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

Abstract

The embodiment of the present application provides a kind of lithium iron manganese phosphate positive electrode material and its preparation method, positive pole piece and lithium ion battery, wherein preparation method includes: lithium source, phosphorus source is dispersed in dispersing agent, then manganese source, lithium iron phosphate is added to form uniform mixed slurry, wherein solid matter ratio is greater than or equal to 45%, dispersing agent includes ethylene glycol and / or water;Mixed slurry is placed in closed device under certain conditions to carry out synthesis reaction, and lithium iron manganese phosphate precursor is obtained;Lithium iron manganese phosphate precursor is sintered at high temperature, and lithium iron manganese phosphate positive electrode material is obtained.The preparation method of lithium iron manganese phosphate positive electrode material provided by the embodiment of the present application uses lithium iron phosphate as template, synthesizes lithium iron manganese phosphate positive electrode material with high compaction and high performance, no waste material and waste gas is generated, green and environmental protection;Dispersing agent is used in small amount, and process is simple and efficient;Reaction atomic utilization rate is high, and dispersing agent can be recycled, which can reduce cost;It can be used for recycling LiFePO4 material, and improve its added value.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of battery, in particular to a lithium manganese iron phosphate positive material, a preparation method thereof, a positive sheet and a lithium ion battery. BACKGROUND

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

[0003] There are many existing disclosed preparation methods of lithium manganese iron phosphate, generally including high-temperature solid-phase reaction method, liquid-phase coprecipitation method, hydrothermal method, sol-gel method, oxidation-reduction method, solid-phase microwave method and mechanical ball milling method, etc. However, most of these preparation methods are complex, and the utilization rate of raw materials is low, which further produces a lot of pollution and resource waste.

[0004] In order to solve the problem of complex process of preparing lithium ion battery positive material, improve the utilization rate of lithium manganese iron phosphate raw materials, and reduce pollution, it is particularly important to modify the preparation process of lithium manganese iron phosphate. SUMMARY

[0005] The technical problem solved by the embodiment of the present application is to provide a preparation method of lithium manganese iron phosphate positive material which is simple, efficient, green and low-cost.

[0006] To solve the above problems, the embodiment of the present application provides a preparation method of lithium manganese iron phosphate positive material, characterized in that it comprises:

[0007] Disperse lithium source and phosphorus source in a dispersing agent, and then add 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 dispersing agent comprises ethylene glycol and / or water;

[0008] Put the mixed slurry into a closed device to perform a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor;

[0009] High-temperature sintering is performed on the lithium manganese iron phosphate precursor to obtain the lithium manganese iron phosphate positive material.

[0010] Optionally, the mass percentage of the dispersing agent is 30%-40%, and the molar ratio of the lithium source, the phosphorus source and the manganese source ranges from 1:1:1 to 1.05:1.05:1.

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

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

[0013] Optionally, the high-temperature sintering specifically comprises: heating to 200 DEG C at a rate of 3 DEG C / min and maintaining for 2 hours, continuing to heat to 450 DEG C and maintaining for 2 hours, and finally heating to 700 DEG 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 and performing a synthesis reaction under certain conditions, the method further comprises: adding a carbon source to the mixed slurry to perform secondary carbon coating on the lithium iron phosphate, and the carbon source comprises glucose or sucrose.

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

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

[0018] Optionally, the phosphorus source comprises 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 content is 45-50%. Optionally, the compaction density of the lithium manganese iron phosphate positive electrode material is ≥1.4 g / cm 3 , preferably ≥2.1 g / cm 3 .

[0020] The embodiment of the present application also provides a lithium manganese iron phosphate positive electrode material, which is prepared by the method described above.

[0021] The embodiment of the present application also provides a positive electrode sheet, which comprises the lithium manganese iron phosphate positive electrode material described above.

[0022] The embodiment of the present application also provides a lithium ion battery, which comprises the positive electrode sheet described above.

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

[0024] The preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the application first disperses a lithium source and phosphoric acid in a dispersing agent, and then adds 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 dispersing agent 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 preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the application 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 preparation method of the lithium iron manganese phosphate positive electrode material provided by the application can avoid subsequent washing and purification processes and reduce production costs because the atomic utilization rate of the raw materials is 100%; further, the preparation method of the application does not produce waste materials and waste gas, and the process is green, simple and easy to operate.

