Polydopamine-coated composite positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a polydopamine-coated composite positive electrode material as well as a preparation method and application thereof. The invention provides a preparation method of a polydopamine-coated composite positive electrode material, and the preparation method comprises the following steps: (1) preparing an MXene composite positive electrode material which comprises an MXene sheet layer and a lithium iron phosphate layer; the MXene sheet layer is embedded into a gap between the lithium iron phosphate layers; (2) carrying out heat treatment on the MXene composite positive electrode material, mixing a product obtained after heat treatment with a dopamine solution, and drying to obtain a polydopamine coated composite positive electrode material; the polydopamine coated composite positive electrode material comprises a polydopamine layer and an MXene composite positive electrode material, the MXene composite positive electrode material is coated with the polydopamine layer. The polydopamine-coated composite positive electrode material prepared by the invention has excellent capacity, rate capability, cycle performance, low-temperature performance and safety.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a polydopamine-coated composite cathode material, its preparation method, and its application. Background Technology

[0002] Traditional lithium iron phosphate (LFP) cathode materials have low intrinsic conductivity. During lithium-ion insertion / extraction, volume changes easily occur within the material, leading to structural collapse and reduced cycle life. LFP and the electrolyte are prone to side reactions at high voltages (such as electrolyte oxidation and decomposition), forming an unstable SEI film, increasing internal resistance and reducing cycle performance. Existing technologies improve conductivity through carbon coating, but the carbon layer can reduce the utilization rate of active materials, thus decreasing the battery's energy density and cycle performance. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the defects of poor conductivity and low cycle performance of lithium iron phosphate cathode materials in the prior art, thereby providing a polydopamine-coated composite cathode material, its preparation method and application.

[0004] Therefore, this application provides the following technical solution.

[0005] This application provides a method for preparing a polydopamine-coated composite cathode material, comprising the following steps:

[0006] (1) An MXene composite cathode material is prepared by at least one of the following methods (A) and (B), wherein the MXene composite cathode material comprises an MXene sheet and a lithium iron phosphate layer; the MXene sheet is embedded in the interlayer voids of the lithium iron phosphate layer;

[0007] (A) Mix MXene and lithium iron phosphate, and spray dry to obtain MXene composite cathode material;

[0008] (B) Mix MXene, iron source, lithium source and phosphorus source, and perform hydrothermal reaction to obtain MXene composite cathode material;

[0009] (2) The MXene composite cathode material was heat-treated, and the heat-treated product was mixed with dopamine solution and dried to obtain polydopamine-coated composite cathode material.

[0010] The polydopamine-coated composite cathode material comprises a polydopamine layer and an MXene composite cathode material; the polydopamine layer coats the MXene composite cathode material. MXene is a class of two-dimensional inorganic compounds in materials science that exhibits high metallic conductivity.

[0011] In one alternative embodiment, the thickness of the polydopamine layer is 2-5 nm.

[0012] In one optional embodiment, in step (A), the lithium iron phosphate has a particle size of 100-500 nm.

[0013] In one optional implementation, in step (A), the mass ratio of MXene to lithium iron phosphate is (1-10):(90-99);

[0014] The spray drying can be carried out using conventional methods in the art, and this application does not impose any limitations; as an example, the inlet temperature of the spray dryer is 200°C and the outlet temperature is 80°C.

[0015] In an optional implementation, in step (B), the ratio of the mass of MXene to the molar amount of iron in the iron source is (5-10):(0.1-0.2), where the mass of MXene is in g and the molar amount of iron source is in mol.

[0016] In an optional embodiment, in step (B), the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is (0.1-0.2):(0.12-0.24):(0.1-0.2).

[0017] In one optional embodiment, in step (B), the lithium source includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide;

[0018] In one optional embodiment, in step (B), the iron source includes at least one of ferrous oxalate, ferric nitrate, ferric sulfate, ferric phosphate, and ferric oxide.

[0019] In one alternative embodiment, in step (B), the phosphorus source includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and phosphoric acid.

[0020] In one optional embodiment, the temperature of the hydrothermal reaction is 180-220°C;

[0021] In one alternative embodiment, the hydrothermal reaction takes 12-24 hours.

