Lithium iron manganese oxide precursor and lithium iron manganese phosphate positive electrode material and preparation method thereof

Abstract

A lithium iron manganese oxide precursor and a preparation method thereof relate to the technical field of lithium-ion battery positive electrode material preparation. The preparation method mixes a manganese source, an iron source, and a lithium source and then sinters to obtain a lithium iron manganese oxide precursor. The lithium iron manganese oxide precursor achieves atomic-level mixing of the three elements of manganese, iron, and lithium, avoiding the problem of component segregation caused by direct mixing of multiple elements in the traditional solid-phase method. An embodiment of the present invention also provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, which adopts the above-mentioned lithium iron manganese oxide precursor and is obtained through secondary sintering and phosphating. The stable oxide structure of lithium iron manganese oxide provides an ordered template for the phosphating reaction. The obtained lithium iron manganese phosphate positive electrode material has the characteristics of high crystallinity and few lattice defects, which can improve the lithium ion diffusion rate. At the same time, its high crystallinity can effectively inhibit the dissolution of manganese ions and improve cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery positive electrode material preparation, and in particular to a lithium iron manganese oxide precursor and a lithium iron manganese phosphate positive electrode material and a preparation method thereof. Background Art

[0002] Lithium iron manganese phosphate (LiMn x Fe 1-x LiFePO4 (LMFP) is an olivine-type lithium-ion battery cathode material that combines the safety of LiFePO4 (LFP) and the high voltage advantage of LiMnPO4 (LMP). It is considered to be one of the core materials for the next generation of high-energy-density, low-cost power batteries.

[0003] Existing methods for preparing lithium iron manganese phosphate include traditional solid-phase methods and liquid-phase methods. The traditional solid-phase method directly mixes lithium, manganese, iron, and phosphorus sources through a one-step reaction and sintering. This method has the problem of uneven dispersion of raw materials, which can easily lead to low crystallinity, coarse particles, and poor electrochemical performance of the product. While the liquid-phase method can improve the uniformity of raw material mixing, its process is complex, costly, and prone to the introduction of impurities, making it difficult to scale up production. In addition, the manganese dissolution phenomenon of lithium iron manganese phosphate itself, that is, during high-voltage cycling, manganese ions are easily dissolved from the crystal lattice, resulting in capacity decay and reduced cycle life, is also a problem that is difficult to solve with existing preparation methods. Summary of the Invention

[0004] The object of the present invention is to provide a lithium iron manganese oxide precursor and a preparation method thereof, which is simple to operate and easy to use, can achieve atomic-level mixing of lithium iron manganese, and avoid the problem of uneven mixing.

[0005] Another object of the present invention is to provide a lithium manganese iron phosphate positive electrode material and a preparation method thereof, which is obtained by phosphating the above-mentioned lithium manganese iron oxide precursor. The product has high crystallinity and few lattice defects, improves the lithium ion diffusion rate, and can inhibit manganese dissolution.

[0006] The present invention is achieved in that:

[0007] A method for preparing a lithium iron manganese oxide precursor, comprising:

[0008] Weigh a lithium source, a manganese source, and an iron source and mix them according to a molar ratio of Li:Mn:Fe of 1:(0.58-0.62):(0.38-0.42) to obtain a first mixed material;

[0009] The first mixed material is calcined under oxygen conditions to obtain a lithium iron manganese oxide precursor.

[0010] A lithium iron manganese oxide precursor is prepared by the above-mentioned method for preparing a lithium iron manganese oxide precursor; the chemical composition of the lithium iron manganese oxide precursor is LiMn 0.6 Fe 0.4 O2.

[0011] A method for preparing a lithium iron manganese phosphate positive electrode material, using the above-mentioned lithium iron manganese oxide precursor, comprises:

[0012] mixing a lithium iron manganese oxide precursor with a phosphorus source to obtain a second mixture;

[0013] The second mixed material is calcined in an inert atmosphere to obtain a lithium manganese iron phosphate positive electrode material.

