Modified manganese iron lithium phosphate cathode material and its manufacturing method and application

Abstract

The present application provides a modified manganese iron lithium phosphate cathode material, and its manufacturing method and application. The modified manganese iron lithium phosphate cathode material includes a doped manganese iron lithium phosphate core and a coating layer formed on the surface of the doped manganese iron lithium phosphate core, where the doped manganese iron lithium phosphate core contains Nb, and the coating layer includes LiNbO3 and Nb2O5. The modified manganese iron lithium phosphate cathode material of the present application is doped with Nb and has a double coating of LiNbO3 and Nb2O5 on its surface. The coating layer of the modified manganese iron lithium phosphate cathode material has good uniformity, conformity, and conductivity, and the cooperation of LiNbO3 and Nb2O5 improves the multiplication performance and long cycle performance of the LMFP electrode material.

Description

[Technical Field]

[0001] This application claims priority to a Chinese patent application bearing application number 202211611334.3, filed with the China Patent Office on December 14, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of lithium-ion battery technology and relates to a modified lithium iron manganese phosphate cathode material and its preparation method and application. [Background technology]

[0003] In recent years, the rapid development of new energy vehicles has led to a rapid increase in demand for lithium-ion power batteries. Currently, the cathode materials for lithium-ion power batteries are mainly lithium iron phosphate (LFP) and ternary materials. Of these, LFP has become the preferred choice for energy storage and power battery companies due to its advantages such as high cost performance, high safety, and limited resource constraints. However, its low energy density remains a major constraint on the large-scale application of lithium iron phosphate.

[0004] Lithium manganese iron phosphate (LMFP) is a cathode material obtained by adding manganese to LFP. Manganese doping allows LMFP to have a higher voltage platform (4.1 V vs. 3.4 V), improving battery energy density by approximately 15%, making it a cathode material with great potential for applications. Currently, LMFP cathode materials are still in the early stages of industrialization. This is primarily due to their relatively low electronic conductivity and ion diffusion rate, low initial Coulombic efficiency, and poor cycling performance, which have significantly hindered their commercialization. Therefore, improving the electronic conductivity, ion transmission rate, and cycling stability of LMFP materials is currently a key technological challenge. Currently, an effective method for addressing this technical challenge is to perform crystal lattice doping and dual-coating integrated modification of LMFP materials.

[0005] CN114335480A provides a method for producing and using doped carbon-coated lithium iron phosphate, in which an iron source, a transition metal compound, and tannic acid are first chelated, and then the chelate is hydrothermally reacted with a phosphorus source and a lithium source to obtain a precursor of tannic acid-coated transition metal ion-doped lithium iron phosphate. Finally, the tannic acid is carbonized in an inert atmosphere to obtain the doped carbon-coated lithium iron phosphate. The chelation reaction used in this method can prevent the loss of transition metal ions, and the carbonization of tannic acid can prevent the aggregation of secondary particles. As a result, the produced positive electrode material can have good scalability and dynamic performance in applications, but the cycle performance is not significantly improved and cannot meet the requirements of power batteries.

[0006] CN113942990A discloses a method for producing a carbon-coated, ion-doped lithium manganese iron phosphate positive electrode material using a coprecipitation reaction. This method overcomes the problems of uneven element distribution, low packing density, and low specific capacity of lithium manganese iron phosphate positive electrode materials, but the cycling stability of the material is poor, and the capacity of the assembled button battery drops to 95.8% after 80 cycles at 1C magnification. Summary of the Invention

[0007] The following is a summary of the invention described in detail herein, which is not intended to limit the scope of protection of the claims.

[0008] The objective of this application is to provide a modified lithium manganese iron phosphate cathode material, its manufacturing method and applications. The modified lithium manganese iron phosphate cathode material of this application is doped with Nb element and has a double coating of LiNbO3 and Nb2O5 on its surface. The coating layer of the modified lithium manganese iron phosphate cathode material has good uniformity, conformity and conductivity, and the cooperation of LiNbO3 and Nb2O5 improves the multiplication performance and long cycle performance of the electrode material for LMFP.