[0022] In one alternative embodiment, the heat treatment is performed under an inert atmosphere;

[0023] In one optional embodiment, the heat treatment temperature is 500-600°C;

[0024] In one optional embodiment, the heat treatment time is 2-4 hours;

[0025] In one alternative implementation, the mixing time is 24-48 hours.

[0026] In one optional implementation, step (2) includes drying parameters including vacuum drying at 60-80°C for 6-12 hours.

[0027] In one alternative implementation, the MXene comprises Ti3C2T x Ti3N2T x and Ti3CNT x At least one of them; with Ti3C2T x For example, Ti3C2T x The T in the text represents the part replaced by -F or -OH. There is no special limitation on the subscript x, which is a common expression in this field.

[0028] In one optional embodiment, the preparation steps of MXene include: mixing aluminum titanium carbide and / or aluminum titanium nitride with a fluorine-containing acidic solution, reacting to obtain a reaction solution; washing the reaction solution by centrifugation until pH > 6, taking the solid phase, and obtaining MXene.

[0029] The fluorinated acidic solution includes common fluorinated inorganic acids in the art, such as hydrofluoric acid, and also includes solutions prepared by mixing fluorides and acidic solutions.

[0030] In one alternative embodiment, when MXene is formed into an MXene composite cathode material, the MXene is added in the form of an MXene dispersion;

[0031] Preferably, the preparation steps of the MXene dispersion include: mixing MXene with water, sonicating at 300-500W for 2-4 hours, and centrifuging at 1000-3000r / min for 10-30 minutes to obtain the MXene dispersion.

[0032] In an optional embodiment, the MXene preparation step further satisfies at least one of the following (a)-(c):

[0033] (a) The ratio of the total mass of the aluminum titanium carbide and / or aluminum titanium nitride to the volume of the fluorinated acidic solution is (10-20):(100-200), and the concentration of the fluorinated acidic solution is 40-50 wt%; wherein, the unit of the total mass of the aluminum titanium carbide and / or aluminum titanium nitride is g, and the unit of the volume of the fluorinated acidic solution is mL;

[0034] (b) The reaction conditions are: stirring at 300-500 r / min for 24-48 h;

[0035] (c) The first centrifugation rate is 3000-5000 r / min.

[0036] This application also provides a polydopamine-coated composite cathode material prepared by the above preparation method.

[0037] This application also provides an application of the polydopamine-coated composite cathode material prepared by the above method in lithium-ion batteries.

[0038] The technical solution of this application has the following advantages:

[0039] 1. The preparation method of the polydopamine-coated composite cathode material provided in this application includes the following steps:

[0040] (1) An MXene composite cathode material is prepared by at least one of the following methods (A) and (B), wherein the MXene composite cathode material comprises an MXene sheet and a lithium iron phosphate layer; the MXene sheet is embedded in the interlayer voids of the lithium iron phosphate layer; (A) MXene and lithium iron phosphate are mixed and spray-dried to obtain the MXene composite cathode material; (B) MXene, an iron source, a lithium source and a phosphorus source are mixed and hydrothermally reacted to obtain the MXene composite cathode material; (2) The MXene composite cathode material is heat-treated, and the heat-treated product is mixed with a dopamine solution and dried to obtain a polydopamine-coated composite cathode material; the polydopamine-coated composite cathode material comprises a polydopamine layer and an MXene composite cathode material; the polydopamine layer coats the MXene composite cathode material.

[0041] The polydopamine-coated composite cathode material prepared in this application has excellent capacity, first-efficiency, and cycle performance.

[0042] MXene sheets are embedded between the layers of the cathode material, forming a three-dimensional conductive network through the conjugated structure of MXene. This improves the transport efficiency of ions and electrons and reduces electrode polarization. It also increases the interlayer spacing, reducing the path resistance for lithium-ion diffusion. The embedding of MXene sheets between the layers of the cathode material can also effectively suppress structural distortion of the cathode material, improve the mechanical strength of the composite cathode material, and thus enhance the bonding force between cathode material particles, thereby improving cycle performance. The two-dimensional layered structure of MXene sheets can also buffer the stress of lithium-ion insertion and extraction, reduce material pulverization, suppress volume expansion, and improve the cycle performance of the battery.