[0014] A lithium iron manganese phosphate positive electrode material is prepared by the above-mentioned preparation method of the lithium iron manganese phosphate positive electrode material; the chemical composition of the lithium iron manganese phosphate positive electrode material is LiMn 0.6 Fe 0.4 PO4.

[0015] The beneficial effects of the embodiments of the present invention are:

[0016] An embodiment of the present invention provides a lithium iron manganese oxide precursor and a preparation method thereof. The preparation method mixes a manganese source, an iron source, and a lithium source and then sinters to obtain a lithium iron manganese oxide precursor. The lithium iron manganese oxide precursor achieves atomic-level mixing of the three elements of manganese, iron, and lithium, avoiding the problem of component segregation caused by directly mixing multiple elements in the traditional solid-phase method. An embodiment of the present invention also provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, which adopts the above-mentioned lithium iron manganese oxide precursor and is obtained by secondary sintering and phosphating. The stable oxide structure of lithium iron manganese oxide provides an ordered template for the phosphating reaction. The obtained lithium iron manganese phosphate positive electrode material has the characteristics of high crystallinity and few lattice defects, which can improve the diffusion rate of lithium ions. At the same time, its high crystallinity can effectively inhibit the dissolution of manganese ions and improve cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is the theoretical model diagram of lithium manganese iron oxide precursor;

[0019] Figure 2 A comparison chart of the XRD spectrum of the lithium iron manganese oxide precursor provided in Example 1 of the present invention and the standard spectra of LiMnO2 and LiFeO2;

[0020] Figure 3 This is an electron microscope image of the lithium iron manganese oxide provided in Example 1 of the present invention;

[0021] Figure 4 This is an electron microscope image of the lithium manganese iron phosphate positive electrode material provided in Example 1 of the present invention;

[0022] Figure 5 This is an electron microscope image of the lithium manganese iron phosphate positive electrode material provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0024] The following describes in detail a composite lithium manganese iron phosphate positive electrode material according to an embodiment of the present invention, and its preparation method and application.

[0025] A method for preparing a lithium iron manganese oxide precursor, comprising:

[0026] S1. Weigh a lithium source, a manganese source, and an iron source and mix them according to a molar ratio of Li:Mn:Fe of 1:(0.58-0.62):(0.38-0.42) to obtain a first mixture.

[0027] S2. calcining the first mixture under oxygen conditions to obtain a lithium iron manganese oxide precursor.

[0028] Furthermore, the particle size of the first mixed material is ≤ 2 μm. Within this particle size range, sintering is more effective, allowing for the formation of stable oxides. The lithium, manganese, and iron sources can be mixed using dry ball milling or a grinding spray method, with particle size controlled during mixing.

[0029] Optionally, it is characterized in that the iron source includes at least one of ferrous oxalate, ferric phosphate, ferric acetate, ferric nitrate and ferric oxide; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate; and the manganese source includes at least one of manganese oxalate, manganese tetraoxide, manganese sulfate, manganese acetate and manganese nitrate.

[0030] The first mixture is calcined at a temperature of 700-900°C for 6-12 hours. This calcination can be performed in an aerobic atmosphere, either air or oxygen. During the calcination process, the manganese iron lithium elements combine with oxygen to form a highly crystalline, stable oxide structure.

[0031] An embodiment of the present invention further provides a lithium iron manganese oxide precursor, which is prepared by the above-mentioned method for preparing the lithium iron manganese oxide precursor. Figure 1 The theoretical model of the lithium iron manganese oxide precursor is shown. It can be seen that the stable lattice composed of four elements of manganese iron lithium oxygen. The chemical composition of the lithium iron manganese oxide precursor is LiMn 0.6 Fe 0.4 O2.

[0032] An embodiment of the present invention further provides a method for preparing a lithium iron manganese phosphate positive electrode material, which uses the above-mentioned lithium iron manganese oxide precursor, comprising:

[0033] S1. The lithium iron manganese oxide precursor is mixed with a phosphorus source to obtain a second mixture;

[0034] S2. calcining the second mixture in an inert atmosphere to obtain a lithium manganese iron phosphate positive electrode material.

