Design method for high-entropy MXene-high-viscosity colloid composite coating battery separator

Abstract

The present invention discloses a method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator, belonging to the technical field of lithium battery separators. The method comprises etching a multilayer high-entropy MAX phase raw material and then passing it through a high-pressure homogenizer to obtain high-entropy MXene nanosheets. A high-viscosity polyacrylamide colloid is dissolved in deionized water to form a homogenous adhesive solution. The high-entropy MXene nanosheets are dispersed in the solution to form a mixed slurry. The slurry is applied to the surface of a polypropylene separator and dried to form a dense coating. The coated separator and a copper current collector are bonded via a hot pressing process to form an integrated interface structure. By leveraging the lithium migration barrier regulation properties of high-entropy MXene and the in-situ film-forming effect of fluorinated functional groups, combined with the strong adhesion of PAM colloids, the method achieves a synergistic effect of accelerating the lithium ion desolvation process, optimizing the SEI components, and homogenizing lithium deposition, thereby inhibiting lithium dendrite growth and improving the cycle stability of negative electrode-free batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a design method for a high-entropy MXene-high-viscosity colloid composite coating battery separator. Background Art

[0002] With the explosive growth in demand for high-energy-density energy storage, anode-free lithium metal batteries have become the focus of next-generation battery technology due to their high theoretical capacity (3860mAh / g), simplified structure, and controllable costs. This system can significantly improve energy density and safety by directly utilizing copper foil current collectors as the lithium deposition substrate, abandoning traditional anode active materials. However, its core challenge lies in the dendrite growth caused by sluggish desolvation kinetics and uneven interfacial ion flux during lithium metal deposition / stripping, which can easily lead to membrane perforation, interface failure, and battery thermal runaway.

[0003] Current modification strategies for separators are mainly focused on improving mechanical strength and regulating ion transport pathways. For example, by introducing ceramic particles (such as Al2O3, SiO2) or polymer coatings (such as PVDF, aramid) on the surface of polyolefin separators, the puncture resistance of the separator can be enhanced and the electrolyte wettability can be improved. However, this type of method has significant limitations: on the one hand, the brittleness of the ceramic coating and the low modulus of the polymer coating make it difficult to achieve both high mechanical strength and flexible adaptation requirements; on the other hand, the single-function design of the traditional coating cannot simultaneously optimize the ion transport kinetics and interface stability, resulting in high desolvation energy barriers and uneven lithium deposition. More seriously, the physical contact gap between the coating and the current collector will aggravate the interfacial impedance and further worsen the lithium deposition behavior.

[0004] In recent years, two-dimensional MXene materials have been regarded as ideal candidates for membrane modification due to their high conductivity, interlayer ion channels and adjustable surface functional groups. However, conventional MXene (such as Ti3C2T x ) seriously weakens its ion screening ability, and the chemical stability of a single metal component is insufficient, making it difficult to maintain structural integrity during long-term cycles. In addition, existing MXene-based composite diaphragms mostly rely on physical coating processes, and their weak interface bonding with the current collector easily causes the coating to fall off, making it impossible to achieve a synergistic improvement in ion transport-mechanical support-interface stability. Therefore, there is an urgent need to develop a diaphragm modification strategy that takes into account high mechanical strength, rapid desolvation kinetics and integrated interface structure. Through material design and process innovation, the performance bottleneck of traditional coatings can be broken through, providing reliable guarantees for the efficient and long-cycle operation of negative electrode-free lithium metal batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for designing high-entropy MXene-high-viscosity colloid composite coating battery separators.