[0043] The functional groups (such as -O, -OH, etc.) on the surface of MXene have good chemical compatibility with the electrolyte, which can reduce the generation of interfacial side reactions, optimize interfacial stability, and improve high-voltage stability. The high specific surface area and intercalation characteristics of MXene construct ion transport channels, enabling lithium ions to have good diffusion kinetics at low temperatures, thereby improving the low-temperature performance of the battery.

[0044] The catechol and amino groups in the polydopamine coating are covalently bonded to the functional groups on the MXene surface, further enhancing the surface adhesion. The porous structure of the polydopamine coating can improve ion transport pathways, providing capacity and energy density. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1 This is a capacity retention diagram of Example 1, Comparative Example 1, and Comparative Example 2 of this application. Detailed Implementation

[0047] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] Example 1

[0050] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0051] (1) Mix 100g of aluminum titanium carbide with 1000ml of hydrofluoric acid (concentration of 40wt%) and stir magnetically at 300r / min for 24h to obtain a reaction solution; wash the reaction solution by centrifugation at 3000r / min until pH>6, and take the solid phase to obtain Ti3C2T. x .

[0052] (2) Take 10g of Ti3C2T xMixed with 90g of lithium iron phosphate cathode material (particle size 100nm), spray dried (inlet temperature 200℃, outlet temperature 80℃) to obtain MXene composite cathode material; heat-treated at 500℃ for 2h under argon atmosphere, immersed in dopamine-Tris buffer (pH=8.5) and stirred for 24h, centrifuged and dried to obtain polydopamine-coated composite cathode material with a polydopamine layer thickness of 3nm.

[0053] Example 2

[0054] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0055] (1) Mix 100g of aluminum titanium carbide with 2000ml of hydrofluoric acid (concentration of 50wt%) and stir magnetically at 500r / min for 48h to obtain a reaction solution; wash the reaction solution by centrifugation at 5000r / min until pH>6, and take the solid phase to obtain Ti3C2T x Take 10g of Ti3C2T x Mix with 200 ml of deionized water, sonicate at 300 W for 2 h, and centrifuge at 1000 r / min for 30 min to obtain MXene dispersion.

[0056] (2) The MXene dispersion obtained in step (1) was mixed with 99g of lithium iron phosphate cathode material (particle size of 500nm), and spray-dried (inlet temperature of 200℃ and outlet temperature of 80℃) to obtain MXene composite cathode material; under argon atmosphere, it was heat-treated at 600℃ for 4h, immersed in dopamine-Tris buffer (pH=8.5) and stirred for 48h, and centrifuged and dried to obtain polydopamine-coated composite cathode material with a polydopamine layer thickness of 5nm.

[0057] Example 3

[0058] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0059] (1) Mix 100g of aluminum titanium carbide with 1000ml of hydrofluoric acid (concentration of 40wt%) and stir magnetically at 300r / min for 24h to obtain a reaction solution; wash the reaction solution by centrifugation at 3000r / min until pH>6, and take the solid phase to obtain Ti3C2T. x .

[0060] (2) 5g Ti3C2T x0.1 mol FePO4·2H2O, 0.12 mol LiOH·H2O, and 0.1 mol NH4H4PO4 were mixed and transferred to a high-pressure reactor. The mixture was hydrothermally reacted at 180℃ for 12 h. After centrifugation, washing, and drying, MXene composite cathode material was obtained. Under an argon atmosphere, the mixture was heat-treated at 500℃ for 2 h, then immersed in dopamine-Tris buffer (pH = 8.5) and stirred for 24 h. After centrifugation and drying, polydopamine-coated composite cathode material was obtained. The thickness of the polydopamine layer was 3 nm.

[0061] Example 4

[0062] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0063] (1) Mix 100g of aluminum titanium carbide with 2000ml of hydrofluoric acid (concentration of 50wt%) and stir magnetically at 500r / min for 48h to obtain a reaction solution; wash the reaction solution by centrifugation at 5000r / min until pH>6, and take the solid phase to obtain Ti3C2T x Take 10g of Ti3C2T x Mix with 200 ml of deionized water, sonicate at 500 W for 4 h, and centrifuge at 3000 r / min for 10 min to obtain MXene dispersion.

