High-compaction positive electrode material, preparation method thereof and battery positive electrode plate

Abstract

The preparation method comprises the following steps: 1, uniformly mixing an iron source, a manganese source, a phosphorus source, a lithium source, a carbon source, a modified additive and a water reducing agent, carrying out wet grinding and mixing by using a grinding machine, and carrying out drying granulation to prepare a precursor; 2, sintering the prepared precursor in an inert or reducing atmosphere; and 3, crushing the sintered material to obtain the high-compaction positive electrode material. On the basis of ensuring the viscosity and other characteristics of the slurry, the solid content of the slurry is increased, reduction of production energy consumption in the grinding and spray granulation stage is facilitated, the used equipment is the same as the equipment in the prior art, additional transformation equipment is not needed, and the method has the characteristics of low production cost and high productivity. In addition, the prepared positive electrode material has the characteristics of high compaction density and long cycle period, and is suitable for popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a high tap density cathode material and a preparation method thereof. Background Art

[0002] With the increasing requirements of society for cruising range, improving the energy density of lithium iron (manganese) phosphate has become a research hotspot in this field in recent years.

[0003] Currently, the commonly used improvement methods mainly include: optimizing the types of raw materials, adjusting the sintering system, and the particle size distribution of large and small particles, etc. The gas generation amount during the sintering process of the phosphate process is much smaller than that of the oxalate route, and it is often used as the raw material for preparing high tap density lithium iron (manganese) phosphate; in addition, adjusting the particle size distribution of the slurry stage and the finished product is also beneficial to improving the tap density; during the sintering process, increasing the sintering temperature can promote particle growth, thereby improving the tap density, but usually accompanied by problems such as excessive magnetic impurities, resulting in a decline in electrical performance; in addition, a secondary sintering process is also used to improve the tap density, but this process has high energy consumption and high cost. Therefore, an effective method is urgently needed to improve the tap density of lithium iron (manganese) phosphate. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to solve the problem of low tap density of lithium iron (manganese) phosphate, and provide a preparation method of a high tap density cathode material.

[0005] Technical Solution: A preparation method of a high tap density cathode material of the present invention includes the following steps:

[0006] S1, using iron source, manganese source, phosphorus source, lithium source, carbon source, modification additive and water reducing agent as raw materials, mixing them evenly and wet grinding the mixture using a grinding machine, and drying and granulating to obtain a precursor;

[0007] S2, sintering the precursor obtained in S1 in an inert or reducing atmosphere;

[0008] S3, crushing the sintered material obtained in S2 through a jet mill to obtain a high tap density cathode material;

[0009] The water reducing agent includes one or more of polycarboxylate water reducing agent, fatty acid water reducing agent, naphthalene water reducing agent and lignosulfonate water reducing agent;

[0010] The chemical formula of the cathode material is LiMn x Fe y PO 4 / C, where x + y = 1, x ≤ 1, y ≤ 1.

[0011] Further, the iron source in the step S1 includes one or more of ferrous oxalate, iron phosphate, manganese iron oxide, and iron manganese phosphate; the manganese source includes one or more of manganese carbonate, manganese dioxide, manganese tetroxide, manganese iron oxide, iron manganese phosphate, and manganese oxalate; the phosphorus source includes one or more of iron phosphate, iron manganese phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; the carbon source includes one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, urea, carbon black, acetylene black, graphite, graphene, and conductive carbon tubes; the additive includes an oxide containing one or more elements of Mg, Zn, Ni, Co, V, Ti, Zr, W, La, Al, Y, Sr, and F.

[0012] Further, the water reducing agent accounts for 1-5% of the total mass of the raw materials.

[0013] Further, the wet grinding particle size D in the S1 50 is 0.05-0.8 μm.

[0014] Further, the solid content of the slurry obtained by wet grinding and mixing in the S1 is controlled at 60-80%, and the viscosity of the slurry is controlled at 1500-4000 mPa·s.

