METHOD FOR PREPARING LITHIUM MANGANESE IRON PHOSPHATE, CATHODE MATERIAL, AND LITHIUM-ION BATTERY

Abstract

The invention provides a method for preparing lithium manganese iron phosphate, which includes the following steps: S1: mixing a manganese source and/or an iron source in solid phase to obtain a first mixture; S2: sintering the first mixture in solid phase at 300° C. to 1200° C. to obtain a manganese iron oxide (MnxFe1−x−y)mOn; S3: mixing the manganese iron oxide (MnxFe1−x−y)mOn with a lithium source, a phosphorus source, and optionally a manganese source and/or an iron source in solid phase to obtain a second mixture; and S4: sintering the second mixture in solid phase at 350° C. to 900° C. to obtain lithium manganese iron phosphate LiMnxFe1−x−yPO4, wherein 0≤x≤1, and 0≤y≤1. The method of the present invention can be used to prepare a lithium manganese iron phosphate material with high tap density, long cycle life, low costs, and high cost-effectiveness.

Claims

1. A method for preparing lithium manganese iron phosphate, comprising steps of: S1: mixing a manganese source and/or an iron source in solid phase to obtain a first mixture; S2: sintering the first mixture in solid phase at 300° C. to 1200° C. to obtain a manganese iron oxide (Mn.sub.xFe.sub.1−x−y).sub.mO.sub.n; S3: mixing the manganese iron oxide (Mn.sub.xFe.sub.1−x−y).sub.mO.sub.n with a lithium source, a phosphorus source, and optionally a manganese source and/or an iron source in solid phase to obtain a second mixture; and S4: sintering the second mixture in solid phase at 350° C. to 900° C. to obtain lithium manganese iron phosphate LiMn.sub.xFe.sub.1−x−yPO.sub.4, wherein 0≤x≤1, 0≤y≤1, 1:2≤m:n≤1:1, and 0≤n≤4.

2. The method for preparing lithium manganese iron phosphate according to claim 1, wherein the manganese source is selected from the group consisting of manganese sulfate, manganese carbonate, manganese acetate, manganese phosphate, manganese nitrate, manganese oxalate and manganese citrate, with or without crystal water.

3. The method for preparing lithium manganese iron phosphate according to claim 1, wherein the iron source is selected from the group consisting of ferrous sulfate, ferrous carbonate, ferrous acetate, ferrous phosphate, ferrous nitrate, ferrous oxalate, ferrous citrate, ferric sulfate, ferric carbonate, ferric acetate, ferric phosphate, ferric nitrate, ferric oxalate and ferric citrate, with or without crystal water.

4. The method for preparing lithium manganese iron phosphate according to claim 1, wherein the lithium source is selected from the group consisting of lithium carbonate, lithium hydroxide, lithium phosphate, lithium oxalate, lithium acetate, lithium sulfate, lithium nitrate, and lithium chloride.

5. The method for preparing lithium manganese iron phosphate according to claim 1, wherein the phosphorus source is selected from the group consisting 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.

6. The method for preparing lithium manganese iron phosphate according to claim 1, wherein in the steps S1 and S3, one or more of a carbon source, an M source, and an N source are added during the solid-phase mixing; and after the solid phase sintering in the steps S2 and S4, manganese iron oxide (Mn.sub.xFe.sub.1−x−y).sub.mO.sub.nN.sub.z/C and lithium manganese iron phosphate LiMn.sub.xFe.sub.1−x−yM.sub.yPO.sub.4−zN.sub.z/C are obtained respectively; wherein, the M source is a doped cation source and the N source is a doped anion source; and 0≤x≤1, 0≤y≤1, 0≤z≤0.1, and 1:2≤m:(n+z)≤1:1.

7. The method for preparing lithium manganese iron phosphate according to claim 6, wherein the carbon source is selected from the group consisting of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, carbon black, acetylene black, graphite, graphene, and conductive carbon tubes.

