Protonated carbon nitride, a preparation method thereof and application thereof in lithium batteries

Abstract

The application belongs to the technical field of batteries, and relates to protonated carbon nitride, a preparation method thereof and application of the protonated carbon nitride in lithium batteries. The preparation method of the protonated carbon nitride comprises the following steps: S1, calcining melamine in stages under an inert atmosphere to obtain carbon nitride; S2, grinding the carbon nitride, washing the carbon nitride to neutral after soaking in an acidic solution, and then ultrasonicating, peeling and drying the washed carbon nitride to obtain protonated carbon nitride; the process of the stage-by-stage calcination is as follows: the temperature of the first-stage calcination is 450-550 DEG C, the temperature rising rate is 5-10 DEG C / min, and the time is 1-3 h; the temperature of the second-stage calcination is 600-750 DEG C, the temperature rising rate is 5-10 DEG C / min, and the time is 1-3 h. The protonated C3N4 and the polymer matrix are used as a protective layer, are spin-coated on a lithium metal interface, stabilize a solid electrolyte interface, and effectively improve the interface stability and long cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a protonated carbon nitride, its preparation method, and its application in lithium batteries. Background Technology

[0002] Lithium metal anodes face numerous challenges in practical applications, primarily including lithium dendrite growth, volume expansion, and pulverization during cycling. These issues lead to sudden failure of lithium metal batteries after a certain number of cycles. To overcome problems such as lithium dendrite growth and volume expansion, researchers have proposed various interface modification methods for lithium metal anodes. These include electrolyte bulk modification, through doping with elements (such as Ta and Al) or introducing fast ion conductors (such as Li3N and Li7P3S). 11 While methods such as optimizing the ionic conductivity and mechanical strength of solid electrolytes can improve the interfacial contact problem, they cannot fundamentally solve the interfacial stress problem, and high mechanical strength can exacerbate interfacial stress, leading to cracks.

[0003] The prior art CN117317385A discloses a method for modifying the negative electrode interface in a solid-state lithium battery using composite two-dimensional materials. This method involves coating a precursor solution onto the surface of a solid electrolyte, followed by an in-situ chemical reaction to form an interfacial intermediate layer, thereby improving interfacial contact. However, coating the solid electrolyte surface cannot guarantee the uniformity of the interfacial layer, which can affect ion transport pathways. Furthermore, the compatibility between the precursor and the polymer matrix presents a problem, leading to easy peeling of the interfacial layer and failing to provide effective protection.

[0004] In-situ generation of SEI layers (such as Li3N, LiF, or polymer-based composite layers) on the surface of lithium metal using chemical / electrochemical methods optimizes lithium-ion transport and lithium metal deposition. However, the preparation process is complex, requires precise control of conditions, and is costly.

[0005] Existing technology CN114899362B discloses a three-dimensional lithium metal anode material with a solid electrolyte interface and its preparation method. This method involves in-situ coating g-C3N4 onto a three-dimensional carbon material, followed by a high-temperature melting reaction to form an artificial solid electrolyte interface film with Li3N, effectively solving the lithium dendrite growth problem. However, the uniformity and density of the coating material significantly affect the material's stability. Furthermore, the high-temperature melting reaction must be carried out in a glove box, resulting in significant energy consumption and high process complexity, which is unfavorable for large-scale production. Summary of the Invention

[0006] The purpose of this invention is to provide a protonated carbon nitride, its preparation method, and its application in lithium batteries, which can effectively improve the interface performance between the solid electrolyte and the lithium metal anode and achieve long-life energy storage.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing protonated carbon nitride includes the following steps:

[0009] The carbon nitride was ground, soaked in an acidic solution, washed until neutral, and then sonicated, peeled off, and dried to obtain protonated carbon nitride.

