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

Abstract

The embodiment of the invention provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive electrode plate and a lithium ion battery, the preparation method comprises the following steps: dispersing a lithium source and a phosphorus source in a dispersant, then adding a manganese source and lithium iron phosphate to form a uniform mixed slurry, the proportion of a solid substance is greater than or equal to 45%, and the dispersant comprises ethylene glycol and / or water; placing the mixed slurry in a closed device, and carrying out a synthetic reaction under a certain condition to obtain a lithium manganese iron phosphate precursor; and carrying out high-temperature sintering on the lithium manganese iron phosphate precursor to obtain the lithium manganese iron phosphate positive electrode material. According to the preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the invention, lithium iron phosphate is adopted as a template, the lithium iron manganese phosphate positive electrode material with high compaction and high performance is synthesized, no waste material or waste gas is generated, and the method is green and environment-friendly; the dispersing agent is small in usage amount and simple and efficient in process; the reaction atom utilization rate is high, the dispersant can be recycled, and the cost can be reduced; the method can be used for recycling the LiFePO4 material, and the additional value of the LiFePO4 material

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of battery technology, and in particular to a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive electrode plate and a lithium ion battery. Background Art

[0002] At present, lithium-ion batteries are a hot research direction in the world. Since the performance of lithium-ion batteries is mainly determined by positive and negative electrode materials and electrolytes, the research and development of positive electrode materials is crucial. Compared with lithium iron phosphate, lithium manganese oxide, ternary materials and other lithium-ion battery positive electrode materials, lithium manganese iron phosphate has the advantages of good cycle performance, high conductivity, high energy density, wide source of raw materials, environmental friendliness, and low cost. In addition, it is in the stable electrochemical window of the existing electrolyte system, and lithium manganese iron phosphate can be used in conjunction with a variety of organic electrolytes.

[0003] There are many methods for preparing lithium manganese iron phosphate, which generally include high temperature solid phase reaction method, liquid phase coprecipitation method, hydrothermal method, sol-gel method, redox method, solid phase microwave method and mechanical ball milling method, etc. However, most of these preparation methods are complicated, with low utilization rate of raw materials, resulting in high pollution and resource waste.

[0004] In order to solve the complexity of the existing process for preparing positive electrode materials for lithium-ion batteries, improve the utilization rate of lithium iron manganese phosphate raw materials and reduce pollution, it is particularly important to modify the preparation process of lithium iron manganese phosphate. Summary of the invention

[0005] The technical problem solved by the embodiment of the present invention is to provide a method for preparing a lithium iron manganese phosphate positive electrode material with simple process, high efficiency, greenness and low cost.

[0006] In order to solve the above problems, an embodiment of the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, which is characterized by comprising:

[0007] Dispersing a lithium source and a phosphorus source in a dispersant, and then adding a manganese source and lithium iron phosphate to form a uniform mixed slurry, wherein the solid matter accounts for greater than or equal to 45%, and the dispersant includes ethylene glycol and / or water;

[0008] Placing the mixed slurry in a closed device to carry out a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor;

[0009] The lithium iron manganese phosphate precursor is sintered at high temperature to obtain the lithium iron manganese phosphate positive electrode material.

[0010] Optionally, the mass percentage of the dispersant is 30%-40%, and the molar ratio of the lithium source, phosphorus source and manganese source is in the range of 1:1:1 to 1.05:1.05:1.

[0011] Optionally, the temperature range of the synthesis reaction is 160° C.-220° C., and the reaction time is 1 h-8 h.

[0012] Optionally, the temperature range of the high-temperature sintering is 200°C-750°C, the sintering time range is 9-19h, the heating rate is 2-20°C / min, and the cooling rate is 2-20°C / min.

[0013] Optionally, the high temperature sintering step specifically includes: heating to 200° C. at 3° C. / min and maintaining for 2 hours, further heating to 450° C. and maintaining for 2 hours, and finally heating to 700° C. and maintaining for 5-15 hours.

