Transition metal phosphide / carbon self-supporting flexible material as well as preparation method and application thereof
By forming transition metal phosphides in situ in the carbon matrix, and using electrospinning and calcining technology to prepare transition metal phosphide/carbon self-supporting flexible materials, the problem of capacity decay caused by volume expansion in lithium batteries is solved, and the effect of maintaining high specific capacity and Coulomb efficiency after long-term circulation is achieved.
Patent Information
- Application Number
- CN202411924944.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-25
- Publication Date
- 2025-05-09
Smart Images
Figure CN119965225A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a negative electrode material for a lithium battery, and in particular to a transition metal phosphide / carbon self-supporting flexible material and a preparation method and application thereof. Background Art
[0002] Lithium-ion batteries are widely used in many fields due to their high energy density, long life, fast charging, safety and reliability. As one of the main electrode materials of lithium batteries, insertion materials can be reversibly charged and discharged, with a cycle life of hundreds to thousands of times. 12 ) as a commonly used intercalation material also has some disadvantages, and the specific capacity provided at the theoretical limit is low. In order to improve energy density and reduce costs, the next generation of lithium-ion batteries is likely to rely on conversion materials containing earth-abundant elements such as iron (Fe), silicon (Si) and phosphorus (P). Si and P have ultra-high theoretical specific capacities (Si is 4212 mAh g -1 , P is 2596mAh g -1 ).
[0003] Transition metal phosphides have attracted extensive attention due to their high specific capacity, low cost and environmental protection. x P y ) Due to multi-electron conversion, it can provide higher capacity than traditional insertion materials, but the larger volume expansion will lead to capacity decay.
[0004] Therefore, there is still a need to develop a negative electrode material based on Si or P with ultra-high theoretical specific capacity and small attenuation variation. Summary of the invention
[0005] The purpose of the present invention is to solve at least one of the above problems and provide a transition metal phosphide / carbon self-supporting flexible material and its preparation method and application, so as to solve the problem that the iron phosphide has a large volume expansion and causes capacity decay in the prior art. The present invention realizes the in-situ formation of M in the carbon matrix. x P y , effectively reducing the structural changes of transition metal phosphide particles, protecting them from being crushed, allowing the electrode to maintain an independent structure after long-term cycling, and thus maintaining a high specific capacity and coulombic efficiency after long-term cycling.
[0006] The purpose of the present invention is achieved through the following technical solutions:
[0007] The first aspect of the present invention discloses a method for preparing a transition metal phosphide / carbon self-supporting flexible material, comprising the following steps:
[0008] The vinylidene fluoride copolymer, polyacrylonitrile, acetylacetonate-based metal complex and phenylphosphoric acid are mixed into a mixed solution, and then electrostatic spinning and calcination are performed to obtain the transition metal phosphide / carbon self-supporting flexible material through in-situ preparation.
[0009] Preferably, the method comprises the following steps:
[0010] S1: dissolving vinylidene fluoride copolymer and polyacrylonitrile in a solvent at high temperature, then adding acetylacetonato metal complex and phenylphosphoric acid, and stirring at room temperature;
[0011] S2: The mixed solution obtained in step S1 is electrospinned into a dry fiber membrane, which is then calcined to prepare the transition metal phosphide / carbon self-supporting flexible material.
[0012] Preferably, in step S1, the vinylidene fluoride copolymer is prepared by the following steps:
[0013] Vinylidene fluoride and the second modified monomer are introduced into the reaction kettle, and then a chain transfer agent and an initiator are injected to react to obtain the vinylidene fluoride copolymer.
[0014] Preferably, the reaction temperature is 55-70° C. and the pressure is 5.5-6.5 MPa.
[0015] Preferably, the second modified monomer includes CTFE, the chain transfer agent includes diethyl carbonate, dimethyl carbonate and ethylene carbonate, the initiator includes dibenzoyl peroxide, tert-butyl perbenzoate and peroxysuccinic acid; the molar ratio of the vinylidene fluoride to the second modified monomer is 90:15 to 50:25.