[0009] To achieve the above object, the present application employs the following technical solutions.

[0010] In a first aspect, an embodiment of the present application provides a modified lithium manganese iron phosphate cathode material, the modified lithium manganese iron phosphate cathode material including a doped lithium manganese iron phosphate core and a coating layer provided on the surface of the doped lithium manganese iron phosphate core, the doped lithium manganese iron phosphate core including Nb element, and the coating layer including LiNbO3 and Nb2O5.

[0011] The modified lithium manganese iron phosphate cathode material of the present application is doped with Nb and has a double coating of LiNbO3 and Nb2O5 on its surface. The strong interatomic interaction after Nb doping stabilizes the crystal lattice structure, improves manganese dissolution, reduces Li / Ni hybridization, and enhances the lithium ion diffusion coefficient. The strong stability of Nb2O5 within the operating voltage range effectively inhibits side reactions between the electrode and the electrolyte, enhances interfacial stability, and improves the cycling stability of the LMFP cathode material. LiNbO3 not only enhances interfacial stability as a physical barrier, but also promotes fast lithium ion conduction as a fast-ion conductor.

[0012] In one embodiment, the doped lithium manganese iron phosphate core has the formula LiNb a Mn x Fe 1-x PO4, where 0 <a≦0.05であり、0<x<1である。

[0013] In one embodiment, the thickness of the coating layer is 10 nm to 50 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.

[0014] In one embodiment, the molar mass ratio of LiNbO3 to Nb2O5 in the coating layer is 1:(0.1-0.4), such as 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, or 1:0.4.

[0015] In a second aspect, the present invention provides a method for manufacturing the modified lithium iron manganese phosphate cathode material of the first aspect, the method comprising the steps of:

[0016] In step (1), a lithium source, a manganese source, an iron source, and a phosphorus source are mixed with a solvent to obtain a mixed salt solution, and the mixed salt solution, a niobium source, and a complexing agent are mixed and dried, followed by a sintering treatment to obtain a fired material.

[0017] In step (2), the fired material obtained in step (1), LiNbO3, and Nb2O5 are mixed with an organic solvent and polished.

[0018] In step (3), the raw material obtained by the grinding treatment in step (2) is subjected to a roasting treatment to obtain the modified lithium iron manganese phosphate positive electrode material.

[0019] In the present embodiment, Nb-doped LMFP is first synthesized, then LiNbO3 and Nb2O5 are mixed in a specific ratio, and the LMFP is dry-mixed with the coating mixture, followed by sintering to obtain a doped and double-coated modified LMFP positive electrode material. The produced coating layer has good uniformity, conformity, and conductivity. The manufacturing process of this method is simple and easy to control, making it suitable for large-scale industrial production.

[0020] In one embodiment, the lithium source in step (1) comprises lithium carbonate and / or lithium dihydrogen phosphate.

[0021] In one embodiment, the manganese source comprises one or a combination of at least two of manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate, or manganese oxalate.

[0022] In one embodiment, the iron source comprises iron phosphate and / or iron powder.

[0023] In one embodiment, the phosphorus source comprises phosphoric acid and / or ammonium dihydrogen phosphate.

[0024] In one embodiment, the molar ratio of each element in the mixed salt solution is Li:Mn:Fe:P=(1-1.6):x:(1-x):1, where 0 <x<1である。

[0025] In one embodiment, the niobium source comprises one or a combination of at least two of niobium oxide, niobium hydroxide, niobium chloride, niobium sulfate, niobium nitrate, or niobium acetate.

[0026] In one embodiment, the complexing agent comprises sodium alginate.

[0027] In one embodiment, the method of drying in step (1) may be spray drying.

[0028] In one embodiment, the sintering temperature is 600°C to 900°C, such as 600°C, 750°C, 800°C, 850°C, or 900°C.

[0029] In one embodiment, the sintering time is 6 hours to 15 hours, such as 6 hours, 8 hours, 10 hours, 12 hours, or 15 hours.