[0025] It can be seen that the preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the application uses lithium iron phosphate as a template to synthesize a lithium iron manganese phosphate positive electrode material with high compaction and high performance, and does not produce waste materials and waste gas, is green and environmentally friendly, has a small amount of dispersing agent, a simple and efficient process, a high atomic utilization rate and recyclable dispersing agent, can reduce costs, and can be used to recycle LiFePO4 materials and improve the added value thereof. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only embodiments of the application, and those skilled in the art can obtain other drawings according to the provided drawings without any creative effort.

[0027] Figure 1 is a flowchart of the preparation method of the lithium iron manganese phosphate positive electrode material provided by the embodiment of the application;

[0028] Figure 2 is a photo of the mixed slurry of the embodiment 1 of the application;

[0029] Figure 3 is a scanning electron microscope photo of the lithium iron manganese phosphate of the embodiment 1 and the comparative example 1 of the application;

[0030] Figure 4 is an XRD comparison chart of the lithium iron manganese phosphate of the embodiment 1 and the comparative example 1 of the application;

[0031] Figure 5 is a scanning electron microscope photo of the electrode sheet of the embodiment 4-6 of the application;

[0032] Figure 6 is a cycle test graph of the button cell of the embodiment 7 and the comparative example 1 of the present application under the condition of 2.5-4.4V, 0.5C. DETAILED DESCRIPTION

[0033] As known from the background, the current preparation method of lithium manganese iron phosphate has a complex process, a low utilization rate of raw materials, and a great pollution and resource waste rate.

[0034] Please refer to Figure 1 To solve the above problems, the embodiment of the present application provides a preparation method of lithium manganese iron phosphate cathode material, which comprises the following steps:

[0035] In step S1, 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 ratio is greater than or equal to 45%, and the dispersant comprises ethylene glycol and / or water.

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

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

[0038] The amount of the dispersant can reach the purpose of infiltrating the powder, and the powder does not need to be in a solution state in the dispersant to improve 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 comprises at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate. The lithium hydroxide can be hydrated lithium hydroxide or anhydrous lithium hydroxide.

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

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

[0042] The application uses lithium iron phosphate as a template to realize 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 has been coated with carbon. 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 again. That is, sucrose or glucose is added during the solvothermal process of step S2 to complete material synthesis and carbon coating in one step.

[0043] It should be noted that the preparation method of the lithium manganese iron phosphate of the application uses lithium iron phosphate as a template to synthesize lithium manganese iron phosphate by a solvothermal method. The amount of dispersant such as ethylene glycol used is very small, which can only wet the powder. Therefore, the solvothermal reaction can occur at high temperature and high pressure. However, the traditional solvothermal method needs a large amount of ethylene glycol to provide a solution environment. Considering the limitation of solubility, the solid content of the reaction is very low (<5%). This means that the preparation method of the application has a higher solid content and higher production capacity. Further, the preparation method of the 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 treatment to save costs (excess LiOH generates Li2SO4 or LiCl during the feeding process of the pure solvothermal method, which needs to be purified, resulting in increased costs. The recovery of a large amount of ethylene glycol solvent further increases the production cost of the pure solvothermal method).

[0044] In step S2, the mixed slurry is placed in a closed device to perform a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor.

[0045] The temperature of the synthesis reaction ranges from 160°C to 220°C, and the reaction time ranges from 1 hour to 8 hours.

[0046] In a specific embodiment, the closed device can be a reaction kettle. The reaction kettle provides a high-temperature and high-pressure reaction environment for the mixed slurry, which is conducive to the forward progress of the 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, H3PO4 as the phosphorus source, and MnCO3 as the manganese source as an example, the mixed slurry undergoes the following chemical reaction in the 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 the lithium manganese iron phosphate positive electrode material provided in the embodiments of the present application can utilize raw materials without by-products (see the chemical reaction equation above) through the solvothermal reaction of step S2, and the atomic utilization rate of the reaction is 100%, so that the production cost can be reduced. On the other hand, only a small amount of dispersant is needed in the experiment, and the process is simple and efficient.

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

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

[0054] The temperature range of the high-temperature sintering is 200-750°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.

[0055] In a specific embodiment, the step of high-temperature sintering specifically comprises: heating at a rate of 3°C / min to 200°C and maintaining for 2h, continuing to heat to 450°C and maintaining for 2h, and finally heating to 700°C and maintaining for 5-15h.

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

[0057] It should be noted that the preparation of commercial battery electrode sheets is complex, and higher active material loading and compaction density can be achieved.

