Lithium manganese iron phosphate material and method for preparing the same, cathode material, lithium-ion battery

Abstract

This invention provides a lithium manganese iron phosphate material that is well-suited to ternary material charge / discharge platforms, can achieve rapid charging needs over a wider SOC range, and combines relatively low powder wire resistance with excellent energy density, capacity, rapid charging capabilities, and safety features. [Solution] The manganese iron lithium phosphate material comprises a manganese iron lithium phosphate material core and a carbon coating layer covering the surface of the manganese iron lithium phosphate material core, and the general chemical formula of the manganese iron lithium phosphate material core is LiFe x Mn y M 1-x-y PO4, where 0.80 ≤ x < 1, and 0

Description

[Technical Field]

[0001] This application claims priority to the Chinese patent application filed with the China National Patent Office on December 31, 2024, with application number 202412000207.5, and all contents of the aforementioned application are incorporated into this application by reference.

[0002] The present invention relates to the technical field of lithium-ion battery materials, and more specifically to manganese iron lithium phosphate material and its preparation method, cathode material, and lithium-ion battery. [Background technology]

[0003] Lithium phosphate materials offer advantages such as low cost and safety, but different types of lithium phosphate materials have different drawbacks. For example, lithium iron phosphate has low energy density, while manganese iron lithium phosphate has low capacity, high impedance, and poor fast-charging performance. Simultaneously, the low energy density of phosphates makes it difficult to meet the needs of next-generation battery systems. Mixing lithium phosphate with high-energy-density oxides such as nickel-cobalt-manganese to meet the high-energy-density needs is one future direction, but the current voltage platform of lithium iron phosphate is low and does not match that of lithium metal oxides. The high manganese content in manganese iron lithium phosphate results in high impedance and does not match the dynamics of ternary materials, making it difficult to meet the needs of compounding applications. Therefore, there is an urgent need to develop lithium phosphate materials that are suitable for compounding applications and that achieve both high energy density and fast-charging performance. [Overview of the project] [Problems that the invention aims to solve]

[0004] Lithium phosphate materials in related technologies struggle to achieve both high energy density and rapid charging performance, and therefore cannot meet the needs for compounding applications. [Means for solving the problem]

[0005] According to the first aspect, an embodiment of the present application provides a lithium iron manganese phosphate material, which includes a lithium iron manganese phosphate material core and a carbon coating layer coated on the surface of the lithium iron manganese phosphate material core. The chemical general formula of the lithium iron manganese phosphate material core is LiFe x Mn y M 1-x-y PO4, where 0.80 ≤ x < 1, 0 < y ≤ 0.20, and x + y < 1. M is selected from any one or more of V element, Si element, Ge element, Sn element, and Zn element. The powder line resistance of the lithium iron manganese phosphate material is 5 - 50 mΩ / mm.

[0006] According to the second aspect, an embodiment of the present application provides a method for preparing the above lithium iron manganese phosphate material. The preparation method includes step S1 of performing a first mixing on raw materials including a manganese source, an iron source, a lithium source, and an acidic compound to obtain a slurry, and step S2 of sequentially performing sanding, spray granulation, and sintering on the slurry and raw materials including a carbon source to obtain a lithium iron manganese phosphate material. Here, the acidic compound is selected from any one or more of H3VO4, H2SiO3, H2GeO3, H2SnO3, and H2ZnO2.

[0007] According to the third aspect, an embodiment of the present application provides a positive electrode material including the above lithium iron manganese phosphate material.

[0008] [[ID=IS]] According to the fourth aspect, an embodiment of the present application provides a lithium ion battery including a positive electrode sheet including a positive electrode material, a negative electrode sheet, and a separator. The positive electrode material is the above positive electrode material.

Advantages of the Invention

[0009] 1. By optimizing the ratios of Fe element, Mn element, and doping element M within the above ranges, the lithium manganese iron phosphate material can have a relatively low impedance, thereby better meeting the needs for fast charging performance. By adopting the above types of doping element M, the lattice size of the Mn element can be directionally optimized, and by realizing relatively high capacity and relatively low impedance characteristics, the energy density can be further improved. The lithium manganese iron phosphate material of the present application can meet the needs for fast charging performance, high energy density, and cycle performance due to its relatively low powder line resistance. In addition, the lithium manganese iron phosphate material of the present application can not only be used alone but is also suitable for compound applications. In compound applications, the lithium manganese iron phosphate material of the present application is well compatible with the charge-discharge platform of ternary materials, can achieve the needs for fast charging in a wider SOC range, and has excellent performance such as energy density, capacity, fast charging, and safety.