[0014] Optionally, the lithium iron phosphate is carbon-coated lithium iron phosphate.

[0015] Optionally, before the step of placing the mixed slurry in a closed device for a synthesis reaction under certain conditions, the method further includes: adding a carbon source to the mixed slurry to perform secondary carbon coating on the lithium iron phosphate, wherein the carbon source includes glucose or sucrose.

[0016] Optionally, the manganese source includes at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide.

[0017] Optionally, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate or lithium dihydrogen phosphate.

[0018] Optionally, the phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0019] Optionally, the phosphorus source is phosphoric acid, and the solid matter accounts for 45%-50%. Optionally, the compaction density of the lithium manganese iron phosphate positive electrode material is ≥1.4g / cm 3 , preferably, ≥2.1g / cm 3 .

[0020] The embodiment of the present invention further provides a lithium iron manganese phosphate positive electrode material, and the lithium iron manganese phosphate positive electrode material is prepared by the above method.

[0021] An embodiment of the present invention further provides a positive electrode plate, wherein the positive electrode plate comprises the aforementioned lithium iron manganese phosphate positive electrode material.

[0022] An embodiment of the present invention further provides a lithium-ion battery, wherein the lithium-ion battery comprises the aforementioned positive electrode plate.

[0023] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0024] The method for preparing the lithium iron manganese phosphate positive electrode material provided in the embodiment of the present invention is as follows: first, a lithium source and phosphoric acid are dispersed in a dispersant, and then a manganese source and lithium iron phosphate are added to form a uniform mixed slurry, wherein the solid matter accounts for greater than or equal to 45%, and the dispersant can be ethylene glycol and / or water; then, the mixed slurry is subjected to a synthesis reaction under certain conditions to obtain a lithium iron manganese phosphate precursor; finally, the lithium iron manganese phosphate precursor is subjected to high-temperature sintering to obtain the lithium iron manganese phosphate positive electrode material. On the one hand, the method for preparing the lithium iron manganese phosphate positive electrode material provided in the embodiment of the present invention has a higher production capacity than the pure solvent method because the solid content of the mixed slurry is not less than 45%; on the other hand, the method for preparing the lithium iron manganese phosphate positive electrode material provided in the present application has a 100% atomic utilization rate of the feed, thereby avoiding subsequent washing and purification processes and reducing production costs; further, the preparation method of the present application does not generate waste materials and waste gas, and the process is green and simple to operate.

[0025] It can be seen that the method for preparing the lithium iron manganese phosphate positive electrode material provided in the embodiment of the present invention adopts lithium iron phosphate as a template to synthesize a lithium iron manganese phosphate positive electrode material with high compaction and high performance, without generating waste materials and exhaust gas, and is green and environmentally friendly; the amount of dispersant used is small, and the process is simple and efficient; the utilization rate of reaction atoms is high and the dispersant is recyclable, which can reduce costs; it can be used to recycle LiFePO4 materials and increase their added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] Figure 1 It is a schematic diagram of a process for preparing a lithium iron manganese phosphate positive electrode material provided in an embodiment of the present invention;

[0028] Figure 2 is a photograph of the mixed slurry of Example 1 of the present invention;

[0029] Figure 3 are scanning electron microscope photographs of the lithium manganese iron phosphate of Example 1 of the present invention and Comparative Example 1;

[0030] Figure 4 is an XRD comparison diagram of lithium manganese iron phosphate of Example 1 of the present invention and Comparative Example 1;

[0031] Figure 5 is a scanning electron microscope photograph of the electrode sheet of Examples 4-6 of the present invention;

[0032] Figure 6 It is a cycle test spectrum of the button battery of Example 7 of the present invention and Comparative Example 1 under the conditions of 2.5-4.4V and 0.5C. DETAILED DESCRIPTION

[0033] As can be seen from the background technology, the current preparation methods of lithium manganese iron phosphate are mostly complicated, with low utilization rate of raw materials, and thus generate great pollution and waste of resources.