[0058] The preparation method of the lithium manganese iron phosphate positive electrode material provided by the embodiment of the present application adopts lithium iron phosphate as a template to synthesize the lithium manganese iron phosphate positive electrode material with high compaction and high performance, generates no waste gas and waste material, is green and environmentally friendly, has small dispersant usage, simple and efficient process, high atomic utilization rate and recyclable dispersant, can reduce cost, and can be used for recycling LiFePO4 material and improving additional value of the LiFePO4 material.

[0059] To solve the above problems, the embodiment of the present application further provides a lithium manganese iron phosphate positive electrode material, which is prepared by the method.

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

[0061] To solve the above problems, the embodiment of the present application further provides a positive electrode sheet, which comprises the lithium manganese iron phosphate positive electrode material.

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

[0063] To solve the above problems, the embodiment of the present application further provides a lithium ion battery, which comprises the positive electrode sheet.

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

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

[0066] Embodiment 1

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

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

[0069] Step 2: The black slurry is transferred into a reaction kettle, kept at 180℃ for 2h, and the product is taken out and dried to obtain a black product.

[0070] Step 3: The black product is subjected to staged sintering: first 200℃ for 2h, then 450℃ for 2h, and finally 700℃ for 5h to obtain the lithium manganese iron phosphate positive electrode material (LMFP), which is denoted as LMFP-1. The sample LMFP-1 is subjected to electron microscope morphology analysis and XRD analysis, and the results are shown in Figure 3 and Figure 4 .

[0071] As can be seen from Figure 3 , the particles of Example 1 are more uniform. As can be seen from the comparative XRD, Example 1 obtains pure-phase LMFP, while Comparative Example 1 has obvious impurities (there are impurity peaks).

[0072] Example 2

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

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

[0075] The black slurry is transferred into a reaction kettle, kept at 180℃ for 1h, and the product is taken out and dried to obtain a black product.

[0076] The black product is subjected to staged sintering: first 200℃ for 2h, then 450℃ for 2h, and finally 700℃ for 5h to obtain the lithium manganese iron phosphate positive electrode material (LMFP), which is denoted as LMFP-1. The sample LMFP-1 is subjected to electron microscope morphology analysis and XRD analysis, and the results are shown in

[0077] Example 3

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

[0079] A certain amount of LiOH·H2O and phosphoric acid (H3PO4) are dispersed in ethylene glycol, and then a certain amount of MnCO3 is added and mixed uniformly, wherein LiOH:H3PO4:MnCO3 = 1:1:1-1.05:1.05:1 (molar ratio), and then a certain amount of commercial lithium iron phosphate (LiFePO4) powder is added, the mass percentage of ethylene glycol is 30%-40%, and the mass percentage of solid substances is 45%, to obtain a black slurry.

[0080] The black slurry is transferred into a reaction kettle, kept at 180℃ for 8h, and the product is taken out and dried to obtain a black product.

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

[0082] Examples 4-6

[0083] The active electrode material LMFP (93wt%), conductive additive conductive carbon black Super P (2wt%) and conductive graphite KS-6 (2wt%), and binder PVDF solution (3wt%) of Examples 1-3 were mixed uniformly, and then the mixed slurry was uniformly coated on a clean aluminum foil with a doctor blade, with a coating thickness of 250μm, and was placed in a vacuum transition bin at 80°C for drying for 8h, with a LMFP loading of about 10mg cm -2 , and then tabletting with a tablet press to prepare an electrode tab with a diameter of 12mm.

[0084] Test method for the compacted density of the electrode tab

[0085] The mass of 10 electrode tabs with a diameter of 12mm was weighed using a balance, and the average value was taken, as shown in Table 2.

[0086] The cross-section of the electrode tab was characterized using SEM, and the height of the active material in the electrode tab was measured, with three cross-sections at different heights being taken, and the average value taken as the thickness of the active material of the electrode tab, as shown in Table 1 and Figure 5 .

[0087] The compacted density of the electrode tab was calculated using the following formula:

[0088]

[0089] p cd : compacted density of the electrode tab g / cm 3 ;

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

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

[0092] wherein: mass of the active material of the electrode tab = (mass of the electrode tab - mass of the aluminum foil) * 0.93;

[0093] volume of the active material of the electrode tab = area of the electrode tab * thickness of the active material;

[0094] mass of the aluminum foil: 4.78mg; area of the electrode tab: 1.131cm 2 .

[0095] The compacted density of the electrode tab is shown in Table 3.