[0006] To achieve the above objectives, the present invention provides a method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator, comprising the following steps:

[0007] S1. A multilayer high-entropy MAX phase raw material, i.e., TiVNbMoAlC3, is etched in a mixed solution of lithium fluoride and hydrochloric acid, washed with deionized water until neutral, and then cyclically peeled off using a high-pressure homogenizer. Centrifugal separation is performed to obtain high-entropy MXene nanosheets with rich surface fluorinated functional groups, i.e., TiVNbMoC3 nanosheets;

[0008] S2. dissolving polyacrylamide (PAM) colloid in deionized water and stirring at a constant speed to form a homogeneous adhesive solution;

[0009] S3, dispersing the high-entropy MXene nanosheets in S1 into the PAM colloid in S2, and mixing them by a high-speed homogenizer to form a high-entropy MXene / PAM mixed slurry;

[0010] S4, uniformly coating the mixed slurry in S3 on the surface of the polypropylene (PP) diaphragm by a wire rod coating process, and then drying by gradient heating to form a dense composite coating;

[0011] S5. The diaphragm coated in S4 is bonded to the copper current collector through a soft packaging process of first hot pressing and then liquid injection to form an integrated interface structure.

[0012] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S1, the composition of the mixed solution of lithium fluoride and hydrochloric acid is: 1 g of lithium fluoride, a hydrochloric acid concentration of 12 mol / L, and a hydrochloric acid usage of 40 mL; 1 g of high-entropy MAX raw material; the etching temperature of the etching treatment is 45°C, and the treatment time is 72 h; the working pressure of the high-pressure homogenizer is 1100-1200 MPa, and the number of cycle treatments is 10-15 times.

[0013] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S1, the single layer thickness of the high-entropy MXene nanosheet is 1-2 nm, and the number of layers is 3-5 layers.

[0014] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S2, the stirring time for generating the homogeneous adhesive solution is 4-6 hours, and the mass concentration of the adhesive solution is 8%-12%.

[0015] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S3, the speed of the high-speed homogenizer is 2000 r / min, the mixing time is 30-60 min, and the slurry viscosity is controlled at 500-800 mPa·s.

[0016] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S3, the mass ratio of high-entropy MXene to polyacrylamide in the high-entropy MXene / PAM mixed slurry is 8:1, and the solid content of the slurry is 25%.

[0017] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S4, the wire rod coating process uses an OSP-1.5 type wire rod, the coating speed is 0.5-1.5 m / min, and the coating thickness after drying is 4-5 μm.

[0018] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S4, the thickness of the PP separator substrate is 12-16 μm, and the drying conditions are pre-baking at 40°C for 1 hour and final baking at 60°C for 6 hours.

[0019] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S5, the hot pressing process has a hot pressing temperature of 80°C, a pressure of 0.5 MPa, and a holding time of 30-60s.

[0020] Preferably, the composite coating membrane prepared by the above-mentioned high entropy MXene-high viscosity colloid composite coating battery membrane design method has a lithium ion transfer number of 0.76 and a fracture energy of 50.15 J / m 3 , the capacity retention rate of the negative electrode-free soft-pack battery after 100 cycles is 82.6%.

[0021] Therefore, the present invention adopts the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, which has the following beneficial effects:

[0022] (1) The lattice distortion effect of two-dimensional high-entropy MXene strengthens the intrinsic mechanical properties of the diaphragm: the solid solution and distortion of multi-metal element atoms in the MXene lattice form a high-strength covalent bond network, which, combined with the ordered stacking structure of the two-dimensional layers, gives the composite diaphragm excellent puncture resistance and deformation resistance, significantly inhibiting the risk of diaphragm penetration caused by lithium dendrite growth, while maintaining the lightweight characteristics of the diaphragm.

[0023] (2) High-viscosity hot-pressing integrated structure accelerates lithium ion desolvation and transport: Through high-viscosity colloid and the soft packaging process of hot pressing first and then liquid injection, a seamless interface is achieved between the separator coating and the negative electrode current collector, eliminating the ion transport barrier caused by the traditional physical contact gap. This integrated design forces lithium ions to desolvate rapidly during cross-interface transmission, greatly improving ion migration efficiency and guiding lithium ions to deposit uniformly along the interlayer channels of MXene.

