Modified diaphragm, preparation method and lithium metal battery

Abstract

In order to overcome the problems of uncontrollable dendrite growth and serious interface side reactions in lithium metal negative electrodes in the prior art, the present invention provides a modified diaphragm, a preparation method and a lithium metal battery; the modified diaphragm includes a base film and a modified coating, the modified coating is applied on the surface of the base film, the modified coating includes a composite material formed by a carboxyl precursor and carbon nanotubes, the carboxyl precursor is a precursor modified by a carboxyl modifier, and the precursor includes GeS or SnS x The modified separator provided by the present invention, which is prepared by coating a modified coating made of a carboxylated precursor and carbon nanotube spheres, can effectively solve the problems of uncontrolled dendrite growth and the resulting interfacial side reactions in lithium metal negative electrodes of lithium metal batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and in particular relates to a modified diaphragm, a preparation method and a lithium metal battery. Background Art

[0002] With the growing global demand for clean energy and portable electronic devices, the development of energy storage systems with high energy density, long cycle life, and high safety has become a research hotspot. Lithium metal batteries, with their theoretical specific capacity (3860 mAh / g) far exceeding that of traditional graphite anodes (372 mAh / g), are considered a key candidate for next-generation energy storage technology. However, the application of lithium metal anodes faces significant challenges, particularly the uncontrolled growth of lithium dendrites, which not only limits the battery's cycling stability and safety but can also lead to internal short circuits, and in severe cases, thermal runaway or even explosion.

[0003] Although existing strategies for inhibiting lithium dendrites, such as the use of electrolyte additives and the construction of artificial SEI membranes, have achieved certain results, it is still difficult to fundamentally balance the uniformity and efficiency of lithium deposition. In this context, exploring new modified membrane technologies has become a key way to break through the performance bottleneck of lithium metal batteries. Modified membranes aim to physically block the penetration of lithium dendrites by introducing special functional materials on their surface or structure, such as polymer coatings, inorganic nanoparticle embedding, or three-dimensional porous structure design. However, the special functional materials introduced on the surface of the membrane have the problem of blocking the ion transmission channel during the ion insertion and extraction process, which is not conducive to the transmission of ions. Summary of the Invention

[0004] To address the problems of uncontrollable dendrite growth and severe interface side reactions in lithium metal negative electrodes in the prior art, a modified diaphragm, a preparation method and a lithium metal battery are provided.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] In one aspect, the present invention provides a modified membrane, comprising a base membrane and a modified coating, wherein the modified coating is applied to the surface of the base membrane, and the modified coating comprises a carboxyl precursor and a carbon nanotube composite material, wherein the carboxyl precursor is a precursor modified by a carboxyl modifier, and the precursor comprises GeS or SnS x One of the following, where x=1-2.

[0007] Optionally, in the composite material of the carboxylated precursor and the carbon nanotube, the mass ratio of the precursor, the carboxyl modified substance and the carbon nanotube is 1:1-20:0.05-1.

[0008] Optionally, the modified coating has a thickness of 0.1-20 μm.

[0009] Optionally, the particle size of the precursor is 0.02-10 μm.

[0010] Optionally, the base film material includes one of a polyethylene base film, a polypropylene base film, a polyethersulfone base film and a polytetrafluoroethylene base film.

[0011] Optionally, the modified coating further includes a binder, and the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, acrylic resin, and styrene butadiene rubber.

[0012] Optionally, the carboxyl modifier includes a carboxylated silane coupling agent, and the carboxylated silane coupling agent includes one or more carboxylated derivatives of 3-(trimethoxysilyl)propionic acid, 3-(triethoxysilyl)propionic acid and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0013] Optionally, the method for preparing the modified diaphragm comprises the following operations:

[0014] S1: Preparation of precursors;

[0015] S2: mixing the precursor with a carboxyl-modified substance for carboxylation to obtain a carboxylated precursor;

[0016] S3: ball-milling the carboxyl precursor and the carbon nanotubes to obtain a composite material of the carboxyl precursor and the carbon nanotubes;

[0017] S4: preparing a slurry for a modified coating by preparing a carboxylated precursor and a carbon nanotube composite material;

[0018] S5: applying the slurry of the modified coating on the surface of the base film, and obtaining the modified diaphragm after drying.

