Composite positive electrode flame-retardant additive and preparation method and application thereof

Abstract

The invention belongs to the technical field of flame-retardant materials, and discloses a composite positive electrode flame-retardant additive as well as a preparation method and application thereof. The composite positive electrode flame-retardant additive comprises a solid flame retardant and a conductive polymer layer coating the solid flame retardant. The surface of the solid flame retardant is coated with a layer of conductive polymer, and the conductive polymer layer can improve the conductivity of the positive plate, so that the rate capability of the positive plate is improved, meanwhile, the flame retardant is prevented from being in direct contact with a positive active material, and the adverse effect of the flame retardant on the electrochemical performance of the battery is reduced; the core flame retardant absorbs a large amount of heat and captures active oxygen released by the positive electrode material at the initial stage of thermal runaway of the battery, so that thermal runaway of the battery is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and in particular relates to a composite positive electrode flame retardant additive 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, environmental friendliness, and wide operating temperature range. However, the thermal runaway safety issues of lithium-ion batteries caused by overcharging, short circuits, and impacts have severely limited their commercialization.

[0003] At present, the methods to improve the safety of lithium-ion batteries include modification of electrolyte, surface treatment of diaphragm, modification of cathode, development of battery management system and application of flame retardant. The application of flame retardant is one of the simplest and most effective methods, which has been widely studied in recent years. Alkyl phosphates, such as trimethyl phosphate, triethyl phosphate and tributyl phosphate, are early flame retardants for lithium-ion batteries, with good flame retardant effect, but due to high viscosity and poor compatibility with electrode materials, the ionic conductivity of electrolyte is reduced and the cycle life of battery is shortened. When flame retardant is directly added to the battery, the adverse effect of flame retardant on the electrochemical performance of the battery is inevitable. In power batteries, mainly ternary materials and lithium iron phosphate, their electronic conductivity is low, resulting in poor rate performance, and in the process of high rate charge and discharge, due to the rapid migration of lithium ions, it is very easy to release more active oxygen on the surface of positive electrode materials, thereby inducing thermal runaway of the battery.

[0004] Therefore, it is necessary to develop a flame retardant additive that can improve the rate performance of the positive electrode material and achieve a flame retardant effect. 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 composite positive electrode flame retardant additive and a preparation method and application thereof. The composite positive electrode flame retardant additive of the present invention has both flame retardant effect and electronic conductivity. The composite positive electrode flame retardant additive of the present invention is applied to lithium-ion batteries, which can reduce the adverse effects of flame retardants on the electrochemical performance of batteries while ensuring the safety performance of batteries, and further improve the battery rate performance.

[0006] A first aspect of the present invention provides a composite positive electrode flame retardant additive.

[0007] Specifically, a composite positive electrode flame retardant additive includes a solid flame retardant and a conductive polymer layer coating the solid flame retardant.

[0008] Preferably, the conductive polymer layer accounts for 2-15% of the total weight of the composite positive electrode flame retardant additive, and more preferably 3-12%.

[0009] Preferably, the solid flame retardant accounts for 85-98% of the total weight of the composite positive electrode flame retardant additive, and more preferably 88-97%.

[0010] Preferably, the solid flame retardant includes at least one of ammonium polyphosphate (APP), melamine polyphosphate (MPP), calcium hypophosphite, aluminum hypophosphite, antimony trioxide, magnesium hydroxide, and aluminum hydroxide.

[0011] Preferably, the particle size of the solid flame retardant is 0.5-12 μm, more preferably 1-10 μm.

[0012] Preferably, the conductive polymer layer comprises at least one of polypyrrole, polyaniline or polythiophene.

[0013] Preferably, the general structural formula of the polypyrrole is:

[0014]

[0015] Wherein, R1 and R2 are independently selected from H, -COOH, -COOCH3, -C m H 2m+1 Saturated alkyl, 1 <m≤6;

[0016] R3 is selected from H, -CH3, -CH=CH2, -CH2CH2OOCC(CH3)=CH2(ethyl methacrylate);

[0017] 10≤n≤800.

[0018] Preferably, the general structural formula of the polyaniline is:

[0019]

[0020] Wherein, R4 is selected from H or -CH3;

[0021] R5 is selected from H, -CH3, -CH2CH3, -Cl, -OCH3;

[0022] 10≤n≤800.

[0023] Preferably, the general structural formula of the polythiophene is:

[0024]

[0025] R6, R7 are selected from H, -COOH, -COOCH3, -B(OH)2, -C m H2m+1 Saturated alkyl, 1 <m≤6;

[0026] 10≤n≤800.

