Preparation method of fast ion composite nanofiber conductive agent and application of fast ion composite nanofiber conductive agent in solid-state battery

Abstract

According to the preparation method of the fast ion composite nanofiber conductive agent and the application of the fast ion composite nanofiber conductive agent in the solid-state battery, the surface of the nanofiber conductive agent is coated with a layer of fast ion conductor material through a self-template method, and finally a one-dimensional nanofiber material with a dual-conductive function is obtained. The fast ion conductive material comprises a polymer solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, Li3N and other binary fast ion materials. The self-template method adopted by the invention is simple in process, the fast ion composite nanofiber conductive agent material prepared through physical / chemical adsorption or chemical reaction is applied to the field of semi-solid batteries, has dual electron and ion conductance, and can form a three-dimensional long-range conductive network among active particle materials; the lithium ion migration path is shortened, the lithium ion migration rate is increased, meanwhile, mechanical flexibility is achieved, and the rate performance and the cycle performance of the semi-solid lithium battery are greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for preparing a fast ion composite nanofiber conductive agent and its application in solid-state batteries. Background Art

[0002] Lithium-ion batteries are widely used in digital products and new energy vehicles due to their high energy density and low self-discharge characteristics. However, the energy density of traditional organic liquid electrolytes has reached a bottleneck, and in extreme cases, they are prone to fire and explosion accidents, limiting the commercial application of large-capacity and high-energy lithium secondary batteries. Therefore, it is crucial to improve the safety and electrochemical performance of lithium-ion batteries, especially to design and develop high-performance electrolytes.

[0003] Solid-state electrolytes have significant safety advantages over traditional organic electrolytes because they can reduce the flammable components in the battery. However, solid-state electrolytes also face problems such as large solid-solid interface impedance and low ionic conductivity, which affect the battery's charge and discharge performance and rate performance. Polymer solid electrolytes can significantly improve the safety and cycle performance of lithium-ion batteries due to their good flexibility and excellent interface contact properties. However, at room temperature, the low ionic conductivity of polymer solid electrolytes limits their industrial application.

[0004] In order to solve these problems, researchers usually use organic / inorganic composite solid electrolytes to improve the interface contact and ion conductivity of solid-state batteries. However, the solid electrolyte with micro-nano particle structure has a small contact area with the active material, and the non-uniform distribution of polymer electrolytes leads to a shortage of lithium ion migration paths, which in turn causes the ion transport inside the electrode to fail to form a continuous three-dimensional network distribution, resulting in poor experimental repeatability of the composite electrolyte and reduced electrochemical rate and cycle performance. Therefore, it is necessary to develop a fast ion composite nanofiber conductive agent to improve the ionic conductivity to improve the rate and cycle performance of solid-state batteries. Summary of the invention

[0005] The present invention provides a preparation method of a fast ion composite nanofiber conductive agent and its application in solid-state batteries to solve the problem of limited ion transmission in semi-solid-state batteries in the prior art. The developed nanofibers with fast ion conductor properties can form long-range lithium ion transmission between multiple active material particles in an electrode sheet, shorten the transmission distance of lithium ions, and can greatly improve the rate and cycle performance of solid-state batteries.

[0006] The present invention provides a method for preparing a fast ion composite nanofiber conductive agent, comprising the following steps:

[0007] S1. Surface functionalization of nanofiber conductive agent:

[0008] A. Prepare a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:1 to 4;

[0009] B. adding the nanofiber conductive agent to the prepared mixed acid solution for treatment for 1 to 5 hours, filtering, rinsing and drying to obtain the functionalized nanofiber conductive agent;

[0010] S2. Preparation method of "polymer-conductive lithium salt" system coating:

[0011] A. drying the polymer that can be used as a solid electrolyte and the conductive lithium salt in a vacuum at a temperature below their respective melting points for later use;

[0012] B. dissolving the polymer and the conductive lithium salt in the organic solvent acetonitrile, and stirring to fully form a uniformly mixed organic polymer solid electrolyte solution; the molar ratio of the polymer to the conductive lithium salt is 5 to 20:1;