[0030] In one embodiment, the sintering atmosphere comprises a nitrogen atmosphere.

[0031] In one embodiment, the organic solvent in step (2) comprises ethanol.

[0032] In one embodiment, the polishing speed is 500 rpm to 1000 rpm, such as 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm.

[0033] In one embodiment, the polishing time is 0.3 to 1 hour, such as 0.3, 0.5, 0.6, 0.8, or 1 hour.

[0034] In one embodiment, the ratio of the total mass of the LiNbO3 and the Nb2O5 to the mass of the fired material is (0.1-10):100, for example, 0.1:100, 0.5:100, 1:100, 5:100 or 10:100, and preferably 0.5-2:100.

[0035] In one embodiment, the temperature of the roasting treatment in step (3) is 200°C to 650°C, such as 200°C, 300°C, 400°C, 500°C, or 650°C.

[0036] In one embodiment, the roasting time is 2 hours to 15 hours, such as 2 hours, 5 hours, 8 hours, 10 hours, or 15 hours.

[0037] In a third aspect, embodiments of the present application provide a cathode sheet, the cathode sheet comprising the modified lithium iron manganese phosphate cathode material of the first aspect.

[0038] In a fourth aspect, an embodiment of the present application provides a lithium ion battery, the lithium ion battery including the positive electrode sheet of the third aspect. [Effects of the Invention]

[0039] Compared with the related art, the present application has the following inventive advantages:

[0040] (1) The modified lithium manganese iron phosphate cathode material of the present application is doped with Nb element and has a double coating of LiNbO3 and Nb2O5 on the surface. The coating layer of the modified lithium manganese iron phosphate cathode material has good uniformity, conformity, and conductivity. The cooperation of LiNbO3 and Nb2O5 improves the multiplication performance and long-cycle performance of the LMFP electrode material.

[0041] (2)Nb 5+ The doping of layered transition metal oxide cathode materials can suppress cation intermixing and significantly improve the material's charge-discharge performance and cycle stability. The modified LiNbO3-coated cathode material has high lithium ion conductivity, which can effectively block the organic electrolyte and ensure that the charge-discharge performance of the material is not reduced. Therefore, Nb 5+By constructing a structure of doping and LiNbO3 coating, a cooperative effect can be achieved, which can significantly improve the charging performance, cycle performance, and safety performance. T-Nb2O5 (T-phase niobium oxide) has a special lithium ion transmission channel and has excellent charging performance, comparable to the best solid electrolytes. Currently, T-phase niobium oxide is used as a high charging anode material for lithium batteries. By using T-Nb2O5 as the niobium source, Nb 5+ While constructing the doping and LiNbO3 coating structure, excess niobium source (T-Nb2O5) is left on the material surface, which continues to function as a physical protective layer and does not reduce the magnification performance of the material.

[0042] Other aspects can be understood with reference to the following detailed description. DETAILED DESCRIPTION OF THE INVENTION

[0043] Example 1

[0044] This embodiment provides a modified lithium manganese iron phosphate cathode material, which is prepared by the following method:

[0045] (1) Weigh out lithium carbonate, manganese sulfate, iron powder, and phosphoric acid in a molar ratio of Li:Mn:Fe:P = 1.08:0.7:0.3:1, disperse them in deionized water, and stir them in a ball mill. Then add niobium chloride and sodium alginate. Stir at a stirring speed of 1000 rpm for 3 hours, then spray-dry. Place in a nitrogen-protected box furnace, heat to 780°C at a heating rate of 5°C / min, and hold the temperature for 10 hours to obtain the fired material.

[0046] (2) LiNbO3 and Nb2O5 are mixed in a high-speed mixer in a ratio of 1:0.25, and mixed at a rotation speed of 800 rpm for 0.5 hours to obtain a coating mixture. The coating mixture and the fired material obtained in step (1) are then dispersed in ethanol solvent, stirred, and polished, in which the proportion of the coating mixture is 1%, the ball mill speed is 600 rpm, and the ball mill time is 2 hours.