[0019] Optionally, a dispersant is added during the ball milling process of S3, and the dispersant includes one or more of anhydrous ethanol, acetone, polyvinyl pyrrolidone and sodium lauryl sulfate.

[0020] Optionally, in S5, the drying temperature is 60-120°C.

[0021] Optionally, the preparation method S1 of the modified diaphragm includes:

[0022] The S1 comprises the following steps:

[0023] mixing a sulfur source with a solvent to obtain a mixed solution;

[0024] Germanium salt or tin salt is added to the mixed solution, and the precursor is obtained after drying.

[0025] Optionally, in S1, the solvent includes one or more of methanol, ethanol, propanol and deionized water.

[0026] Optionally, the sulfur source includes one or more of sodium sulfide, ammonium sulfide, sodium thiosulfate, diethyl sulfide, thiourea and cysteine; and / or, the germanium salt includes one or more of sodium germanate, germanium chloride, potassium germanate, ammonium germanate and tetraethyl germanate; and / or, the tin salt includes one or more of stannous chloride, tin oxide, tin sulfate and tin acetate.

[0027] On the other hand, the present invention provides a lithium metal battery comprising a positive electrode, a lithium metal negative electrode, and the modified diaphragm or the modified diaphragm prepared by the preparation method of the modified diaphragm;

[0028] The side of the modified separator coated with the modified coating faces the lithium metal negative electrode.

[0029] The beneficial effects of the present invention are:

[0030] The modified diaphragm provided by the present invention includes a base film and a modified coating, wherein the modified coating includes a composite material formed by a carboxyl precursor and carbon nanotubes. The carboxyl functional group in the carboxyl precursor can increase the wettability of the electrolyte, thereby better promoting the infiltration of the electrolyte into the modified diaphragm. In addition, it can also interact with the lithium ions in the electrolyte to promote lithium ion transmission. In addition, the carboxyl precursor can be in the precursor (GeS or SnS x ) form strong hydrogen bonds between particles, inhibiting the growth of GeS or SnS x The dissociation in the electrolyte makes the GeS or SnS coated on the base film x It is released slowly and gradually during the charge and discharge process of the battery, ensuring that Li-Ge or Li-Sn alloy and a protective SEI film rich in Li2S will always form on the surface of the lithium metal negative electrode, thereby improving the electrochemical performance of the lithium metal negative electrode.

[0031] On the other hand, carbon nanotubes can be well wrapped on the surface of carboxylated precursors. The porous structure of carbon nanotubes can provide additional lithium ion transmission channels, improve ion conductivity, and provide structural support to avoid GeS or SnS x The rapid dissolution in the organic electrolyte further enhances the sustainable release characteristics of the carboxyl precursor. The carboxyl functional group modification and carbon nanotube composite play a synergistic role in improving the performance of GeS or SnS x The ionic conductivity of the coated base film solves the problems of uncontrollable growth of dendrites and the resulting interfacial side reactions in the lithium metal negative electrode of the lithium metal battery, and promotes the efficient conduct of the electrochemical reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the modified diaphragm provided by the present invention;

[0033] Figure 2 Schematic diagram of the application of the modified diaphragm provided by the present invention in a lithium metal battery;

[0034] Figure 3 2 is a cycle-capacity retention curve of the embodiments of the present invention and the comparative example.

[0035] The reference numerals in the drawings of the specification are as follows:

[0036] 1. Modified coating; 2. Base film; 3. SEI film; 4. Lithium metal anode; 5. Alloy layer. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0039] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0040] Reference Figure 1 The present invention provides a modified membrane, comprising a base membrane 2 and a modified coating 1, wherein the modified coating 1 is coated on the surface of the base membrane 2, and the modified coating 1 comprises a carboxyl precursor and a carbon nanotube composite material, wherein the carboxyl precursor is a precursor modified by a carboxyl modifier, and the precursor comprises GeS or SnS x One of the following, where x=1-2.