[0015] Further, the sintering system in the S2 is to heat up to 600-800 °C at a heating rate of 0.5-5 °C / min and hold for 6-16 h.

[0016] The present invention provides a high-compaction cathode material prepared by the above preparation method.

[0017] The present invention provides a battery cathode pole piece prepared by the above high-compaction cathode material.

[0018] Principle and beneficial effects: During the preparation process of the present invention, by adding a water reducing agent, the viscosity of the slurry is ensured to be appropriate, avoiding industrial problems such as difficult mixing, high load of the sand mill, and difficult spraying caused by too high viscosity. On this basis, the solid content of the slurry is increased. Compared with the conventional solid content in the grinding stage that must be controlled between 35% and 45% to make the slurry viscosity appropriate, the preparation method of the present invention can greatly increase the solid content while still maintaining the required slurry viscosity. On the one hand, it helps to reduce the production energy consumption in the grinding and spray granulation stages; on the other hand, after the slurry is granulated by spray drying, a large number of fine voids are left between the particles due to the evaporation of water between the particles. The lower the solid content of the slurry, the more voids there are. After the present invention increases the solid content of the slurry, the gap between the primary particles is reduced, and more effective components of the same size particles are formed. In addition, the reduction of the gap helps the mass transfer of substances during the sintering process, and the primary particles can better fuse and grow, thereby realizing the improvement of the overall compaction density of the material. Brief Description of the Drawings

[0019] Figure 1 SEM picture of Example 1 of the present invention;

[0020] Figure 2 SEM picture of Comparative Example 1 of the present invention. Detailed Embodiments

[0021] The technical solutions of the present invention will be further described below in conjunction with the drawings. The equipment and raw materials used can all be purchased from the market or are commonly used in the art.

[0022] Example 1

[0023] Weigh lithium iron phosphate and lithium carbonate according to the molar ratio of Li:Fe = 1.03:1. Add glucose, polyethylene glycol, titanium dioxide, and the water reducing agent methyl methacrylate / methyl acrylate copolymer according to 10%, 5%, 1%, and 2% of the weights of lithium iron phosphate and lithium carbonate respectively, and mix with pure water to form a slurry with a solid content of 80%. Grind it to a particle size of 0.45 μm through a sand mill, measure the viscosity of the slurry to be 2800 mPa·s, and then granulate it through a spray dryer to obtain a precursor powder; the precursor powder is heated to 770 °C at a heating rate of 1 °C / min under the protection of a nitrogen atmosphere and kept warm for 10 h, and finally crushed through a jet mill to obtain the finished lithium iron phosphate product.

[0024] Example 2

[0025] Weigh lithium iron phosphate, manganese tetroxide, and lithium carbonate according to the molar ratio of Li:Fe:Mn = 1.03:0.4:0.6. Supplement phosphoric acid according to the ratio of (Fe + Mn) / P = 0.985. Add glucose, polyethylene glycol, titanium dioxide, and the water reducer methacrylic acid / methyl acrylate copolymer mixed with pure water to form a slurry with a solid content of 60% according to 8%, 8%, 2%, and 5% of the weights of lithium iron phosphate, manganese tetroxide, lithium carbonate, and phosphoric acid respectively, and grind it to a particle size of 0.25 μm through a sand mill. The viscosity of the slurry is tested to be 3400 mPa·s, and then granulate it through a spray dryer to obtain the precursor powder. The precursor powder is heated to 650 °C at a heating rate of 1 °C / min under the protection of a nitrogen atmosphere and held for 10 h, and finally, the finished product of lithium iron manganese phosphate is obtained by crushing through a jet mill.

[0026] Example 3

[0027] The steps are the same as those in Example 1, except that the type of water reducer is changed to an amide / imide type polycarboxylic acid polymer.

[0028] Example 4

[0029] The steps are the same as those in Example 1, except that the type of water reducer is changed to a naphthalene sulfonate formaldehyde condensate.

[0030] Example 5

[0031] The steps are the same as those in Example 1, except that the type of water reducer is changed to a sulfonated acetone formaldehyde condensate.