[0064] (2) The MXene dispersion obtained in step (1), 0.1 mol Fe(NO3)3, 0.24 mol CH3COOLi, and 0.2 mol H3PO4 were mixed and transferred to a high-pressure reactor. The mixture was hydrothermally reacted at 220℃ for 24 h. After centrifugation, washing, and drying, the MXene composite cathode material was obtained. Under an argon atmosphere, the mixture was heat-treated at 600℃ for 4 h, immersed in dopamine-Tris buffer (pH=8.5) and stirred for 48 h. After centrifugation and drying, the polydopamine-coated composite cathode material was obtained. The thickness of the polydopamine layer was 4 nm.

[0065] Example 5

[0066] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0067] (1) A fluorinated acidic solution with a concentration of 40 wt% was prepared by mixing NaF and HCl. 200 g of aluminum titanium nitride was mixed with 1000 ml of the fluorinated acidic solution and the mixture was magnetically stirred at 400 r / min for 36 h to obtain a reaction solution. The reaction solution was centrifuged at 4000 r / min for the first time and washed until the pH was > 6. The solid phase was then collected to obtain Ti3N2T. x .

[0068] (2) 1g Ti3N2T xMixed with 90g of lithium iron phosphate cathode material (particle size 300nm), spray dried (inlet temperature 200℃, outlet temperature 80℃) to obtain MXene composite cathode material; heat-treated at 550℃ for 2h under argon atmosphere, immersed in dopamine-Tris buffer (pH=8.5) and stirred for 36h, centrifuged and dried to obtain polydopamine-coated composite cathode material with a polydopamine layer thickness of 3.5nm.

[0069] Example 6

[0070] This embodiment provides a method for preparing a polydopamine-coated composite cathode material, including the following steps:

[0071] (1) A fluorinated acidic solution with a concentration of 45 wt% was prepared by mixing NaF and HCl. 200 g of aluminum titanium nitride was mixed with 1500 ml of the fluorinated acidic solution and the mixture was magnetically stirred at 300 r / min for 24 h to obtain a reaction solution. The reaction solution was centrifuged at 3000 r / min for the first time and washed until the pH was > 6. The solid phase was then collected to obtain Ti3C2T. x .

[0072] (2) 5g Ti3C2T x 0.1 mol FePO4·2H2O, 0.2 mol LiOH·H2O, and 0.05 mol NH4H4PO4 were mixed and transferred to a high-pressure reactor. The mixture was hydrothermally reacted at 200℃ for 18 h. After centrifugation, washing, and drying, MXene composite cathode material was obtained. Under an argon atmosphere, the mixture was heat-treated at 500℃ for 3 h, then immersed in dopamine-Tris buffer (pH = 8.5) and stirred for 24 h. After centrifugation and drying, polydopamine-coated composite cathode material was obtained. The thickness of the polydopamine layer was 2.5 nm.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing an MXene composite cathode material. The only difference from Example 1 is that it is not immersed in dopamine-Tris buffer.

[0075] Comparative Example 2

[0076] This comparative example provides a commercially available lithium iron phosphate cathode material.

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing polydopamine-coated lithium iron phosphate, comprising the following steps:

[0079] 90g of lithium iron phosphate cathode material was immersed in dopamine-Tris buffer (pH=8.5) and stirred for 24h, then centrifuged and dried to obtain polydopamine-coated lithium iron phosphate cathode material.

[0080] Test case

[0081] The performance of the cathode materials prepared in the above embodiments and comparative examples was tested, as follows:

[0082] A slurry of positive electrode material, polyvinylidene fluoride, and conductive carbon black was prepared at a mass ratio of 95:3:2. Aluminum foil was then laid flat on a coating machine for coating (area density of 13.3-13.5 mg / cm³). 2 The compacted density is 3.4-3.6 g / cm³. 3 The material is placed in an 80°C forced-air drying oven for 3 hours; then it is drilled, weighed, and the electrode sheets are baked to form a button cell. The positive electrode material is selected from the various embodiments and comparative examples.

[0083] The specific test method for electrochemical performance is to place the coin cell into the Blue Electric test system for electrochemical performance testing at room temperature. The test voltage range is 2.5-4.25V. The battery's 0.2C discharge specific capacity, initial efficiency, capacity retention rate after 50 cycles at 1C, and capacity retention rate after 50 cycles at 5C are measured. The results are shown in Table 1.