[0027] A second aspect of the present invention provides a method for preparing a composite positive electrode flame retardant additive.

[0028] Specifically, a method for preparing a composite positive electrode flame retardant additive comprises the following steps:

[0029] (1) mixing a solid flame retardant with a solvent to obtain a suspension A;

[0030] (2) The oxidant is mixed with the acid solution to obtain a solution B, and then the monomer and the solution B are added to the suspension A for mixing and reacting to obtain the composite positive electrode flame retardant additive.

[0031] Preferably, in step (1), the solvent is selected from at least one of toluene, dichloromethane, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and N-methylpyrrolidone.

[0032] Preferably, in step (1), the mixing process is carried out by ultrasonic dispersion.

[0033] Preferably, in step (2), the oxidant is at least one of ammonium persulfate ((NH4)2S2O8), potassium dichromate (K2Cr2O7), ferric chloride (FeCl3), and hydrogen peroxide (H2O2).

[0034] Preferably, in step (2), the acid solution comprises at least one of hydrochloric acid, β-naphthalenesulfonic acid, dodecylbenzenesulfonic acid, and camphorsulfonic acid. The acid solution may be an aqueous solution of hydrochloric acid, β-naphthalenesulfonic acid, dodecylbenzenesulfonic acid, or camphorsulfonic acid. The role of the acid solution is to dope and modify the conductive polymer to improve the conductivity of the conductive polymer; conductive polymers such as polypyrrole, polyaniline, and polythiophene are inherently non-conductive.

[0035] Preferably, in step (2), the monomer is selected from at least one of pyrrole, aniline, thiophene and their derivatives.

[0036] Preferably, in step (2), the molar ratio of the oxidant to the monomer is (0.3-1.2):1, more preferably (0.5-1):1.

[0037] Preferably, in step (2), the mass of the monomer is 0.5-5.5% of the mass of the flame retardant, more preferably 1-5%.

[0038] Preferably, in step (2), the reaction is carried out in an ice-water bath for 4-8 hours, more preferably for 12-24 hours.

[0039] Preferably, in step (2), after the reaction is completed, the process of filtration, washing and drying is also included.

[0040] The third aspect of the present invention provides an application of a composite positive electrode flame retardant additive.

[0041] A battery comprises a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material and the composite positive electrode flame retardant additive.

[0042] Preferably, the positive electrode active material is selected from at least one of LiCoO2, LiFePO4, and NCM (nickel cobalt manganese material), and more preferably NCM811.

[0043] Preferably, in the positive electrode sheet, the mass ratio of the positive electrode active material to the composite positive electrode flame retardant additive is less than 92:5. That is, a sufficient amount of the composite positive electrode flame retardant additive needs to be added.

[0044] Preferably, the negative electrode sheet contains a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, silicon carbon, silicon oxygen, pure silicon, and lithium titanate, and more preferably graphite.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] The composite positive electrode flame retardant additive provided by the present invention comprises a core solid flame retardant and a conductive polymer coating layer. The core solid flame retardant absorbs a large amount of heat at the initial stage of thermal runaway of the battery, captures the active oxygen released by the positive electrode material, and thus prevents the battery from thermal runaway; the conductive polymer coated on the surface of the solid flame retardant has good electron conduction ability, which can not only improve the conductivity of the positive electrode sheet, but also further improve the rate performance of the positive electrode; at the same time, the flame retardant is blocked from direct contact with the positive electrode active material, reducing the adverse effects of the flame retardant on the electrochemical performance of the battery. DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] Example 1

[0050] A composite positive electrode flame retardant additive comprises a solid flame retardant and a conductive polymer layer covering the solid flame retardant. The conductive polymer layer comprises polypyrrole.

[0051] A method for preparing a composite positive electrode flame retardant additive comprises the following steps:

[0052] (1) adding 10 g of solid flame retardant (ammonium polyphosphate) into N-methylpyrrolidone (NMP) organic solvent and performing ultrasonic dispersion for 30 min to obtain suspension A;

[0053] (2) Dissolve 0.43 g of ammonium persulfate in 1 M (M represents mol / L) dodecylbenzene sulfonic acid solution to obtain solution B, then add 0.25 g of pyrrole monomer and solution B to the suspension A of step (1) and mix evenly, react in an ice water bath for 6 h, and after the reaction is completed, filter, wash, and dry to finally obtain a composite positive electrode flame retardant additive.