[0013] C. Finally, the nanofiber conductive agent obtained from S1 is added to the solution of S2, ultrasonicated for 30 minutes, magnetically stirred and dispersed for 4 to 12 hours, filtered and vacuum dried to obtain a fast ion composite nanofiber conductive agent;

[0014] S3, preparation method of oxide and sulfide solid electrolyte system coating:

[0015] A. Add the nano oxide / sulfide solid electrolyte and the dispersant into anhydrous ethanol and stir to form a uniformly mixed solution for use;

[0016] B. Add the nanofiber conductive agent obtained in S1 to the solution of S3, ultrasonicate for 30 min, disperse by magnetic stirring for 4-12 h, filter and vacuum dry to obtain a fast ion composite nanofiber conductive agent;

[0017] Preparation method of binary fast ion coating such as S4 and Li3N:

[0018] A layer of fast ion material is deposited on the surface of the nanofiber conductive agent by a physical vapor deposition method.

[0019] Preferably, CNT is selected as the fast ion composite nanofiber conductive agent, and the CNT has a diameter of 10-50 nm and a length of 10-50 um.

[0020] Preferably, in S1 / S2 / S3, sodium dodecylbenzene sulfonate, trition x-100, and polyvinylpyrrole (PVP) are used as dispersants.

[0021] Preferably, the conductive lithium salt in S2 includes any one of lithium halide (LiX, X=F, Cl, Br, I), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4), or a combination of at least two of them.

[0022] Preferably, the polymer in S2 is selected from any one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyethylene glycol diacrylate (PEGDA), polymethyl methacrylate (PMMA), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or a combination of at least two thereof, and preferably polyethylene oxide is selected as the grafted polymer.

[0023] Preferably, the polymer and the conductive lithium salt in S2 are stirred in acetonitrile for 12-24 hours.

[0024] Preferably, the nano oxide / sulfide solid-state starvation mechanism in S3 includes any one or a combination of at least two of Li(3x)La(2 / 3-x)TiO3, Li1+xAlxTi2-x(PO4)3 (x=0.2-0.5, preferably x=0.3), Li7-xLa3Zr2-xMxO12 (M is one of the Nb / Ta / Y / Ca metal elements, x=0-2), and sulfur-LISICON (Li10MP2S12, M=Ge, Si, Sn, such as Li10GeP2S12 and Li9.54Si1.74P1.44S11.7Cl0.3); preferably, the diameter of the nanoparticles is 3-10nm.

[0025] Beneficial effects:

[0026] (1) The present invention is simple to prepare, and the reaction conditions are easy to control and implement. At the same time, the polymer macromolecule on the surface of the fast ion composite nanofiber conductive agent reduces the surface activity of the composite material, which can make the material more effectively dispersed in the solvent. When used in the electrode, the conductive agent can be evenly distributed;

[0027] (2) Compared with traditional nanofiber conductive agents, fast ion composite nanofiber conductive agents not only have conventional electronic conductivity, but also have ion transmission ability, realizing efficient composite of material properties.

[0028] (3) The fast ion composite nanofiber conductive agent is evenly dispersed in the electrode, forming an effective 3D interconnected electron and ion dual transport network between the active material particles, which can effectively improve the migration of Li+ in the solid electrolyte;

[0029] (4) The three-dimensional structure formed by the fast ion composite nanofiber conductive agent and its large specific surface area form a continuous and tight inorganic / organic polymer interface, which improves the transmission rate of Li+ at the interface;

[0030] (5) Fast ion composite nanofiber conductive agents are used in semi-solid lithium batteries. They have good mechanical and electrochemical properties and can greatly improve the rate performance and cycle performance of the battery.

[0031] The above description is only an overview of the technical solution of the embodiment of the present invention. In order to more clearly understand the technical means of the embodiment of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is specifically listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the structure of polymer-coated carbon nanotubes of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the oxide-coated carbon nanotubes of the present invention.