[0041] Specifically, the present invention uses a hydrothermal / solvothermal method to prepare germanium sulfide (GeS2) or tin sulfide (SnS x , x=1-2) precursor, and then the precursor is carboxylated by using a carboxyl modifier to obtain a carboxylated precursor (COOH-GeS or COOH-SnS x ), COOH-GeS or COOH-SnS x The composite is ball-milled with carbon nanotubes (CNTs), and then calcined in a tube furnace for annealing to remove impurities, thereby obtaining carboxylated germanium sulfide / carbon nanotubes (COOH-GeS / CNTs) or carboxylated tin sulfide / carbon nanotubes (COOH-SnSx / CNTs).

[0042] Specifically, in the preparation of the germanium sulfide precursor, the amount of germanium salt added accounts for 50%-95% of the precursor; in the preparation of the tin sulfide precursor, the amount of tin salt added accounts for 50%-95% of the precursor.

[0043] In the modified membrane provided by the present invention, the carboxyl functional group in the carboxyl precursor can increase the wettability of the electrolyte, thereby better promoting the infiltration of the electrolyte into the modified membrane, and can also interact with the lithium ions in the electrolyte to promote lithium ion transmission. In addition, the carboxyl precursor can be in the precursor (GeS or SnS x ) form strong hydrogen bonds between particles, inhibiting the growth of GeS or SnS x The dissociation in the electrolyte makes the GeS or SnS coated on the base film 2 x It is released slowly and gradually during the charge and discharge process of the battery, ensuring that Li-Ge or Li-Sn alloy and a protective SEI film 3 rich in Li2S are always formed on the surface of the lithium metal negative electrode 4, thereby improving the electrochemical performance of the lithium metal negative electrode 4.

[0044] On the other hand, after the carboxylation precursor and carbon nanotubes are ball-milled, the carbon nanotubes can be well wrapped on the surface of the carboxylation precursor. The porous structure of the carbon nanotubes can provide additional lithium ion transmission channels, improve ion conductivity, and provide structural support to avoid GeS or SnS x The rapid dissolution in the organic electrolyte further enhances the sustainable release characteristics of the carboxyl precursor. The carboxyl functional group modification and carbon nanotube composite play a synergistic role in improving the performance of GeS or SnS x The ionic conductivity of the coated base film 2 solves the problems of uncontrolled growth of dendrites and the resulting interface side reactions in the lithium metal negative electrode 4 of the lithium metal battery.

[0045] In some embodiments, in the composite material of the carboxylated precursor and the carbon nanotube, the mass ratio of the precursor, the carboxyl modification, and the carbon nanotube is 1:1-20:0.05-1.

[0046] Specifically, in the carboxylation precursor and the carbon nanotube composite material, when the carboxylation modifier is too little, the corresponding carboxylate groups on the surface of the modified carboxylation precursor are less, which is not conducive to its function. If the carboxylation modifier is too much, it is not conducive to cost control. Through previous relevant tests, in the modified coating 1, the mass ratio of the carboxylation modifier to other substances is controlled within the above range, which can fully exert its function and is also conducive to cost control; if the CNT content is too little, it is not conducive to its function; too much not only has high cost, but also due to the extremely high aspect ratio of CNT, it is difficult to disperse, which is not conducive to performance.

[0047] In some embodiments, the modified coating 1 has a thickness of 0.1-20 μm.

[0048] Specifically, the thickness of the modified coating 1 may be 0.1 μm, 0.5 μm, 1 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm or 20 μm.

