Positive electrode material and preparation method and application thereof

Abstract

The invention provides a positive electrode material as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The preparation method of the positive electrode material comprises the following steps: S1, adding a zinc source, a lithium source and benzene dicarboxylic acid into a solvent according to a mass ratio of 1: (0.6.0-7): (1.7-1.8), and uniformly mixing to obtain a mixed solution; carrying out heating reaction on a matrix and the mixed solution to obtain a mixture; and S2, uniformly mixing the mixture, aniline and trichloromethane, adding ferric chloride, uniformly stirring, centrifuging and drying to obtain the positive electrode material. The prepared positive electrode material has a double-layer coating structure, so that the interface stability is ensured, and the electrochemical performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of science and technology and the continuous rise of energy demand, developing efficient, safe and environmentally friendly energy conversion and storage systems has become the key to achieving the goal of sustainable development. In recent years, lithium ion batteries as power sources have shown great application potential in portable electronic products, electric vehicles and energy storage fields. Among them, the positive electrode material as the core component of the lithium ion battery plays a decisive role in the capacity and cycle performance of the battery.

[0003] The common positive electrode materials currently include LiCoO2, LiNiO2, LiMnO2 and LiNi X Co y Mn 1-x-y O2 (NCM). Compared with other positive electrode materials, NCM has the advantages of low cost, large discharge capacity and excellent cycle performance. In order to improve the battery capacity, an effective method is to increase the nickel (Ni) content in the NCM material. However, with the increase of the Ni content, the number of phase transitions in the charging and discharging process will also increase significantly. For example, when the Ni content is 33%, only one pair of redox peaks appears in the cyclic voltammetry test; and when the Ni content is more than 80%, four pairs of redox peaks appear in the cyclic voltammetry test, and the H2-H3 phase transition at 4.2 V is the main reason for the capacity attenuation of high-nickel ternary materials. SUMMARY

[0004] Based on the technical problems existing in the background art, the application provides a positive electrode material and a preparation method and application thereof.

[0005] The positive electrode material provided by the application comprises a substrate and a Li2Zn(BDC)2 layer and a PANI layer coated on the surface of the substrate in sequence.

[0006] The Li2Zn(BDC)2 layer in the application can accelerate the diffusion rate of Li + and inhibit the side reaction on the surface of the substrate, in addition, PANI as a conductive polymer, the excellent conductivity accelerates the transfer of Li + Both of them not only inhibit the occurrence of H2-H3 phase transition in the charging and discharging process, but also improve the interface stability, and further inhibit the side reaction on the surface. Therefore, after the modification of the positive electrode material, the rate performance is improved, thereby improving the charging and discharging performance of the whole battery system.

[0007] Preferably, the substrate is selected from LiCoO2, LiNiO2, LiMnO2 and LiNix Co y Mn 1-x-y O2, wherein 0.6≤x<1, 0≤y≤0.3, 0

[0008] Preferably, the particle size D50 of the substrate is 2.5-4 μm, the thickness of the Li2Zn(BDC)2 layer is 5-50 nm, and the thickness of the PANI layer is 10-30 nm.

[0009] The positive electrode material provided by the application is a double-layer coated positive electrode material, which is beneficial to ensuring interface stability and improving the rate performance and cycle stability of the battery.

[0010] The application further provides a preparation method of the positive electrode material.

[0011] S1, a zinc source, a lithium source and a benzenedicarboxylic acid are added into a solvent in a mass ratio of 1:(0.6.0-7):(1.7-1.8) and uniformly mixed to obtain a mixed solution; and the substrate and the mixed solution are subjected to a heating reaction to obtain a mixture;

[0012] S2, the mixture, aniline and chloroform are uniformly mixed, and then iron chloride is added and uniformly stirred, and then centrifuged and dried to obtain the positive electrode material.

[0013] The preparation method of the positive electrode material provided by the application is simple, the raw materials are abundant, the energy consumption is low, the production process is safe and reliable, the production cost is low, and the production is easy to scale up.

[0014] Preferably, in S1, the zinc source is selected from one or more of Zn(NO3)2, ZnCl2 and ZnSO4.

[0015] Preferably, in S1, the lithium source is selected from one or more of LiNO3 and Li2CO3.

[0016] The selection of the types of the zinc source and the lithium source helps to optimize the experimental process, for example, the pyrolysis products NO of Zn(NO3)2 and LiNO3 are easy to remove. x easy to remove.