[0010] In one preferred embodiment, the carbon nitride is prepared by: calcining melamine in stages under an inert atmosphere to obtain carbon nitride;

[0011] The segmented calcination process is as follows: the first stage calcination temperature is 450-550℃, the heating rate is 5-10℃ / min, and the time is 1-3h; the second stage calcination temperature is 600-750℃, the heating rate is 5-10℃ / min, and the time is 1-3h.

[0012] The first stage of calcination aims to form the basic structure of carbon nitride, converting melamine into carbon nitride. If the temperature is too low, melamine may not be fully converted to carbon nitride, resulting in insufficient crystallinity of the product; if the temperature is too high, it may lead to excessive decomposition or structural collapse of the carbon nitride, destroying its layered structure. The second stage of calcination oxidizes the carbon nitride, removing impurities, increasing porosity, and improving the specific surface area of ​​the material. If the temperature is too low, the oxidation process will be insufficient, failing to effectively remove impurities. If the temperature is too high, it may create excessive defects or amorphous regions.

[0013] In one preferred embodiment, the inert gas flow rate is 40–60 mL / min.

[0014] In one preferred embodiment, the inert gas is argon, nitrogen, or helium.

[0015] In one preferred embodiment, the acidic solution is hydrochloric acid.

[0016] In one preferred embodiment, the hydrochloric acid concentration is 3-6 mol / L.

[0017] In one preferred embodiment, the soaking time in the acidic solution is 1-2 hours.

[0018] In one preferred embodiment, carbon nitride is ground to a particle size of 25-75 μm.

[0019] In one preferred embodiment, the washing is performed using distilled water.

[0020] In one preferred embodiment, the ultrasonic process is as follows: working for 3-5 seconds, intermittent for 3-5 seconds, and ultrasonic time for 1-3 hours.

[0021] In one preferred embodiment, the stripping process is as follows: mixing carbon nitride and salt and ball milling at a speed of 400-700 r / min for 2-4 h.

[0022] Salt particles are used as abrasive media and templates during the stripping process to achieve efficient stripping.

[0023] In one preferred embodiment, the salt is one or more of sodium chloride, ammonium sulfate, and potassium chloride.

[0024] In one preferred embodiment, the drying process is as follows: drying at 140-160°C for 6-9 hours.

[0025] In one preferred embodiment, the porosity of protonated carbon nitride is 20%-30%.

[0026] Excessive porosity can reduce the mechanical strength of materials, make their structure unstable, and affect their stability in practical applications. Insufficient porosity will restrict ion transport and affect the electrochemical performance of materials.

[0027] In one preferred embodiment, the micropores of protonated carbon nitride have a diameter of 0.5-1 nm.

[0028] The micropores on protonated carbon nitride provide a high specific surface area and excellent lithium-ion adsorption performance. However, when the pore size is too small (less than 0.5 nm), the diffusion rate of lithium ions within the material decreases, hindering rapid lithium-ion transport. Conversely, when the pore size is too large (greater than 2 nm), the specific surface area of ​​the carbon nitride material decreases, leading to a reduced contact area with lithium ions. This reduces the adsorption efficiency of lithium ions and affects their transport rate.

[0029] Based on the unified inventive concept, this invention also claims protection for protonated carbon nitride prepared by the preparation method.

[0030] Based on the unified inventive concept, this invention also claims protection for the application of the protonated carbon nitride in improving the interface performance between the solid electrolyte and the lithium metal anode.

[0031] Based on the same inventive concept, the present invention also claims protection for a polymer slurry containing protonated carbon nitride.

[0032] In one preferred embodiment, the polymer slurry contains, by weight, 1-5 parts of the protonated carbon nitride, 8-12 parts of an olefin polymer and 3-8 parts of a lithium salt.

[0033] In one preferred embodiment, the olefin polymer is one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, and poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer.

[0034] In one preferred embodiment, the lithium salt is one or more of LiCl, LiF, LiBr, LiI, Li2SO4, LiNO3, LiPF6, LiTFSI, LiFSI, and LiDFOB.

[0035] In one preferred embodiment, the polymer slurry further includes 70-90 parts of a polar solvent.