[0035] Unlike the traditional solid-phase method, the preparation method of the embodiment of the present invention is to perform phosphating on the basis of the stable structure of the lithium manganese iron oxide precursor. Its highly crystalline structure provides an ordered template for the addition of phosphorus. The obtained lithium manganese iron phosphate positive electrode material can retain its high crystallinity and few lattice defects, thereby improving the lithium ion diffusion rate.

[0036] Furthermore, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate. 0.6 Fe 0.4 The molar ratio of O2:P is 1:(0.95~1.05). Under the above ratio, the efficiency of phosphating is better, which is beneficial to improving the electrical properties of the product.

[0037] Optionally, a carbon source is added to the second mixture, and the carbon source includes at least one of glucose, sucrose and polyethylene glycol; adding the carbon source to the second mixture can simultaneously complete the carbon coating work while phosphating the lithium manganese iron oxide. 0.6 Fe 0.4 The molar ratio of O2:C is 1:(0.3~0.5). Within the above ratio range, the carbon coating effect is better and a uniform and stable carbon layer can be obtained.

[0038] Furthermore, the second mixed material is calcined at a temperature of 600-800°C for 6-10 hours. The above reaction conditions are conducive to the phosphating reaction and achieve better phosphating effects.

[0039] The embodiment of the present invention also provides a lithium iron manganese phosphate positive electrode material, which is prepared by the above-mentioned preparation method of the lithium iron manganese phosphate positive electrode material; the chemical composition of the lithium iron manganese phosphate positive electrode material is LiMn 0.6 Fe0.4 PO4.

[0040] This lithium manganese iron phosphate cathode material has high crystallinity and few lattice defects, which can improve the diffusion rate of lithium ions. At the same time, its high crystallinity can reduce lattice distortion during charge and discharge, effectively inhibiting the dissolution of manganese ions from the lattice, significantly improving cycle stability.

[0041] The features and performance of the present invention are further described in detail below with reference to the embodiments. Example 1

[0042] This embodiment provides a lithium iron manganese oxide precursor and a lithium iron manganese phosphate positive electrode material, and the preparation method thereof is as follows:

[0043] S1. Lithium carbonate, manganese dioxide, and iron oxide (Li:Mn:Fe = 1:0.6:0.4) were mixed by a grinding spray method and calcined in air at 800°C for 8 h to obtain a lithium iron manganese oxide precursor.

[0044] S2. Lithium iron manganese oxide precursor is mixed with phosphoric acid and glucose (LiMn 0.6 Fe 0.4 The obtained carbon-coated lithium manganese iron phosphate cathode material was prepared by mixing, grinding, spray drying, and calcining at 700°C for 10 h.

[0045] The obtained lithium manganese iron oxide was subjected to X-ray diffraction, and its XRD pattern was as follows Figure 2 As shown, its peak shape matches that of LiMnO2 and LiFeO2 in the standard library, indicating that the product was successfully prepared and can exist stably. Figure 3 An electron microscope image of the lithium iron manganese oxide precursor is shown, showing that its particles have obvious edges and corners, indicating that it has a high degree of crystallinity. Example 2

[0046] This embodiment provides a lithium iron manganese oxide precursor and a lithium iron manganese phosphate positive electrode material, and the preparation method thereof is as follows:

[0047] S1. Lithium hydroxide, manganese oxalate, and ferrous oxalate (Li:Mn:Fe = 1:0.58:0.42) were mixed using a grinding spray method and calcined in air at 700°C for 12 hours to obtain a lithium iron manganese oxide precursor.

[0048] S2. The lithium iron manganese oxide precursor is mixed with ammonium dihydrogen phosphate and polyethylene glycol (LiMn 0.6 Fe 0.4 The obtained carbon-coated lithium manganese iron phosphate cathode material was prepared by mixing, grinding, spray drying, and calcining at 600°C for 10 h. Example 3

[0049] This embodiment provides a lithium iron manganese oxide precursor and a lithium iron manganese phosphate positive electrode material, and the preparation method thereof is as follows:

[0050] S1. Dry-mill lithium carbonate, lithium nitrate, manganese acetate, and ferric nitrate (Li:Mn:Fe = 1:0.62:0.38) and calcine in air at 900°C for 6 h to obtain a lithium iron manganese oxide precursor.