[0010] 2. By adding and doping the above types of acidic compounds in step S1, since the acidic compounds have more active hydrogen bonds, the metal-oxygen bond reaction with the manganese source becomes easier. On the one hand, the doping element and the manganese element are combined by the first mixing, and the doping element can stabilize the manganese element, thereby reducing the influence of the manganese element on the impedance of the lithium manganese iron phosphate material, and thus improving the fast charging performance of the lithium manganese iron phosphate material. On the other hand, the doping element can optimize the lattice size of manganese phosphate, thereby realizing relatively high capacity and relatively low impedance characteristics, and thus improving the energy density of the lithium manganese iron phosphate material. Therefore, the lithium manganese iron phosphate material obtained by the above preparation method not only has both fast charging performance and high energy density but is also suitable for compound applications.

[0011] 3. The positive electrode material containing the above-mentioned lithium iron manganese phosphate material is well adapted to the charge-discharge platform of the ternary material and can achieve the rapid charging needs in a wider SOC range.

[0012] 4. The lithium ion battery containing the above positive electrode material has a relatively high energy density, good rapid charging performance and cycle performance.

Brief Description of the Drawings

[0013] The drawings of the specification constituting a part of the present application are used to provide a further understanding of the present invention. The schematic embodiments and their descriptions of the present invention are for interpreting the present invention and do not constitute an improper limitation to the present invention. In the accompanying drawings, [Figure 1] The charge-discharge graph of the lithium ion battery obtained by preparing the positive electrode material in Example 1 of the present application is shown.

Modes for Carrying Out the Invention

[0014] To make the purpose, technical solution and advantages of the present application clearer, the following will further describe the present application in more detail with reference to the examples. It should be understood that the specific examples described here are only used for interpreting the present application and not for limiting the present application.

[0015] In some embodiments of the present application, a lithium iron manganese phosphate material is provided. The lithium iron manganese phosphate material includes a lithium iron manganese phosphate material core and a carbon coating layer coated on the surface of the lithium iron manganese phosphate material core. The chemical general formula of the lithium iron manganese phosphate material core is LiFe x Mn y M 1-x-y PO4, where 0.80 ≤ x < 1, 0 < y ≤ 0.20, and x + y < 1. M is selected from any one or more of V element, Si element, Ge element, Sn element and Zn element. The powder line resistance of the lithium iron manganese phosphate material is 5 - 50 mΩ / mm.

[0016] This invention enables the lithium manganese iron phosphate material to have relatively low impedance by optimizing the ratio of Fe, Mn, and doping element M within the above range, thereby better meeting the needs for rapid charging performance. By employing the above-mentioned types of doping element M, the lattice size of the Mn element can be directionally optimized, achieving relatively high capacity and relatively low impedance characteristics, thereby further improving energy density. The lithium manganese iron phosphate material of this invention has relatively low powder wire resistance, thus meeting the needs for rapid charging performance, high energy density, and cycle performance. Furthermore, the lithium manganese iron phosphate material of this invention can be used alone, as well as in compound applications. In compound applications, the lithium manganese iron phosphate material of this invention is well-suited to ternary material charge / discharge platforms, can achieve rapid charging needs over a wider SOC range, and combines excellent energy density, capacity, rapid charging, and safety performance.

[0017] To further improve the rapid charging performance and energy density of the manganese iron lithium phosphate material, in one embodiment of the present application, 0.85 ≤ x ≤ 0.95 and 0.05 ≤ y ≤ 0.15, and M is element V and / or element Si.

[0018] In some embodiments of this application, the mass percentage of the carbon coating layer in the manganese iron lithium phosphate material is 0.6 to 1.9%, and / or the Dv50 particle size of the manganese iron lithium phosphate material is 0.2 to 1.5 μm, and / or the press density of the manganese iron lithium phosphate material is 2.5 to 2.7 g / m². 3 That is the case.