[0024] (3) Fluorinated terminals on the MXene surface induce the construction of a stable SEI chemical composition: The fluorinated functional groups generated in situ during the etching process preferentially react with lithium in the early stages of the battery cycle, forming an SEI film dominated by lithium fluoride with high ionic conductivity. This SEI component effectively passivates the electrode interface, reduces the kinetic barrier for lithium deposition, and inhibits electrolyte side reactions, achieving highly reversible lithium metal deposition / stripping behavior.

[0025] This invention solves the core problems of dendrite growth, ion transport hysteresis and interface instability in negative electrode-free batteries through structural strengthening of high-entropy MXene, integrated interface bonding and in-situ regulation of fluorinated SEI, providing an innovative technical path for high-safety, high-energy density lithium metal batteries.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the XRD pattern of high entropy MAX and high entropy MXene in Example 1 of the present invention;

[0028] Figure 2 This is the state density diagram of the unit MXene in Comparative Example 1 of the present invention;

[0029] Figure 3 is a high entropy MXene state density diagram in Example 1 of the present invention;

[0030] Figure 4 These are the SEM and EDS images of the high-entropy MXene in Example 1 of the present invention;

[0031] Figure 5 is an AFM image of the high entropy MXene in Example 1 of the present invention;

[0032] Figure 6 is a TEM image of the high entropy MXene in Example 1 of the present invention;

[0033] Figure 7 This is a peeling force diagram of the modified PP diaphragm 1 and the copper foil after hot pressing in Example 1 of the present invention;

[0034] Figure 8 This is a peeling force diagram of the modified PP diaphragm 2 and the copper foil after hot pressing in Comparative Example 1 of the present invention;

[0035] Figure 9 1 is a comparison diagram of the contact angles of the modified PP membrane 1 in Example 1 of the present invention and the modified PP membrane 2 in Comparative Example 1;

[0036] Figure 10 1 is a comparison chart of the fracture energies of the modified PP membrane 1 in Example 1 of the present invention, the modified PP membrane 2 in Comparative Example 1, and the modified PP membrane 3 in Comparative Example 2;

[0037] Figure 11 1 is a comparison chart of the lithium ion migration numbers of the modified PP membrane 1 in Example 1 of the present invention, the modified PP membrane 2 in Comparative Example 1, and the modified PP membrane 3 in Comparative Example 2;

[0038] Figure 12 1 is a comparison chart of the cycle stability performance of lithium symmetrical batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0039] Figure 13 1 is a comparison chart of the cycle curves of the negative electrode-free button batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0040] Figure 14 It is a comparison diagram of the cycle rate curves of the negative electrode-free button batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0041] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a," "an," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0043] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the product or device comprising the element.

[0044] The present invention provides a method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator, comprising the following steps:

[0045] S1. A multilayer high-entropy MAX phase raw material, i.e., TiVNbMoAlC3, is etched in a mixed solution of lithium fluoride and hydrochloric acid, washed with deionized water until neutral, and then cyclically peeled off using a high-pressure homogenizer. Centrifugal separation is performed to obtain high-entropy MXene nanosheets with rich surface fluorinated functional groups, i.e., TiVNbMoC3 nanosheets;

[0046] S2. dissolving polyacrylamide (PAM) colloid in deionized water and stirring at a constant speed to form a homogeneous adhesive solution;

[0047] S3, dispersing the high-entropy MXene nanosheets in S1 into the PAM colloid in S2, and mixing them by a high-speed homogenizer to form a high-entropy MXene / PAM mixed slurry;

[0048] S4, uniformly coating the mixed slurry in S3 on the surface of the polypropylene (PP) diaphragm by a wire rod coating process, and then drying by gradient heating to form a dense composite coating;

[0049] S5. The diaphragm coated in S4 is bonded to the copper current collector through a soft packaging process of first hot pressing and then liquid injection to form an integrated interface structure.

[0050] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S1, the composition of the mixed solution of lithium fluoride and hydrochloric acid is: 1 g of lithium fluoride, a hydrochloric acid concentration of 12 mol / L, and a hydrochloric acid usage of 40 mL; 1 g of high-entropy MAX raw material; the etching temperature of the etching treatment is 45°C, and the treatment time is 72 h; the working pressure of the high-pressure homogenizer is 1100-1200 MPa, and the number of cycle treatments is 10-15 times.