8. The method for preparing lithium manganese iron phosphate according to claim 6, wherein the cation source includes one or more of aluminum, magnesium, nickel, cobalt, titanium, copper, calcium, niobium, chromium, zinc, lanthanum, antimony, tellurium, strontium, tungsten, indium, and yttrium, and the anion source includes fluorine or/and sulfur.

9. A cathode material, obtained by mixing one or more of an olivine-type lithium manganese iron phosphate material, layered lithium salt of polybasic acid, spinel-type lithium manganate, and layered manganese-rich lithium-based material, wherein the olivine-type lithium manganese iron phosphate material, the layered lithium salt of polybasic acid, the spinel-type lithium manganate, and the layered manganese-rich lithium-based material are prepared by the method according to claim 1.

10. A lithium ion battery, comprising a cathode plate, an anode plate, an electrolyte solution, and a separator, wherein the cathode plate is prepared from the cathode material according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is an XRD pattern of (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3 in Example 1 of the present invention;

[0037] FIG. 2 is an SEM image of (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3 in Example 1 of the present invention;

[0038] FIG. 3 is an SEM image of LiMn.sub.0.9Fe.sub.0.1PO.sub.4 in Example 1 of the present invention;

[0039] FIG. 4 is an SEM image of LiMn.sub.0.9Fe.sub.0.1PO.sub.4 in Example 2 of the present invention; and

[0040] FIG. 5 is a cyclic performance test diagram of cylindrical full batteries prepared in Example 3 and Comparative Example 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Unless otherwise defined, meanings of all technical and scientific terms used in this specification are the same as those usually understood by a person skilled in the art. Terms used in this specification are merely intended to describe objectives of specific embodiments, but are not intended to limit the present invention. The term “and/or” used herein includes any and all combinations of one or more of associated items listed.

[0042] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand implement the present invention, but the embodiments described are not intended to limit the present invention.

[0043] The methods given in examples below are all conventional methods, unless otherwise stated. The materials and reagents are all commercially available unless otherwise stated.

EXAMPLE 1

[0044] MnSO.sub.4.Math.H.sub.2O was used as a manganese source and FeSO.sub.4.Math.7H.sub.2O was used as an iron source. The molar ratio of MnSO.sub.4.Math.H.sub.2O to FeSO.sub.4.Math.7H.sub.2O was 9:1. Then, the two materials were mixed in solid phase. The uniformly mixed materials were heated to 600° C. and sintered in solid phase to obtain a lithium manganese iron phosphate precursor (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3. The reaction equation was:

18MnSO.sub.4.Math.H.sub.2O+2FeSO.sub.4.Math.7H.sub.2O.fwdarw.10(Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3+20SO.sub.2↑+32H.sub.2O↑+5O.sub.2↑.

[0045] (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3, lithium carbonate, and ammonium dihydrogen phosphate were mixed and milled, and sintered in solid phase at 500° C. to obtain lithium manganese iron phosphate LiMn.sub.0.9Fe.sub.0.1PO.sub.4. The reaction equation was:

2(Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3+2Li.sub.2CO.sub.3+4NH.sub.4H.sub.2PO.sub.4.fwdarw.4LiMn.sub.0.9Fe.sub.0.1PO.sub.4+2CO.sub.2↑+4NH.sub.3↑+6H.sub.2O↑+O.sub.2↑.

[0046] The black thick line in FIG. 1 denotes an X-ray diffraction (XRD) pattern of (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3, i.e., the precursor of LiMn.sub.0.9Fe.sub.0.1PO.sub.4. It can be seen that the substance synthesized by this scheme corresponds well to the (Mn.sub.0.983Fe.sub.0.017).sub.2O.sub.3peak of colorimetric card PDF#24-0507.

[0047] FIG. 2 is an SEM image of (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3, showing that this substance is a homogeneous substance with good morphology. The particle size and tap density of the material were measured. The D50 diameter was 6 μm, and the tap density was as high as 2.4 g/cm.sup.3. Therefore, the compound synthesized in this scheme was manganese iron oxide, not a simple mixture of manganese oxide and ferric oxide.