[0019] By selecting to control the mass ratio of the carbon coating layer in the manganese iron lithium phosphate material within the above range, it is possible to enhance the structural stability of the manganese iron lithium phosphate material, thereby improving the high-magnification performance of lithium-ion batteries and making them more suitable for high-speed charge and discharge scenarios. By selecting to control the Dv50 particle size and press density of the manganese iron lithium phosphate material within the above range, it is possible to improve the charge and discharge efficiency and cycle stability of lithium-ion batteries. Here, the Dv50 particle size is the particle size value corresponding to the point where the cumulative volume percentage reaches 50% in the particle size distribution of particulate matter.

[0020] In some embodiments of the present application, a method for preparing the above-mentioned manganese iron lithium phosphate material is provided, the preparation method comprising: step S1 of performing a first mixing of raw materials containing a manganese source, an iron source, a lithium source and an acidic compound to obtain a slurry; and step S2 of sequentially performing sanding, spray granulation and sintering of the raw materials containing the slurry and a carbon source to obtain the manganese iron lithium phosphate material, wherein the acidic compound is selected from one or more of H3VO4, H2SiO3, H2GeO3, H2SnO3 and H2ZnO2.

[0021] By doping with the above-mentioned type of acidic compound in step S1, the acidic compound has more active hydrogen bonds, thus facilitating the metal-oxygen bonding reaction with the manganese source. On the one hand, the first mixing bonds the doping element with the manganese element, and the doping element can stabilize the manganese element, thereby reducing the influence of the manganese element on the impedance of the manganese iron lithium phosphate material, and thus further improving the rapid charging performance of the manganese iron lithium phosphate material. On the other hand, the doping element can optimize the lattice size of manganese phosphate, thereby achieving relatively high capacity and relatively low impedance characteristics, and thus improving the energy density of the manganese iron lithium phosphate material. Therefore, the manganese iron lithium phosphate material obtained by the above preparation method not only possesses both rapid charging performance and high energy density, but is also suitable for compounding applications.

[0022] In some embodiments of the present application, step S1 further comprises step S11 of performing a second mixing of a raw material containing a manganese source and an acidic compound to obtain slurry A, step S12 of performing a third mixing of a raw material containing an iron source and a lithium source to obtain slurry B, and step S13 of mixing the raw material containing slurry A and slurry B to obtain slurry, wherein the solid content of slurry A is 20-50%, the solid content of slurry B is 30-60%, and / or the time of the second mixing is 180-360 min, and / or the time of the third mixing is 60-180 min.

[0023] By mixing the manganese source and the acidic compound separately in step S11 and controlling the time of the second mixing within the above range, it is possible to preferentially bond some of the doping metal elements with the manganese element, thereby directionally optimizing the high impedance and high strain properties of the manganese element, and consequently improving the rapid charging and power characteristics of the manganese iron lithium phosphate material. By selecting the above stepwise mixing method and controlling the time of the third mixing and the solid content of slurry A and slurry B within the above range, sufficient reaction between each component is facilitated, thereby improving the activity and stability of the manganese iron lithium phosphate material. By selecting to perform the second and third mixing using ball milling in a coarse polishing tank, better bonding between the doping element and the manganese element can be achieved with low-cost ball milling, thereby enabling the preparation of a more uniformly doped and stronger doping mixture.

[0024] In some embodiments of the present application, the manganese source is selected from one or more of Mn3O4, MnCO3, and MnSO4, and / or the iron source is nanoscale amorphous iron phosphate, and / or the lithium source is lithium carbonate and / or lithium phosphate, and / or the manganese element in the manganese source and the metal element and / or the Si element in the acidic compound, with a molar ratio of manganese source to acidic compound of 0.01~0.2:0.01~0.05, and / or the lithium element in the lithium source and the iron element in the iron source, with a molar ratio of lithium source to iron source of 1~1.02:0.8~1.