[0051] S2. The lithium iron manganese oxide precursor was mixed with phosphoric acid and sucrose (LiMn 0.6 Fe 0.4 The obtained carbon-coated lithium manganese iron phosphate cathode material was prepared by mixing, grinding, spray drying, and calcining at 900°C for 8 h.

[0052] Comparative Example 1

[0053] This comparative example provides a lithium manganese iron phosphate positive electrode material, and the preparation method thereof is as follows:

[0054] Lithium carbonate, manganese manganese oxide, iron oxide, phosphoric acid, and glucose (Li:Mn:Fe:P:C = 1:0.6:0.4:1:0.3) were mixed by a grinding spray method and calcined at 800°C in air for 8 hours to obtain lithium manganese iron phosphate positive electrode material.

[0055] Comparative Example 2

[0056] This comparative example provides a lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S1, the raw material ratio is adjusted to Li:Mn:Fe=1:0.7:0.3.

[0057] Comparative Example 3

[0058] This comparative example provides a lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S1, the raw material ratio is adjusted to Li:Mn:Fe=1:0.5:0.5.

[0059] Comparative Example 4

[0060] This comparative example provides a lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S2, the raw material ratio is adjusted to LiMn 0.6 Fe 0.4 O2:P=1:1.5.

[0061] Test example

[0062] The performance of the lithium manganese iron phosphate cathode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was compared, and the test results are shown in Table 1. (Test contents may be increased or decreased as needed)

[0063] Table 1. Lithium manganese iron phosphate cathode materials and performance comparison

[0064] Experiment number Compaction (g / cc) D50 / μm 0.1C discharge specific capacity (mAh / g) 1C discharge specific capacity (mAh / g) Manganese dissolution / ppm Powder resistivity (Ω·cm) Example 1 2.35 0.55 153.1 144.1 11 65 Example 2 2.30 0.60 150.79 143.3 10.6 103 Example 3 2.31 0.57 151.26 143.7 12 96 Comparative Example 1 2.16 0.70 149.5 134.7 37.2 865 Comparative Example 2 2.18 0.78 148.9 131.4 39 1200 Comparative Example 3 2.21 0.69 150.2 133 31.5 896.6 Comparative Example 4 2.29 0.63 147.4 129.5 48 1606

[0065] From Table 1 and Figure 4 It can be seen that the lithium manganese iron phosphate positive electrode material prepared in the embodiment of the present invention has distinct particles and high sphericity, and has a high compaction density of more than 2.30 g / cc. The lithium manganese iron phosphate positive electrode material also exhibits high capacity and high rate performance in terms of capacity play. The 0.1C discharge specific capacity reaches more than 150 mAh / g, which is slightly better than the traditional process of Comparative Example 1. The 1C discharge specific capacity reaches more than 143 mAh / g, which is significantly better than Comparative Example 1. In addition, since the lithium manganese iron phosphate positive electrode material has a higher degree of crystallinity, it has better electrical conductivity and can effectively inhibit manganese dissolution. Its powder resistivity reaches less than 103Ω·cm, and manganese dissolution does not exceed 12ppm, which is significantly better than Comparative Example 1.

[0066] Comparative Example 1 adopts solid phase mixing one-step sintering method, and through electron microscope image ( Figure 5 ) It can be seen that the obtained lithium manganese iron phosphate positive electrode material particles are adhered, the physical indicators are reduced, the carbon coating is poor and the crystal form is incomplete, resulting in a significant reduction in electrical performance. The powder resistivity reaches 865Ω·cm, which is 8 to 14 times that of the embodiment of the present invention.