[0016] Preferably, the mass ratio of the vinylidene fluoride copolymer to polyacrylonitrile is 4:1 to 1:4; and the solvent comprises one or two of N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide.
[0017] Preferably, the acetylacetonate metal complex comprises ferric acetylacetonate, cobalt acetylacetonate and nickel acetylacetonate; and the mass ratio of the vinylidene fluoride copolymer, the acetylacetonate metal complex and phenyl phosphoric acid is 5:0.65 to 0.95:0.57.
[0018] Preferably, the calcination temperature is 650-850°C.
[0019] The second aspect of the present invention discloses a transition metal phosphide / carbon self-supporting flexible material, which is prepared by any of the above methods.
[0020] The third aspect of the present invention discloses an application of the above-mentioned transition metal phosphide / carbon self-supporting flexible material in a negative electrode of a lithium battery. The transition metal phosphide / carbon self-supporting flexible material is used as a negative electrode of a lithium battery, so that the metal phosphide is in situ confined in the carbon nanofiber, which not only provides good conductivity, but also ensures structural stability during long-term cycles and slows down capacity decay.
[0021] The transition metal phosphide / carbon self-supporting flexible material is used as the negative electrode material of the lithium battery. The electrode has good flexibility and can be cut into round pieces with a diameter of 14 to 20 mm, with a loading of 0.95 to 1.3 mg / cm 2 .
[0022] The working principle of the present invention is:
[0023] The vinylidene fluoride copolymer is polymerized by a first monomer, vinylidene fluoride, and a second modified monomer, CTFE. The addition of the second modified monomer, CTFE, improves thermal stability and flexibility, while the further addition of polyacrylonitrile further enhances interface stability.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] The present invention provides a transition metal phosphide (M x P y ) / Carbon self-supporting flexible material method, wherein the material is copolymerized with vinylidene fluoride and a second monomer, and the polar fluorine-containing functional group has a high cohesive energy density to provide good flexibility, and polyacrylonitrile, ferric acetylacetonate and phosphate are added to form M in situ in the carbon matrix through spinning and calcination. x P y This carbon matrix can effectively reduce the structural changes of iron phosphide particles, protect them from being crushed, and enable the electrode to maintain an independent structure after long-term cycling.
[0026] (1) In the present invention, the polar functional groups of the polymerizable fluorine-containing monomers make the vinylidene fluoride copolymer have lower crystallinity, better thermal stability, and improved flexibility. The addition of PAN further enhances the interface stability and mechanical stability.
[0027] (2) Electrospinning can well mix P(VDF-CTFE), PAN, phenyl phosphate, and acetylacetonate-based metal complexes to evenly generate dry fiber membranes, which are then directly prepared in situ into transition metal phosphide / carbon self-supporting flexible materials through a one-step calcination method.
[0028] The application of this composite material in lithium-ion batteries achieves flexibility, lightness and high energy storage. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1This is the infrared spectrum of the polymer P (VDF-CTFE) of Example 1 of the present invention;
[0030] Figure 2 The XRD pattern of the Fe2P / C composite material prepared in Example 1 of the present invention;
[0031] Figure 3 (a), (b) and (c), (d) are physical pictures of the composite materials of Example 1 of the present invention and Comparative Example 1 respectively;
[0032] Figure 4 This is a battery cycle life diagram of the self-supporting composite material of Example 1 of the present invention as a lithium battery negative electrode. DETAILED DESCRIPTION
[0033] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.
[0034] Unless otherwise specified in the following description, the reagents used are conventional commercially available products and the methods used are well known in the art.
[0035] A method for preparing a self-supporting flexible material, which is used as a negative electrode for lithium batteries, allows metal phosphides to be in-situ confined in carbon nanofibers, which not only provides good conductivity, but also ensures structural stability during long-term cycles and slows down capacity decay. The preparation is specifically as follows:
[0036] 1) Add deionized water and dispersant to the reactor, stir evenly, raise the temperature to 55-70° C., increase the pressure to 5.5-6.5 MPa by adding VDF / CTFE mixed monomer, inject chain transfer agent and initiator, and start the reaction.