[0025] By selecting to control the types of manganese source, acidic compound, iron source, and lithium source, the molar ratio of manganese source to acidic compound, and the molar ratio of lithium source to iron source within the above ranges, it is possible to effectively adjust the chemical composition of the lithium manganese iron phosphate material, thereby optimizing its electrochemical properties and relatively low impedance, and ultimately better meeting the needs of rapid charging performance.

[0026] In some embodiments of the present invention, in step S2 above, the raw materials containing the slurry and carbon source are sanded to obtain a mixture, wherein the particle size of the mixture is 0.1 to 1.2 μm, the sanding time is 120 to 360 min, and / or the carbon source is glucose and / or sucrose, and / or the mass ratio of slurry A, slurry B and carbon source is 3 to 5:93 to 96:1 to 2, and / or the sintering atmosphere is nitrogen gas, and / or the sintering temperature is 720 to 780°C, and / or the sintering time is 24 to 36 h.

[0027] Selecting the sanding time and carbon source type within the above range helps to form a more uniform carbon coating layer during the sanding process, thereby improving the conductivity of the manganese iron lithium phosphate material. Selecting the mass ratio of slurry A, slurry B, and carbon source within the above range helps to precisely adjust the proportions of Fe, Mn, and M elements and the mass of the carbon coating layer, thereby ensuring that the manganese iron lithium phosphate material achieves optimal electrochemical properties. Selecting the sintering atmosphere, sintering temperature, and sintering time within the above range helps to optimize the crystal structure of the manganese iron lithium phosphate material, thereby improving conductivity and reducing impedance, and consequently improving the rapid charging performance and energy density of the manganese iron lithium phosphate material.

[0028] In some embodiments of the present application, a cathode material comprising the above-described manganese iron lithium material is provided.

[0029] The cathode materials containing the above-mentioned manganese iron lithium phosphate material are well-suited to ternary material charge / discharge platforms and can meet the needs for rapid charging over a wider state of charge (SOC) range.

[0030] In some embodiments of the present application, the positive electrode material further comprises a lithium nickel cobalt manganese oxide material, and the mass ratio of the lithium iron manganese phosphate material to the lithium nickel cobalt manganese oxide material in the positive electrode material is 100:5 to 35.

[0031] In compounding applications, by combining the lithium manganese iron phosphate material and lithium nickel cobalt manganese oxide material of this application as cathode materials, and by selecting to control the mass ratio of the lithium manganese iron phosphate material to the lithium nickel cobalt manganese oxide material in the cathode material within the above range, it is possible to further improve the rapid charging performance and energy density of lithium-ion batteries, thereby making them more suitable for charge and discharge platforms.

[0032] In some embodiments of the present application, a lithium-ion battery is provided which includes a positive electrode sheet containing a positive electrode material, a negative electrode sheet, and a separator, wherein the positive electrode material includes the positive electrode material described above.

[0033] Lithium-ion batteries containing the above-mentioned cathode material have relatively high energy density, good rapid charging performance, and good cycle performance.

[0034] The beneficial effects of this application will be further explained below in relation to the examples.

[0035] Example 1 In the manganese source, Mn3O4 and H3VO4 were mixed in a molar ratio of 0.15:0.05 in a rough polishing tank A for 240 mins to obtain slurry A, which had a solid content of 35%. Simultaneously, lithium carbonate and nanoscale amorphous iron phosphate were mixed in a molar ratio of 1:0.8 in a rough polishing tank B for 80 mins to obtain slurry B, which had a solid content of 45%. Slurry A and Slurry B were mixed to obtain a slurry, and glucose was added. Sanding was performed in a sanding tank for 240 minutes. The mass ratio of Slurry A, Slurry B, and glucose was 5:94:1. After sanding until the target particle size was 0.5 μm, spray granulation and sintering were performed sequentially at 750°C for 30 hours in a nitrogen gas atmosphere. Then, the material was crushed into Dv50 particles with a particle size of 1 μm. These particles were pressed with a pressure of 3T to obtain manganese iron lithium material LiFe0.8 Mn 0.15 V 0.05 Obtained MnPO4, where the mass ratio of the carbon coating layer in the lithium iron manganese phosphate material was 1.6%.