[0047] (3) Sintering in a nitrogen atmosphere, the heating rate of sintering is 8°C / min, the sintering temperature is 650°C, and the firing time is 2 hours. Then, cooling to room temperature in a nitrogen atmosphere is performed to obtain the modified manganese iron lithium phosphate positive electrode material, and the coating layer of the modified manganese iron lithium phosphate positive electrode material has a thickness of 25 nm.

[0048] Example 2

[0049] This embodiment provides a modified lithium manganese iron phosphate cathode material, which is prepared by the following method:

[0050] (1) Weigh out lithium carbonate, manganese sulfate, iron powder, and phosphoric acid in a molar ratio of Li:Mn:Fe:P = 1.08:0.7:0.3:1, disperse them in deionized water, and stir them in a ball mill. Then add niobium chloride and sodium alginate. Stir at a stirring speed of 1200 rpm for 3 hours, then spray-dry. Place in a nitrogen-protected box furnace, heat to 790°C at a heating rate of 8°C / min, and hold the temperature for 9 hours to obtain the fired material.

[0051] (2) LiNbO3 and Nb2O5 are mixed in a high-speed mixer in a ratio of 1:0.3, and mixed at a rotation speed of 850 rpm for 0.5 hours to obtain a coating mixture. The coating mixture and the fired material obtained in step (1) are then dispersed in ethanol solvent, stirred, and polished, in which the proportion of the coating mixture is 1%, the ball mill speed is 600 rpm, and the ball mill time is 2 hours.

[0052] (3) Sintering in a nitrogen atmosphere, the sintering temperature rising rate is 8°C / min, the sintering temperature is 680°C, the sintering time is 2 hours, and then cooling to room temperature in a nitrogen atmosphere to obtain the modified manganese iron lithium phosphate positive electrode material.

[0053] Example 3

[0054] This embodiment differs from the first embodiment in that the mass ratio of LiNbO3 to Nb2O5 is 1:0.05, but the other requirements and parameters are exactly the same as those of the first embodiment.

[0055] Example 4

[0056] This embodiment differs from the first embodiment in that the mass ratio of LiNbO3 to Nb2O5 is 1:0.6, but the other requirements and parameters are exactly the same as those of the first embodiment.

[0057] Comparative Example 1

[0058] This comparative example differs from Example 1 in that the core is not doped with Nb, but the other requirements and parameters are exactly the same as those of Example 1.

[0059] Comparative Example 2

[0060] This comparative example differs from Example 1 in that LiNbO3 is not added, but the other requirements and parameters are exactly the same as those of Example 1.

[0061] Comparative Example 3

[0062] This comparative example differs from Example 1 in that Nb2O5 is not added, and the other requirements and parameters are exactly the same as those of Example 1.

[0063] The performance measurements are as follows:

[0064] The lithium manganese iron phosphate prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was selected as the positive electrode material, a graphite carbon material as the negative electrode material, and a PE / PP polymer material as the separator. These were then wound or stacked onto a core, sealed in an aluminum case or aluminum laminate film, and filled with a lithium ion electrolyte consisting of EC / EMC and LiPF6. The battery was then assembled into an aluminum case or soft-pack lithium ion battery, and its discharge rate at 3C and its capacity retention rate after 1000 cycles at 1C and 25°C were measured. The measurement results are shown in Table 1.

[0065] [Table 1]

[0066] A comparison between Example 1 and Examples 3 and 4 reveals the following: In the modified lithium manganese iron phosphate cathode material of the present application, the mass ratio of LiNbO3 to Nb2O5 affects its performance. When the mass ratio of LiNbO3 to Nb2O5 is adjusted to 1:(0.1-0.4), the performance of the manufactured cathode material is good. If the mass ratio of LiNbO3 is too large, the stability of the material decreases and the cycle capacity retention rate decreases. If the mass ratio of Nb2O5 is too large, the multiplication performance of the material decreases.