[0037] 2) During the reaction process, the pressure in the reactor is kept constant, and the initiator is added to the reactor twice every 40 minutes. After the reaction is completed, the temperature is reduced and the pressure is released to recover the remaining gas. The material is washed and dried to obtain a vinylidene fluoride copolymer P (VDF-CTFE).
[0038] 3) P(VDF-CTFE) and PAN were added to 40-60 mL of a specific solvent in a certain mass ratio, dissolved at 80° C. for 2 hours, and then acetylacetonate metal complex and phenylphosphoric acid were added in a certain ratio and stirred at room temperature for 6 hours.
[0039] 4) The above solution is prepared into a dry fiber membrane by electrospinning, and a self-supporting flexible metal phosphide / carbon material is prepared by high-temperature calcination in one step.
[0040] in,
[0041] The molar ratio of the first monomer VDF to the second modified monomer CTFE is 90:15 to 50:25. The dispersant is one of polyoxyethylene alkylphenol ether, sorbitol alkylate, hydroxymethyl cellulose, and polyethylene glycol; the chain transfer agent is one of diethyl carbonate, dimethyl carbonate, and ethylene carbonate; the initiator is at least one of dibenzoyl peroxide, tert-butyl perbenzoate, and peroxysuccinic acid.
[0042] The addition ratio of P(VDF-CTFE) and PAN is 1:4 to 4:1, and the specific solvent is one or two of N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide.
[0043] The acetylacetonate metal complex is one of acetylacetonate iron, acetylacetonate cobalt and acetylacetonate nickel; the high temperature calcination temperature is between 650 and 850°C.
[0044] The material prepared by the above method is applied to the pole piece, has good flexibility, can be cut into discs with a diameter of 14 to 20 mm, and has a loading of 0.95 to 1.3 mg / cm 2 .
[0045] Example 1
[0046] 1) Add 6kg of deionized water and 3.0g of polyethylene glycol to a 10L high-pressure polymerization reactor, stir, heat to 60°C, introduce VDF / CTFE mixed monomers into the reactor, and the pressure reaches 6.0MPa, with VDF accounting for 85% of the mixed gas (molar fraction, the same below). Use a metering pump to pump 2.5g of ethylene carbonate and 4.85g of peroxysuccinic acid aqueous solution into the reactor respectively, start the reaction, and maintain a constant pressure. Add 1.8g of peroxysuccinic acid every 40 minutes, twice in total; when the amount of the reaction mixed gas reaches the initial set value of 480g, the reaction ends, cools down and releases the pressure, and recovers the gas. Demulsify the emulsion, wash it, and dry it to obtain P (VDF-CTFE) powder.
[0047] 2) Weigh 5.0 g of P(VDF-CTFE) powder, with a mass ratio of PAN:P(VDF-CTFE) of 2:3, add it to 60 mL of dimethylformamide, stir at 80°C for 2 hours, and after it is completely dissolved, add 0.85 g of ferric acetylacetonate and 0.57 g of phenylphosphoric acid, and stir at room temperature for 6 hours.
[0048] 3) The above solution was spun at a voltage of 20 kV, and the prepared fiber membrane was cut into 20 mm discs, placed in a tubular furnace, and calcined at 800 ° C in a 4% hydrogen-argon mixed gas atmosphere to obtain a self-supporting flexible Fe2P / C composite material, which was cut into 16 mm diameter discs as electrodes.
[0049] like Figure 1 The infrared spectrum of the polymer P (VDF-CTFE) in this example shows that the vinylidene fluoride copolymer was successfully prepared. Figure 2 The XRD diagram of the Fe2P / C composite material prepared in this example is consistent with the Fe2P peak position of the library standard card.