[0051] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S1, the single layer thickness of the high-entropy MXene nanosheet is 1-2 nm, and the number of layers is 3-5 layers.

[0052] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S2, the stirring time for generating the homogeneous adhesive solution is 4-6 hours, and the mass concentration of the adhesive solution is 8%-12%.

[0053] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S3, the speed of the high-speed homogenizer is 2000 r / min, the mixing time is 30-60 min, and the slurry viscosity is controlled at 500-800 mPa·s.

[0054] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S3, the mass ratio of high-entropy MXene to polyacrylamide in the high-entropy MXene / PAM mixed slurry is 8:1, and the solid content of the slurry is 25%.

[0055] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S4, the wire rod coating process uses an OSP-1.5 type wire rod, the coating speed is 0.5-1.5 m / min, and the coating thickness after drying is 4-5 μm.

[0056] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S4, the thickness of the PP separator substrate is 12-16 μm, and the drying conditions are pre-baking at 40°C for 1 hour and final baking at 60°C for 6 hours.

[0057] Preferably, in the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery separator design method, in S5, the hot pressing process has a hot pressing temperature of 80°C, a pressure of 0.5 MPa, and a holding time of 30-60s.

[0058] Preferably, the composite coating membrane prepared by the above-mentioned high entropy MXene-high viscosity colloid composite coating battery membrane design method has a lithium ion transfer number of 0.76 and a fracture energy of 50.15 J / m 3 , the capacity retention rate of the negative electrode-free soft-pack battery after 100 cycles is 82.6%.

[0059] In order to more clearly and in detail introduce the high-entropy MXene-high-viscosity colloid composite coating battery separator design method provided by the embodiment of the present invention, it will be described below in conjunction with specific examples.

[0060] Example 1

[0061] S1. Place 1g of multilayer high-entropy MAX phase raw material (TiVNbMoAlC3) in a mixed solution of 1g of lithium fluoride and 40mL of 12mol / L hydrochloric acid, etch it at a constant temperature of 45°C for 72h, and then wash it with deionized water until it is neutral; the etched product is cyclically peeled off 10-15 times by a high-pressure homogenizer at a pressure of 1100-1200MPa, and centrifuged at a speed of 6000r / min to obtain high-entropy MXene (TiVNbMoC3) nanosheets with a single layer thickness of 1-2nm and 3-5 layers, which are rich in fluorinated functional groups on the surface.

[0062] S2. Dissolve polyacrylamide (PAM) colloid in deionized water, stir uniformly at a speed of 500 r / min for 4-6 hours, and prepare a homogeneous adhesive solution with a mass concentration of 8%-12%.

[0063] S3. Disperse the high-entropy MXene nanosheets in S1 in the PAM colloid in S2 at a mass ratio of 8:1, mix them in a high-speed homogenizer at a speed of 8000-12000 r / min for 30-60 min, control the slurry viscosity to 500-800 mPa·s, and form a high-entropy MXene / PAM mixed slurry with a solid content of 25%.

[0064] S4. The mixed slurry in S3 is evenly coated on the surface of a polypropylene (PP) diaphragm with a thickness of 12-16 μm using an OSP-1.5 wire rod at a coating speed of 0.5-1.5 m / min for thickness control screening; then a gradient drying process is performed with pre-baking at 40°C for 1 hour and final baking at 60°C for 6 hours to form a dense composite coating.

[0065] S5. Place the negative electrode-free lithium metal soft-pack battery assembled with the coated diaphragm and copper current collector in S4 in a hot press, maintain the pressure at 80°C and 0.5 MPa for 30-60 seconds to form a seamlessly bonded integrated interface structure between the coating and the current collector, and then perform the liquid injection operation in a vacuum glove box.

