cycles. Then, the activated battery was placed in a constant temperature chamber set at 45°C, and the battery was charged and discharged using an electrochemical workstation. The test was started at 1C under full discharge conditions, and the initial discharge capacity (after activation) and the discharge capacity after 200 cycles were recorded.

[0305] Capacity retention rate (%) after 200 cycles = discharge capacity after 200 cycles / initial discharge capacity (after activation).

[0306] The test results are listed in Table 4 below:

[0307] Table 4

[0308]

[0309] Based on the above data, it can be seen that when the lithium manganese iron phosphate material prepared in the examples is applied to batteries, the reversible discharge capacity at 0.1C can reach more than 118 mAh / g, the reversible discharge capacity at 1C can reach more than 107.3 mAh / g, the initial discharge capacity at 5C can reach more than 71.2 mAh / g, and the capacity retention rate after 200 cycles at 45℃ can reach more than 84.3%, indicating that the lithium manganese iron phosphate material prepared in the examples has excellent electrical performance when applied to batteries.

[0310] Based on the results of Examples 1-3, it is evident that using sodium hydroxide as a precipitant in Examples 1 and 2 resulted in lithium manganese iron phosphate materials exhibiting superior performance in terms of 0.1C reversible discharge capacity, 1C reversible discharge capacity, 5C initial discharge capacity, and capacity retention after 200 cycles at 45°C. This may be because NaOH is more alkaline, leading to a more complete reaction and non-volatile behavior. Furthermore, pH also has a certain impact on electrical performance, possibly because pH affects the precipitation of iron, manganese, and phosphorus.

[0311] This invention employs a first hydrothermal reaction followed by a second hydrothermal reaction under supercritical conditions, which effectively removes introduced Na compared to existing technologies that use simple water washing and filtration. + K + NH4 + The presence of impurity elements, such as sodium manganese phosphate and ammonium manganese phosphate, may be due to impurity cations being embedded in the ferric manganese phosphate precursor during the hydrothermal treatment process, forming phases such as sodium ferric manganese phosphate and ammonium ferric manganese phosphate. These impurity cations then react with Li during the subsequent supercritical reaction. + Due to similarities and concentration gradients, these impurities can be replaced, resulting in better removal of impurity cations.

[0312] According to the results of the examples and comparative examples 1-2, the second hydrothermal reaction was not carried out under supercritical conditions in comparative examples 1-2, which resulted in a significant deterioration in the reversible discharge capacity at 0.1C, the reversible discharge capacity at 1C, the initial discharge capacity at 5C, and the capacity retention rate after 200 cycles at 45°C.

[0313] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium manganese iron phosphate material, characterized in that, The lithium manganese iron phosphate material satisfies the following requirements: S 2 (C) Fe / C Mn =10~500ppm; and C 杂质离子 ≤500ppm; Among them, C Fe / C Mn S represents the molar ratio of iron to manganese in the lithium manganese iron phosphate particles of the lithium manganese iron phosphate material. 2 (C) Fe / C Mn () represents the sample variance of the molar ratio of iron and manganese in different lithium manganese phosphate particles; C 杂质离子 This indicates that the impurity ion Na in the lithium manganese iron phosphate material + NH4 + and K + Total molar content.

2. The lithium manganese iron phosphate material as described in claim 1, characterized in that, It satisfies one or more of the following conditions (a) to (e): (a) The molar ratio of iron to manganese in the lithium manganese iron phosphate material is x:(1-x), where 0<x<1; (b) The molar ratio of the sum of the molar amounts of iron and manganese in the lithium manganese phosphate material to that of lithium is 1:(1~2). (c) The lithium manganese iron phosphate material further includes doping elements, wherein the doping elements are transition metals, and the transition metals include one or more of Ti, V, Nb and Zr; (d) The compaction density of the lithium manganese iron phosphate material is 2.45~2.55 g / cm³. 3 ; (e) The surface of the lithium manganese iron phosphate particles includes a carbon coating layer; (f) The lithium manganese iron phosphate particles include a first particle and a second particle, at least a portion of the first particle is attached to the surface of the second particle to form a secondary particle; the particle size of the first particle is smaller than the particle size of the second particle.

