Coated composite positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and discloses a coated composite positive electrode material as well as a preparation method and application thereof. The coated composite positive electrode material comprises a positive electrode active material and a coating layer coating the positive electrode active material, and the coating layer comprises a polymer containing a conductive electron chain segment and a flame retardant chain segment. The coated composite positive electrode material inhibits the interface reaction between a positive electrode active material and an electrolyte, so that the cycling stability of a battery is improved, and the interface problem between a positive electrode and an electrolyte layer is relieved; and a conductive electron chain segment and a flame retardant chain segment are introduced into the polymer of the coating layer, so that the rate capability, the thermal stability and the safety performance of the positive electrode active material can be obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a coated composite positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic products, electric vehicles, aerospace, and energy storage systems due to their high energy density, good cycle stability, green environmental protection, and wide operating temperature range. As a key component of lithium-ion batteries, positive electrode materials play an important role in determining the energy density, safety, and cycle life of lithium-ion batteries. Currently, high-nickel materials are one of the most promising positive electrode materials for high-energy-density lithium-ion batteries. However, high-nickel materials generally have problems such as poor structural stability and electrochemical stability, which also hinders their commercialization in the field of lithium-ion batteries.

[0003] During the charge and discharge process, the crystal structure of high-nickel materials repeatedly undergoes a structural transformation from the original layered (R3m) structure to the disordered spinel (Fd3m) structure, and then transforms into an inactive rock salt (Fm3m) structure during the cycle, which eventually leads to structural collapse and capacity attenuation during the cycle, and poor rate performance. 4+ It is in a highly oxidized state and is prone to side reactions at the electrode-electrolyte interface under charged conditions, leading to transition metal dissolution, electrolyte consumption, and the formation of a non-passivation film at the interface layer, which enhances the kinetic barrier to lithium ion diffusion and reduces battery cycle performance.

[0004] Therefore, it is necessary to develop a safe positive electrode material that not only has good rate performance and cycle performance, but also has good thermal stability. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a coated composite positive electrode material and a preparation method and application thereof. The coated composite positive electrode material of the present invention comprises a positive electrode active material and a coating layer coating the positive electrode active material, wherein the coating layer comprises a polymer containing a conductive electronic segment and a flame retardant segment.

[0006] The coated composite positive electrode material of the present invention inhibits the interfacial reaction between the positive electrode active material and the electrolyte, thereby improving the cycle stability of the battery and alleviating the interface problem between the positive electrode and the electrolyte layer; the introduction of conductive electronic segments and flame retardant segments into the polymer of the coating layer can significantly improve the rate performance, thermal stability and safety performance of the positive electrode active material.

[0007] A first aspect of the present invention provides a coated composite positive electrode material.

[0008] Specifically, a coated composite positive electrode material includes a positive electrode active material and a coating layer coating the positive electrode active material, wherein the coating layer is composed of a polymer containing a conductive electronic segment and a flame retardant segment.

[0009] Preferably, the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary positive electrode material (NCM) and a lithium-nickel-cobalt-aluminum material (NCA).

[0010] Preferably, the nickel-cobalt-manganese ternary positive electrode material includes NCM811, whose chemical formula is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0011] Preferably, the lithium nickel cobalt aluminum material (NCA) comprises LiNi 0.8 Co 0.15 Al 0.05 O2.

[0012] Preferably, the particle size of the positive electrode active material is 2-15 μm, more preferably 5-12 μm.

[0013] Preferably, the structural formula of the polymer is

[0014] Wherein, R1 is selected from H or -CH3 alkyl;

[0015] R2 is selected from H, -CH3, -CH2CH3, -Cl, -OCH3;

[0016] The value range of n is 10-1000.

[0017] A second aspect of the present invention provides a method for preparing a coated composite positive electrode material.

[0018] Specifically, a method for preparing a coated composite positive electrode material comprises the following steps:

[0019] (1) mixing and dispersing the positive electrode active material with an organic solvent to obtain a suspension A;

[0020] (2) mixing an oxidant with an acid solution to obtain a solution B, and mixing the aniline substance and the solution B with the suspension A to obtain a mixture C;

[0021] (3) adding a flame retardant and polyformaldehyde to the mixture C for reaction to obtain the coated composite positive electrode material. Preferably, in step (1), the organic solvent comprises at least one of N,N-dimethylformamide, N-methylpyrrolidone, toluene, dichloromethane, tetrahydrofuran, and acetonitrile.

[0022] Preferably, in step (1), the mixing and dispersing is carried out by ultrasonic mixing and dispersing for 20-40 minutes, for example, 20 minutes, 30 minutes, or 40 minutes.

[0023] Preferably, in step (2), the acid solution comprises hydrochloric acid.

[0024] Preferably, in step (2), the oxidant comprises ammonium persulfate.