[0048] FIG. 3 is a scanning electron microscopy (SEM) image of lithium manganese iron phosphate LiMn.sub.0.9Fe.sub.0.1PO.sub.4, showing that the morphology of the material was good. The particle size and tap density of the material were measured. The D50 diameter was 2 μm, and the tap density was as high as 1.5 g/cm.sup.3.

EXAMPLE 2

[0049] MnSO.sub.4.Math.H.sub.2O was used as a manganese source and FeSO.sub.4.Math.7H.sub.2O was used as an iron source. The molar ratio of MnSO.sub.4.Math.H.sub.2O to FeSO.sub.4.Math.7H.sub.2O was 6:4. Then, the two materials were mixed in solid phase. The uniformly mixed materials were heated to 500° C. and sintered in solid phase to obtain a lithium manganese iron phosphate precursor (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3. The reaction equation was:

12MnSO.sub.4.Math.H.sub.2O+8FeSO.sub.4.Math.7H.sub.2O.fwdarw.10(Mn.sub.0.6Fe.sub.0.4).sub.2O.sub.3+20SO.sub.2↑+68H.sub.2O↑+5O.sub.2↑.

[0050] (Mn.sub.0.9Fe.sub.0.1).sub.2O.sub.3, lithium carbonate, and ammonium dihydrogen phosphate were mixed and milled, and sintered in solid phase at 500° C. to obtain lithium manganese iron phosphate LiMn.sub.0.6Fe.sub.0.4PO.sub.4. The reaction equation was:

2(Mn.sub.0.6Fe.sub.0.4).sub.2O.sub.3+2Li.sub.2CO.sub.3+4NH.sub.4H.sub.2PO.sub.4.fwdarw.4LiMn.sub.0.6Fe.sub.0.4PO.sub.4+2CO.sub.2↑+4NH.sub.3↑+6H.sub.2O↑+O.sub.2↑.

[0051] FIG. 4 is a scanning electron microscopy (SEM) image of lithium manganese iron phosphate LiMn.sub.0.6Fe.sub.0.4PO.sub.4. It can be seen from the image that the prepared lithium manganese iron phosphate material has a good morphology.

[0052] The particle size, specific surface area, and tap density of the material were tested. The results showed that the D50 diameter of the material was 1.5 μm; the specific surface area of the material was 15 m.sup.2/g, much lower than the specific surface area of 20 m.sup.2/g of currently commonly used commercial materials; the tap density of the material was as high as 1.3 g/cm.sup.3, much higher than the tap density of 0.8 to 1.0 g/cm.sup.3 of currently commonly used commercial materials; and the compaction density of the material was 2.8 g/cm.sup.3, much higher than the compaction density of 2.3 g/cm.sup.3 of currently commonly used commercial materials. A higher compaction density allows for a high roll density of electrode plates, and as the thickness of electrode plates is reduced, a given battery case can accommodate more electrode plates, enabling the battery to have a higher energy density. In addition, the low specific surface area can reduce the content of binder, make the proportion of active substances higher, thereby further improving the energy density of the battery. Moreover, the low specific surface area reduces the side reactions between the material and the electrolyte solution, and improves the storage performance and cycle life of the battery.

EXAMPLE 3

[0053] A mixture of spinel-type lithium manganate LiMn.sub.2O.sub.4 and the lithium manganese iron phosphate LiMn.sub.0.6Fe.sub.0.4PO.sub.4prepared in Example 2 was used as an active material of a cathode plate of a lithium-ion battery. The spinel-type lithium manganate material and the lithium manganese iron phosphate material respectively accounted for 80% and 20% of the active material.

[0054] The cathode active material was mixed with a conductive agent and a binder to prepare a cathode slurry. Solid substances in the slurry included 97.2% of the active material, 1.7% of the conductive agent (conductive carbon black, conductive graphite, conductive carbon nanotubes, and graphene), and 1.1% of the binder (polyvinylidene fluoride). The content of a solvent N-methylpyrrolidone was adjusted so that the solid content of the slurry was about 75%. The evenly mixed slurry was respectively coated on surfaces of a current collector aluminum foil, which was then dried, rolled and cut to obtain a cathode plate.

