Doped lithium iron manganese phosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to a doped lithium iron manganese phosphate positive electrode material and a preparation method and application thereof, and relates to the technical field of lithium ion battery materials, the preparation method of the doped lithium iron manganese phosphate positive electrode material comprises the following steps: mixing a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dopant 1, a dopant 2 and a solvent, and then carrying out wet grinding to obtain the doped lithium iron manganese phosphate positive electrode material. A mixture A is obtained; and carrying out spray drying on the mixture A, and sintering in inert gas to obtain the doped lithium iron manganese phosphate positive electrode material. The rare earth fluoride is used for co-doping the rare earth element and F, so that the electrical property of the lithium manganese iron phosphate can be remarkably improved, the first discharge capacity and the cycle performance of the lithium ion battery are improved, and the defects in the prior art are overcome.

Description

Technical Field

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

[0002] Lithium-ion batteries have advantages such as high conversion efficiency, high energy density and power density, no memory effect, and long service life, and have become the battery system with the most mature technology and the widest application. It is expected that lithium-ion battery materials have lower costs, higher energy density, and higher safety performance.

[0003] Lithium iron manganese phosphate material (LMFP) is obtained by doping and introducing Mn ions into lithium iron phosphate material (LFP). Since the working voltage of LMFP is higher (it can reach 4.1V), compared with LFP, LMFP potentially has a higher energy density (about 20% higher than LFP). The advantages of LMFP such as low cost, high stability, and environmental friendliness also make this material have broad development prospects.

[0004] However, the lithium iron manganese phosphate material itself has some disadvantages, such as: the J-T effect of Mn3+ during the charge and discharge process causes lattice distortion, which will damage the structural stability; the electronic conductivity is relatively low (about 1×10 -9 s / cm); the lithium ion diffusion coefficient is relatively low (about 5.1×10 -14 cm 2 / s), etc. During the processing and preparation process, it is easy to come into contact with air and cause problems such as excessive moisture. The electrochemical properties such as the charge and discharge performance and cycle efficiency of lithium-ion batteries still need to be improved. Summary of the Invention

[0005] To solve the above problems, the present invention provides a doped lithium iron manganese phosphate cathode material, a preparation method thereof, and an application thereof.

[0006] In a first aspect, the present invention provides a preparation method of a doped lithium iron manganese phosphate cathode material. The preparation method of the doped lithium iron manganese phosphate cathode material includes the following steps:

[0007] Mix a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dopant 1, a dopant 2, and a solvent, and then perform wet grinding to obtain a mixture A;

[0008] Perform spray drying on the mixture A, and then sinter it under an inert gas to obtain the doped lithium iron manganese phosphate cathode material;

[0009] The doping element in the dopant 1 is one or more of aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, yttrium;

[0010] The chemical formula of the dopant 2 is MF3, where M is at least one of rare earth elements La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd.

[0011] Furthermore, the molar ratio of the total amount of the iron source and the manganese source, the lithium source, and the phosphorus source is 1:1 - 1.10:1; the weight percentage of the addition amount of the dopant 1 is 0.1 wt% - 1.5 wt%; the weight percentage of the addition amount of the dopant 2 is 0.1 wt% - 0.6 wt%; the weight percentage of the addition amount of the carbon source is 10 wt% - 25 wt%.

[0012] Furthermore, the lithium salt is at least one of lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium hydroxide, lithium carbonate, lithium oxalate, lithium chloride, lithium acetate, and lithium phosphate.

[0013] Furthermore, the iron source is at least one of iron nitrate, iron carbonate, iron phosphate, iron powder, iron oxide, ferrous oxalate dihydrate, ferrous nitrate, and ferrous acetate.

[0014] Furthermore, the manganese source is at least one of manganese dioxide, manganese tetroxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese dichloride, and manganese sulfate.

[0015] Furthermore, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium tripolyphosphate, phosphoric acid, calcium phosphate, phosphate ester, lithium dihydrogen phosphate, iron phosphate, lithium phosphate, lithium dihydrogen phosphate, and manganese phosphate.

[0016] Furthermore, the carbon source is at least one of starch, glucose, sucrose, corn flour, carbonate, citric acid, sodium acetate, polyethylene, polyethylene glycol, and polyvinyl alcohol; the solvent is one or more of water, ethanol, ethylene glycol, and isopropyl alcohol.