[0066] Comparative Example 1

[0067] S1. Place 1g of unit MAX phase raw material (Ti3AlC2) in a mixed solution of 1g of lithium fluoride and 40mL of 12mol / L hydrochloric acid, etch it at a constant temperature of 45℃ for 24h, and then wash it with deionized water until it is neutral; ultrasonically peel the etched product to obtain unit MXene (Ti3C2) nanosheets with a single layer thickness of 1-2nm and 8-10 layers.

[0068] S2. Sodium carboxymethyl cellulose (CMC) colloid is dissolved in deionized water and stirred at a constant speed of 500 r / min for 4-6 hours to prepare a homogeneous adhesive solution with a mass concentration of 8%-12%. The solution is then mixed with the unit MXene nanosheets in S1 at a ratio of 8:1 by magnetic stirring for 1 hour to obtain a mixed slurry.

[0069] S3. Use a scraper to apply the mixed slurry in S2 to the surface of a polypropylene (PP) diaphragm with a thickness of 12-16 μm, and dry it at 40°C for 6 hours to form a composite coating.

[0070] Comparative Example 2

[0071] S1. Place 1g of high-entropy MAX phase raw material (TiVNbMoAlC3) in a mixed solution of 1g of lithium fluoride and 40mL of 12mol / L hydrochloric acid, etch it at a constant temperature of 45℃ for 72h, and then wash it with deionized water until it is neutral; ultrasonically peel the etched product to obtain high-entropy MXene (TiVNbMoC3) nanosheets with a single layer thickness of 1-2nm and 8-10 layers.

[0072] S2. Dissolve polyacrylamide (PAM) colloid in deionized water, stir uniformly at a speed of 500 r / min for 4-6 hours, and prepare a homogeneous adhesive solution with a mass concentration of 8%-12%.

[0073] S3. Disperse the high-entropy MXene nanosheets in S1 in the PAM colloid in S2 at a mass ratio of 8:1, and mix them for 30-60 minutes at a speed of 8000-12000 r / min using a high-speed homogenizer to form a high-entropy MXene / PAM mixed slurry with a solid content of 25%.

[0074] S4. The mixed slurry in S3 is evenly coated on the surface of a polypropylene (PP) diaphragm with a thickness of 12-16 μm using an OSP-1.5 wire rod at a coating speed of 0.5-1.5 m / min for thickness control screening; then a gradient drying process is performed with pre-baking at 40°C for 1 hour and final baking at 60°C for 6 hours to form a dense composite coating.

[0075] Test Example 1

[0076] a. X-ray diffractometer (XRD) characterization

[0077] Figure 1 The XRD patterns of high entropy MAX and high entropy MXene in Example 1 of the present invention are as follows: Figure 1 As shown in the figure, after etching, the high-entropy MXene product after etching showed an obvious (002) characteristic peak compared with the high-entropy MAX raw material, proving the successful etching of the material.

[0078] b. Density of states (DOS) calculation

[0079] Figure 2 This is the state density diagram of the unit MXene in Comparative Example 1 of the present invention; Figure 3 This is the state density diagram of the high-entropy MXene in Example 1 of the present invention. By comparison, it can be seen that the state density of the high-entropy MXene is closer to the 0eV Fermi level, and its structure is more conducive to the migration of electrons.

[0080] c. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) characterization

[0081] Figure 4 The SEM and EDS images of the high entropy MXene in Example 1 of the present invention are as follows: Figure 4 As shown, the high-entropy MXene product after etching presents an obvious layered exfoliation structure in which various metal elements are evenly distributed. At the same time, fluorine elements attached to the surface of the high-entropy MXene are observed.

[0082] d. Atomic force microscopy (AFM) characterization

[0083] Figure 5 This is an AFM image of the high entropy MXene in Example 1 of the present invention, as shown in FIG. Figure 5 As shown, the stacking thickness of the high entropy MXene prepared in Example 1 is 4-7 nm.

[0084] e. Transmission electron microscopy (TEM) characterization

[0085] Figure 6 This is a TEM image of the high entropy MXene in Example 1 of the present invention. The high entropy MXene prepared in Example 1 of the present invention was characterized by TEM. The results are as follows Figure 6 shown.

