A positive electrode material precursor and preparation method thereof

Abstract

The present invention discloses a positive electrode material precursor and a preparation method thereof, which is simple to prepare and can achieve uniform distribution of manganese and iron. x Fe y M z PO 4 , where 0.4≤x≤0.8, 0.3≤y≤0.7, 0≤z≤0.1, 0.9≤x+y+z≤1.1. M is at least one of Ni, Co, Mn, Zn, Ti, Nb, Ta, Mg, B, and Al. Mn x Fe y M z PO 4 From hematite α-Fe 2 O 3 , α-Mn 2 O 3 synthesis.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a positive electrode material precursor and a preparation method thereof. Background Art

[0002] Compared with other rechargeable battery systems, lithium-ion secondary batteries have the advantages of high operating voltage, light weight, small size, no memory effect, low self-discharge rate, long cycle life, and high energy density. They are currently widely used in mobile terminal products such as mobile phones, laptops, and tablet computers. In recent years, due to environmental protection considerations, electric vehicles have been rapidly developed under the promotion of governments and automobile manufacturers, and lithium-ion secondary batteries have become the ideal power source for the new generation of electric vehicles due to their excellent performance. At present, the positive active materials of lithium-ion secondary batteries that people are concerned about can be roughly divided into three categories: layered materials represented by lithium cobalt oxide (LiCoO2), olivine materials represented by lithium iron phosphate (LiFePO4), and spinel structure materials represented by lithium manganese oxide (LiMn2O4).

[0003] Lithium manganese iron phosphate material, as an advanced positive electrode active material, is considered to be the most likely positive electrode active material for the next generation of high-performance lithium batteries. The key to achieving the performance of lithium manganese iron phosphate material lies in the quality of the precursor, especially the uniformity of manganese and iron in the precursor is crucial to the final performance of lithium manganese iron phosphate. Among them, achieving uniform distribution of manganese and iron in lithium manganese iron phosphate precursor is currently a research hotspot. Summary of the invention

[0004] In view of the shortcomings of the above background technology, an object of the present invention is to provide a positive electrode material precursor and a preparation method thereof, which is simple to prepare and can achieve uniform distribution of manganese and iron.

[0005] To solve the above technical problems, the purpose of the present invention is achieved as follows:

[0006] A positive electrode material precursor, whose chemical formula is Mn x Fe y M z PO4, where 0.4≤x≤0.8, 0.3≤y≤0.7, 0≤z≤0.1, 0.9≤x+y+z≤1.1.

[0007] On the basis of the above scheme and as a preferred scheme of the above scheme: M is at least one of Ni, Co, Mn, Zn, Ti, Nb, Ta, Mg, B, and Al.

[0008] On the basis of the above scheme and as a preferred scheme of the above scheme: Mn x Fe y Mz PO4 is synthesized from hematite α-Fe2O3 and α-Mn2O3.

[0009] A method for preparing a positive electrode material precursor comprises the following steps:

[0010] Step 1: sand-grinding α-Fe2O3, α-Mn2O3 and dopants containing M elements in water to make the D50 of the powder mixture in the slurry reach 20-500nm;

[0011] Step 2: spray drying the powder mixture in the slurry to obtain a dry mixture powder, wherein the D50 of the dry mixture powder is between 1um and 10um;

[0012] Step 3: sintering the dried mixture powder at 750° C.-1050° C. to obtain an iron-manganese oxide eutectic;

[0013] Step 4: reacting the iron-manganese oxide eutectic with phosphoric acid, wherein the reaction temperature is maintained between 40-100° C., placing an ultrasonic probe, and reacting the system under ultrasonic action;

[0014] Step 5: Wash and dry the mixture after the reaction, and heat treat it at 150-500° C. for 1-20 hours to obtain a positive electrode material precursor.

[0015] On the basis of the above scheme and as a preferred scheme of the above scheme: a dispersant is added in step 1. For better mixing and dispersion, an appropriate dispersant may be added.

[0016] On the basis of the above scheme and as a preferred scheme of the above scheme: the dispersant is polyethylene glycol or PVP. Polyethylene glycol, PVP and other common dispersants in industry and research.

[0017] On the basis of the above scheme and as the preferred scheme of the above scheme:

[0018] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects:

[0019] The positive electrode material precursor and preparation method thereof of the present invention, the inventors found in experiments that mixing α-crystalline ferric oxide and α-crystalline manganese trioxide can obtain iron-manganese oxide with uniform distribution of manganese and iron, and then converting the oxide into ferromanganese phosphate and synthesizing lithium ferromanganese phosphate can generate lithium ferromanganese phosphate material with excellent performance. However, replacing the above-mentioned ferric oxide raw materials and manganese trioxide raw materials with raw materials of other crystal structures will not obtain a precursor with uniform mixture of iron and manganese.