[0036] The lithium iron manganese phosphate material and the lithium nickel cobalt manganese oxide material LiNi 0.8 Co 0.1 Mn 0.1 O2 were mixed at a mass ratio of 0.85:0.15 to obtain a cathode material.

[0037] Example 2 In the manganese source, with the manganese element, and in the acidic compound, with the Si element, MnCO3 and H2SiO3 were mixed in a molar ratio of 0.15:0.03 in a rough grinding tank A for 210 min to obtain slurry A, and the solid content of slurry A was 20%. At the same time, in the lithium source, with the lithium element, and in the iron source, with the iron element, lithium carbonate and nanoscale amorphous iron phosphate were mixed in a molar ratio of 1:0.82 in a rough grinding tank B for 90 min to obtain slurry B, and the solid content of slurry B was 30%. Slurry A and slurry B were mixed to obtain a slurry, and glucose was added and sanding was carried out in a sanding tank for 240 min. The mass ratio of slurry A, slurry B and glucose was 5:94:1. After sanding until the target particle size reached 0.1 μm, spray granulation and sintering were sequentially carried out at 720 °C for 36 h in an atmosphere of nitrogen gas, and then crushed into particles with a Dv50 particle size of 0.2 μm. The particles were pressed at a pressure of 3 T to obtain the lithium iron manganese phosphate material LiFe 0.82 Mn 0.15 Si 0.03 PO4, where the mass ratio of the carbon coating layer in the lithium iron manganese phosphate material was 1.6%.

[0038] The lithium iron manganese phosphate material and the lithium nickel cobalt manganese oxide material LiNi 0.8 Co 0.1 Mn 0.1The cathode material was obtained by mixing O2 in a mass ratio of 0.85:0.15.

[0039] Example 3 In the manganese source, MnCO3 and H2SiO3 were mixed in a molar ratio of 0.07:0.03 in a rough polishing tank A for 180 mins to obtain slurry A, which had a solid content of 50%. Simultaneously, lithium carbonate and nanoscale amorphous iron phosphate were mixed in a molar ratio of 1:0.9 in a rough polishing tank B for 120 mins to obtain slurry B, which had a solid content of 60%. Slurry A and Slurry B were mixed to obtain a slurry, and sucrose was added. Sanding was performed in a sanding tank for 240 minutes. The mass ratio of Slurry A, Slurry B, and glucose was 3:96:1. After grinding until the target particle size was 1.2 μm, spray granulation and sintering were performed sequentially at 780°C for 24 hours in a nitrogen gas atmosphere, and then the material was crushed into Dv50 particles with a particle size of 1.5 μm. These particles were pressed with a pressure of 3T to produce manganese iron lithium material LiFe 0.9 Mn 0.07 Si 0.03 PO4 was obtained, and the mass percentage of the carbon coating layer in the manganese iron lithium phosphate material was 1.6%.

[0040] Lithium iron manganese phosphate material and lithium nickel cobalt manganese oxide material (LiNi) 0.8 Co 0.1 Mn 0.1 The cathode material was obtained by mixing O2 in a mass ratio of 0.85:0.15.

[0041] Example 4 The difference from Example 1 is that the mass ratio of slurry A, slurry B, and glucose is 5:94:1.5, and ultimately a manganese iron lithium phosphate material and a cathode material are obtained, in which the mass percentage of the carbon coating layer in the manganese iron lithium phosphate material is 1.9%.

[0042] Example 5 The difference from Example 1 is that the mass ratio of slurry A, slurry B, and glucose is 5:94:3, and ultimately a manganese iron lithium phosphate material and a cathode material are obtained, in which the mass percentage of the carbon coating layer in the manganese iron lithium phosphate material is 2.5%.

[0043] Example 6 The difference from Example 1 is that the solid content of slurry A is 50%, the solid content of slurry B is 60%, and ultimately the lithium manganese iron phosphate material and cathode material are obtained.

[0044] Example 7 The difference from Example 1 is that the solid content of slurry A is 55%, the solid content of slurry B is 65%, and ultimately the lithium manganese iron phosphate material and cathode material are obtained.

[0045] Example 8 The difference from Example 1 is that the sintering temperature is 780°C, the sintering time is 24 hours, and ultimately, the lithium manganese iron phosphate material and cathode material are obtained.