[0017] Furthermore, the solid content of the wet grinding is 35 wt% - 50 wt%; the material is wet - ground to a particle size D50 of 0.2 - 0.6 μm; the conditions for spray drying are: the inlet air temperature is 180 - 240 °C, and the outlet air temperature is 100 - 110 °C; the sintering temperature is 300 - 850 °C, the heating rate is 3 - 5 °C / min, and the sintering time is 2 - 20 h; the inert gas is one or more of nitrogen, helium, and argon.

[0018] In the second aspect, the present invention provides a doped lithium iron manganese phosphate cathode material, which is prepared by using the preparation method of the doped lithium iron manganese phosphate cathode material according to any one of the first aspect.

[0019] In a third aspect, the present invention provides an application of the doped lithium iron manganese phosphate cathode material according to any one of the second aspects in the preparation of a lithium battery.

[0020] The above technical solutions provided by the embodiments of the present invention have at least the following advantages compared with the prior art:

[0021] The embodiments of the present invention provide a doped lithium iron manganese phosphate cathode material, a preparation method and an application thereof. The present invention uses rare earth fluoride for co-doping of rare earth elements and F to improve the ion doping efficiency. During the sintering process, the rare earth fluoride plays a catalytic role, making the distribution of manganese and iron elements uniform and alleviating the dissolution of Mn elements; secondly, rare earth elements are introduced for doping, and the rare earth element M can effectively penetrate into the crystal lattice, improve the crystal lattice defects, increase the conductivity and cycle performance of the material, and extend the service life of the battery; at the same time, F elements are introduced to form a special Mn-F-C transfer channel, improve the ionic conductivity of the battery, and effectively improve the electrical properties of the material. Description of the Drawings

[0022] The drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present invention and used together with the specification to explain the principles of the present invention.

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic flow chart of a preparation method of a doped lithium iron manganese phosphate cathode material provided by an embodiment of the present invention.

[0025] Figure 2 It is a first charge-discharge curve graph of a doped lithium iron manganese phosphate cathode material provided by Embodiment 1 of the present invention.

[0026] Figure 3 It is a cyclic experiment result graph of a doped lithium iron manganese phosphate cathode material provided by Embodiment 1 of the present invention. Detailed Embodiments

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0028] Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or prepared by existing methods.

[0029] In a first aspect, the present invention provides a method for preparing a doped lithium iron manganese phosphate cathode material, as Figure 1 shown, the method for preparing the doped lithium iron manganese phosphate cathode material includes the following steps:

[0030] Mix a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dopant 1, a dopant 2, and a solvent, and then perform wet grinding to obtain a mixture A;

[0031] Perform spray drying on the mixture A, and then sinter it under an inert gas to obtain the doped lithium iron manganese phosphate cathode material;

[0032] The doping element in the dopant 1 is one or more of aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, and yttrium;

[0033] The chemical formula of the dopant 2 is MF3, where M is at least one of the rare earth elements La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd.

[0034] The embodiments of the present invention provide a doped lithium iron manganese phosphate cathode material. The present invention uses rare earth fluorides for co-doping of rare earth elements and F to improve the ion doping efficiency. During the sintering process, the rare earth fluorides play a catalytic role, making the distribution of manganese and iron elements uniform and alleviating the dissolution of Mn elements; secondly, rare earth elements are introduced for doping. The rare earth element M can effectively penetrate into the crystal lattice, improve lattice defects, increase the conductivity and cycle performance of the material, and extend the service life of the battery; at the same time, F elements are introduced to form a special Mn-F-C transfer channel, improve the ionic conductivity of the battery, and effectively improve the electrical properties of the material.

[0035] In some specific embodiments, the molar ratio of the total amount of the iron source and the manganese source, the lithium source, and the phosphorus source is 1:1 - 1.10:1; the addition amount of the dopant 1 accounts for 0.1 wt% - 1.5 wt% by weight; the addition amount of the dopant 2 accounts for 0.1 wt% - 0.6 wt% by weight; the addition amount of the carbon source accounts for 10 wt% - 25 wt% by weight.

[0036] In some specific embodiments, the lithium salt is at least one of lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium hydroxide, lithium carbonate, lithium oxalate, lithium chloride, lithium acetate, and lithium phosphate.