[0086] f. Peel force test

[0087] The modified PP diaphragm 1 in Example 1 and the modified PP diaphragm 2 in Comparative Example 1 were subjected to a peeling force test. Figure 7 is a peeling force diagram of the modified PP diaphragm 1 in Example 1 of the present invention, Figure 8 This is the peeling force diagram of the modified PP membrane 2 in comparative example 1 of the present invention. It can be seen that the modified PP membrane 1 in Example 1 has a greater peeling force with the copper current collector than the modified PP membrane in comparative example 1, which proves that the modified PP membrane 1 prepared in Example 1 can more effectively realize the integrated structure of the membrane and the negative electrode interface from a mechanical perspective.

[0088] g. Contact angle test

[0089] The contact angle test was performed on the modified PP membrane 1 in Example 1 and the modified PP membrane 2 in Comparative Example 1. Figure 9 The contact angle comparison diagram of the modified PP diaphragm in Example 1 of the present invention and the modified PP diaphragm in Comparative Example 1 is shown in FIG. Figure 9 As shown, it can be seen that the modified PP membrane 1 in Example 1 has a smaller electrolyte contact angle than the modified PP membrane 2 in Comparative Example 1 due to the addition of PAM containing polar amide groups, which proves that the modified PP membrane 1 prepared in Example 1 has better wettability to the electrolyte.

[0090] h. Fracture energy test

[0091] Stress-strain tests were performed on the modified PP membrane 1 in Example 1, the modified PP membrane 2 in Comparative Example 1, and the modified PP membrane 3 in Comparative Example 2. Figure 10 The stress-strain curve comparison diagram of the modified PP diaphragm 1 in Example 1 of the present invention, the modified PP diaphragm 2 in Comparative Example 1, and the modified PP diaphragm 3 in Comparative Example 2 is shown in FIG. The fracture energy data is obtained by performing area integration on the curves. The results are as follows: Figure 10 As shown, by comparison, the mechanical properties of the modified PP diaphragm 1 in Example 1 are greatly improved.

[0092] Test Example 2

[0093] a. Lithium ion migration number test (it)

[0094] Figure 11 It is a comparison chart of the ion migration numbers of the traditional PP membrane and the modified PP membrane one in Example 1, the modified PP membrane two in Comparative Example 1, and the modified PP membrane three in Comparative Example 2. It can be seen from the comparison that the lithium ion migration number (0.76) of the modified PP membrane one in Example 1 is greater than the lithium ion migration number (0.56) of the modified PP membrane two in Comparative Example 1 and the lithium ion migration number (0.63) of the modified PP membrane three in Comparative Example 2.

[0095] b. Electrochemical performance test

[0096] Figure 12 The lithium symmetrical batteries are respectively assembled from the modified PP diaphragm 1 in Example 1, the modified PP diaphragm 2 in Comparative Example 1, and the modified PP diaphragm 3 in Comparative Example 2. The cycle stability comparison diagram of the three lithium symmetrical batteries is as follows: Figure 12 As shown, compared with the two groups of comparative examples, the polarization voltage of the modified PP membrane in Example 1 is significantly reduced and the stable cycle time is greatly improved.

[0097] The modified PP diaphragm 1 in Example 1, the modified PP diaphragm 2 in Comparative Example 1, and the modified PP diaphragm 3 in Comparative Example 2 were respectively assembled with the lithium iron phosphate positive electrode to form a negative electrode-free soft pack battery. Figure 13 1 is a comparison chart of the cycle curves of the negative electrode-free button batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2, respectively; Figure 14 The figure is a comparison of the cycle rate curves of the negative electrode-free button batteries assembled in Example 1, Comparative Example 1 and Comparative Example 2. Figure 13 、 14 It can be seen that the modified PP separator prepared in Example 1 has better capacity retention and rate performance.