[0067] A comparison between Example 1 and Comparative Example 1 reveals that the modified lithium manganese iron phosphate core of the present invention has a strong interatomic interaction after being doped with Nb, which can stabilize the crystal lattice structure, improve manganese elution, reduce Li / Ni intermixing, and improve the lithium ion diffusion coefficient.

[0068] A comparison between Example 1 and Comparative Example 2 reveals the following: LiNbO3 not only acts as a physical barrier to enhance interface stability, but also as a fast ion conductor to promote fast conduction of lithium ions.

[0069] A comparison between Example 1 and Comparative Example 3 reveals that Nb2O5 has strong stability within the operating voltage range, which can effectively suppress side reactions between the electrode and the electrolyte, strengthen the interface stability, and improve the cycle stability of the LMFP positive electrode material.

Claims

1. The doped lithium manganese iron phosphate core includes a doped lithium manganese iron phosphate core and a coating layer formed on the surface of the doped lithium manganese iron phosphate core, the doped lithium manganese iron phosphate core containing Nb element, and the coating layer is LiNbO ３ and Nb ２ O ５ and Modified lithium iron manganese phosphate cathode material.

2. The doped lithium manganese iron phosphate core has the chemical formula LiNb ａ Mn ｘ Fe １－ｘ P.O. ４ where 0<a≦0.05 and 0<x<1; 10. The modified lithium iron manganese phosphate cathode material of claim 1.

3. the thickness of the coating layer is 10 nm to 50 nm; Preferably, the coating layer is made of LiNbO ３ and Nb ２ O ５ The mass ratio of 3. The modified lithium iron manganese phosphate cathode material of claim 1 or 2.

4. A method for producing the modified lithium iron manganese phosphate cathode material according to any one of claims 1 to 3, comprising: Step (1) of mixing a lithium source, a manganese source, an iron source, and a phosphorus source with a solvent to obtain a mixed salt solution, mixing the mixed salt solution, a niobium source, and a complexing agent, drying the mixture, and then performing a sintering treatment to obtain a fired material; The fired material obtained by step (1), LiNbO ３ , Nb ２ O ５ Step (2) of mixing the above with an organic solvent and performing a polishing treatment; and step (3) of roasting the raw material obtained by the grinding treatment of step (2) to obtain the modified lithium iron manganese phosphate positive electrode material. Manufacturing method.

5. the lithium source in step (1) comprises lithium carbonate and / or lithium dihydrogen phosphate; Preferably, the manganese source comprises one or a combination of at least two of manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate, or manganese oxalate; Preferably, the iron source comprises iron phosphate and / or iron powder; Preferably, the phosphorus source comprises phosphoric acid and / or ammonium dihydrogen phosphate; Preferably, the molar ratio of each element in the mixed salt solution is Li:Mn:Fe:P=(1 to 1.6):x:(1 to x):1, where 0<x<1; Preferably, the niobium source comprises one or a combination of at least two of niobium oxide, niobium hydroxide, niobium chloride, niobium sulfate, niobium nitrate, or niobium acetate; Preferably, the complexing agent comprises sodium alginate. The method of claim 4.

6. The drying method described in step (1) is spray drying, Preferably, the temperature of the sintering treatment is 600°C to 900°C; Preferably, the sintering time is 6 hours to 15 hours, Preferably, the sintering treatment is performed in a nitrogen atmosphere. The method according to claim 4 or 5.

7. the organic solvent in step (2) comprises ethanol; Preferably, the speed of the polishing process is between 500 rpm and 1000 rpm; Preferably, the polishing time is 0.3 h to 1 h, Preferably, the LiNbO ３ and Nb ２ O ５ The ratio of the total mass of the calcined material to the mass of the calcined material is (0.1 to 10):100, preferably 0.5 to 2:100; The method according to any one of claims 4 to 6.

8. The temperature of the roasting treatment in step (3) is 200°C to 650°C; Preferably, the roasting treatment time is 2 hours to 15 hours. The method according to any one of claims 4 to 7.

9. A modified lithium iron manganese phosphate cathode material according to any one of claims 1 to 3, Positive electrode sheet.

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