[0020] Compared with the prior art, the preparation method designed in this patent has simple steps, the morphology of the synthesized material is controllable, and it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the SEM image of the modified lithium manganese iron phosphate material prepared in Example 1. DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the accompanying drawings by way of specific embodiments; the following are specific embodiments, which are intended to further explain the present invention in detail, so as to help the technical personnel and researchers in the field to further understand the present invention, and the relevant technical conditions do not constitute any limitation to the present invention. Any form of modification made within the scope of the claims of the present invention is within the scope of protection of the claims of the present invention.

[0023] Example 1

[0024] (1) Step 1: Grind 16 g of α-Fe2O3, 15.8 g of α-Mn2O3, 0.1 g of TiO2 and 3 g of polyethylene glycol in water until the D50 reaches 80-100 nm.

[0025] Step 2: spray-drying the powder mixture of the slurry to obtain a dry mixture powder, wherein the D50 of the dry mixture powder is 4-5 um.

[0026] Step 3: Sinter the dried mixture powder at 800° C. for 5 hours to obtain an iron-manganese oxide eutectic.

[0027] Step 4: The above iron-manganese oxide eutectic is reacted with 48.4 g of phosphoric acid (85%), wherein the reaction temperature is maintained at 65° C. An ultrasonic probe is placed in the system, and the system is reacted for 10 hours under the action of ultrasound.

[0028] Step 5: Wash and dry the mixture after the reaction, and heat treat it at 350° C. for 5 hours to obtain a lithium manganese iron phosphate precursor.

[0029] Step 6: Weigh 15 g of the precursor material, add 20 g of pure water, add 3.68 g of battery-grade lithium carbonate and 1 g of food-grade glucose under stirring, and grind in a small sand mill. During the sand milling process, add 0.5 g of polyethylene glycol aqueous solution, spray dry the above slurry, and then transfer the resulting powder into an atmosphere furnace. Under a nitrogen protective atmosphere, first heat from room temperature to 420 degrees at a rate of 3°C / min, keep warm for 4 hours, then heat to 580 degrees at a rate of 3°C / min, keep warm for 8 hours, and then cool naturally, pass through a 250-mesh sieve to obtain a lithium manganese iron phosphate product.

[0030] Figure 1The morphology of the precursor prepared in Example 1 is shown. The precursor has a loose spherical structure, which is conducive to the diffusion of the lithium source during subsequent use.

[0031] The chemical reaction equation for preparing the precursor in this embodiment 1 is as follows:

[0032] 2α-Fe2O3+3α-Mn2O3→ 5 Fe 0.8 Mn 1.2 O3

[0033] Fe 0.8 Mn 1.2 O3+2 H3PO4 → Fe 0.8 Mn 1.2 (PO4)2+ 2 H2O

[0034] Example 2

[0035] (1) Step 1: Grind 12.8 g of α-Fe2O3, 19 g of α-Mn2O3, 0.1 g of TiO2 and 3 g of polyethylene glycol in water until the D50 reaches 80-100 nm.

[0036] Step 2: spray-drying the slurry mixture to obtain a dry mixture powder, wherein the D50 of the dry mixture powder is 4-5 um.

[0037] Step 3: Sinter the dried mixture powder at 800° C. for 5 hours to obtain an iron-manganese oxide eutectic.

[0038] Step 4: The above iron-manganese oxide eutectic is reacted with 48.4 g of phosphoric acid (85%), wherein the reaction temperature is maintained at 65° C. An ultrasonic probe is placed in the system, and the system is reacted for 10 hours under the action of ultrasound.

[0039] Step 5: Wash and dry the mixture after the reaction, and heat treat it at 350° C. for 5 hours to obtain a lithium manganese iron phosphate precursor.

[0040] Step 6: Weigh 15 g of the precursor material, add 20 g of pure water, add 3.68 g of battery-grade lithium carbonate and 1 g of food-grade glucose under stirring, and grind in a small sand mill. During the sand milling process, add 0.5 g of polyethylene glycol aqueous solution, spray dry the above slurry, and then transfer the resulting powder into an atmosphere furnace. Under a nitrogen protective atmosphere, first heat from room temperature to 420 degrees at a rate of 3°C / min, keep warm for 4 hours, then heat to 580 degrees at a rate of 3°C / min, keep warm for 8 hours, and then cool naturally, pass through a 250-mesh sieve to obtain a lithium manganese iron phosphate product.