[0017] Preferably, in S1, the benzenedicarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid and phthalic acid.

[0018] The mass ratio of the zinc source, the lithium source and the benzenedicarboxylic acid within a certain range helps to improve the uniformity, compactness and adhesion of the Li2Zn(BDC)2 coating layer and avoid the presence of metal oxide and lithium salt impurities.

[0019] Preferably, in S1, the solvent is selected from one or more of ethanol and water.

[0020] More preferably, the volume ratio of the ethanol and water is (3-10):(0.5-1).

[0021] Preferably, in S1, the proportion of the solvent in the mixed solution is greater than 99%.

[0022] Preferably, in S1, the mass ratio of the substrate and the mixed solution is 1:(6-13).

[0023] The mass ratio of the substrate and the mixed solution within a certain range helps to ensure the uniformity and reasonable thickness of the Li2Zn(BDC)2coating layer on the surface of the substrate. If it is too thick, it will hinder the diffusion of Li + migration (decrease in rate performance), and if it is too thin, it cannot effectively block the side reaction.

[0024] Preferably, in S1, the heating reaction includes first reacting the substrate and the mixed solution at 400-500°C for 0.5-2h and cooling to room temperature, and then reacting at 250-400°C for 1-3h under a protective gas atmosphere.

[0025] More preferably, the heating reaction includes first reacting the atomized liquid of the substrate and the mixed solution at 400-500°C for 0.5-2h and cooling to room temperature, and then annealing at 250-400°C for 1-3h under a protective gas atmosphere.

[0026] More preferably, the protective gas is selected from one or more of nitrogen and argon.

[0027] The heating reaction is to coat a layer of Li2Zn(BDC)2on the surface of the substrate by pyrolysis of the atomized liquid of the mixed solution, thereby constructing an effective coating layer that can accelerate the diffusion rate of Li + . At the same time, as a physical barrier, the coating layer effectively suppresses the side reaction between the substrate material and the electrolyte, reduces the occurrence of H2-H3 phase change during charging and discharging, thereby ensuring the stability of the interface and improving the rate performance and cycle stability of the battery.

[0028] Preferably, in S1, the mixture is a material coated with a layer of Li2Zn(BDC)2on the surface of the substrate.

[0029] Preferably, in S2, the mass ratio of the mixture, aniline, chloroform, and iron chloride is 1:(0.001-0.06):(5-20):(0.001-0.18).

[0030] The mass ratio of the mixture, aniline, and chloroform within a certain range helps to uniformly disperse the mixture, avoid agglomeration, and ensure that the dissolved aniline and the subsequently added iron chloride are fully polymerized.

[0031] Preferably, in S2, the mass ratio of aniline to ferric chloride is 1:(1-3).

[0032] The mass ratio of aniline to ferric chloride within a certain range helps to reduce the generation of by-products and ensure that the PANI layer is in a pure state.

[0033] Preferably, in S2, the stirring speed is 300-500 r / min, and the stirring time is 4-8 h.

[0034] Controlling the stirring speed within a certain range can ensure that the liquid does not splash, and controlling the stirring time within a certain range helps to fully carry out the polymerization reaction.

[0035] Preferably, in S2, the centrifugal speed is 9000-13000 r / min, and the centrifugal time is 3-5 min.

[0036] The centrifugal speed and time are both obtained from laboratory experience, to ensure that the color after centrifugation is as colorless and transparent as possible, and if the reaction is not complete, there may be a slight light yellow color.

[0037] Preferably, in S2, the drying temperature is 60-90℃.

[0038] Preferably, in S2, the positive electrode material comprises a matrix and a Li2Zn(BDC)2 layer and a PANI layer successively coated on the surface of the matrix, and the matrix is selected from one or more of LiCoO2, LiNiO2, LiMnO2, LiNi x Co y Mn 1-x-y O2, wherein 0.6≤x<1, 0≤y≤0.3, and 0<x+y≤1.

[0039] On the basis of coating Li2Zn(BDC)2 in the inner layer, the present application further coats a layer of polyaniline (PANI) in the outer layer by in-situ polymerization. In-situ polymerization enables the PANI to form a uniform and continuous layered structure on the surface of the matrix material. As a conductive polymer, PANI has excellent conductivity, which accelerates the migration of Li + and further improves the cycle performance of the battery.

[0040] The positive electrode material or the positive electrode material prepared by the above preparation method is applied in a lithium ion battery.