[0050] like Figure 3 (a) and (b) are the plan view and bending view of the Fe2P / C composite material prepared in Example 1, respectively. It can be seen that the composite material can be directly used as a self-supporting electrode, and the electrode exhibits excellent flexibility and can be bent at will without breaking.
[0051] The Fe2P / C composite material prepared in this example was used as a negative electrode for lithium battery at 2A g -1 The cycle performance test was carried out under constant current, and the results were as follows Figure 4 As shown in Figure 2, the specific capacity remains at 500 mAh g after 1600 cycles. -1 The coulombic efficiency is close to 100%, and there is basically no attenuation compared with the initial specific capacity and coulombic efficiency, indicating that the composite material has good cycle performance as a lithium battery negative electrode.
[0052] Example 2
[0053] 1) Add 6kg of deionized water and 3.0g of polyethylene glycol to a 10L high-pressure polymerization reactor, stir, heat to 60°C, introduce VDF / CTFE mixed monomers into the reactor, and the pressure reaches 6.0MPa, with VDF accounting for 75% of the mixed gas. Use a metering pump to pump 2.5g of ethylene carbonate and 4.85g of peroxysuccinic acid aqueous solution into the reactor, start the reaction, and maintain a constant pressure. Add 1.8g of peroxysuccinic acid every 40 minutes, twice in total; when the amount of the reaction mixed gas reaches the initial set value of 480g, the reaction ends, cools down and releases the pressure, and recovers the gas. Demulsify the emulsion, wash it, and dry it to obtain the P (VDF-CTFE) material.
[0054] 2) Weigh 5.0 g of P(VDF-CTFE) powder, with a mass ratio of PAN:P(VDF-CTFE) of 2:3, add it to 60 mL of dimethylformamide, stir at 80°C for 2 hours, and after it is completely dissolved, add 0.95 g of ferric acetylacetonate and 0.57 g of phenylphosphoric acid, and stir at room temperature for 6 hours.
[0055] 3) The above solution was spun at a voltage of 20 kV, and the prepared fiber membrane was cut into 20 mm discs, placed in a tubular furnace, and calcined at 800 ° C in a 4% hydrogen-argon mixed gas atmosphere to obtain a self-supporting flexible Fe2P / C composite material, which was cut into 16 mm diameter discs as electrodes.
[0056] Example 3
[0057] 1) Add 6kg of deionized water and 3.0g of polyethylene glycol to a 10L high-pressure polymerization reactor, stir, heat to 60°C, introduce VDF / CTFE mixed monomers into the reactor, and the pressure reaches 6.0MPa, with VDF accounting for 65% of the mixed gas. Use a metering pump to pump 2.5g of ethylene carbonate and 4.85g of peroxysuccinic acid aqueous solution into the reactor, start the reaction, and maintain a constant pressure. Add 1.8g of peroxysuccinic acid every 40 minutes, twice in total; when the amount of the reaction mixed gas reaches the initial set value of 480g, the reaction ends, cools down and releases the pressure, and recovers the gas. Demulsify the emulsion, wash it, and dry it to obtain the P (VDF-CTFE) material.
[0058] 2) Weigh 5.0 g of P(VDF-CTFE) powder, with a mass ratio of PAN:P(VDF-CTFE) of 2:3, add it to 60 mL of dimethylformamide, stir at 80°C for 2 hours, and after it is completely dissolved, add 0.75 g of ferric acetylacetonate and 0.57 g of phenylphosphoric acid, and stir at room temperature for 6 hours.
[0059] 3) The above solution was spun at a voltage of 20 kV, and the prepared fiber membrane was cut into 20 mm discs, placed in a tubular furnace, and calcined at 800 ° C in a 4% hydrogen-argon mixed gas atmosphere to obtain a self-supporting flexible Fe2P / C composite material, which was cut into 16 mm diameter discs as electrodes.