[0096] Table 1: Active material volume of each substance of the pole piece

[0097]

[0098] Table 2: Active material mass of each substance of the pole piece

[0099]

[0100] Table 3: Compaction density of each substance

[0101]

[0102] Examples 7-9

[0103] Assembling of button cell

[0104] The glove box was operated under the protection of Ar atmosphere (MBRAUN LABMASTER 130), the electrolyte was 1M LiPF6(EC / DMC / EMC = 1:1:1), 2% VC as additive, the separator was Celgard-2500 polypropylene microfilm, and the electrode pole piece of examples 4-6 was used as the working electrode, and the counter electrode was a fresh lithium sheet.

[0105] The button cell was subjected to relevant performance tests. Among them, the charge and discharge mode was constant current charge and discharge, the voltage range was 2.5-4.4V, and the specific capacity, cycle performance, rate performance, etc. of the test battery were tested, and the test results are shown in Tables 4-6 and Figure 6

[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) was dispersed in ethylene glycol, and a certain mass of MnCO3 was added and uniformly mixed, 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 was added, the mass percentage of ethylene glycol was 30%-40%, and the mass percentage of solid substances was 48.6%, to obtain a black slurry. After drying, a black product was obtained.

[0109] The black product was subjected to staged sintering: first 200°C for 2h, then 450°C for 2h, and finally 700°C for 5h, to obtain a lithium manganese iron phosphate positive electrode material (LMFP), denoted 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 rest of the operations are the same as Example 1. ​

[0111] Preparation process of the electrode sheet:

[0112] LMFP-D1 (93wt%), conductive additive conductive carbon black Super P (2wt%) and conductive graphite KS-6 (2wt%), and binder PVDF solution (3wt%) were mixed uniformly, then the mixed slurry was uniformly coated on a clean aluminum foil by a doctor blade, with a coating thickness of 250μm, and placed in a vacuum transition bin at 80°C for drying for 8h, and the LMFP loading was about 10mg / cm 2 , and then the electrode sheet was prepared by rolling with an electric roller press, with a rolling thickness of about 1.1mm, and then tabletting with a tablet press to prepare an electrode sheet with a diameter of 12mm.

[0113] Assembling of the button cell

[0114] The glove box was operated under Ar atmosphere protection (MBRAUN LABMASTER 130), the electrolyte was 1M LiPF6(EC / DMC / EMC = 1:1:1), 2% VC as an additive, and the separator was Celgard-2500 polypropylene microfilm, and 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 subjected to relevant performance tests. Among them, the charge and discharge mode was constant current charge and discharge, the voltage range was 2.5-4.4V, and the specific capacity, cycle performance, rate performance, etc. of the test battery were tested, and the test results are shown in Tables 4-6 and Figure 6 .

[0116] Table 4 Charge and discharge capacity and first cycle coulombic efficiency of each substance

[0117]

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

[0119]

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

[0121]

[0122] It can be seen from Tables 4-6 and Figure 6 that the lithium manganese iron phosphate battery prepared by the application has a first cycle coulombic efficiency as high as 94.4%, a discharge specific capacity as high as 136.8mAh g -1 , and a capacity retention rate as high as 94.8% after 300 long cycles, and the lithium manganese iron phosphate positive electrode material prepared by the preparation method of the application can significantly improve the cycle performance of the lithium battery.

[0123] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended 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 and performing a synthesis reaction under certain conditions to obtain a lithium manganese iron phosphate precursor; wherein the synthesis reaction temperature range is 160° C.-220° C., and the reaction time is 1 hour-8 hours; The lithium manganese iron phosphate precursor is sintered at a high temperature to obtain the lithium manganese iron phosphate positive electrode material.

2. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, wherein: 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.

3. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, wherein: 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.

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

5. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 4, characterized in that: The lithium iron phosphate is carbon-coated lithium iron phosphate.

6. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 5, wherein: Before placing the mixed slurry in a closed device to perform a synthesis reaction under certain conditions, the method further includes: adding a carbon source to the mixed slurry to perform a secondary carbon coating on the lithium iron phosphate, wherein the carbon source includes glucose or sucrose.

7. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 4, characterized in that: The manganese source includes at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese dioxide.

8. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 4, characterized in that: The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, or lithium dihydrogen phosphate.

9. The method for preparing the lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 4, characterized in that: The phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

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

11. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 9, wherein: The compaction density of the lithium manganese iron phosphate positive electrode material is greater than or equal to 1.4 g / cm 3 .

12. The method for preparing the lithium manganese iron phosphate positive electrode material according to claim 11, wherein: The compaction density of the lithium manganese iron phosphate positive electrode material is 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 plate, characterized in that: The positive electrode plate comprises the lithium manganese iron 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 according to claim 14.

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