[0054] A preparation process of a soft pack battery comprises the following steps:

[0055] (1) NCM811(LiNi 0.8 Co 0.1 Mn 0.1 O2) the positive electrode active material, the composite positive electrode flame retardant additive prepared in this embodiment, the SP carbon black conductive agent, and the PVDF polyvinylidene fluoride binder are added to the NMP solvent in a mass ratio of 92:5:1.5:1.5, and are fully mixed to prepare a positive electrode slurry, and the solid content is controlled at 70%. The positive electrode slurry is evenly coated on an aluminum foil, and a positive electrode sheet is obtained through baking, rolling, slitting, and die-cutting processes;

[0056] (2) Add graphite negative electrode material, SP carbon black conductive agent, SBR styrene-butadiene rubber, and CMC sodium carboxymethyl cellulose into water in a mass ratio of 96:1.5:1:1.5, mix thoroughly and evenly to prepare negative electrode slurry, with the solid content controlled at 50%. Evenly coat the negative electrode slurry on copper foil, and obtain negative electrode sheets through baking, rolling, slitting, and die-cutting processes.

[0057] (3) The diaphragm is a commercial alumina ceramic diaphragm, and the electrolyte is 1M LiPF6 / EC (ethylene carbonate) + DEC (diethyl carbonate) + DMC (dimethyl carbonate) in a volume ratio of 1:1:1. The positive electrode sheet, electrolyte, diaphragm, and negative electrode sheet are stacked to form a soft-pack battery.

[0058] Example 2

[0059] A method for preparing a composite positive electrode flame retardant additive comprises the following steps:

[0060] (1) adding 10 g of solid flame retardant (ammonium polyphosphate) into N-methylpyrrolidone (NMP) organic solvent and performing ultrasonic dispersion for 30 min to obtain suspension A;

[0061] (2) Dissolve 0.17 g of ammonium persulfate in 1 M (M represents mol / L) dodecylbenzene sulfonic acid solution to obtain solution B, then add 0.1 g of pyrrole monomer and solution B to the suspension A of step (1) and mix evenly, react in an ice water bath for 6 h, and after the reaction is completed, filter, wash, and dry to finally obtain a composite positive electrode flame retardant additive.

[0062] The preparation process of the soft pack battery is the same as that in Example 1.

[0063] Example 3

[0064] A method for preparing a composite positive electrode flame retardant additive comprises the following steps:

[0065] (1) adding 10 g of solid flame retardant (ammonium polyphosphate) into N-methylpyrrolidone (NMP) organic solvent and performing ultrasonic dispersion for 30 min to obtain suspension A;

[0066] (2) Dissolve 0.85 g of ammonium persulfate in 1 M (M represents mol / L) dodecylbenzene sulfonic acid solution to obtain solution B, then add 0.5 g of pyrrole monomer and solution B to the suspension A of step (1) and mix evenly, react in an ice water bath for 6 h, and after the reaction is completed, filter, wash, and dry to finally obtain a composite positive electrode flame retardant additive.

[0067] The preparation process of the soft pack battery is the same as that in Example 1.

[0068] Example 4

[0069] Compared with Example 1, the only difference in Example 4 is that the composite positive electrode flame retardant additive, SP carbon black conductive agent, and PVDF polyvinylidene fluoride binder are added to the NMP solvent in a mass ratio of 87:10:1.5:1.5 and are fully mixed to prepare the positive electrode slurry. The rest of the process is exactly the same as in Example 1.

[0070] Comparative Example 1

[0071] Compared with Example 1, the difference between Comparative Example 1 and Example 1 is that an equal amount of ammonium polyphosphate is used to replace the composite positive electrode flame retardant additive in Example 1 to prepare a soft-pack battery. That is, in Comparative Example 1, no ammonium polyphosphate is coated.

[0072] Comparative Example 2

[0073] Compared with Example 1, the difference between Comparative Example 2 and Example 1 is that the composite positive electrode flame retardant additive is not used in the process of preparing the soft-pack battery.

[0074] Comparative Example 3

[0075] Compared with Example 1, the difference between Comparative Example 2 and Example 1 is that, in the preparation process of the composite positive electrode flame retardant additive, an equal amount of polyurea formaldehyde is used to replace the pyrrole in Example 1, and the rest of the process is exactly the same as that of Example 1.