[0049] Setting the coating thickness of the modified coating 1 within this range can ensure that the carboxyl functional groups in the modified coating 1 improve the wettability of the electrolyte and the wettability of GeS or The particles can stabilize and control the release without causing excessive obstruction to ion transmission due to the coating being too thick. The advantages of the conductive network constructed by CNT and the additional ion transmission channels it provides can also be better demonstrated. While maintaining good ionic conductivity, the protective effect on the lithium metal negative electrode 4 can also be more fully reflected, so that the battery's cycle life, inhibition of dendrite growth and other electrochemical properties can be better optimized.

[0050] In some embodiments, the particle size of the precursor is 0.02-10 μm.

[0051] Specifically, the particle size of the precursor may be 0.02 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 5 μm, 8 μm or 10 μm.

[0052] The particle size of the precursor is within the relatively small particle size range, which means that the unit mass of the precursor has a larger specific surface area. For such a precursor, the larger specific surface area allows it to expose more active sites, resulting in higher reactivity, whether in the interaction with the carboxyl functional groups in the carboxylated precursor to form hydrogen bonds, or in subsequent reactions with the electrolyte and the lithium metal negative electrode 4 during the battery's charge and discharge process. For example, in terms of forming hydrogen bonds to inhibit its dissociation in the electrolyte, more surface area can participate in the construction of hydrogen bonds, which can more effectively stabilize its own structure, making it more dispersible in the electrolyte and more conducive to the expected slow and gradual release, thereby better acting on the surface of the lithium metal negative electrode 4. At the same time, its fine particles can be relatively evenly dispersed in the modified coating 1, without causing significant blockage of the ion transport channel. On the contrary, due to its high activity and sufficient contact with surrounding substances, it helps to optimize the ion transport environment, and together with the carboxyl functional groups, promotes lithium ions to pass through the modified coating 1 more smoothly, thereby improving the ionic conductivity of the entire battery system, reducing polarization during the charge and discharge process, and improving the battery's charge and discharge efficiency.

[0053] In some embodiments, the base film 2 is made of a material selected from the group consisting of a polyethylene-based film, a polypropylene-based film, a polyethersulfone-based film, and a polytetrafluoroethylene-based film.

[0054] In some embodiments, the modified coating 1 further includes a binder, and the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, acrylic resin, and styrene butadiene rubber.

[0055] In some embodiments, the method for preparing the modified membrane comprises the following operations:

[0056] S1: Preparation of precursors;

[0057] S2: mixing the precursor with a carboxyl-modified substance for carboxylation to obtain a carboxylated precursor;

[0058] S3: ball-milling the carboxyl precursor and the carbon nanotubes to obtain a composite material of the carboxyl precursor and the carbon nanotubes;

[0059] S4: preparing a slurry for a modified coating by preparing a carboxylated precursor and a carbon nanotube composite material;

[0060] S5: applying the slurry of the modified coating on the surface of the base film, and obtaining the modified diaphragm after drying.

[0061] Specifically, the preparation method of the modified diaphragm includes the following specific operations:

[0062] a) fully dissolving a sulfur source in deionized water or other solvent to obtain a mixed solution 1;

[0063] b) adding a germanium salt or a tin salt to the first mixed solution and fully dispersing the mixture to obtain a second mixed solution;

[0064] c) transferring the second mixed solution into a Teflon autoclave for reaction;

[0065] d) collecting the precipitate by centrifugation, washing it three times with deionized water and anhydrous ethanol, respectively, and then drying it in an oven overnight to obtain the precursor;

[0066] e) subjecting the precursor obtained in step d to carboxylation;

[0067] f) ball milling the carboxylated precursor and CNT;

[0068] g) The precursor prepared in step f is placed in a tube furnace and annealed at a certain temperature for a certain time in a hydrogen-argon (Ar / 5% vol H2) atmosphere to obtain COOH-GeS / CNT or COOH-SnS x / CNT;

[0069] h) COOH-GeS / CNT or COOH-SnS x / CNT and polyvinylidene fluoride (PVDF) were mixed in N-methyl-2-pyrrolidone (NMP) solution to prepare COOH-GeS / CNT or COOH-SnSx / CNT slurry;

[0070] i) COOH-GeS / CNT or COOH-SnS x The NMP / CNT slurry was coated on the base film 2 and dried in an oven overnight to remove the NMP solvent to obtain a modified separator.