[0060] Example 4
[0061] 1) Add 6kg of deionized water and 3.0g of polyethylene glycol to a 10L high-pressure polymerization reactor, stir, heat to 60°C, introduce VDF / CTFE mixed monomers into the reactor, and the pressure reaches 6.0MPa, with VDF accounting for 55% of the mixed gas. Use a metering pump to pump 2.5g of ethylene carbonate and 4.85g of peroxysuccinic acid aqueous solution into the reactor, start the reaction, and maintain a constant pressure. Add 1.8g of peroxysuccinic acid every 40 minutes, twice in total; when the amount of the reaction mixed gas reaches the initial set value of 480g, the reaction ends, cools down and releases the pressure, and recovers the gas. Demulsify the emulsion, wash it, and dry it to obtain the P (VDF-CTFE) material.
[0062] 2) Weigh 5.0 g of P(VDF-CTFE) powder, with a mass ratio of PAN:P(VDF-CTFE) of 2:3, add it to 60 mL of dimethylformamide, stir at 80°C for 2 hours, and after it is completely dissolved, add 0.65 g of ferric acetylacetonate and 0.57 g of phenylphosphoric acid, and stir at room temperature for 6 hours.
[0063] 3) The above solution was spun at a voltage of 20 kV, and the prepared fiber membrane was placed in a tubular furnace and calcined at 800° C. in a 4% hydrogen-argon mixed gas atmosphere to obtain a self-supporting flexible Fe2P / C composite material, which was cut into 16 mm diameter discs as electrodes.
[0064] Comparative Example 1
[0065] 1) Add 6kg of deionized water and 3.0g of polyethylene glycol to a 10L high-pressure polymerization reactor, stir, heat to 60°C, and introduce VDF monomer into the reactor to a pressure of 6.0MPa. Use a metering pump to pump 2.5g of ethylene carbonate and 4.85g of peroxysuccinic acid aqueous solution into the reactor, start the reaction, and maintain a constant pressure. Add 1.8g of peroxysuccinic acid every 40 minutes, twice in total; when the amount of the reaction mixed gas reaches the initial set value of 480g, the reaction ends, cools down and releases the pressure, and recovers the gas. Demulsify the emulsion, wash it, and dry it to obtain PVDF powder.
[0066] 2) Weigh 5.0 g of PVDF powder, with a mass ratio of PAN:PVDF of 2:3, add it to 60 mL of dimethylformamide, stir at 80°C for 2 hours, and after it is completely dissolved, add 0.85 g of ferric acetylacetonate and 0.57 g of phenylphosphoric acid, and stir at room temperature for 6 hours.
[0067] 3) The above solution was spun at 20 kV, and the prepared fiber membrane was cut into 20 mm discs, placed in a tubular furnace, and calcined at 800 ° C in a 4% hydrogen-argon mixed gas atmosphere to obtain a Fe2P / C composite material, which was cut into 16 mm diameter discs as electrodes.
[0068] like Figure 3 (c) and (d) show the plan view and bending view of the composite material prepared in Comparative Example 1, respectively. It can be seen from the figure that the edges of the circular pole piece are damaged a lot, and obvious cracks appear after bending it, indicating that its flexibility has deteriorated; at the same time, when it is used as a lithium battery negative electrode and the cycle performance is tested under the same conditions as in Example 1, it is found that the cycle performance has deteriorated, which may be due to the brittleness of the pole piece, which has broken and fallen off during the lithium battery packaging process or the cycle process. In contrast, the use of the polymerizable fluorine-containing monomer polar functional group contained in the vinylidene fluoride copolymer in Example 1 can make the composite material have lower crystallinity, better thermal stability, and effectively improve flexibility.
[0069] Example 5
[0070] This embodiment is basically the same as embodiment 1, the main difference being that in step 1), the reaction temperature is 55° C. and the pressure is 6.5 MPa.
[0071] Example 6
[0072] This embodiment is basically the same as embodiment 1, the main difference being that in step 1), the reaction temperature is 70° C. and the pressure is 5.5 MPa.
[0073] Example 7
[0074] This embodiment is basically the same as embodiment 1, the main difference being that in step 1), the dispersant used is polyoxyethylene alkylphenol ether, the chain transfer agent is diethyl carbonate, and the initiator is dibenzoyl peroxide.