[0037] In some specific embodiments, the iron source is at least one of iron nitrate, iron carbonate, iron phosphate, iron powder, iron oxide, ferrous oxalate dihydrate, ferrous nitrate, and ferrous acetate.

[0038] In some specific embodiments, the manganese source is at least one of manganese dioxide, manganese tetroxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese dichloride, and manganese sulfate.

[0039] In some specific embodiments, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium tripolyphosphate, phosphoric acid, calcium phosphate, phosphate ester, lithium dihydrogen phosphate, iron phosphate, lithium phosphate, lithium dihydrogen phosphate, and manganese phosphate.

[0040] In some specific embodiments, the carbon source is at least one of starch, glucose, sucrose, corn flour, carbonate, citric acid, sodium acetate, polyethylene, polyethylene glycol, and polyvinyl alcohol; the solvent is one or more of water, ethanol, ethylene glycol, and isopropyl alcohol.

[0041] In some specific embodiments, the solid content of the wet grinding is 35wt%-50wt%; the material is wet ground to a particle size D50 of 0.2-0.6 μm; the conditions for spray drying are: the inlet air temperature is 180-240°C, and the outlet air temperature is 100-110°C; the sintering temperature is 300-850°C, the heating rate is 3-5°C / min, and the sintering time is 2-20 h; the inert gas is one or more of nitrogen, helium, and argon.

[0042] In a second aspect, the present invention provides a doped lithium iron manganese phosphate cathode material, which is prepared by using the preparation method of the doped lithium iron manganese phosphate cathode material according to any one of the first aspect.

[0043] In a third aspect, the present invention provides an application of the doped lithium iron manganese phosphate cathode material according to any one of the second aspect in the preparation of a lithium battery.

[0044] It should be noted that for the component raw materials involved in the doped lithium iron manganese phosphate cathode material and its preparation method and application provided in the embodiments of the present invention, if there is no special limitation or specific description, commercially available products can be directly used or self-made by using existing publicly disclosed preparation methods; at the same time, for the steps and parameters involved, if there is no special limitation or specific description, they can be carried out according to the processing technology of the existing technology or directly using existing equipment, and the present invention document will not elaborate one by one.

[0045] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions indicated in the following embodiments, they are generally determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0046] Example 1

[0047] S1. Lithium carbonate, ammonium dihydrogen phosphate, ferrous oxalate, and manganese sulfate are proportioned according to the elemental molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1, and 0.3 wt% CeF3, 0.5 wt% magnesium oxide, and 15 wt% glucose are added, and mixed with deionized water at a solid content of 40 wt%; then ball-milled at a speed of 400 r / min to obtain slurry A, and the particle size D50 of the slurry after ball-milling is 0.5 μm;

[0048] S2. The slurry A obtained in S1 is sprayed with an inlet air temperature of 200 °C and an outlet air temperature of 100 °C. After completion, it is heated to 350 °C at a rate of 3 °C / min in a nitrogen atmosphere, held for 2 h, then heated to 750 °C, held for 8 h, cooled to 530 °C, annealed and held for 3 h, and then naturally cooled to 100 °C and taken out of the furnace to complete sintering, obtaining a lithium iron manganese phosphate composite material.

[0049] Example 2

[0050] The difference between Example 2 and Example 1 is only that the addition amount of CeF3 is changed, and the addition amount of CeF3 is 0.1 wt%.

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is only that the addition amount of CeF3 is changed, and the addition amount of CeF3 is 0.6 wt%.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is only that the type of rare earth oxide is changed, and CeF3 is replaced by LaF3.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 1 is only that CeF3 is not added.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 1 is only that the F element is not introduced, and CeF3 is replaced by CeO2.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 1 is only that Ce element is not introduced and CeF3 is replaced by NH4F.

[0061] Test Example

[0062] The lithium iron manganese phosphate composite materials of Examples 1-4 and Comparative Examples 1-3 were detected. Test method: Refer to the national standard "Carbon Composite Lithium Iron Phosphate Cathode Material for Lithium Ion Batteries" GB / T 30835-2014 for the tests of relevant physical and chemical properties and electrochemical properties, in which button cells were fabricated (the mass ratio of the active material, conductive agent and binder was 90:5:5, and the charge and discharge voltage range was 2.0-4.4V).