[0025] Preferably, in step (2), the aniline substance is selected from any one of the following:

[0026]

[0027] Preferably, in step (2), the molar ratio of the oxidant to the aniline substance is (0.3-1.2):1, more preferably (0.5-1):1.

[0028] Preferably, in step (2), the mass of the aniline substance is 3-15% of the mass of the positive electrode active material, and more preferably 5-15%.

[0029] Preferably, in step (2), the aniline substance and the B solution are mixed and stirred with the suspension A in an ice-water bath for 1-3 hours (eg, 2 hours) to obtain a mixture C.

[0030] Preferably, in step (3), the flame retardant comprises 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO).

[0031] The structural formula of DOPO is

[0032] The structural formula of paraformaldehyde is Where m is 1 or 2.

[0033] Preferably, in step (3), the molar ratio of the flame retardant to the aniline substance is (1-3.5):1, and more preferably (1-3):1.

[0034] Preferably, in step (3), the molar ratio of the paraformaldehyde to the flame retardant is (0.4-1.2):1, more preferably (0.5-1):1.

[0035] Preferably, in step (3), the reaction temperature is 50-80°C, and the reaction time is 4-8 hours. More preferably, the reaction temperature is 60-80°C, and the reaction time is 6-8 hours.

[0036] Preferably, in step (3), after the reaction is completed, suction filtration, methanol washing and drying are performed to obtain the coated composite positive electrode material.

[0037] The third aspect of the present invention provides an application of a coated composite positive electrode material.

[0038] A lithium-ion battery comprises a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the positive electrode sheet comprises the above-mentioned coated composite positive electrode material.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The coated composite positive electrode material of the present invention comprises a positive electrode active material and a coating layer coating the positive electrode active material, wherein the coating layer comprises a polymer containing a conductive electronic segment and a flame retardant segment.

[0041] The coated composite positive electrode material of the present invention inhibits the interfacial reaction between the positive electrode active material and the electrolyte, thereby improving the cycle stability of the battery and alleviating the interface problem between the positive electrode and the electrolyte layer; the introduction of conductive electronic segments and flame retardant segments into the polymer of the coating layer can significantly improve the rate performance, thermal stability and safety performance of the positive electrode active material. DETAILED DESCRIPTION

[0042] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0043] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0044] Example 1

[0045] A coated composite positive electrode material comprises a positive electrode active material and a coating layer coating the positive electrode active material, wherein the coating layer comprises a polymer containing a conductive electronic segment and a flame retardant segment.

[0046] A method for preparing a coated composite positive electrode material comprises the following steps:

[0047] (1) 100 g of positive electrode active material (NCM811) was added to N,N-dimethylformamide (DMF) and ultrasonically dispersed for 30 min to obtain suspension A;

[0048] (2) dissolving 12.25 g of ammonium persulfate in a 1 mol / L HCl solution to obtain a solution B, then adding 10 g of aniline and the solution B to the suspension A of step (1), mixing evenly, and mechanically stirring in an ice-water bath for 2 h to obtain a mixture C;

[0049] (3) Add 23.19 g of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and 3.22 g of polyformaldehyde to the mixture C in step (2), and carry out mechanical stirring reaction at 60° C. for 6 h. After the reaction, filter, wash with methanol, and dry to finally obtain a coated composite positive electrode material.

[0050] The preparation process of the coated composite positive electrode materials corresponding to Examples 2-3 and Comparative Examples 1-5 is the same as that of Example 1, except that the amount of raw materials used is different. The amount of raw materials used corresponding to Examples 1-3 and Comparative Examples 1-5 is shown in Table 1.

[0051] Table 1

[0052] NCM811(g) Aniline(g) Ammonium persulfate(g) DOPO(g) Paraformaldehyde(g) Example 1 100 10 12.25 23.19 3.22 Example 2 100 5 6.13 23.19 1.61 Example 3 100 15 18.38 104.37 14.50 Comparative Example 1 100 10 12.25 23.19 / Comparative Example 2 100 10 12.25 / 3.22 Comparative Example 3 100 / / 23.19 / Comparative Example 4 100 / / / 3.22 Comparative Example 5 100 10 12.25 / /

[0053] Example 4

[0054] Compared with Example 1, the only difference of Example 4 is that the reaction temperature in step (3) is 80° C., and the rest of the process is the same as Example 1.

[0055] Comparative Example 6

[0056] The comparative example is 100 g of NCM811 without any treatment.

[0057] Comparative Example 7

[0058] Compared with Example 1, Comparative Example 7 uses an equal amount of ammonia monohydrate to replace the aniline in Example 1, and the other processes are the same as those in Example 1.

[0059] Comparative Example 8

[0060] Compared with Example 1, Comparative Example 8 uses an equal amount of trimethyl phosphate (TMP) organic flame retardant to replace DOPO in Example 1, and the other processes are the same as those in Example 1.