[0075] Example 8
[0076] This embodiment is basically the same as embodiment 1, with the main difference being that in step 1), the dispersant used is hydroxymethyl cellulose, the chain transfer agent is dimethyl carbonate, and the initiator is tert-butyl perbenzoate.
[0077] Example 9
[0078] This embodiment is basically the same as embodiment 1, with the main difference being that in step 3), the calcination temperature is 650°C.
[0079] Example 10
[0080] This embodiment is basically the same as embodiment 1, with the main difference being that in step 3), the calcination temperature is 850°C.
[0081] In summary, the test results show that the self-supporting composite material prepared by the method of the present invention has excellent flexibility, and when used in lithium-ion batteries, it exhibits a higher specific capacity and good cycle stability. This special structure not only promotes the transfer of electrons / ions, but also minimizes structural changes in long-term cycles.
[0082] The present invention provides a transition metal phosphide (M x P y ) / carbon self-supporting flexible material method, wherein the material is copolymerized with vinylidene fluoride and a second modified monomer, and the polar fluorine-containing functional group has a high cohesive energy density to provide good flexibility, and polyacrylonitrile, acetylacetonate-based metal (such as iron) complex and phosphate are added to form M in situ in the carbon matrix through spinning and calcination. x P y This carbon matrix can effectively reduce the structural changes of iron phosphide particles, protect them from being crushed, and enable the electrode to maintain an independent structure after long-term cycling.
[0083] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.
Claims
1. A method for preparing a transition metal phosphide / carbon self-supporting flexible material, characterized in that: The steps include: The vinylidene fluoride copolymer, polyacrylonitrile, acetylacetonate-based metal complex and phenylphosphoric acid are mixed into a mixed solution, and then electrostatic spinning and calcination are performed to obtain the transition metal phosphide / carbon self-supporting flexible material through in-situ preparation.
2. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 1, characterized in that: The steps include: S1: dissolving vinylidene fluoride copolymer and polyacrylonitrile in a solvent at high temperature, then adding acetylacetonato metal complex and phenylphosphoric acid, and stirring at room temperature; S2: The mixed solution obtained in step S1 is electrospinned into a dry fiber membrane, which is then calcined to prepare the transition metal phosphide / carbon self-supporting flexible material.
3. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 2, characterized in that: In step S1, the vinylidene fluoride copolymer is prepared by the following steps: Vinylidene fluoride and the second modified monomer are introduced into the reaction kettle, and then a chain transfer agent and an initiator are injected to react to obtain the vinylidene fluoride copolymer.
4. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 3, characterized in that: The reaction temperature is 55-70°C and the pressure is 5.5-6.5MPa.
5. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 3, characterized in that: The second modified monomer includes CTFE, the chain transfer agent includes diethyl carbonate, dimethyl carbonate and ethylene carbonate, the initiator includes dibenzoyl peroxide, tert-butyl perbenzoate and peroxysuccinic acid; the molar ratio of the vinylidene fluoride to the second modified monomer is 90:15 to 50:
25.
6. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 2, characterized in that: The mass ratio of the vinylidene fluoride copolymer to polyacrylonitrile is 4:1-1:4; the solvent comprises one or two of N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide.
7. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 2, characterized in that: The acetylacetonate metal complex comprises acetylacetonate iron, acetylacetonate cobalt and acetylacetonate nickel; the mass ratio of the vinylidene fluoride copolymer, the acetylacetonate metal complex and the phenylphosphoric acid is 5:0.65-0.95:0.
57.
8. The method for preparing a transition metal phosphide / carbon self-supporting flexible material according to claim 2, characterized in that: The calcination temperature is 650-850°C.
9. A transition metal phosphide / carbon self-supporting flexible material, characterized in that: The method is prepared by any one of claims 1 to 8.
10. Use of the transition metal phosphide / carbon self-supporting flexible material as claimed in claim 9 in a negative electrode of a lithium battery.