[0055] The cathode plate was assembled into a cylindrical full battery. The full battery was charged at 0.5 C and discharged at 1 C to test cycle performance. The cylindrical battery has a model of R34235, with a diameter of 34 mm and a height of 235 mm.

Comparative Example 1

[0056] A mixture of spinel-type lithium manganate LiMn.sub.2O.sub.4 and a lithium manganese iron phosphate LiMn.sub.0.6Fe.sub.0.4PO.sub.4prepared by a conventional liquid phase method was used as an active material of a cathode plate of a lithium-ion battery. As a contrast sample, the spinel-type lithium manganate material and the lithium manganese iron phosphate material respectively accounted for 80% and 20% of the active material.

[0057] The cathode active material was prepared into a cylindrical full battery according to the same method as in Example 3.

[0058] As shown in FIG. 5, for cycle fading to 70%, the battery assembled from the lithium manganese iron phosphate synthesized in Example 2 can be cycled 1100 times, with an energy density of 140 Wh/kg. A battery assembled from the lithium manganese iron phosphate prepared by the conventional liquid phase method in Comparative Example 1 can be cycled 800 times, with an energy density of 130 Wh/kg. The improvement of cycle performance and energy density is mainly due to the high compaction density of the material.

[0059] The battery was allowed to stand in the fully charged state at room temperature for 28 days. The capacity before standing was defined as 100%, the remaining capacity ratio after standing, and charge-discharge recovered capacity ratio can reflect the self-discharge of the battery and the side reactions between the material and the electrolyte solution. The performance of the batteries of Example 3 and Comparative Example 1 before and after standing in the fully charged state at room temperature for 28 days was tested. The results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Standing in the fully charged state at Comparative room temperature for 28 days Example 1 Example 3 Before standing 100.00% 100.00% Remaining 92.44% 94.79% Recovered 96.35% 98.05%

[0060] As can be seen from Table 2, in Comparative Example 1, the remaining capacity ratio of the battery after standing is 92.44%, and the recovery capacity ratio is 96.35%; in Example 3, the remaining capacity ratio of the battery after standing is 94.79%, and the recovery capacity ratio is 98.05%, both of which are better than those of the battery in Comparative Example 1, indicating that the material synthesized in the present invention has few side reactions with the electrolyte solution, which is mainly due to the small specific surface area of the material of Example 3.

EXAMPLE 4

[0061] Industrial grade MnSO.sub.4.Math.H.sub.2O, which was used as a manganese source, was milled to micron size by a sand mill, heated to 150° C. so that manganese sulfate lost its crystal water, and then heated to 900° C. for thermal decomposition to form a lithium manganese phosphate precursor Mn.sub.3O.sub.4. The overall reaction equation was:

3MnSO.sub.4.Math.H.sub.2O.fwdarw.Mn.sub.3O.sub.4+3SO.sub.2↑+3H.sub.2O↑.

[0062] Mn.sub.3O.sub.4, lithium carbonate, and ammonium dihydrogen phosphate were mixed and milled, and sintered in solid phase at 600° C. to obtain lithium manganese phosphate LiMnPO.sub.4. The reaction equation was:

4Mn.sub.3O.sub.4+6Li.sub.2CO.sub.3+12NH.sub.4H.sub.2PO.sub.4.fwdarw.12LiMnPO.sub.4+6CO.sub.2↑+12NH.sub.3↑+12H.sub.2O↑+5O.sub.2↑.