[0084] First-cycle efficiency = First-cycle discharge capacity (0.2C) / First-cycle charge capacity (0.2C) × 100%

[0085] The capacity retention rates of batteries formed from the cathode materials prepared in each embodiment and comparative example are plotted at various cycle counts within 50 cycles at 1C. See [link / reference]. Figure 1 .

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, the polydopamine-coated composite cathode material prepared in this application has excellent capacity, first-efficiency and cycle performance.

[0089] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for preparing a polydopamine-coated composite cathode material, characterized in that, Includes the following steps: (1) An MXene composite cathode material is prepared by at least one of the following methods (A) and (B), wherein the MXene composite cathode material comprises an MXene sheet and a lithium iron phosphate layer; the MXene sheet is embedded in the interlayer voids of the lithium iron phosphate layer; (A) Mix MXene and lithium iron phosphate, and spray dry to obtain MXene composite cathode material; (B) Mix MXene, iron source, lithium source and phosphorus source, and perform hydrothermal reaction to obtain MXene composite cathode material; (2) The MXene composite cathode material was heat-treated, and the heat-treated product was mixed with dopamine solution and dried to obtain polydopamine-coated composite cathode material. The polydopamine-coated composite cathode material includes a polydopamine layer and an MXene composite cathode material; the polydopamine layer coats the MXene composite cathode material.

2. The preparation method according to claim 1, characterized in that, The thickness of the polydopamine layer is 2-5 nm.

3. The preparation method according to claim 1 or 2, characterized in that, In step (A), the lithium iron phosphate has a particle size of 100-500 nm; and / or, In step (A), the mass ratio of MXene to lithium iron phosphate is (1-10):(90-99); and / or, In step (B), the ratio of the mass of MXene to the molar amount of iron in the iron source is (5-10):(0.1-0.2), where the mass of MXene is in grams and the molar amount of the iron source is in mol; and / or, In step (B), the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is (0.1-0.2):(0.12-0.24):(0.1-0.2); and / or, In step (B), the lithium source includes at least one selected from lithium carbonate, lithium acetate, and lithium hydroxide; and / or, In step (B), the iron source includes at least one of ferrous oxalate, ferric nitrate, ferric sulfate, ferric phosphate, and ferric oxide; and / or, In step (B), the phosphorus source includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and phosphoric acid.

4. The preparation method according to any one of claims 1-3, characterized in that, The hydrothermal reaction temperature is 180-220℃; and / or, The hydrothermal reaction takes 12-24 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The heat treatment is performed under an inert atmosphere; and / or, The heat treatment temperature is 500-600℃; and / or, The heat treatment time is 2-4 hours; and / or, The mixing time is 24-48 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The MXene includes Ti3C2T x Ti3N2T x and Ti3CNT x At least one of them; and / or, The preparation steps of MXene include: mixing aluminum titanium carbide and / or aluminum titanium nitride with a fluorine-containing acidic solution, reacting to obtain a reaction solution; washing the reaction solution by centrifugation until pH > 6, taking the solid phase to obtain MXene.

7. The preparation method according to claim 6, characterized in that, Mix MXene with water, sonicate at 300-500W for 2-4 hours, and centrifuge at 1000-3000r / min for 10-30 minutes to obtain an MXene dispersion.

8. The preparation method according to claim 6 or 7, characterized in that, The preparation steps of the MXene also satisfy at least one of the following (a)-(c): (a) The ratio of the total mass of the aluminum titanium carbide and / or aluminum titanium nitride to the volume of the fluorinated acidic solution is (10-20):(100-200), and the concentration of the fluorinated acidic solution is 40-50 wt%; wherein, the unit of the total mass of the aluminum titanium carbide and / or aluminum titanium nitride is g, and the unit of the volume of the fluorinated acidic solution is mL; (b) The reaction conditions are: stirring at 300-500 r / min for 24-48 h; (c) The first centrifugation rate is 3000-5000 r / min.

9. The polydopamine-coated composite cathode material prepared by the preparation method according to any one of claims 1-8.

10. The application of the polydopamine-coated composite cathode material prepared by the preparation method according to any one of claims 1-8 in lithium-ion batteries.

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