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present invention. The appearance of the phrase "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive of other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. Combination Figure 1 , Figure 2 Shown:

[0037] Embodiment 1:

[0038] S1. Surface functionalization of nanofiber conductive agent:

[0039] A. Prepare 50 ml of a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:4;

[0040] B. Take 0.2g of carbon nanotubes and put them into a beaker, add the prepared mixed acid solution, ultrasonicate for 30min, magnetically stir for 2h, filter, rinse with anhydrous ethanol, and vacuum dry to obtain functionalized carbon nanotube carboxyl groups.

[0041] S2. Preparation method of "polymer-conductive lithium salt" system coating:

[0042] A. PEO was vacuum dried at 50°C for 10 h and LiTFSI was vacuum dried at 80°C for 10 h for later use;

[0043] B. 0.02 g PEO with a molecular weight of 200,000-400,000 and 0.013 g LiTFSI lithium salt were dissolved in 20 ml of acetonitrile, an organic solvent, and stirred for 12 hours to form a uniform mixed solution; the molar ratio of polymer to conductive lithium salt was 10:1;

[0044] C. Add 0.2g carboxyl carbon nanotubes and 0.002g PVP prepared in S1 into 30ml anhydrous acetonitrile solution, ultrasonically disperse for 30min, and magnetically stir for 2h; then add the dispersed carbon nanotube acetonitrile solution into the solution of PEO and lithium salt mixed evenly, magnetically stir for 12h, filter, rinse, and vacuum dry to obtain a fast ion composite nanofiber conductive agent.

[0045] Embodiment 2:

[0046] S1. Surface functionalization of nanofiber conductive agent:

[0047] A. Prepare 50 ml of a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:4;

[0048] B. Take 0.2g of carbon nanotubes and put them into a beaker, add the prepared mixed acid solution, ultrasonicate for 30min, magnetically stir for 2h, filter, rinse with anhydrous ethanol, and vacuum dry to obtain functionalized carbon nanotube carboxyl groups.

[0049] S2. Preparation method of "polymer-conductive lithium salt" system coating:

[0050] A. PEO was vacuum dried at 50°C for 10 h and LiTFSI was vacuum dried at 80°C for 10 h for later use;

[0051] B. 0.02 g PEO with a molecular weight of 200,000-400,000 and 0.0088 g LiTFSI lithium salt were dissolved in 20 ml anhydrous acetonitrile and stirred for 12 h to form a uniform mixed solution; the molar ratio of polymer to conductive lithium salt was 15:1;

[0052] C. Add 0.2g carboxyl carbon nanotubes and 0.002g PVP prepared in S1 into 30ml anhydrous acetonitrile solution, ultrasonically disperse for 30min, and magnetically stir for 2h; then add the dispersed carbon nanotube acetonitrile solution into the solution of PEO and lithium salt mixed evenly, magnetically stir for 12h, filter, rinse, and vacuum dry to obtain a fast ion composite nanofiber conductive agent.

[0053] Embodiment three:

[0054] S1. Surface functionalization of nanofiber conductive agent:

[0055] A. Prepare 50 ml of a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:4;

[0056] B. Take 0.2g of carbon nanotubes and put them into a beaker, add the prepared mixed acid solution, ultrasonicate for 30min, magnetically stir for 2h, filter, rinse with anhydrous ethanol, and vacuum dry to obtain functionalized carbon nanotube carboxyl groups.

[0057] S2. Preparation method of "polymer-conductive lithium salt" system coating:

[0058] A. PEO was vacuum dried at 50°C for 10 h and LiTFSI was vacuum dried at 80°C for 10 h for later use;

[0059] B. 0.04 g PEO with a molecular weight of 200,000-400,000 and 0.026 g LiTFSI lithium salt were dissolved in 20 ml of acetonitrile, an organic solvent, and stirred for 12 hours to form a uniform mixed solution; the molar ratio of polymer to conductive lithium salt was 10:1;

[0060] C. Add 0.2g carboxyl carbon nanotubes and 0.002g PVP prepared in S1 into 30ml anhydrous acetonitrile solution, ultrasonically disperse for 30min, and magnetically stir for 4h; then add the dispersed carbon nanotube acetonitrile solution into the solution of PEO and lithium salt mixed evenly, magnetically stir for 12h, filter, rinse, and vacuum dry to obtain a fast ion composite nanofiber conductive agent.