[0041] The positive electrode material provided by the present application is applied in a lithium ion battery, which helps to improve the charge-discharge performance of the entire battery system.

[0042] The present application has the following beneficial effects:

[0043] The application provides a preparation method of a positive electrode material, comprising the following steps: firstly, obtaining a matrix Li2Zn(BDC)2 composite material through a spray pyrolysis reaction, then in-situ polymerizing a layer of polyaniline (PANI) on the surface of the matrix Li2Zn(BDC)2 composite material, and obtaining a ternary positive electrode composite material matrix Li2Zn(BDC)2 / PANI. The double-layer coated positive electrode material provided by the application not only helps to improve the conductivity of the positive electrode material, but also can inhibit the surface side reaction. In the application, Li2Zn(BDC)2 effectively inhibits the side reaction between the matrix and the electrolyte, and reduces the occurrence of H2-H3 phase change in the charging and discharging process, so as to ensure the stability of the interface. In addition, polyaniline (PANI) is a conductive polymer, and its excellent conductivity accelerates the migration of lithium ions (Li + ). The synergistic effect of the two can significantly improve the rate performance and cycle stability of the high-nickel ternary material and inhibit the surface side reaction. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The rate curve graphs of Example 1 and Comparative Example 1 provided by the application at 0.2C, 0.33C, 1C, 0.2C and the 50-cycle curve graph at 1C are shown in the following figures. DETAILED DESCRIPTION

[0045] The technical solutions of the application are described in detail through specific examples.

[0046] The materials, reagents and the like used in the following examples and comparative examples can be obtained from commercial channels unless otherwise specified.

[0047] Example 1

[0048] A preparation method of a positive electrode material, comprising the following steps:

[0049] S1, 3.40 mg of Zn(NO3)2, 2.21 mg of LiNO3 and 5.95 mg of H2BDC are dissolved in 80 ml of 95% ethanol aqueous solution to obtain a mixed solution; 8 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and the atomized liquid of the mixed solution A are jointly injected into a high-temperature reactor at 500 DEG C and react for 1.5 h, after the reaction is completed, the temperature is cooled to room temperature, and the obtained solid powder is annealed at 300 DEG C for 2 h in an argon atmosphere, to obtain a mixture, which is a material coated with a Li2Zn(BDC)2 layer on the surface of LiNi 0.8 Co 0.1 Mn 0.1 O2;

[0050] S2. Mix 5 g of the mixture, 0.1 g of aniline, and 50 g of chloroform until homogeneous. Then add 0.15 g of ferric chloride and stir at 400 r / min for 6 h. Centrifuge at 10000 r / min for 4 min and dry at 70 °C to obtain the cathode material, namely LiNi. 0.8 Co 0.1 Mn 0.1 The O2 surface is coated with a material consisting of two layers of Li2Zn(BDC) and a layer of PANI.

[0051] Example 2

[0052] The only difference between Example 2 and Example 1 is that the amount of aniline added is adjusted from "0.1g" to "0.005g" and the amount of ferric chloride added is adjusted from "0.15g" to "0.0075g". The rest is the same as Example 1.

[0053] Example 3

[0054] The only difference between Example 3 and Example 1 is that the amount of aniline added is adjusted from "0.1g" to "0.3g" and the amount of ferric chloride added is adjusted from "0.15g" to "0.45g". The rest is the same as Example 1.

[0055] Comparative Example 1

[0056] The cathode material in Comparative Example 1 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0057] Comparative Example 2

[0058] The only difference between Comparative Example 2 and Example 1 is that step S2 was not performed, and the cathode material was LiNi. 0.8 Co 0.1 Mn 0.1 The material with an O2 surface coated with a Li2Zn(BDC)2 layer is the same as in Example 1.

[0059] Comparative Example 3

[0060] The only difference between Comparative Example 3 and Example 1 is that step S1 was not performed, and the cathode material was LiNi. 0.8 Co 0.1 Mn 0.1 The material used to coat the O2 surface with a PANI layer is the same as in Example 1.

[0061] Test case

[0062] The above-mentioned positive electrode material is prepared into a positive electrode sheet by: dissolving the positive electrode material, Super P and PVDF in NMP at a mass ratio of 8:1:1, stirring for 2 hours to form a positive electrode slurry, coating the positive electrode slurry onto both surfaces of an aluminum foil, and then vacuum drying at 110°C for 20 hours. After rolling, slicing and weighing, a positive electrode sheet including a positive electrode active layer is obtained.