[0098] A systematic comparison of the examples and comparative examples demonstrates that the high-entropy MXene-based composite separator proposed in this invention exhibits significant performance advantages in anode-free lithium metal batteries. Compared to conventional single-metal MXene-coated separators or pure polymer coatings, this invention utilizes atomic-level solid solution design of multiple metal elements (Ti / V / Nb / Mo) to induce lattice distortion. This allows the composite separator to maintain an ultra-thin thickness (16-20μm) while significantly improving mechanical strength, completely eliminating the potential short-circuit risk caused by dendrite penetration. Furthermore, thanks to the in-situ conversion of the high-entropy MXene surface's high-density fluorinated functional groups, the lithium fluoride-rich SEI film formed during cycling significantly suppresses electrolyte decomposition side reactions, maintaining a stable Coulombic efficiency above 99%. Comparative experiments demonstrate that the anode-free battery employing this solution exhibits a capacity retention exceeding 80% after 100 cycles at a 0.5C rate, far exceeding the 59.1% and 21.3% of the comparative examples, respectively, demonstrating its long-term cycling stability.

[0099] The core innovation of this invention lies in the synergistic optimization of multi-dimensional performance through material genetic design and interface engineering. First, the lattice distortion effect and strong covalent bond network of high-entropy MXene impart mechanical rigidity to the ceramic separator. Its two-dimensional layered structure, through orderly stacking, constructs continuous lithium-ion transport channels, overcoming the mutually exclusive bottleneck of mechanical strength and ion flux in traditional modified separators. Second, the synergistic effect of the high-viscosity PAM colloid and the hot-press bonding process creates an integrated interface between the separator coating and the copper current collector, completely eliminating the ion transport barrier caused by the traditional physical contact gap and forcing lithium ions to rapidly desolvate during cross-interface migration, achieving a migration number of 0.76. Furthermore, the fluorinated terminals (-F, -OF) introduced in situ during the MXene etching process preferentially react with lithium during the initial electrochemical cycle, forming a SEI film dominated by high-ionic conductivity lithium fluoride. Its dense passivation properties not only reduce the lithium polarization voltage but also block the path of continuous electrolyte decomposition, achieving dynamic interface stability for up to 900 hours.

[0100] Based on the above technological innovations, the composite diaphragm of the present invention successfully overcomes the core problems that have long existed in the field of negative electrode-free lithium metal batteries, such as runaway dendrites, interface failure, and short cycle life. Its ultra-thin and lightweight features are expected to enable the battery energy density to exceed 400Wh / kg, an increase of more than 40% compared to traditional graphite negative electrode systems. At the same time, the integrated interface design is compatible with existing roll-to-roll manufacturing processes and has the feasibility of large-scale mass production. This technology not only provides a reliable technical path for the commercialization of high-energy-density lithium metal batteries, but can also be expanded to emerging fields such as sodium metal batteries and solid-state batteries, promoting the innovation process of next-generation energy storage systems.

[0101] Therefore, the present invention adopts the above-mentioned high-entropy MXene-high-viscosity colloid composite coating battery diaphragm design method, and the lattice distortion effect of two-dimensional high-entropy MXene enhances the intrinsic mechanical properties of the diaphragm: the solid solution and distortion of multi-metal element atoms in the MXene lattice form a high-strength covalent bond network, combined with the ordered stacking structure of the two-dimensional sheets, giving the composite diaphragm excellent puncture resistance and deformation resistance, significantly inhibiting the risk of diaphragm penetration caused by lithium dendrite growth, while maintaining the lightweight characteristics of the diaphragm.

[0102] The high-viscosity hot-pressed integrated structure accelerates lithium-ion desolvation and transport: A high-viscosity colloid and a soft-packing process involving hot pressing followed by liquid injection achieve a seamless interface between the separator coating and the anode current collector, eliminating the ion transport barrier caused by traditional physical contact gaps. This integrated design forces lithium ions to rapidly desolvate during cross-interface transport, significantly improving ion migration efficiency and guiding lithium ions to uniformly deposit along the interlayer channels of the MXene.