[0061] Embodiment 4:

[0062] S1. Surface functionalization of nanofiber conductive agent:

[0063] A. Prepare 50 ml of a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:4;

[0064] B. Take 0.2g of carbon nanotubes and put them into a beaker, add the prepared mixed acid solution, ultrasonicate for 30min, magnetically stir for 2h, filter, rinse with anhydrous ethanol, and vacuum dry to obtain functionalized carbon nanotube carboxyl groups.

[0065] S3, preparation method of oxide and sulfide solid electrolyte system coating:

[0066] A. Add 0.02 g of nano-LLZO oxide particles (3-10 nm) and 0.002 g of PVP into 30 ml of anhydrous ethanol and stir for 4 h to form a uniformly mixed solution S3;

[0067] B. Add 0.2 g of carboxyl carbon nanotubes prepared in S1 to the solution of S3, ultrasonicate for 30 min, magnetically stir for 10 h, filter, rinse, and vacuum dry to obtain a fast ion composite nanofiber conductive agent.

[0068] A method for preparing a fast ion composite nanofiber conductive agent and its application in solid-state batteries, button battery production, comprising the following steps:

[0069] 1) Weigh 0.90 g of NCM Ni90 material, 0.03 g of super-P, 0.05 g of PVDF and 0.02 g of carbon nanotubes respectively, add 4 mL of NMP and stir magnetically for 12 h to obtain a cathode slurry;

[0070] 2) The positive electrode slurry is evenly coated on the surface of the aluminum foil and dried at 120° C. for 1 h. The aluminum foil is then placed in a vacuum drying oven and dried at 120° C. for 12 h before being sliced ​​and prepared into button-type lithium batteries.

[0071] 3) The in-situ solidified electrolyte precursor includes a polymerizable monomer, an initiator, a lithium salt, an inorganic filler, an inhibitor, and an organic solvent. The mass percentage of the polymerizable monomer is 3%, the mass percentage of the initiator to the mass percentage of the polymerizable monomer is 1%, the mass percentage of the inorganic filler to the mass percentage of the polymerizable monomer is 5%, the mass percentage of the inhibitor to the mass percentage of the polymerizable monomer is 0.5%, and the mass percentage of the additive is 5%.

[0072] The polymerization monomer includes a combination of methyl methacrylate and pentaerythritol tetraacrylate; the initiator includes azobisisobutyronitrile; the lithium salt includes lithium bistrifluoromethylsulfonyl imide and lithium hexafluorophosphate; the inorganic filler includes a combination of SiO2 and ZrO2; the inhibitor includes 2,6-di-tert-butyl-p-cresol, and the additives include vinylene carbonate and fluoroethylene carbonate.

[0073] 4) After the liquid is injected, the mixture is allowed to stand at room temperature for 24 hours, and then cured at 60°C for 10 hours to produce a semi-solid button battery.

[0074] Application Example 1:

[0075] The carbon nanotubes used were prepared in Example 1;

[0076] Application Example 2:

[0077] The carbon nanotubes used were prepared in Example 2;

[0078] Application Example 3:

[0079] The carbon nanotubes used were prepared in Example 3;

[0080] Application Example 4:

[0081] The carbon nanotubes used were prepared in Example 4;

[0082] Experimental example:

[0083] The carbon nanotubes used are conventional carbon nanotubes.

[0084] Conductivity test: The semi-solid batteries made of the positive electrode sheets obtained in each application example were tested for their ion conductivity;

[0085] AC impedance: The batteries of each embodiment and comparative example were tested on an electrochemical workstation. The AC impedance voltage signal of the battery was 10mV, and the frequency range was 10 6 -10 -2 Hz, ionic conductivity is calculated by EIS results combined with the ionic conductivity formula; δ = L / RA (L is thickness, A is area, R is resistance)

[0086] The performance of the batteries prepared by the various embodiments of the present invention was tested, and the data obtained are shown in the following table:

[0087]