[0046] Example 9 The difference from Example 1 is that the sintering temperature is 800°C, the sintering time is 20 hours, and ultimately, the lithium manganese iron phosphate material and cathode material are obtained.

[0047] Example 10 The difference from Example 1 is that the lithium manganese iron phosphate material is used directly as the cathode material.

[0048] Example 11 The difference from Example 1 is that, in the manganese source, the metal element in the acidic compound, the lithium element in the lithium source, and the iron element in the iron source, Mn3O4, H3VO4, lithium phosphate, and nanoscale amorphous iron phosphate were mixed in a molar ratio of 0.15:0.05:1:0.8 in a rough polishing tank for 320 mins to obtain a slurry, and finally, manganese iron lithium phosphate material LiFe was obtained. 0.8 Mn 0.15 V 0.05 The goal is to obtain PO4 and cathode materials.

[0049] Comparative Example 1 Lithium carbonate, nanoscale amorphous iron phosphate, and MnCO3 were mixed in a molar ratio of 1:0.5:0.5 in a rough grinding tank for 240 mins to obtain a slurry. The slurry and glucose were sanded for 240 mins, with a mass ratio of slurry to glucose of 99:1. After sanding until the target particle size was 0.5 μm, spray granulation and sintering at 750°C for 30 hours in a nitrogen atmosphere were sequentially performed, and then the material was crushed into Dv50 particles with a particle size of 1 μm. These particles were pressed under a pressure of 3T to form a manganese iron lithium phosphate material (LiFe). 0.5 Mn 0.5 I obtained PO4.

[0050] Lithium iron manganese phosphate material and lithium nickel cobalt manganese oxide material (LiNi) 0.8 Co 0.1 Mn 0.1 The cathode material was obtained by mixing O2 in a mass ratio of 0.85:0.15.

[0051] Comparative Example 2 In a lithium source, lithium element was used, and in an iron source, iron element was used. Lithium phosphate and nanoscale amorphous iron phosphate were mixed in a 1:1 molar ratio in a coarse grinding tank for 120 min to obtain a slurry. The slurry and glucose were sanded for 240 min, with a mass ratio of slurry to glucose of 98:2. After grinding until the target particle size was 0.5 μm, spray granulation and sintering were sequentially performed at 750°C for 30 h in a nitrogen gas atmosphere, and then the material was crushed into Dv50 particles with a particle size of 1 μm. These particles were pressed under a pressure of 3 T to obtain lithium iron phosphate material LiFePO4.

[0052] Lithium iron manganese phosphate material and lithium nickel cobalt manganese oxide material (LiNi) 0.8 Co 0.1 Mn 0.1 The cathode material was obtained by mixing O2 in a mass ratio of 0.85:0.15.

[0053] Comparative Example 3 The difference from Example 1 is that a second mixing was performed with Mn3O4 and metal oxide V2O5 to obtain slurry A, and finally manganese iron lithium phosphate material LiFe 0.8 Mn 0.15 V 0.05 The goal is to obtain PO4.

[0054] Lithium iron manganese phosphate material and lithium nickel cobalt manganese oxide material (LiNi) 0.8 Co 0.1 Mn 0.1 The cathode material was obtained by mixing O2 in a mass ratio of 0.85:0.15.

[0055] Testing method: Positive electrode sheet: The positive electrode materials from the above examples and comparative examples, adhesive PVDF, and conductive agent acetylene black were mixed in a mass ratio of 94:3:3, NMP was added, and the mixture was stirred to form a positive electrode slurry. The viscosity of the positive electrode slurry was 6000 mPa·s, and the solid content of the positive electrode slurry was 50%. The positive electrode slurry was applied to an aluminum foil current collector and roll-pressed, resulting in a coating surface density of 200 g / m².2 The press density is 2.7 g / m². 3 Prepare a positive electrode sheet.

[0056] Negative electrode sheet: The negative electrode material, graphite, the conductive agent, acetylene black, and the adhesives, sodium carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR), are mixed in a mass percentage of 94:1:2:3. Deionized water is then added as a solvent, and after uniform stirring, a negative electrode slurry is obtained. This negative electrode slurry is then uniformly coated onto two surfaces of the copper foil of the negative electrode current collector. After drying, roller pressing, and slicing, the coating surface density is 90 g / cm³. 3 The pressed density is 1.6 g / cm³. 3 Prepare the negative electrode sheet.