3. The lithium manganese iron phosphate material as described in claim 2, characterized in that, It satisfies one or more of the following conditions (a) to (f): (a) The Dn50 of the lithium manganese iron phosphate material is 5~10μm; (b) The Dn99 of the lithium manganese iron phosphate material is 100~200μm; (c) The particle size of the first particle is D1 = (0.9~1.1)Dn50, wherein Dn50 is the Dn50 of the lithium manganese iron phosphate material; (d) The particle size of the second particle is D2 = (0.5~1.0)Dn99, wherein Dn99 is the Dn99 of the lithium manganese iron phosphate material; (e) In the secondary particles, the ratio of the volume of the second particle to the total volume of the first particle is 1:(8~10). (f) The secondary particles account for 5% to 16% of the volume percentage of the lithium manganese iron phosphate material.

4. A method for preparing lithium manganese iron phosphate material, characterized in that, It includes the following steps: S1. The iron-manganese phosphate precursor is subjected to a first hydrothermal reaction to obtain a first mixture; S2. The second mixture is subjected to a second hydrothermal reaction under supercritical conditions to obtain an intermediate; The second mixture comprises the first mixture and a lithium source; S3. The third mixture is sintered to obtain the lithium manganese iron phosphate material; The third mixture includes the intermediate and the carbon source.

5. The method for preparing lithium manganese iron phosphate material as described in claim 4, characterized in that, It satisfies one or more of the following conditions (a) to (i): (a) The temperature of the first hydrothermal reaction is 100~200℃; (b) The duration of the first hydrothermal reaction is 5 to 32 hours; (c) The iron-manganese phosphate precursor includes impurity ions, wherein the impurity ions include Na + NH4 + and K + One or more of the following; the molar content of the impurity ions is 5000~10000ppm; (d) The solid content of the first mixture is 20~70 g / L; (e) The temperature of the second hydrothermal reaction is 364~390℃; (f) The pressure of the second hydrothermal reaction is 22.1~23.0 MPa; (g) The second hydrothermal reaction takes 3 to 12 hours; (h) The molar content of impurity ions in the intermediate is less than 200 ppm, wherein the impurity ions include Na. + NH4 + and K + One or more of the following; (i) The second mixture further includes a dopant source, wherein the dopant source includes a transition metal element.

6. The method for preparing lithium manganese iron phosphate material as described in claim 4, characterized in that, It satisfies one or more of the following conditions (a) to (f): (a) The holding temperature during the sintering process is 700~1000℃; (b) The holding time for the sintering process is 5-12 hours; (c) The heating rate during the heating stage of the sintering process is 4~8℃ / min; (d) The sintering process is carried out in an inert gas atmosphere; (e) Prior to the sintering process, the third mixture is further dried and ground; (f) Prior to the sintering process, the third mixture is pre-sintered, and the temperature of the pre-sintering holding stage is 300~450°C.

7. The method for preparing lithium manganese iron phosphate material as described in claim 4, characterized in that, It satisfies one or more of the following conditions (a) to (f): (a) The lithium source includes one or more of lithium nitrate, lithium carbonate, lithium acetate, lithium oxalate, lithium hydroxide, lithium phosphate, lithium monohydrogen phosphate and lithium dihydrogen phosphate; (b) The molar ratio of the lithium source to the manganese iron phosphate precursor is (4~15):1; (c) The carbon source includes one or more of sucrose, glucose, fructose, oxalic acid, citric acid, ascorbic acid, graphene, graphyne, polyethylene glycol ether, polyethylene glycol, polyethylene glycol sulfate and polyoxyethylene ethyl ether; (d) The carbon source is 5% to 15% of the theoretical mass of lithium manganese iron phosphate material, wherein the theoretical mass of lithium manganese iron phosphate material is calculated based on the chemical reaction formula of each material; (e) The iron-manganese phosphate precursor is prepared by a co-precipitation method, comprising the following steps: first, the mixture is oxidized with an oxidant, and then precipitated with a precipitant; wherein the mixture comprises an iron source, a manganese source and a phosphorus source; (f) The method for preparing the second mixture includes: ball milling or sand milling the first mixture and the lithium source.

8. A lithium manganese iron phosphate material prepared by the method described in any one of claims 4 to 7.

9. An electrochemical device, characterized in that, The positive electrode of the electrochemical device comprises lithium manganese iron phosphate material as described in any one of claims 1 to 3 and 8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

Images