[0036] In one preferred embodiment, the polar solvent is one or both of tetrahydrofuran and acetone.

[0037] Based on the unified inventive concept, the present invention also claims protection for a lithium metal anode coated with the polymer slurry.

[0038] Based on the same inventive concept, the present invention also claims protection for a solid-state battery, wherein the solid state includes the lithium metal anode.

[0039] Based on the unified inventive concept, this invention also claims a method for improving the interface performance between a solid electrolyte and a lithium metal anode, comprising the following steps:

[0040] (1) The protonated carbon nitride, olefin polymer, polar solvent and lithium salt are mixed evenly to obtain a polymer slurry;

[0041] (2) Spin-coating the polymer slurry onto the lithium metal surface and drying it to obtain a lithium metal anode;

[0042] (3) Assemble the positive electrode, polymer-based solid electrolyte and lithium metal negative electrode to obtain a solid-state battery.

[0043] In one preferred embodiment, the mixing is stirring, the stirring time is 6-14 hours, and the temperature is 45℃-70℃.

[0044] In one preferred embodiment, the spin coating speed is 200-600 r / min, the spin coating thickness is 10-30 μm, and the drying time is 6-10 h.

[0045] In one preferred embodiment, the dew point of the spin-coating and drying environment is less than -50°C.

[0046] In one preferred embodiment, the lithium metal thickness is 80-120 μm.

[0047] In one preferred embodiment, the cathode is a nickel-cobalt-manganese oxide type cathode.

[0048] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0049] 1. This invention aims to provide a method and application for improving the interface between a solid electrolyte and a lithium metal anode. Protonated C3N4 and a polymer matrix are used as protective layers, which are spin-coated onto the lithium metal interface, enabling in-room preparation and assembly. By coating the lithium metal surface with a nitrogen-rich organic / inorganic protective layer of a polymer, the solid electrolyte interface is stabilized, effectively improving interface stability and long-cycle performance.

[0050] 2. This invention uses thermal polymerization and protonation to prepare carbon nitride. By protonating, the surface is given a positive charge, which allows it to be better dispersed in the solution. At the same time, the layered structure of carbon nitride is destroyed, forming more micropores of 0.5-1 nm, providing high specific surface area and good lithium ion adsorption performance.

[0051] 3. This invention employs an organic / inorganic interface coating modification method to spin-coat a protonated nitrogen-rich C3N4 polymer solution onto the lithium foil anode side to improve the lithium metal anode interface. The carbon nitride and polymer combine to form a uniform C3N4-polymer composite layer. This composite layer not only possesses good mechanical stability and ionic conductivity, thus avoiding the grain boundary problems present in traditional solid electrolyte interphase (SEI) interfaces, but also achieves uniform current density and lithium-ion flux distribution, thereby inducing uniform lithium metal deposition. Furthermore, the protonated carbon nitride possesses an ordered microporous structure and high lithium-ion selectivity, providing rapid lithium-ion transport channels, reducing the tortuosity of the transport path, promoting uniform lithium metal nucleation, further inducing uniform lithium metal deposition, and improving the overall battery performance.

[0052] 4. The lithium solid-state battery proposed in this invention, combined with an organic / inorganic composite layer lithium metal anode, has a wide electrochemical window and high ion mobility number. The lithium-lithium symmetric battery can cycle stably for 2000 hours, and the full cell can cycle stably for 1200 cycles at 2C rate at room temperature with a capacity retention of >80%. The pouch cell assembled with the organic / inorganic composite layer lithium metal anode can achieve 160 stable cycles, which is of great value for industrial application. Attached Figure Description

[0053] Figure 1 This is a schematic diagram illustrating the working principle of the protonated lithium nitride-polymer coating prepared in the embodiments of the present invention.

[0054] Figure 2 This is a SEM image of the protonated lithium nitride prepared in Example 1 of the present invention.