[0057] Electrolyte: Ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a 1:1:1 volume ratio to obtain an organic solvent. Then, a thoroughly dried lithium salt LiPF6 is dissolved in the organic solvent to prepare an electrolyte with a molar concentration of 1 mol / L.

[0058] Battery core assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, then the tabs are welded and baked, and after moisture passes, an appropriate amount of electrolyte is injected. After packaging, aging, chemical conversion, and degassing are performed to prepare the lithium-ion battery.

[0059] Electrical characteristics test: Cycle Test: DCR Test: After discharging the lithium-ion battery to 50% capacity at room temperature, it was further discharged at 2C for 10s (C is the battery's rated capacity). The voltage V1 immediately before the end of the discharge period was planned, and the voltage V2 immediately before the end of the discharge period was recorded. The DCR value = (V1-V2) / 2C was recorded. The lithium-ion battery was placed in a 45°C incubator and charged to 4.25V with a constant current and voltage of 1C, cutoff at 0.02C, and then discharged at 1C. The cycle capacity and average voltage were recorded to obtain the number of cycles at which 80% capacity retention was achieved, and the voltage drop was also recorded.

[0060] Powder Wire Resistance Test: Using an ST2742b fully automatic powder resistance meter, the test was performed according to GB / T40007-2021 using the 4-probe method. 1.5g of manganese iron lithium material powder was placed in a mold, a pressure of 1 ton was applied, the thickness of the powder molded body, current and voltage were recorded, and the resistance per unit length was tested, i.e., the powder wire resistance.

[0061] Press Density Test: Using a punching module, punch out electrode pieces from a unit area, weigh the electrode pieces, and subtract the mass of the aluminum foil per unit area to obtain the mass of the positive electrode material. Measure the thickness of the positive electrode material and calculate its volume. Press density of the positive electrode material = Quality of the positive electrode material / Volume of the positive electrode material.

[0062] The test results are shown in Table 1. [Table 1]

[0063] Here, Figure 1 shows the charge-discharge graph of a lithium-ion battery obtained by preparing the positive electrode material in Example 1. As can be seen from Figure 1, the lithium manganese iron phosphate material of the present invention has a wider charge-discharge range, with no sudden changes in the 10% to 80% SOC range, and is useful for rapid charging from 10% to 80%.

[0064] As can be seen from the above description, the above embodiment of the present invention achieves the following technical effects, namely, This invention enables the lithium manganese iron phosphate material to have relatively low impedance by optimizing the ratio of Fe, Mn, and doping element M within the above range, thereby better meeting the needs for rapid charging performance. By employing the above-mentioned types of doping element M, the lattice size of the Mn element can be directionally optimized, achieving relatively high capacity and relatively low impedance characteristics, thereby further improving energy density. The lithium manganese iron phosphate material of this invention has relatively low powder wire resistance, thus meeting the needs for rapid charging performance, high energy density, and cycle performance. Furthermore, the lithium manganese iron phosphate material of this invention can be used alone, as well as in compound applications. In compound applications, the lithium manganese iron phosphate material of this invention is well-suited to ternary material charge / discharge platforms, can achieve rapid charging needs over a wider SOC range, and combines excellent energy density, capacity, rapid charging, and safety performance.

[0065] The foregoing are merely embodiments of the present invention and are not intended to limit it. To those skilled in the art, the present invention is subject to various modifications and changes. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium manganese iron phosphate material comprising a lithium manganese iron phosphate material core and a carbon coating layer covering the surface of the lithium manganese iron phosphate material core, The general chemical formula for the manganese iron lithium phosphate material core is LiFe ｘ Mn ｙ M １－ｘ－ｙ PO ４ A lithium manganese iron phosphate material characterized in that, where 0.80 ≤ x < 1, 0 < y ≤ 0.20, and x + y < 1, M is selected from one or more of the elements V, Si, Ge, Sn, and Zn, and the powder wire resistance of the lithium manganese iron phosphate material is 5 to 50 mΩ / mm.