[0034] Please refer to Figure 1 To solve the above problems, an embodiment of the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising:

[0035] Step S1, dispersing a lithium source and phosphoric acid in a dispersant, and then adding a manganese source and lithium iron phosphate to form a uniform mixed slurry, wherein the solid matter accounts for greater than or equal to 45%, and the dispersant includes ethylene glycol and / or water;

[0036] The solid matter ratio refers to the mass of solid powder / (mass of solid powder + mass of liquid phase), that is, the solid content percentage.

[0037] It should be noted that the phosphorus source in the present application can be either a liquid phase or a solid phase. Specifically, the phosphorus source can be at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. When the phosphorus source is a liquid phase (for example, phosphoric acid), the solid matter ratio refers to the mass of solid powder / (mass of solid powder + mass of dispersant + mass of phosphorus source), that is, (the sum of the masses of lithium source, manganese source, and lithium iron phosphate) / (the total mass of lithium source, phosphorus source, manganese source, lithium iron phosphate, and dispersant); when the phosphorus source is a solid phase, the solid matter ratio refers to the mass of solid powder / (mass of solid powder + mass of dispersant), that is, (the sum of the masses of lithium source, phosphorus source, manganese source, and lithium iron phosphate) / (the total mass of lithium source, phosphorus phosphate source, manganese source, lithium iron phosphate, and dispersant). In a specific embodiment, the phosphorus source is phosphoric acid, and the solid content accounts for 45%-50%.

[0038] The amount of the dispersant used can achieve the purpose of wetting the powder, and the powder does not need to be in a solution state in the dispersant, so as to increase the solid content of the reaction and increase the production capacity. In a specific embodiment, the mass percentage of the dispersant is 30%-40%.

[0039] The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate or lithium dihydrogen phosphate, wherein the lithium hydroxide may be hydrated lithium hydroxide or anhydrous lithium hydroxide.

[0040] In a specific embodiment, the manganese source may be manganese carbonate. Of course, in other embodiments, the manganese source may also be at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide.

[0041] The molar ratio of the lithium source, phosphorus source and manganese source is in the range of 1:1:1 to 1.05:1.05:1. The excess LiOH and H3PO4 can finally form a Li3PO4 coating, further improving the surface stability of the lithium manganese iron phosphate positive electrode material.

[0042] This application uses lithium iron phosphate as a template to achieve the recycling of retired lithium iron phosphate. The raw material lithium iron phosphate can be obtained from battery recycling, and the recycled lithium iron phosphate itself has been carbon-coated. By recycling the lithium iron phosphate in the waste lithium iron phosphate battery, the added value of lithium iron phosphate is increased. In addition, the carbon-coated lithium iron phosphate can be carbon-coated for a second time, that is, sucrose or glucose is added during the solvothermal process of step S2, so that the material synthesis and carbon coating can be completed in one step.

[0043] It should be noted that the preparation method of lithium manganese iron phosphate of the present application uses lithium iron phosphate as a template and synthesizes lithium manganese iron phosphate by a solvothermal method. The amount of dispersant such as ethylene glycol used is very small, and the purpose of wetting the powder is sufficient, so that a solvothermal reaction can occur under high temperature and high pressure. The traditional solvothermal method requires a large amount of ethylene glycol to provide a solution environment. Considering the solubility limitation, the solid content of the reaction is very low (<5%). This means that the preparation method of the present application has a higher solid content and a higher production capacity; further, the preparation method of the present application directly uses lithium manganese iron phosphate as a template, which can realize the recycling of retired lithium iron phosphate, and can also avoid subsequent washing and purification treatments to save costs (LiOH excessively generates Li2SO4 or LiCl during the pure solvothermal method, which needs to be purified, resulting in increased costs, and a large amount of ethylene glycol solvent recovery further leads to a further increase in the production cost of the pure solvent method).

[0044] Step S2, placing the mixed slurry in a closed device to perform a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor;

[0045] The temperature range of the synthesis reaction is 160° C.-220° C., and the reaction time is 1 h-8 h.