[0103] Fluorinated terminals on the MXene surface induce the construction of a stable SEI chemistry: Fluorinated functional groups generated in situ during the etching process preferentially react with lithium during the initial battery cycle, forming an SEI film dominated by highly ionic-conductive lithium fluoride. This SEI effectively passivates the electrode interface, lowering the kinetic barrier for lithium deposition while suppressing electrolyte side reactions, enabling highly reversible lithium metal deposition and stripping.

[0104] This invention solves the core problems of dendrite growth, ion transport hysteresis and interface instability in negative electrode-free batteries through structural strengthening of high-entropy MXene, integrated interface bonding and in-situ regulation of fluorinated SEI, providing an innovative technical path for high-safety, high-energy density lithium metal batteries.

[0105] Finally, it should be noted that 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 preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator, characterized in that: The following steps are involved: S1. Etching a multilayer high-entropy MAX phase raw material, TiVNbMoAlC3, in a mixed solution of lithium fluoride and hydrochloric acid. After washing with deionized water until neutral, the multilayer high-entropy MAX phase raw material is cyclically peeled off by a high-pressure homogenizer and centrifuged to obtain TiVNbMoC3 nanosheets rich in fluorinated functional groups on the surface. S2. dissolving polyacrylamide colloid in deionized water and stirring at a constant speed to form a homogeneous adhesive solution; S3, dispersing the high-entropy MXene nanosheets in S1 in the polyacrylamide colloid in S2, and mixing them by a high-speed homogenizer to form a high-entropy MXene / polyacrylamide mixed slurry; S4, uniformly coating the mixed slurry in S3 on the surface of the polypropylene diaphragm by a wire rod coating process, and then drying by gradient heating to form a dense composite coating; S5, bonding the coated diaphragm in S4 to the copper current collector through a hot pressing process in a soft packaging process of first hot pressing and then liquid injection to form an integrated interface structure; The composite coating battery separator prepared by steps S1-S5 is used for lithium batteries.

2. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, characterized in that: In S1, the composition of the lithium fluoride and hydrochloric acid mixed solution is: lithium fluoride 1g, hydrochloric acid concentration of 12mol / L, hydrochloric acid usage amount is 40mL; high entropy MAX raw material is 1g; The etching temperature of the etching treatment is 45° C., the treatment time is 72 hours; the working pressure of the high-pressure homogenizer is 1100-1200 MPa, and the number of cycle treatments is 10-15 times.

3. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, characterized in that: In S1, the single layer thickness of the high entropy MXene nanosheet is 1-2 nm, and the number of layers is 3-5.

4. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, wherein: In S2, the stirring time for generating the homogeneous binder solution is 4-6 hours, and the mass concentration of the binder solution is 8%-12%.

5. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, characterized in that: In S3, the rotation speed of the high-speed homogenizer is 2000 r / min, the mixing time is 30-60 min, and the slurry viscosity is controlled at 500-800 mPa·s.

6. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, characterized in that: In S3, the mass ratio of high entropy MXene to polyacrylamide in the high entropy MXene / polyacrylamide mixed slurry is 8:1, and the solid content of the slurry is 25%.

7. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, characterized in that: In S4, the wire rod coating process uses an OSP-1.5 wire rod, the coating speed is 0.5-1.5 m / min, and the coating thickness after drying is 4-5 μm.

8. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, wherein: In S4, the polypropylene separator has a thickness of 12-16 μm, and the drying conditions are pre-baking at 40° C. for 1 hour and final baking at 60° C. for 6 hours.

9. The method for designing a high-entropy MXene-high-viscosity colloid composite coating battery separator according to claim 1, wherein: In S5, the hot pressing process is performed at a temperature of 80° C., a pressure of 0.5 MPa, and a holding time of 30-60 seconds.

10. The composite coating membrane prepared by the high entropy MXene-high viscosity colloid composite coating battery membrane design method according to any one of claims 1 to 9, characterized in that: The lithium ion transference number of the separator is 0.76 and the fracture energy is 50.15 J / m 3 , the capacity retention rate of the negative electrode-free soft-pack battery after 100 cycles is 82.6%.

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