2. The manganese iron lithium phosphate material according to claim 1, characterized in that 0.85 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.15, and M is element V and / or element Si.

3. The manganese iron lithium phosphate material according to claim 1, characterized in that the mass ratio of the carbon coating layer in the manganese iron lithium phosphate material is 0.6 to 1.9%.

4. The manganese iron lithium phosphate material according to claim 1, characterized in that the Dv50 particle size of the manganese iron lithium phosphate material is 0.2 to 1.5 μm.

5. The press density of the aforementioned manganese iron lithium phosphate material is 2.5 to 2.7 g / m². ３ The manganese iron lithium phosphate material according to claim 1, characterized in that it is such.

6. A method for preparing a lithium manganese iron phosphate material according to any one of claims 1 to 5, Step S1 involves performing a first mixing of raw materials containing manganese source, iron source, lithium source, and acidic compounds to obtain slurry. Step S2 includes sequentially performing sanding, spray granulation, and sintering on the raw materials containing the slurry and carbon source to obtain the manganese iron lithium phosphate material, Here, the acidic compound is H ３ VO ４ 、H ２ SiO ３ 、H ２ GeO ３ 、H ２ SnO ３ and H ２ ZnO ２ The method for preparing a lithium iron manganese phosphate material according to any one of claims 1 to 5, characterized in that it is selected from any one or more of them.

7. Step S1 is, Step S11 involves performing a second mixing of the manganese source and the raw material containing the acidic compound to obtain slurry A. Step S12 involves performing a third mixing on the raw materials containing the iron source and the lithium source to obtain slurry B. The method further includes step S13, which involves mixing raw materials containing slurry A and slurry B to obtain the slurry, The preparation method according to claim 6, characterized in that the solid content of slurry A is 20 to 50%, and the solid content of slurry B is 30 to 60%.

8. The preparation method according to claim 7, characterized in that the time for the second mixing is 180 to 360 minutes.

9. The preparation method according to claim 7, characterized in that the time for the third mixing is 60 to 180 minutes.

10. The manganese source is Mn ３ O ４ MnCO ３ and MnSO ４ The preparation method according to claim 6, characterized in that one or more of the above are selected.

11. The preparation method according to claim 6, characterized in that the iron source is nanoscale amorphous iron phosphate.

12. The preparation method according to claim 6, characterized in that the lithium source is lithium carbonate and / or lithium phosphate.

13. The preparation method according to claim 6, characterized in that the manganese element in the manganese source and the metal element and / or Si element in the acidic compound are in a molar ratio of 0.01 to 0.2:0.01 to 0.05 for the manganese source and the acidic compound.

14. The preparation method according to claim 6, characterized in that the molar ratio of the lithium element in the lithium source and the iron element in the iron source is 1 to 1.02:0.8 to 1.

15. The preparation method according to claim 6, characterized in that in step S2, the raw material containing the slurry and the carbon source is sanded to obtain a mixture, the particle size of the mixture is 0.1 to 1.2 μm, and the sanding time is 120 to 360 min.

16. The preparation method according to claim 7, characterized in that in step S2, the carbon source is glucose and / or sucrose, and / or the mass ratio of slurry A, slurry B and the carbon source is 3-5:93-96:1-2.

17. The preparation method according to claim 6, characterized in that, in step S2, the sintering atmosphere is nitrogen gas, and / or the sintering temperature is 720 to 780°C, and / or the sintering time is 24 to 36 hours.

18. It is a positive electrode material, The positive electrode material is characterized in that the positive electrode material includes the manganese iron lithium phosphate material described in any one of claims 1 to 5.

19. The positive electrode material according to claim 18, further comprising a lithium nickel cobalt manganese oxide material, wherein the mass ratio of the lithium manganese iron phosphate material to the lithium nickel cobalt manganese oxide material in the positive electrode material is 100:5 to 35.

20. A lithium-ion battery comprising a positive electrode sheet containing a positive electrode material, a negative electrode sheet, and a separator, A lithium-ion battery characterized in that the positive electrode material is the positive electrode material described in claim 18.

Images