[0063] The test results are shown in Table 1 and Figure 2 and Figure 3 as shown.

[0064] Table 1 Performance of the lithium iron manganese phosphate composite materials of Examples 1-4 and Comparative Examples 1-3

[0065] Test sample Charge capacity (mAh / g) Discharge capacity (mAh / g) 1C 100-cycle (%) Example 1 158.4 154.2 97.8 Example 2 158.1 153.8 97.6 Example 3 157.9 153.6 97.5 Example 4 158.3 154.1 97.6 Comparative example 1 154.2 149.6 93.1 Comparative example 2 155.4 150.3 97.4 Comparative example 3 157.8 153.5 94.2

[0066] It can be seen from the above data that after adding rare earth fluorides, both the specific capacity and cycling performance of the lithium iron manganese phosphate composite materials are improved. Among them, the 0.1C discharge specific capacity of the lithium iron manganese phosphate composite material in Example 1 is 4.6 mAh / g higher than that of Comparative Example 1 without adding rare earth fluorides, and the 1C 100-cycle performance is 4.7% higher; compared with Comparative Example 2 with only Ce introduced and no F introduced, the 0.1C specific capacity is 3.9 mAh / g higher; compared with Comparative Example 3 with only F introduced and no Ce introduced, the 1C 100-cycle performance is 3.6% higher.

[0067] In summary, the embodiments of the present invention provide a doped lithium iron manganese phosphate cathode material, its preparation method and application. The present invention uses rare earth fluorides for co-doping of rare earth elements and F, which can significantly improve the electrical properties of lithium iron manganese phosphate, thereby improving the first discharge capacity and cycling performance of lithium ion batteries, making up for the deficiencies of the prior art.

[0068] The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the description of the range from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0069] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a doped lithium manganese iron phosphate positive electrode material, characterized in that: The preparation method of the doped lithium manganese iron phosphate positive electrode material comprises the following steps: A lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dopant 1, a dopant 2 and a solvent are mixed, and then wet-grinded to obtain a mixture A; The mixture A is spray-dried, and then sintered under an inert gas to obtain the doped lithium manganese iron phosphate positive electrode material; The doping element in the dopant 1 is one or more of aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, and yttrium; The chemical formula of the dopant 2 is MF3, wherein M is at least one of the rare earth elements La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd.

2. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the total amount of the iron source and the manganese source, the lithium source and the phosphorus source is 1:1-1.10:1; the weight ratio of the added amount of the dopant 1 is 0.1wt%-1.5wt%; the weight ratio of the added amount of the dopant 2 is 0.1wt%-0.6wt%; the weight ratio of the added amount of the carbon source is 10wt%-25wt%.

3. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The lithium salt is at least one of lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium hydroxide, lithium carbonate, lithium oxalate, lithium chloride, lithium acetate and lithium phosphate.

4. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The iron source is at least one of ferric nitrate, ferric carbonate, ferric phosphate, iron powder, ferric oxide, ferrous oxalate dihydrate, ferrous nitrate and ferrous acetate.

5. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The manganese source is at least one of manganese dioxide, manganese tetraoxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese dichloride and manganese sulfate.

6. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium tripolyphosphate, phosphoric acid, calcium phosphate, phosphate ester, lithium dihydrogen phosphate, iron phosphate, lithium phosphate, lithium dihydrogen phosphate, and manganese phosphate.

7. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The carbon source is at least one of starch, glucose, sucrose, corn flour, carbonate, citric acid, sodium acetate, polyethylene, polyethylene glycol and polyvinyl alcohol; the solvent is one or more of water, ethanol, ethylene glycol and isopropanol.

8. The method for preparing the doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The solid content of the wet grinding is 35wt%-50wt%; the material is wet ground to a particle size D50 of 0.2-0.6μm; the spray drying conditions are: the inlet air temperature is 180-240°C, and the outlet air temperature is 100-110°C; the sintering temperature is 300-850°C, the heating rate is 3-5°C / min, and the sintering time is 2-20h; the inert gas is one or more of nitrogen, helium, and argon.

9. A doped lithium manganese iron phosphate positive electrode material, characterized in that: The doped lithium iron manganese phosphate positive electrode material is prepared by the preparation method of the doped lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 8.

10. Use of the doped lithium manganese iron phosphate positive electrode material according to claim 9 in the preparation of a lithium battery.

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