[0061] Product effect testing

[0062] The coated composite positive electrode materials obtained in the above examples and comparative examples were assembled into lithium-ion batteries according to the following methods.

[0063] The assembly process of lithium-ion batteries is as follows:

[0064] Preparation of positive electrode sheet: Add the coated composite positive electrode material, SP (conductive carbon black), CNTs (carbon nanotubes), and PVDF (polyvinylidene fluoride) in a mass ratio of 96:1.5:0.5:2 into the solvent (DMF), mix thoroughly and evenly to prepare the positive electrode slurry, and control the solid content at 70%. Evenly coat the positive electrode slurry on aluminum foil, and obtain the positive electrode sheet through baking, rolling, slitting, and die-cutting processes.

[0065] Preparation of negative electrode sheet: Add graphite negative electrode material, SP, SBR (styrene butadiene rubber), and CMC (carboxymethyl cellulose) in a mass ratio of 96:1.5:1:1.5 into a solvent (DMF), mix thoroughly and evenly to prepare negative electrode slurry, and control the solid content at 50%. Evenly coat the negative electrode slurry on copper foil, and obtain the negative electrode sheet through baking, rolling, slitting, and die-cutting processes.

[0066] The diaphragm is an alumina coated ceramic diaphragm, and the electrolyte is 1 mol / L LiPF6 / EC (ethylene carbonate) + DEC (diethyl carbonate) + DMC (dimethyl carbonate) in a volume ratio of 1:1:1. The positive electrode sheet, diaphragm, and negative electrode sheet are stacked to form a soft-pack lithium-ion battery.

[0067] The performance of the lithium-ion battery was tested, and the results are shown in Table 2. The test method is as follows:

[0068] First coulombic efficiency: The lithium-ion battery is charged and discharged at a rate of 0.1C. The first coulombic efficiency = first discharge capacity / first charge capacity × 100%;

[0069] Cycle life: At room temperature, the lithium-ion battery is charged and discharged at 0.3C. The life ends when the discharge capacity is less than 80% of the initial discharge capacity.

[0070] 150℃ hot box test: At 100% SOC (fully charged), the hot box is heated from ambient temperature to 150℃±2℃ at a rate of 5℃ / min, and this temperature is maintained for 30 minutes before stopping heating. The battery is observed for 1 hour to monitor whether it catches fire or explodes.

[0071] Table 2

[0072]

[0073]

[0074] It can be seen from Table 2 that the coated composite positive electrode materials corresponding to Examples 1-4 of the present invention have higher first coulombic efficiency than those of Comparative Examples 1-8. The coated composite positive electrode materials corresponding to Examples 1-4 simultaneously meet good cycle performance, rate performance and thermal stability, and are safer.

Claims

1. A coated composite positive electrode material, characterized in that: The invention comprises a positive electrode active material and a coating layer covering the positive electrode active material, wherein the coating layer comprises a polymer containing a conductive electronic segment and a flame retardant segment.

2. The coated composite positive electrode material according to claim 1, characterized in that: The positive electrode active material includes at least one of a nickel-cobalt-manganese ternary positive electrode material and a lithium-nickel-cobalt-aluminum material.

3. The coated composite positive electrode material according to claim 1, characterized in that: The particle size of the positive electrode active material is 2-15 μm.

4. The coated composite positive electrode material according to claim 1, characterized in that: The structural formula of the polymer is Wherein, R1 is selected from H or -CH3 alkyl; R2 is selected from H, -CH3, -CH2CH3, -Cl, -OCH3; and the value range of n is 10-1000.

5. The method for preparing the coated composite positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) mixing and dispersing the positive electrode active material with an organic solvent to obtain a suspension A; (2) mixing an oxidant with an acid solution to obtain a solution B, and mixing the aniline substance and the solution B with the suspension A to obtain a mixture C; (3) Adding a flame retardant and polyformaldehyde to the mixture C to react, thereby obtaining the coated composite positive electrode material.

6. The preparation method according to claim 5, characterized in that: In step (2), the acid solution includes hydrochloric acid; and / or, in step (2), the oxidant includes ammonium persulfate.

7. The preparation method according to claim 5, characterized in that: In step (2), the aniline substance is selected from any one of the following:

8. The preparation method according to claim 5, characterized in that: In step (2), the molar ratio of the oxidant to the aniline substance is (0.3-1.2):1; and / or the mass of the aniline substance is 3-15% of the mass of the positive electrode active material.

9. The preparation method according to claim 5, characterized in that: In step (3), the flame retardant includes 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; and / or the molar ratio of the flame retardant to the aniline substance is (1-3.5):1; and / or the molar ratio of the polyformaldehyde to the flame retardant is (0.4-1.2):1; and / or the reaction temperature is 50-80°C and the reaction time is 4-8 hours.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the positive electrode sheet comprises the coated composite positive electrode material according to any one of claims 1 to 4.

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