[0055] Figure 3 This is a graph showing the room temperature electrochemical window test results of the assembled half-cells in Example 1 and Comparative Example 1 of the present invention.

[0056] Figure 4 This is a room temperature stability test diagram of the coated and modified lithium metal symmetric battery assembled in Example 1 of the present invention.

[0057] Figure 5 The image shows the room-temperature electrochemical performance of the coated lithium metal coin cell assembled in Example 1 of this invention at 2C.

[0058] Figure 6 This is a schematic diagram of the assembly of lithium metal pouch cells in Examples 1-6 and Comparative Examples 1-11 of the present invention.

[0059] Figure 7 The electrochemical performance of the coated lithium metal pouch cell assembled in Example 1 of the present invention at room temperature at 0.2C is shown. Detailed Implementation

[0060] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0061] Example 1

[0062] according to Figure 1 The working principle diagram of the protonated lithium nitride-polymer coating is shown below. The process of preparing the protonated lithium nitride-polymer coating is as follows:

[0063] Modification of lithium foil: (1) Commercial melamine powder was placed in a tube furnace and calcined in stages under the protection of argon atmosphere. The pressure valve of argon was controlled so that the gas flow rate was 50 mL / min, the first stage calcination temperature was 500℃ and the heating rate was 5℃ / min, the second stage calcination temperature was 650℃ and the heating rate was 5℃ / min, and block carbon nitride was obtained.

[0064] (2) Grind the blocky carbon nitride obtained in step (1) into powder, remove impurities in hydrochloric acid solution, wash three times with distilled water, measure the pH to be neutral, use the probe of the spin coater to sonicate for 2 hours, the working mode is 3 seconds working and 3 seconds intermittent, and finally freeze dry to obtain protonated carbon nitride.

[0065] (3) Weigh 0.05g of the protonated C3N4 obtained in step (2) and dissolve it in 10mL of tetrahydrofuran solvent. Weigh 0.25g of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP, weight average molecular weight of 400,000) and 0.1g of lithium bis(fluorosulfonyl)imide (LIFSI) and dissolve them in the above homogeneous solution. Stir at 60℃ for 10h to obtain a uniform polymer slurry.

[0066] (4) Place a 100μm lithium foil in a spin coater and add the polymer slurry obtained in step (3) into the spin coater. The spin coater speed is 400r / min and the spin coating thickness is 20μm. Let the coated lithium foil stand in a dry room for 8 hours to obtain the modified lithium foil. The entire process is carried out in a dry room, requiring a dew point of less than -50℃.

[0067] The protonated lithium nitride prepared in Example 1 was analyzed by SEM, and the results are as follows: Figure 2 As shown.

[0068] Preparation of the positive electrode: using lithium nickel cobalt manganese (LiNi) 0.8 Co 0.1 Mn 0.1 O2) is used as the active material. It is mixed with conductive agent (acetylene black) and binder [polyvinylidene fluoride (PVDF)] at a mass ratio of 80:10:10. The mixture is coated on carbonized aluminum foil and dried in a vacuum drying oven at 80°C for 24 hours to remove the solvent.

[0069] Preparation of electrolyte: 0.4 g of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP, weight average molecular weight of 400,000) and 0.4 g of LiFSI were dissolved in 4 mL of DMF solution and stirred at 50 degrees Celsius for 8 h until completely dissolved. The resulting solution was then uniformly cast into a film and placed in a vacuum drying oven at 60 degrees Celsius for 24 h to obtain a solid electrolyte.

[0070] Assembly of the electrochemical window battery (half-cell): The battery was assembled in the order of negative electrode shell, gasket, solid electrolyte, coated modified lithium sheet, and positive electrode shell, and the electrochemical window of the solid electrolyte was tested.

[0071] The electrochemical window at room temperature was tested for the coated lithium metal half-cell assembled in Example 1. Figure 3 As shown.