[0063] In an argon-atmospheric glove box, the positive electrode sheet, lithium metal sheet, and separator prepared by wet process are assembled into a CR2016 coin cell. The electrolyte includes EC, DEC, and EMC in a volume ratio of 1:1:1, and LiPF6 with a solute concentration of 1.0 mol / L.

[0064] The assembled button cells were subjected to the following performance tests, with a test voltage range of 2.8-4.35V. First, they were subjected to one charge-discharge cycle at constant currents of 0.2C, 0.33C, and 0.1C, respectively, followed by one charge-discharge cycle at a constant current of 0.2C. Figure 1 The first four points were then subjected to 50 charge-discharge cycles at a constant current of 1C. The test results are shown in Table 1. Figure 1 .

[0065] Table 1

[0066] Sample 0.2 C first charge (mAh / g) 0.2 C first discharge (mAh / g) First coulombic efficiency (%) 0.33C 1 C discharge (mAh / g) 0.33 C / 0.2 C (%) 1 C / 0.2 C (%) Example 1 230.5 205.8 89.32 203.5 195.6 98.88 95.04 Example 2 230.2 204.3 88.75 201.0 192.5 98.38 94.22 Example 3 229.8 203.1 88.47 200.5 190.2 98.72 93.65 Comparative Example 1 229.5 190.8 82.85 184.2 173.5 96.54 90.93 Comparative Example 2 232.0 202.5 86.95 197.8 185.6 97.68 91.65 Comparative Example 3 231.8 201.7 86.82 197.2 185.8 97.77 92.12

[0067] The data above shows that, compared with Comparative Examples 1-3, Examples 1-3 exhibit a significant improvement in discharge capacity and initial efficiency, indicating a substantial improvement in the electrical properties of the material itself after coating. Examples 1-3 also demonstrate that different amounts of aniline slightly affect the final PANI produced, thus influencing the material's performance. Figure 1 The cycling curves of Example 1 and Comparative Example 1 also clearly show that the rate performance of the material is significantly improved.

[0068] In summary, the cathode material provided by this invention helps to improve the electrochemical performance of batteries.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, The matrix includes a substrate and a Li₂Zn(BDC)₂ layer and a PANI layer sequentially coated on the substrate surface; the substrate is selected from LiCoO₂, LiNiO₂, LiMnO₂, and LiNi x Co y Mn 1-x-y One or more of O2, wherein 0.6≤x<1, 0≤y≤0.3, and 0<x+y≤1.

2. A method for preparing the positive electrode material according to claim 1, characterized in that, Includes the following steps: S1. Add zinc source, lithium source, and diphenylcarboxylic acid to a solvent at a mass ratio of 1:(0.6.0-7):(1.7-1.8) and mix thoroughly to obtain a mixed solution; then heat the matrix and the mixed solution to react and obtain a mixture. S2. Mix the mixture, aniline, and chloroform evenly, then add ferric chloride, stir evenly, centrifuge, and dry to obtain the positive electrode material.

3. The preparation method according to claim 2, characterized in that, In S1, the zinc source is selected from one or more of Zn(NO3)2, ZnCl2, and ZnSO4; the lithium source is selected from one or more of LiNO3 and Li2CO3; the diphenylcarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid, and phthalic acid; and the solvent is selected from one or more of ethanol and water.

4. The preparation method according to claim 2, characterized in that, In S1, the mass ratio of the matrix to the mixed solution is 1:(6-13).

5. The preparation method according to claim 2, characterized in that, In S1, the heating reaction includes reacting the matrix and the mixed solution at 400-500℃ for 0.5-2h, cooling to room temperature, and then reacting at 250-400℃ for 1-3h under a protective gas atmosphere; the protective gas is selected from one or more of nitrogen and argon.

6. The preparation method according to claim 2, characterized in that, In S2, the mass ratio of the mixture, aniline, chloroform, and ferric chloride is 1:(0.001-0.06):(5-20):(0.001-0.18).

7. The preparation method according to claim 2, characterized in that, In step S2, the stirring speed is 300-500 r / min and the stirring time is 4-8 h; the centrifugation speed is 9000-13000 r / min and the centrifugation time is 3-5 min.

8. The application of the cathode material according to claim 1 or the cathode material prepared by any one of claims 2-7 in a lithium-ion battery.

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