[0076] Comparative Example 4

[0077] Compared with Example 1, the only difference of Comparative Example 4 is that the composite positive electrode flame retardant additive, SP carbon black conductive agent, and PVDF polyvinylidene fluoride binder are added to the NMP solvent in a mass ratio of 96:1:1.5:1.5 and are fully mixed to prepare a positive electrode slurry. The rest of the process is exactly the same as that of Example 1.

[0078] Product effect testing

[0079] The soft-pack batteries prepared in the above examples and comparative examples were subjected to the first coulombic efficiency, rate performance and needle puncture tests. The test methods are as follows. The test results are shown in Table 1:

[0080] First coulombic efficiency: The soft-pack battery is charged and discharged at a rate of 0.1C, with a voltage operating range of 2.75-4.2V. The first coulombic efficiency = first discharge capacity / first charge capacity × 100%;

[0081] Rate performance: At room temperature, the discharge performance of the soft-pack battery at rates of 0.1C, 0.5C, 1C, and 2C was tested respectively;

[0082] Needle puncture test: At 100% SOC (fully charged) state, use a high-temperature resistant steel needle (needle tip angle 60°, the needle surface is smooth, without rust, oxide layer and oil stains), at a speed of (25±5) mm / s, to penetrate the battery cell from a direction perpendicular to the battery cell, and the needle stays in the battery cell; observe for 1 hour to monitor whether the battery cell catches fire or explodes.

[0083] Table 1

[0084]

[0085] It can be seen from Table 1 that the composite positive electrode flame retardant additive prepared in the embodiment of the present invention is applied in a battery, which not only significantly improves the safety of the battery, but also significantly improves the electrochemical performance of the battery.

Claims

1. A composite positive electrode flame retardant additive, characterized in that: The invention comprises a solid flame retardant and a conductive polymer layer covering the solid flame retardant.

2. The composite positive electrode flame retardant additive according to claim 1, characterized in that: The conductive polymer layer accounts for 2-15% of the total weight of the composite positive electrode flame retardant additive.

3. The composite positive electrode flame retardant additive according to claim 1, characterized in that: The solid flame retardant accounts for 85-98% of the total weight of the composite positive electrode flame retardant additive.

4. The composite positive electrode flame retardant additive according to claim 1, characterized in that: The solid flame retardant includes at least one of ammonium polyphosphate, melamine polyphosphate, calcium hypophosphite, aluminum hypophosphite, antimony trioxide, magnesium hydroxide, and aluminum hydroxide.

5. The composite positive electrode flame retardant additive according to claim 1, characterized in that: The conductive polymer layer comprises at least one of polypyrrole, polyaniline or polythiophene.

6. The composite positive electrode flame retardant additive according to claim 5, characterized in that: The general structural formula of the polypyrrole is: Wherein, R1 and R2 are independently selected from H, -COOH, -COOCH3, -C m H 2m+1 Saturated alkyl, 1 <m≤6; R3 is selected from H, -CH3, -CH=CH2, -CH2CH2OOCC(CH3)=CH2(ethyl methacrylate); 10≤n≤800； And / or, the general structural formula of the polyaniline is: Wherein, R4 is selected from H or -CH3; R5 is selected from H, -CH3, -CH2CH3, -Cl, -OCH3; 10≤n≤800； And / or, the general structural formula of the polythiophene is: R6, R7 are selected from H, -COOH, -COOCH3, -B(OH)2, -C m H 2m+1 Saturated alkyl, 1 <m≤6; 10≤n≤800。 7. The method for preparing the composite positive electrode flame retardant additive according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) mixing a solid flame retardant with a solvent to obtain a suspension A; (2) The oxidant is mixed with the acid solution to obtain a solution B, and then the monomer and the solution B are added to the suspension A for mixing and reacting to obtain the composite positive electrode flame retardant additive.

8. The preparation method according to claim 7, characterized in that: The oxidant is at least one of ammonium persulfate, potassium dichromate, ferric chloride, and hydrogen peroxide; and / or the acid solution includes at least one of hydrochloric acid, β-naphthalenesulfonic acid, dodecylbenzenesulfonic acid, and camphorsulfonic acid; and / or the monomer is selected from at least one of pyrrole, aniline, thiophene, and derivatives thereof.

9. The preparation method according to claim 7, characterized in that: The molar ratio of the oxidant to the monomer is (0.3-1.2):1; and / or, the mass of the monomer is 0.5-5.5% of the mass of the flame retardant; and / or, the reaction is carried out in an ice-water bath environment for 4-8 hours.

10. A 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 a positive electrode active material and the composite positive electrode flame retardant additive according to any one of claims 1 to 6.

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