[0041] Comparative Example 1

[0042] The preparation method is basically the same as that in Example 1, except that α-Fe2O3 and α-Mn2O3 in Example 1 are replaced by γ-Fe2O3 and γ-Mn2O3.

[0043] Table 1. Ratios of manganese and iron in the precursors of Example 1 of the present invention and the comparative example

[0044] sample Example 1 Comparative Example 1 Design Mn / Fe molar ratio 1.5 1.5 Actual molar ratio of manganese and iron identified by element scanning under electron microscope 1.48 1.32

[0045] From the above, it can be seen that the distribution of manganese and iron in the precursor synthesized by the method of this patent is more uniform, and the theoretical designed manganese-iron ratio and the actual manganese-iron ratio can be closer.

[0046] Performance Testing

[0047] The lithium iron manganese phosphate product materials prepared in Examples 1-2 and Comparative Example 1 were assembled into button batteries according to the following steps.

[0048] (1) Preparation of positive electrode sheet

[0049] The positive electrode active material prepared in the example, carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 80:10:10, and mixed evenly to prepare a uniform positive electrode slurry.

[0050] The positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 15 μm, and dried at 55 °C to form a pole piece with a thickness of 100 μm. The pole piece was placed on a roller press (pressure of about 1 MPa×1.5 cm 2 ), cut into discs with a diameter of φ14 mm, and then placed in a vacuum oven at 120°C for 6 hours. After natural cooling, it is taken out and placed in a glove box for use as a positive electrode.

[0051] (2) Assembly of lithium-ion secondary batteries

[0052] In a glove box filled with an inert atmosphere, metallic lithium is used as the negative electrode of the battery, a three-layer film of PP / PE / PP coated with aluminum oxide on both sides is placed between the positive electrode and the negative electrode as a separator, a commonly used carbonate non-aqueous electrolyte is added dropwise, and the positive electrode sheet prepared in step (1) is used as the positive electrode to assemble a button battery of model CR2032.

[0053] Cycle test:

[0054] The prepared button cell was left at room temperature (25°C) for 10 hours, and then the button cell was activated by charge and discharge, and then the button cell was tested for charge and discharge cycles using a battery charge and discharge tester. First, it was cycled at a rate of 0.1C for 1 week at room temperature (25°C), and then it was cycled for 49 weeks at a rate of 0.2C. The measured data are listed in Table 1.

[0055] Table 2. Electrochemical properties of the positive electrode active materials of various embodiments of the present invention

[0056] sample Example 1 Example 2 Comparative Example 1 Initial reversible capacity mAh / g 154 152 142 Reversible capacity after 50 cycles mAh / g 149 146 105

[0057] It can be seen from the data in the above table that compared with the lithium iron manganese phosphate material synthesized in Comparative Example 1, the lithium iron manganese phosphate positive electrode active material prepared in Examples 1-2 of the present invention has better electrochemical performance. This is because the distribution of iron and manganese in the precursor prepared in Examples 1-2 is more uniform, which ultimately significantly improves the cycle performance of the battery.

[0058] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a positive electrode material precursor, characterized in that: The following steps are involved: Step 1: sand-grinding α-Fe2O3 and α-Mn2O3 and a dopant containing an M element in water to make the D50 of the powder mixture in the slurry reach 20-500nm; M is at least one of Ni, Co, Mn, Zn, Ti, Nb, Ta, Mg, B, and Al; Step 2: spray drying the powder mixture in the slurry to obtain a dry mixture powder, wherein the D50 of the dry mixture powder is between 1 μm and 10 μm; Step 3: sintering the dried mixture powder at 750° C.-1050° C. to obtain an iron-manganese oxide eutectic; Step 4: reacting the iron-manganese oxide eutectic with phosphoric acid, wherein the reaction temperature is maintained between 40-100° C., placing an ultrasonic probe, and reacting the system under ultrasonic action; Step 5: Wash and dry the mixture after the reaction, and heat treat it at 150-500° C. for 1-20 hours to obtain a positive electrode material precursor.

2. The method for preparing a cathode material precursor according to claim 1, characterized in that: In step one, a dispersant is added.

3. The method for preparing a cathode material precursor according to claim 2, characterized in that: The dispersant is polyethylene glycol or PVP.

4. A cathode material precursor prepared by the preparation method according to any one of claims 1 to 3, characterized in that: Its chemical formula is Mn x Fe y M z PO4, where 0.4≤x≤0.8, 0.3≤y≤0.7, 0≤z≤0.1, 0.9≤x+y+z≤1.1; M is at least one of Ni, Co, Mn, Zn, Ti, Nb, Ta, Mg, B, and Al.

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