[0046] In a specific embodiment, the closed device can be a reactor. The reactor provides a high temperature and high pressure reaction environment for the mixed slurry, which is conducive to the positive reaction. Of course, in other embodiments, the closed device can also be other closed containers that can provide a high temperature and high pressure environment.

[0047] Taking LiOH·H2O as the lithium source, phosphoric acid as the phosphorus source, and MnCO3 as the manganese source as an example, the mixed slurry undergoes the following chemical reactions in a closed container:

[0048] LiOH·H2O+H3PO4→LiH2PO4+H2O

[0049] LiH2PO4+MnCO3→LiMnPO4+H2O+CO2

[0050] xLiMnPO4+(1-x)LiFePO4→LiMn x Fe 1-x PO4

[0051] It can be seen that the preparation method of lithium manganese iron phosphate positive electrode material provided in the embodiment of the present application can utilize all the raw materials through the solvent thermal reaction in step S2, there are no by-products (see the above chemical reaction equation), and the reaction atom utilization rate reaches 100%. The high reaction atom utilization rate can reduce production costs. On the other hand, only a small amount of dispersant is needed during the experiment, and the process is simple and efficient.

[0052] In addition, the carbon-coated lithium iron phosphate can be subjected to secondary carbon coating. Specifically, before the step of placing the mixed slurry in a closed device for synthesis reaction under certain conditions, the step further includes: adding a carbon source to the mixed slurry to perform secondary carbon coating on the lithium iron phosphate, wherein the carbon source includes glucose or sucrose, that is, adding sucrose or glucose during the solvothermal process of step S2, thereby completing material synthesis and carbon coating in one step.

[0053] Step S3, sintering the lithium iron manganese phosphate precursor at high temperature to obtain the lithium iron manganese phosphate positive electrode material.

[0054] The temperature range of the high-temperature sintering is 200° C.-750° C., the sintering time range is 9-19 hours, the heating rate is 2-20° C. / min, and the cooling rate is 2-20° C. / min.

[0055] In a specific embodiment, the high temperature sintering step specifically includes: heating to 200°C at 3°C / min and maintaining for 2 hours, further heating to 450°C and maintaining for 2 hours, and finally heating to 700°C and maintaining for 5-15 hours.

[0056] The compaction density of the lithium manganese iron phosphate material is greater than or equal to 1.4 g / cm 3 , preferably, greater than or equal to 2.1 g / cm 3 High compaction means that after the electrode is made, the compaction density of the electrode sheet is high. High compaction means that more active materials can be loaded per unit volume, and the battery's (volume) energy density is higher.

[0057] It should be noted that the preparation of commercial battery electrodes is more complex and can achieve higher active material loading and compaction density.

[0058] The method for preparing the lithium iron manganese phosphate positive electrode material provided in the embodiment of the present invention adopts lithium iron phosphate as a template to synthesize a lithium iron manganese phosphate positive electrode material with high compaction and high performance, without generating waste materials and exhaust gas, and being green and environmentally friendly; the amount of dispersant used is small, and the process is simple and efficient; the utilization rate of reaction atoms is high and the dispersant is recyclable, which can reduce costs; it can be used to recycle LiFePO4 materials to increase their added value.

[0059] In order to solve the above problems, an embodiment of the present invention further provides a lithium iron manganese phosphate positive electrode material, and the lithium iron manganese phosphate positive electrode material is prepared by the above method.

[0060] The lithium iron manganese phosphate positive electrode material provided in the embodiment of the present invention has high compaction performance and can improve the cycle performance of the battery.

[0061] In order to solve the above problems, an embodiment of the present invention further provides a positive electrode plate, wherein the positive electrode plate comprises the above-mentioned lithium iron manganese phosphate positive electrode material.

[0062] The positive electrode sheet provided in the embodiment of the present invention comprises the lithium manganese iron phosphate positive electrode material prepared by the aforementioned method, and has high compaction and high cycle performance.

[0063] To solve the above problems, an embodiment of the present invention further provides a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned positive electrode plate.