[0067] Comparative Examples 2 and 3 adjusted the manganese-iron ratio. Incorrect ratios prevented stable oxidation products, leading to manganese distortion and abnormally increased resistivity, reaching 1200Ω·cm and 896.6Ω·cm, respectively. Furthermore, the incomplete structure of the finished products led to poor rate performance, with the 1C discharge capacity dropping to around 130mAh / g.

[0068] Comparative Example 4 increased the phosphorus dosage during the phosphating process. While excessive phosphating increased the crystalline form of the finished LMFP, it also produced excessive inert matter, making lithium transport more difficult. This resulted in extremely poor electrical performance, with the powder resistivity reaching 1606 Ω·cm. Furthermore, its 1C discharge capacity decreased significantly, to 129.5 mAh / g.

[0069] In summary, an embodiment of the present invention provides a lithium iron manganese oxide precursor and a preparation method thereof, wherein the preparation method mixes a manganese source, an iron source, and a lithium source and then sinters to obtain a lithium iron manganese oxide precursor. The lithium iron manganese oxide precursor realizes atomic-level mixing of the three elements of manganese, iron, and lithium, and avoids the problem of component segregation caused by direct mixing of multiple elements in the traditional solid-phase method. An embodiment of the present invention also provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, which adopts the above-mentioned lithium iron manganese oxide precursor and is obtained by secondary sintering and phosphating. The stable oxide structure of lithium iron manganese oxide provides an ordered template for the phosphating reaction. The obtained lithium iron manganese phosphate positive electrode material has the characteristics of high crystallinity and few lattice defects, which can improve the diffusion rate of lithium ions. At the same time, its high crystallinity can effectively inhibit the dissolution of manganese ions and improve the cycle stability.

[0070] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium iron manganese oxide precursor, characterized in that: include: Weigh a lithium source, a manganese source, and an iron source and mix them according to a molar ratio of Li:Mn:Fe of 1:(0.58-0.62):(0.38-0.42) to obtain a first mixed material; The first mixed material is calcined under oxygen conditions to obtain the lithium iron manganese oxide precursor.

2. The preparation method according to claim 1, characterized in that The particle size of the first mixed material is ≤2 μm.

3. The preparation method according to claim 1, characterized in that The iron source includes at least one of ferrous oxalate, ferric phosphate, ferric acetate, ferric nitrate and ferric oxide; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate; and the manganese source includes at least one of manganese oxalate, manganese tetraoxide, manganese sulfate, manganese acetate and manganese nitrate.

4. The preparation method according to claim 1, wherein The first mixed material is calcined at a temperature of 700-900° C. for 6-12 hours.

5. A lithium iron manganese oxide precursor, characterized in that: It is prepared by the preparation method of the lithium iron manganese oxide precursor according to any one of claims 1 to 4; the chemical composition of the lithium iron manganese oxide precursor is LiMn 0.6 Fe 0.4 O2.

6. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: The lithium iron manganese oxide precursor according to claim 5 comprises: The lithium iron manganese oxide precursor is mixed with a phosphorus source to obtain a second mixed material; the lithium iron manganese oxide precursor, LiMn in the phosphorus source 0.6 Fe 0.4 The molar ratio of O2:P is 1:(0.95~1.05); The second mixed material is calcined in an inert atmosphere to obtain the lithium manganese iron phosphate positive electrode material.

7. The preparation method according to claim 6, characterized in that The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

8. The preparation method according to claim 6, characterized in that The second mixture is further added with a carbon source, the carbon source including at least one of glucose, sucrose and polyethylene glycol; the lithium iron manganese oxide precursor, the LiMn 0.6 Fe 0.4 The molar ratio of O2:C is 1:(0.3~0.5).

9. The preparation method according to claim 6, characterized in that The second mixed material is calcined at a temperature of 600-800° C. for 6-10 hours.

10. A lithium manganese iron phosphate positive electrode material, characterized in that: It is prepared by the preparation method of the lithium manganese iron phosphate positive electrode material according to any one of claims 6 to 9; the chemical composition of the lithium manganese iron phosphate positive electrode material is LiMn 0.6 Fe 0.4 PO4.

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