[0088] In summary, the preparation method of the present invention is simple. A layer of fast ion conductor material is coated on the surface of the nanofiber conductive agent through a self-template method, and finally a one-dimensional nanofiber material with dual conductive functions is obtained. The fast ion composite nanofiber conductive agent is evenly dispersed in the electrode, and an effective 3D interconnected electron and ion dual transmission network is formed between the active material particles, which can effectively improve the migration of Li+ in the solid electrolyte, shorten the lithium ion migration path and increase the lithium ion migration rate. At the same time, it has mechanical flexibility, which greatly improves the rate performance and cycle performance of the semi-solid lithium battery.

[0089] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fast ion composite nanofiber conductive agent, characterized in that: The method comprises the following steps: coating a layer of fast ion conductor material on the surface of the nanofiber conductive agent by a self-template method; S1. Surface functionalization of nanofiber conductive agent: A. Prepare a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 1:1 to 4; B. adding the nanofiber conductive agent to the prepared mixed acid solution for treatment for 1 to 5 hours, filtering, rinsing and drying to obtain the functionalized nanofiber conductive agent; S2. Preparation method of "polymer-conductive lithium salt" system coating: A. drying the polymer that can be used as a solid electrolyte and the conductive lithium salt in a vacuum at a temperature below their respective melting points for later use; B. dissolving the polymer and the conductive lithium salt in the organic solvent acetonitrile, and stirring to fully form a uniformly mixed organic polymer solid electrolyte solution; the molar ratio of the polymer to the conductive lithium salt is 5 to 20:1; C. Finally, the nanofiber conductive agent obtained from S1 is added to the solution of S2, ultrasonicated for 30 minutes, magnetically stirred and dispersed for 4 to 12 hours, filtered and vacuum dried to obtain a fast ion composite nanofiber conductive agent; S3, preparation method of oxide and sulfide solid electrolyte system coating: A. Add the nano oxide / sulfide solid electrolyte and the dispersant into anhydrous ethanol and stir to form a uniformly mixed solution for use; B. Add the nanofiber conductive agent obtained in S1 to the solution of S3, perform ultrasonic treatment for 30 minutes, disperse by magnetic stirring for 4 to 12 hours, filter and vacuum dry to obtain a fast ion composite nanofiber conductive agent. Preparation method of binary fast ion coating such as S4 and Li3N: A layer of fast ion material is deposited on the surface of the nanofiber conductive agent by a physical vapor deposition method.

2. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: The nanofiber conductive agent includes any one of carbon nanotubes, VGCF, polyaniline, polypyrrole, etc., or a combination of at least two of them.

3. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: A dispersant is also added to the S1 / S2 / S3 to effectively disperse the nanofibers. Preferably, sodium dodecylbenzene sulfonate, trition x-100, and polyvinylpyrrole (PVP) are used as the dispersant.

4. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: The conductive lithium salt in S2 is selected from any one of lithium halides (LiX, X=F, Cl, Br, I), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4), or a combination of at least two thereof.

5. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: The polymer in S2 is selected from any one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyethylene glycol diacrylate (PEGDA), polymethyl methacrylate (PMMA), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), or a combination of at least two thereof; Preferably, PEO is chosen as the polymer.

6. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: The polymer and the conductive lithium salt in S2 are stirred in acetonitrile for 12-24 hours.

7. The method for preparing a fast ion composite nanofiber conductive agent according to claim 1, characterized in that: The nano oxide / sulfide solid-state starvation mechanism in S3 includes any one or a combination of at least two of Li(3x)La(2 / 3-x)TiO3, Li1+xAlxTi2-x(PO4)3 (x=0.2-0.5, preferably x=0.3), Li7-xLa3Zr2-xMxO12 (M is one of the Nb / Ta / Y / Ca metal elements, x=0-2), and sulfur-LISICON (Li10MP2S12, M=Ge, Si, Sn, such as Li10GeP2S12 and Li9.54Si1.74P1.44S11.7Cl0.3).

8. A fast ion composite nanofiber conductive material prepared by the preparation method described in claim 1 and used in a solid-state battery.

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