[0071] In the present invention, the preparation principle of the modified coating 1 is as follows: using a hydrothermal / solvothermal method, in a sealed reactor, germanium (Ge) salt or tin (Sn) salt and a sulfur source are dissolved in water or other solvents, and reacted under high temperature and high pressure conditions to promote the diffusion and crystallization of ions to obtain nano-sized or micron-sized germanium sulfide (GeS2) or tin sulfide (SnS x ) precursor, and use the silane coupling agent method to carboxylate it and introduce carboxyl functional groups into the precursor; then the carboxyl (-COOH) precursor is crushed, dispersed, refined and compounded with CNT by ball milling. During the ball milling process, the carboxyl (-COOH) precursor and carbon nanotubes are evenly dispersed and tightly combined by mechanical force. The ball milling process also promotes the chemical bonding between the carboxyl precursor and carbon nanotubes, forming a stronger interface bond. Subsequently, it is calcined in a tube furnace for annealing to remove impurities and obtain COOH-GeS / CNT or COOH-SnS x / CNT

[0072] Wherein, in step c), the heating temperature is 120-200°C and the holding time is 6-24 h;

[0073] In step g), the heating temperature is 300-800° C., the heating time is 1-12 hours, and the heating rate is 2-10° C. / min; the solvent in step a) includes one or more of methanol, ethanol, propanol, and deionized water.

[0074] In some embodiments, in step S3, a dispersant is added during the ball milling process, and the dispersant includes one or more of anhydrous ethanol, acetone, polyvinyl pyrrolidone and sodium lauryl sulfate.

[0075] Specifically, due to the ball milling process, the carboxylated precursors, GeS or Particles of materials such as carbon nanotubes are prone to aggregate together to form agglomerates due to the interactions between their own surfaces and the van der Waals force between the particles. Therefore, dispersants are added during the ball milling process. The dispersants can be adsorbed on the surface of these particles and prevent the particles from approaching each other through steric hindrance effects or electrostatic repulsion, thereby effectively avoiding the occurrence of agglomeration.

[0076] In some embodiments, in step S5, the drying temperature is 60-120°C.

[0077] In some embodiments, the carboxyl modifier includes a carboxylated silane coupling agent, and the carboxylated silane coupling agent includes one or more carboxylated derivatives of 3-(trimethoxysilyl)propionic acid, 3-(triethoxysilyl)propionic acid, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0078] Specifically, the precursor is carboxylated using a silane coupling agent method to introduce carboxyl functional groups into the precursor. On the one hand, the carboxyl group can enhance the wettability to the electrolyte, promote lithium ion transport, and improve the relevant performance of the electrolyte. On the other hand, it can also react with GeS or The precursor particles interact with each other, such as forming coordination bonds or hydrogen bonds with some active sites on the surface of the precursor through the carboxyl group, to help stabilize the precursor and control its release process in the electrolyte.

[0079] In some embodiments, the sulfur source includes one or more of sodium sulfide, ammonium sulfide, sodium thiosulfate, diethyl sulfide, thiourea and cysteine; and / or, the germanium salt includes one or more of sodium germanate, germanium chloride, potassium germanate, ammonium germanate and tetraethyl germanate; and / or, the tin salt includes one or more of stannous chloride, tin oxide, tin sulfate and tin acetate.

[0080] Another embodiment of the present invention provides a lithium metal battery, comprising a positive electrode, a lithium metal negative electrode 4, and the modified diaphragm or the modified diaphragm prepared by the preparation method of the modified diaphragm;

[0081] The side of the modified separator coated with the modified coating 1 faces the lithium metal negative electrode 4 .