[0072] Assembly of lithium metal symmetric batteries: Li||Li symmetric batteries (lithium metal symmetric batteries) were assembled in the following order: negative electrode shell, coated modified lithium sheet, solid electrolyte, coated modified lithium sheet, and positive electrode shell. The stability of lithium metal and ion transference number were then tested.

[0073] The lithium metal symmetric battery with modified coating assembled in Example 1 was subjected to a room temperature lithium stability test, and the results are as follows: Figure 4 As shown.

[0074] Assembly of lithium metal coin cells: The positive electrode, solid electrolyte, and coated modified lithium metal are assembled into a lithium solid-state battery (coin cell) and its electrochemical performance is tested.

[0075] The electrochemical performance of the coated lithium metal coin cell assembled in Example 1 at room temperature under 2C was tested, and the results were as follows: Figure 5 As shown.

[0076] Assembly of lithium metal pouch cells: The positive electrode sheet is cut to 43×56mm, the coated modified lithium metal is cut to 45×58mm, and the solid electrolyte is cut to 50×65mm. For example... Figure 6 As shown, the cells are stacked and sealed in an inert atmosphere in the order of positive electrode, solid electrolyte, and lithium metal, and then placed on a cabinet for pouch cell cycle performance testing.

[0077] The electrochemical performance of the coated lithium metal pouch cell assembled in Example 1 at room temperature under 0.2C was tested, and the results were as follows: Figure 7 As shown.

[0078] Example 2

[0079] Compared with Example 1, most aspects are the same, except that the calcination temperature in step (1) is 450°C for the first stage and 700°C for the second stage. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this example were tested, and the test results are shown in Table 1.

[0080] Example 3

[0081] The process is largely the same as in Example 1, except that the protonation process in step (2) is ultrasonically treated for 1 hour. The ion transport number, electrochemical window, and cycle performance of the coin cell and pouch cell in this example were tested, and the results are shown in Table 1.

[0082] Example 4

[0083] The process is largely the same as in Example 1, except that the protonation process in step (2) is subjected to ultrasonic treatment for 3 hours. The ion transport number, electrochemical window, and cycle performance of coin cells and pouch cells in this example were tested, and the results are shown in Table 1.

[0084] Example 5

[0085] Compared with Example 1, most aspects are the same, except that the spin coater rotation speed in step (4) is 200 r / min and the spin coat thickness is 10 μm. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this example were tested, and the test results are shown in Table 1.

[0086] Example 6

[0087] Compared with Example 1, most aspects are the same, except that the spin coater in step (4) is rotated at 600 r / min and the coating thickness is 30 μm. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this example were tested, and the test results are shown in Table 1.

[0088] Comparative Example 1

[0089] The results are largely the same as in Example 1, except that the negative electrode uses uncoated lithium metal foil. The ion transference number, electrochemical window, and cycle performance of coin and pouch cells in this comparative example were tested, and the results are shown in Table 1.

[0090] Assembly of the battery for testing the electrochemical window: The battery was assembled in the order of negative electrode shell, gasket, solid electrolyte, coated modified lithium sheet, and positive electrode shell, and the electrochemical window of the solid electrolyte was tested.

[0091] The room temperature electrochemical window test results for the half-cells assembled in Example 1 and Comparative Example 1 are as follows: Figure 3 As shown.

[0092] Comparative Example 2

[0093] The results are largely the same as in Example 1, except that steps (1) and (2) are omitted, and a coating that does not introduce carbon nitride is used in step (3). The ion transport number, electrochemical window, and cycle performance of coin and pouch cells in this comparative example were tested, and the results are shown in Table 1.

[0094] Comparative Example 3

[0095] Compared with Example 1, most aspects are the same, except that step (2) is omitted, protonation treatment is not performed, and the bulk carbon nitride prepared in step (1) is used directly in step (3). The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries of this comparative example were tested, and the test results are shown in Table 1.

[0096] Comparative Example 4

[0097] Compared with Example 1, most aspects are the same, except that step (1) is omitted, and the melamine powder is directly protonated instead of undergoing thermal polymerization. The ion transference number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this comparative example were tested, and the test results are shown in Table 1.