[0032] Comparative Example 1

[0033] The steps are the same as those in Example 1, except that there is no water reducer and the sintering temperature is increased to 790 °C and held for 12 h.

[0034] Comparative Example 2

[0035] The steps are the same as those in Example 1, except that there is no water reducer and secondary sintering is carried out. The process of secondary sintering is to heat to 780 °C at a heating rate of 2 °C / min and hold for 6 h.

[0036] To verify the progressiveness of the embodiments of the present application, the following performance tests were carried out on the above Examples 1-4: The above materials were respectively mixed with SP, PVDF, and carbon nanotubes according to the ratio of 96:0.5:3:0.5 to prepare a positive electrode sheet. Using metallic lithium as the negative electrode sheet, assemble it into a half-cell in a conventional manner, and then test the half-cell with a Neware half-cell test system. The charge-discharge test voltage is 2.0-4.5 V, and the test results are shown in Table 1 below:

[0037] Table 1

[0038]

[0039]

[0040] It can be seen from the above results that the electrochemical performances of Examples 1-5 are consistent with those of Comparative Examples 1-2. However, in terms of the compaction density, the data of the examples are significantly better than those of the comparative examples. The specific surface area of the dried materials shows that the specific surface area of the examples is significantly smaller than that of the comparative examples, because after adding water reducing agents, there are fewer voids in the materials of the examples after drying. Figure 1 and Figure 2 SEM pictures of the dried materials of Example 1 and Comparative Example 1 are respectively shown. It can be seen that the voids in Example 1 are significantly fewer than those in Comparative Example 1.

Claims

1. A method for preparing a high-density cathode material, characterized in that: The following steps are involved: S1, using an iron source, a manganese source, a phosphorus source, a lithium source, a carbon source, a modification additive and a water reducing agent as raw materials, mixing them evenly, wet-grinding and mixing them using a grinder, and drying and granulating them to obtain a precursor; S2, sintering the precursor obtained in S1 in an inert or reducing atmosphere; S3, crushing the sintered material obtained in S2 by air jet milling to obtain a high-density positive electrode material; The water reducer includes one or more of a polycarboxylic acid water reducer, a fatty acid water reducer, a naphthalene water reducer and a lignin sulfonate water reducer; The chemical formula of the positive electrode material is LiMn x Fe y PO4 / C, where x+y=1, x≤1, y≤1.

2. The method for preparing a high-density cathode material according to claim 1, characterized in that: The iron source in step S1 includes one or more of ferrous oxalate, ferric phosphate, manganese iron oxide, and manganese iron phosphate; the manganese source includes one or more of manganese carbonate, manganese dioxide, manganese tetraoxide, manganese iron oxide, manganese iron phosphate, and manganese oxalate; the phosphorus source includes one or more of ferric phosphate, manganese iron phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; the carbon source includes one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, urea, carbon black, acetylene black, graphite, graphene, and conductive carbon tubes; the modifying additive includes an oxide containing one or more elements of Mg, Zn, Ni, Co, V, Ti, Zr, W, La, Al, Y, Sr, and F.

3. The method for preparing a high-density cathode material according to claim 1, characterized in that: The water reducing agent accounts for 1-5% of the total mass of the raw materials.

4. The method for preparing a high-density cathode material according to claim 1, characterized in that: The wet grinding particle size D in S1 50 It is 0.05~0.8μm.

5. The method for preparing a high-density cathode material according to claim 1, characterized in that: The solid content of the slurry obtained by wet grinding and mixing in S1 is controlled at 60-80%, and the viscosity of the slurry is controlled at 1500-4000 mPa·s.

6. The method for preparing a high-density cathode material according to claim 1, characterized in that: The sintering system in S2 is to heat the temperature to 600-800° C. at a heating rate of 0.5-5° C. / min and keep the temperature for 6-16 hours.

7. A high-density cathode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. A positive electrode plate for a battery, characterized in that: Prepared from the high-density positive electrode material according to claim 7.

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