[0082] Specifically, refer to Figure 2 The modified diaphragm is coated with the modified coating 1 and faces the lithium metal negative electrode 4. When the battery is working, COOH-GeS or COOH-SnS x It will dissociate into Ge in the electrolyte 4+ 、S 2- and COOH- or Sn 2+ 、Sn 4+ 、S 2- and COOH-, due to G e4+ 、Sn 2+ 、Sn 4+ Compared with lithium ion (Li + ) has a higher redox potential, free Ge 4+ 、Sn 2+ 、Sn 4+ It is easily reduced by the lithium metal on the lithium metal negative electrode to form a Li-Ge or Li-Sn alloy / alloy layer 5 on the lithium metal surface. + The surface energy of Li-Ge or Li-Sn alloys is lower than that of lithium metal, making the subsequent Li + Tends to deposit on Li-Ge or Li-Sn alloys, allowing for uniform Li + flux, inhibiting the growth of lithium dendrites and dissociating S 2- and COOH- can form a stable protective SEI film 3 rich in Li2S on the surface of the lithium metal negative electrode 4, reducing the interface impedance and inhibiting the continuous side reaction between the lithium metal surface and the electrolyte.

[0083] The present invention is further described below with reference to the following examples.

[0084] Example 1

[0085] This example is used to illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes the following operations:

[0086] 3g of Na2S was added to 60ml of deionized water and magnetically stirred for 2h. Then, 2g of Na2GeO3 was dispersed into the above solution and magnetically stirred for 4h until mixed. The mixed solution was transferred to a 100ml Teflon autoclave, kept in an oven at 150℃ for 15h, and removed after cooling to room temperature. The precipitate was collected by centrifugation, washed three times with deionized water and anhydrous ethanol respectively, and then dried in an oven at 80℃ overnight. 2g of the precipitate and 10.7g of 3-(trimethoxysilyl)propionic acid were dissolved in 100ml of deionized water, stirred at room temperature for 12h, and then centrifuged to collect the product, washed three times with deionized water and anhydrous ethanol respectively, and then dried in an oven at 80℃ overnight to obtain a carboxylated GeS2 precursor. 2g of carboxylated GeS2 precursor, 1g of CNT, and 50ml of anhydrous ethanol were added to a ball mill and milled for 2h to form a composite. The composite was then placed in a tube furnace filled with a hydrogen and argon atmosphere and annealed at 500°C for 4h at a heating rate of 5°C / min to obtain COOH-GeS / CNT. COOH-GeS / CNT and PVDF were mixed in NMP at a mass ratio of 9:1 to obtain a COOH-GeS / CNT modified coating slurry. This slurry was then coated onto an 18μm-thick PP substrate using a 5μm scraper and dried in an oven at 60°C overnight to remove the NMP solvent, resulting in a COOH-GeS / CNT-coated modified separator.

[0087] LiFePO4 slurry was prepared by mixing lithium iron phosphate (LiFePO4) powder, acetylene black, and PVDF in a mass ratio of 8:1:1 in NMP. The slurry was then coated on aluminum foil using a 12μm scraper. After drying in an 80°C oven overnight, the slurry was removed and punched into electrodes with a diameter of 12mm.

[0088] Lithium metal was used as the negative electrode and LiFePO4 as the positive electrode. The side of the modified diaphragm coated with COOH-GeS / CNT faced the negative electrode. The lithium metal battery A1 was assembled in a glove box. The electrolyte was a 1 mol / L lithium hexafluorophosphate solution, and the solvent of the electrolyte was ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

[0089] Example 2

[0090] This example is used to illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0091] In the preparation of the diaphragm, SnS x (Na2S) precursor to obtain COOH-SnS x / CNT-coated modified separator.

[0092] Example 3

[0093] This example is used to illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0094] The thickness of the modified coating on the surface of the base film is 0.5 μm.

[0095] Example 4

[0096] This example is used to illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0097] The thickness of the modified coating on the surface of the base film is 18 μm.

[0098] Example 5

[0099] This example is used to illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0100] In the preparation of the diaphragm, the amount of the carboxyl-modified substance 3-(trimethoxysilyl)propionic acid added was 5 g.