[0064] The lithium ion battery provided by the embodiment of the present invention has high compaction and high cycle performance.

[0065] The lithium iron manganese phosphate positive electrode material and its preparation method, positive electrode sheet and lithium ion battery of the present invention are further described in detail below in combination with specific embodiments and comparative examples.

[0066] Example 1

[0067] Preparation method of lithium manganese iron phosphate positive electrode material:

[0068] Step 1, a certain mass of LiOH·H2O and phosphoric acid (H3PO4) are dispersed in ethylene glycol, and a certain mass of MnCO3 is added and mixed evenly, wherein LiOH:H3PO4:MnCO3=1:1:1~1.05:1.05:1 (molar ratio), and a certain mass of commercial lithium iron phosphate (LiFePO4) powder is added, the mass percentage of ethylene glycol is 30%-40%, and the mass percentage of solid matter is 48.6%, to obtain a black slurry, such as Figure 2 shown.

[0069] Step 2, transfer the black slurry into a reactor, maintain it at 180°C for 2h, take out the product, and dry it to obtain a black product.

[0070] Step 3, the black product was sintered in stages: first at 200°C for 2 hours, then at 450°C for 2 hours, and finally at 700°C for 5 hours to obtain a lithium manganese iron phosphate positive electrode material (LMFP), which was recorded as LMFP-1. The electron microscope morphology analysis and XRD analysis of sample LMFP-1 were performed, and the results were as follows: Figure 3 and Figure 4 shown.

[0071] Depend on Figure 3 It can be seen that the particles of Example 1 are more uniform. Comparison of XRD shows that pure phase LMFP is obtained in Example 1, while obvious impurities (miscellaneous peaks) exist in Comparative Example 1.

[0072] Example 2

[0073] Preparation method of lithium manganese iron phosphate positive electrode material:

[0074] A certain mass of LiOH·H2O and phosphoric acid (H3PO4) are dispersed in ethylene glycol, and a certain mass of MnCO3 is added and mixed evenly, wherein LiOH:H3PO4:MnCO3=1:1:1~1.05:1.05:1 (molar ratio), and then a certain mass of commercial lithium iron phosphate (LiFePO4) powder is added, the mass percentage of ethylene glycol is 30%-40%, and the mass percentage of solid matter is 45%, to obtain a black slurry.

[0075] The black slurry was transferred into a reactor, maintained at 180°C for 1 h, the product was taken out and dried to obtain a black product.

[0076] The black product was sintered in stages: first at 200°C for 2 h, then at 450°C for 2 h, and finally at 700°C for 5 h to obtain lithium manganese iron phosphate positive electrode material (LMFP), recorded as LMFP-2.

[0077] Example 3

[0078] Preparation method of lithium manganese iron phosphate positive electrode material:

[0079] A certain mass of LiOH·H2O and phosphoric acid (H3PO4) are dispersed in ethylene glycol, and a certain mass of MnCO3 is added and mixed evenly, wherein LiOH:H3PO4:MnCO3=1:1:1~1.05:1.05:1 (molar ratio), and then a certain mass of commercial lithium iron phosphate (LiFePO4) powder is added, the mass percentage of ethylene glycol is 30%-40%, and the mass percentage of solid matter is 50%, to obtain a black slurry.

[0080] The black slurry was transferred into a reactor and maintained at 180°C for 8 h. The product was taken out and dried to obtain a black product.

[0081] The black product was sintered in stages: first at 200°C for 2 h, then at 450°C for 2 h, and finally at 700°C for 5 h to obtain lithium manganese iron phosphate positive electrode material (LMFP), recorded as LMFP-3.

[0082] Embodiment 4-6

[0083] The active electrode material LMFP (93 wt%) of Examples 1-3, the conductive additives conductive carbon black Super P (2 wt%) and conductive graphite KS-6 (2 wt%), and the binder PVDF solution (3 wt%) were mixed evenly, and then the mixed slurry was evenly coated on a clean aluminum foil with a scraper, with a coating thickness of 250 μm, and placed in a vacuum transition chamber at 80 ° C for 8 h to dry. The LMFP loading was about 10 mg cm -2 , rolled with an electric double-roller press, the rolled bottom thickness is about 1.1 mm, and then pressed with a tablet press to prepare an electrode sheet with a diameter of 12 mm.