EXAMPLE 5

[0063] Industrial grade FeSO.sub.4.Math.7H.sub.2O, which was used as iron source, was milled to micron size by a sand mill, heated to 70° C. to 98° C. so that ferric sulfate began to lose crystal water and generate FeSO.sub.4.Math.4H.sub.2O, then continued to be heated. At 86° C. to 159° C., FeSO.sub.4.Math.4H.sub.2O lost crystal water to form FeSO.sub.4.Math.H.sub.2O, and lost all the crystal water at 227° C. to 283° C. to form FeSO.sub.4. Starting from 300° C., FeSO.sub.4 began to melt and prepare for thermal decomposition. Then, when heated to 653° C. to 716° C., FeSO4 was thermal decomposed to form a lithium iron phosphate precursor Fe.sub.2O.sub.3. The overall reaction equation was:

4FeSO.sub.4.Math.7H.sub.2O.fwdarw.2Fe.sub.2O.sub.3+4SO.sub.2↑+28H.sub.2O↑+O.sub.2↑.

[0064] Fe.sub.2O.sub.3, lithium carbonate, and ammonium dihydrogen phosphate were mixed and milled, and sintered in solid phase at 700° C. to obtain lithium iron phosphate LiFePO.sub.4. The reaction equation was:

Fe.sub.2O.sub.3+Li.sub.2CO.sub.3+2NH.sub.4H.sub.2PO.sub.4.fwdarw.2LiFePO.sub.4+CO.sub.2↑+2NH.sub.3↑+2H.sub.2O↑+O.sub.2↑.

EXAMPLE 6

[0065] Industrial grade FeSO.sub.4.Math.7H.sub.2O, which was used as an iron source, was milled to micron size by a sand mill, heated to 200° C. so that iron sulfate lost its crystal water, and then heated to 1000° C. for thermal decomposition to form a lithium manganese iron phosphate precursor Fe.sub.2O.sub.3. The overall reaction equation was:

4FeSO.sub.4.Math.7H.sub.2O.fwdarw.2Fe.sub.2O.sub.3+4SO.sub.2↑+28H.sub.2O↑+O.sub.2↑.

[0066] Fe.sub.2O.sub.3, lithium carbonate, manganese dihydrogen phosphate, and Mn.sub.2O.sub.3 were mixed and milled, and sintered in solid phase at 700° C. to obtain lithium manganese iron phosphate LiFeMnPO.sub.4. The reaction equation was:

2Mn.sub.2O.sub.3+8Fe.sub.2O.sub.3+20Li.sub.2CO.sub.3+20Mn(H.sub.2PO.sub.4).sub.2.Math.2H.sub.2O.fwdarw.40LiMn.sub.0.6Fe.sub.0.4PO.sub.4+20CO.sub.2↑+80H.sub.2O↑+5O.sub.2↑.

EXAMPLE 7

[0067] Industrial grade MnSO.sub.4.Math.H.sub.2O, which was used as a manganese source, was milled to micron size by a sand mill, heated to 150° C. so that manganese sulfate lost its crystal water, and then heated to 900° C. for thermal decomposition to form a lithium manganese iron phosphate precursor Mn.sub.3O.sub.4. The overall reaction equation was:

3MnSO.sub.4.Math.H.sub.2O.fwdarw.Mn.sub.3O.sub.4+3SO.sub.2↑+3H.sub.2O↑.

[0068] Mn.sub.3O.sub.4, lithium carbonate, iron phosphate, and ammonium dihydrogen phosphate were mixed and milled, and sintered in solid phase at 600° C. to obtain lithium manganese iron phosphate LiMn.sub.0.6Fe.sub.0.4PO.sub.4. The reaction equation was:

6NH.sub.4H.sub.2PO.sub.4+2Mn.sub.3O.sub.4+5Li.sub.2CO.sub.3+4FePO.sub.4.Math.2H.sub.2O.fwdarw.10LiMn.sub.0.6Fe.sub.0.4PO.sub.4+5CO.sub.2↑+17H.sub.2O↑+2O.sub.2↑+6NH.sub.3↑.

[0069] The above-described embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions or modifications can be made by those skilled in the art based on the present invention, which are within the scope of the present invention as defined by the claims. The scope of the present invention is defined by the appended claims.