[0101] Comparative Example 1

[0102] This comparative example is used to compare and illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0103] A commercially available diaphragm was used.

[0104] Comparative Example 2

[0105] This comparative example is used to compare and illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0106] During the preparation of the coating slurry, the precursor was not subjected to carboxyl modification and no carbon nanotubes were added.

[0107] Comparative Example 3

[0108] This comparative example is used to compare and illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0109] No carbon nanotubes were added during the preparation of the coating slurry.

[0110] Comparative Example 4

[0111] This comparative example is used to compare and illustrate a modified diaphragm, preparation method, and lithium metal battery disclosed in the present invention, and includes most of the operations in Example 1, except that:

[0112] During the preparation of the coating slurry, the precursor was not subjected to carboxyl modification.

[0113] Performance Testing

[0114] The lithium metal batteries prepared in Examples 1-5 and Comparative Examples 1-4 were electrochemically tested at room temperature. The charge and discharge mode was 0.1C / 0.1C for the first three weeks, followed by 1C / 1C charge and discharge for 200 cycles. The voltage range was 2.5V-3.8V, and 1C=150 mA / g.

[0115] The test results are entered in Table 1.

[0116] Under normal temperature 1°C, the cycle times-capacity retention rate of Example 1-2 and Comparative Example 1-2 were tested, and the results were as follows: Figure 3 The cycle number-capacity retention rate curve is given by Figure 3 It can be seen that the cycle performance of Example 1-2 is better than that of Comparative Example 1-2.

[0117] Table 1

[0118]

[0119] From the test results in Table 1, it can be seen that the test results of the lithium metal batteries prepared in Examples 1-4 in terms of charge specific capacity and cycle performance after charging are better than those in the comparative example;

[0120] Comparing the test results of Example 1 with those of Example 2, the charge specific capacity and cycle performance after charge of Example 1 are better than those of Example 2. The reason may be that the conductivity of GeS is generally higher than that of SnS. x During the battery charging and discharging process, GeS can provide lower resistance, reduce energy loss, and improve the overall efficiency of the battery. x The +2 valence state of COOH-SnS is not stable enough compared to the +2 valence of GeS. Therefore, when reacting with the carboxylated precursor to construct a composite material, side reactions may occur due to valence fluctuations, generating some other tin compound impurities, which are mixed into the composite material system, destroying the uniform and stable structure of the modified coating, causing the final modified coating to have structural defects, thereby leading to COOH-SnS x The volume change during dissociation in the electrolyte is greater than that of GeS, which affects the stability of the modified diaphragm after coating. Therefore, in the test results of Example 1 and Example 2, the overall performance of Example 2 is slightly lower than that of Example 1.

[0121] Compared with Example 1, Example 3 has a coating thickness that is too thin. Therefore, in the performance test, the test results of Example 3 are worse than those of Example 1.

[0122] From the test results of Example 4 and Example 1, it can be seen that the test result of Example 4 is significantly lower than that of Example 1. The reason is that the coating thickness of Example 4 is too thick, which is also not conducive to the improvement of performance.

[0123] Comparing the test results of Example 1 with those of Example 5, the amount of carboxyl modifier added in Example 1 when preparing the modified coating slurry is slightly higher than that in Example 5. Therefore, compared with the two, the performance of Example 1 in the test is also slightly better than that of Example 5.

[0124] Compared with the test results of Comparative Example 2, the carboxylated precursor and CNT composite play a synergistic role in improving the ionic conductivity of the GeS2 coated base film and maintaining the sustainable release of COOH-GeS, thereby improving the cycle stability of the lithium metal battery.

[0125] Compared with the test results of Example 1 and Comparative Example 3, the CNT composite further improves the cycle stability of the lithium metal battery. Compared with Comparative Example 4, the carboxylation characteristics of Example 1 are beneficial to improving the cycle stability of the lithium metal battery.