[0084] Test method for compaction density of pole piece

[0085] Use a balance to weigh the mass of 10 pole pieces with a diameter of 12 mm and take the average value, see Table 2.

[0086] Use SEM to characterize the cross section of the pole piece and measure the height of the active material in the pole piece. Take three cross sections with different heights and take the average value as the thickness of the active material in the pole piece, as shown in Table 1 and Figure 5 shown.

[0087] The calculation formula of the pole piece compaction density is:

[0088]

[0089] ρ cd :Pole piece compaction density g / cm 3 ;

[0090] m: mass of active material of the electrode, g;

[0091] V: Volume of active material of the electrode cm 3 ;

[0092] Where: pole piece active material mass = (pole piece mass - aluminum foil mass) * 0.93;

[0093] The mass volume of the active material of the electrode = the area of ​​the electrode * the thickness of the active material;

[0094] Aluminum foil mass: 4.78 mg; electrode area: 1.131 cm 2 .

[0095] The compaction density of the pole piece is shown in Table 3.

[0096] Table 1 The volume of active substances in the electrode of each material

[0097]

[0098] Table 2 The mass of active materials in the electrode of each material

[0099]

[0100] Table 3 Compacted density of each material

[0101]

[0102] Embodiment 7-9

[0103] Button battery assembly

[0104] The operation was carried out in a glove box (MBRAUN LABMASTER 130) under Ar atmosphere protection, the electrolyte was 1M LiPF6 (EC / DMC / EMC=1:1:1), 2% VC was used as an additive, the diaphragm was Celgard-2500 polypropylene microfilm, the electrode sheets of Examples 4-6 were used as working electrodes, and the counter electrode was a fresh lithium sheet.

[0105] The button cell was tested for related performance. The charging and discharging method was constant current charging and discharging, and the voltage range was 2.5 to 4.4 V. The specific capacity, cycle performance, rate performance, etc. of the battery were tested. The test results are shown in Table 4-6 and Figure 6 shown.

[0106] Comparative Example 1

[0107] Preparation method of lithium manganese iron phosphate positive electrode material:

[0108] A certain mass of LiOH and phosphoric acid (H3PO4) are dispersed in ethylene glycol, and a certain mass of MnCO3 is added and mixed evenly, wherein LiOH:H3PO4:MnCO3=1:1:1~1.05:1.05:1 (molar ratio). A certain mass of commercial lithium iron phosphate (LiFePO4) powder is then added, the mass percentage of ethylene glycol is 30%-40%, and the mass percentage of solid matter is 48.6%, to obtain a black slurry, which is then dried to obtain a black product.

[0109] The black product was sintered in stages: first at 200°C for 2 h, then at 450°C for 2 h, and finally at 700°C for 5 h to obtain lithium manganese iron phosphate positive electrode material (LMFP), recorded as LMFP-D1.

[0110] The difference between Comparative Example 1 and Example 1 is that after step 1, the black slurry is directly dried, step 2 is skipped, and step 3 is directly performed, and the remaining operations are the same as in Example 1.

[0111] The preparation process of the electrode:

[0112] LMFP-D1 (93 wt%), conductive additives conductive carbon black Super P (2 wt%) and conductive graphite KS-6 (2 wt%), and binder PVDF solution (3 wt%) were mixed evenly, and then the mixed slurry was evenly coated on a clean aluminum foil with a scraper, with a coating thickness of 250 μm, and placed in a vacuum transition chamber at 80 ° C for 8 h to dry. The LMFP loading was about 10 mg / cm 2 , rolled with an electric double-roller press, the rolled bottom thickness is about 1.1 mm, and then pressed with a tablet press to prepare an electrode sheet with a diameter of 12 mm.

[0113] Button battery assembly

[0114] The operation was carried out in a glove box (MBRAUN LABMASTER 130) under Ar atmosphere protection, the electrolyte was 1M LiPF6 (EC / DMC / EMC=1:1:1), 2% VC was used as an additive, the diaphragm was Celgard-2500 polypropylene microfilm, the electrode sheet of Comparative Example 2 was used as the working electrode, and the counter electrode was a fresh lithium sheet.

[0115] The button cell was tested for related performance. The charging and discharging method was constant current charging and discharging, and the voltage range was 2.5 to 4.4 V. The specific capacity, cycle performance, rate performance, etc. of the battery were tested. The test results are shown in Table 4-6 and Figure 6 shown.

[0116] Table 4 Charge and discharge capacity and first cycle coulomb efficiency of each material

[0117]

[0118] Table 5 Rate performance parameters of Example 1 and Comparative Example 1

[0119]

[0120] Table 6 Cyclic performance parameters of Example 1 and Comparative Example 1

[0121]

[0122] Combined with Table 4-6 and Figure 6 It can be seen that the lithium manganese iron phosphate battery prepared in the embodiment of the present application has a first-cycle coulomb efficiency of up to 94.4% and a discharge specific capacity of up to 136.8 mAh g -1 After 300 long cycles, the capacity retention rate is as high as 94.8%. The lithium manganese iron phosphate positive electrode material prepared by the preparation method of the present application can significantly improve the cycle performance of lithium batteries.

[0123] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0124] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: include: Dispersing a lithium source and a phosphorus source in a dispersant, and then adding a manganese source and lithium iron phosphate to form a uniform mixed slurry, wherein the solid matter accounts for greater than or equal to 45%, and the dispersant includes ethylene glycol and / or water; Placing the mixed slurry in a closed device to carry out a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor; The lithium iron manganese phosphate precursor is sintered at high temperature to obtain the lithium iron manganese phosphate positive electrode material.

2. The method for preparing the lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The mass percentage of the dispersant is 30%-40%, and the molar ratio of the lithium source, the phosphorus source and the manganese source is in the range of 1:1:1 to 1.05:1.05:

1.

3. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The temperature range of the synthesis reaction is 160° C.-220° C., and the reaction time is 1 h-8 h.

4. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The temperature range of the high-temperature sintering is 200° C.-750° C., the sintering time range is 9-19 hours, the heating rate is 2-20° C. / min, and the cooling rate is 2-20° C. / min.

5. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 4, characterized in that: The high temperature sintering step specifically includes: heating to 200° C. at 3° C. / min and maintaining for 2 hours, then heating to 450° C. and maintaining for 2 hours, and finally heating to 700° C. and maintaining for 5-15 hours.

6. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 5, characterized in that: The lithium iron phosphate is carbon-coated lithium iron phosphate.

7. The method for preparing the lithium iron manganese phosphate positive electrode material according to claim 6, characterized in that: Before placing the mixed slurry in a closed device for a synthesis reaction under certain conditions, the step further includes: adding a carbon source to the mixed slurry to perform secondary carbon coating on the lithium iron phosphate, wherein the carbon source includes glucose or sucrose.

8. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 5, characterized in that: The manganese source includes at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide.

9. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 5, characterized in that: The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate or lithium dihydrogen phosphate.

10. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 5, characterized in that: The phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

11. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The phosphorus source is phosphoric acid, and the solid matter accounts for 45%-50%.

12. The method for preparing the lithium iron manganese phosphate positive electrode material according to claim 10, characterized in that: The compaction density of the lithium manganese iron phosphate positive electrode material is greater than or equal to 1.4 g / cm 3 , preferably, greater than or equal to 2.1 g / cm 3 .

13. A lithium manganese iron phosphate positive electrode material, characterized in that: The lithium manganese iron phosphate positive electrode material is prepared by the method according to any one of claims 1 to 12.

14. A positive electrode sheet, characterized in that: The positive electrode plate comprises the lithium iron manganese phosphate positive electrode material as claimed in claim 13.

15. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 14.

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