[0126] From the performance tests of Comparative Examples 1-4, it can be seen that the test result of Comparative Example 1 is the worst, followed by Comparative Example 2. The reason is that the commercially available diaphragm used in Comparative Example 1 is not coated with a modified coating on its surface, and thus cannot improve the dendrite growth of the lithium metal battery and the resulting interfacial side reactions. In the process of preparing the coating slurry in Comparative Example 2, the precursor is not subjected to carboxylation modification treatment and CNTs are not added, which is not conducive to the improvement and optimization of battery performance.

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modified diaphragm for a lithium metal battery, characterized in that: The invention comprises a base film (2) and a modified coating (1), wherein the modified coating (1) is coated on the surface of the base film (2), and the modified coating (1) comprises a composite material formed by a carboxyl precursor and carbon nanotubes, wherein the carboxyl precursor is a precursor modified by a carboxyl modifier, and the precursor comprises GeS or SnS x One of the following, where x=1-2; In the composite material of the carboxyl precursor and the carbon nanotube, the mass ratio of the precursor, the carboxyl modified substance and the carbon nanotube is 1:1-20:0.05-1; The thickness of the modified coating (1) is 0.5-5 μm; The method for preparing the modified diaphragm of the lithium metal battery comprises the following operations: S1: Preparation of precursors; S2: mixing the precursor with a carboxyl-modified substance for carboxylation to obtain a carboxylated precursor; S3: ball-milling the carboxyl precursor and the carbon nanotubes to obtain a composite material of the carboxyl precursor and the carbon nanotubes; S4: preparing a slurry for a modified coating by preparing a carboxylated precursor and a carbon nanotube composite material; S5: applying the modified coating slurry on the surface of the base film, and obtaining a modified diaphragm after drying; The carboxyl modifier includes a carboxylated silane coupling agent, and the carboxylated silane coupling agent includes one or more carboxylated derivatives of 3-(trimethoxysilyl)propionic acid, 3-(triethoxysilyl)propionic acid, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

2. The modified diaphragm for a lithium metal battery according to claim 1, characterized in that: The particle size of the precursor is 0.02-10 μm.

3. The modified separator for a lithium metal battery according to claim 1, characterized in that: The base film (2) is made of a material selected from the group consisting of a polyethylene base film, a polypropylene base film, a polyethersulfone base film and a polytetrafluoroethylene base film.

4. The modified separator for a lithium metal battery according to claim 1, characterized in that: The modified coating (1) further comprises a binder, wherein the binder comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, an acrylic resin and styrene butadiene rubber.

5. The modified separator for lithium metal battery according to claim 1, characterized in that In S3, a dispersant is added during the ball milling process, and the dispersant includes one or more of anhydrous ethanol, acetone, polyvinyl pyrrolidone and sodium lauryl sulfate.

6. The modified separator for lithium metal batteries according to claim 1, characterized in that In the step S5, the drying temperature is 60-120°C.

7. The modified separator for lithium metal batteries according to claim 1, characterized in that The S1 comprises the following steps: mixing a sulfur source with a solvent to obtain a mixed solution; Germanium salt or tin salt is added to the mixed solution, and the precursor is obtained after drying.

8. The modified separator for lithium metal battery according to claim 7, characterized in that In S1, the solvent includes one or more of methanol, ethanol, propanol and deionized water.

9. The modified separator for lithium metal battery according to claim 7, characterized in that The sulfur source includes one or more of sodium sulfide, ammonium sulfide, sodium thiosulfate, diethyl sulfide, thiourea and cysteine; and / or, The germanium salt includes one or more of sodium germanate, germanium chloride, potassium germanate, ammonium germanate and tetraethyl germanate; and / or, The tin salt includes one or more of stannous chloride, tin oxide, tin sulfate and tin acetate.

10. A lithium metal battery, characterized in that: A modified separator for a lithium metal battery comprising a positive electrode, a lithium metal negative electrode (4) and the lithium metal battery as claimed in any one of claims 1 to 9; The side of the modified diaphragm coated with the modified coating faces the lithium metal negative electrode (4).

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