[0098] Comparative Example 5

[0099] Compared with Example 1, most aspects are the same, except for the calcination temperature in step (1): the first calcination temperature is 400°C and the second calcination temperature is 650°C. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this comparative example were tested, and the test results are shown in Table 1.

[0100] Comparative Example 6

[0101] Compared with Example 1, most aspects are the same, except for the calcination temperature in step (1): the first calcination temperature is 500°C and the second calcination temperature is 800°C. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this comparative example were tested, and the test results are shown in Table 1.

[0102] Comparative Example 7

[0103] The results were largely the same as in Example 1, except that the protonation process in step (2) was subjected to ultrasonic treatment for 4 hours. The ion transport number, electrochemical window, and cycle performance of coin cells and pouch cells in this comparative example were tested, and the results are shown in Table 1.

[0104] Comparative Example 8

[0105] The results were largely the same as in Example 1, except that the spin coater in step (4) was operated at a speed of 100 r / min and the coating thickness was 5 μm. The ion transport number, electrochemical window, and cycle performance of the coin cell and pouch cell of this comparative example were tested, and the results are shown in Table 1.

[0106] Comparative Example 9

[0107] Compared with Example 1, most aspects are the same, except that the spin coater in step (4) was rotated at 700 r / min and the coating thickness was 40 μm. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this comparative example were tested, and the test results are shown in Table 1.

[0108] Comparative Example 10

[0109] Compared with Example 1, most of the results are the same, except that steps (3) and (4) are omitted. In step (4), the spin coating is replaced by a coating method, in which the coating liquid is uniformly coated on the surface of the solid electrolyte, the coating thickness is controlled to be 20 μm, and the standing time is 8 h. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries of this comparative example are tested, and the test results are shown in Table 1.

[0110] Comparative Example 11

[0111] Compared with Example 1, most aspects are the same, except for the use of protonated carbon nitride, which omits steps (3) and (4). In step (3), the coating method is changed to molten lithium coating. The protonated carbon nitride is injected with molten lithium in an argon atmosphere (oxygen content ≤0.01ppm, water content ≤0.01ppm, temperature 350℃) and then cooled to room temperature. The ion transport number, electrochemical window, and cycle performance of coin cell and pouch cell batteries in this comparative example were tested, and the test results are shown in Table 1.

[0112] according to Figure 6 The diagram illustrates the assembly of lithium metal pouch cells using Examples 1-6 and Comparative Examples 1-11. The relevant performance tests are as follows:

[0113] Table 1. Performance test results for each embodiment and comparative example.

[0114]

[0115] The ion transport number of the battery was tested using the constant potential polarization method (steady-state current method), the electrochemical window was tested using the linear sweep voltammetry method, and the capacity retention rate at room temperature 2C for 1200 cycles was tested according to the relevant provisions of the national standard GB / T 18287. The cycle performance test method for pouch batteries was based on the relevant provisions of the national standard GB / T 31486-2015 "Cycle Life Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0116] Table 1 shows that when using untreated modified lithium foil in Comparative Example 1, the ion transference number is 0.24, the electrochemical window is only 3.8V, and the Li||Li coin cell can only cycle for 57 hours. The assembled solid-state lithium metal coin cell with NCM811 cathode experiences a capacity drop at 45 cycles under 2C conditions at room temperature. Comparative Example 2 shows that if a coating without carbon nitride is used, the ion transference number is 0.25, the electrochemical window is only 3.9V, and the Li||Li coin cell can only cycle for 83 hours. The assembled solid-state lithium metal coin cell with NCM811 cathode experiences a capacity drop at 61 cycles under 2C conditions at room temperature. This is because the coating lacks the ion-conducting properties of carbon nitride; the coating only increases the ion migration path, resulting in high ion migration impedance and degraded performance. Comparative Example 3 shows that if unprotonated carbon nitride is introduced, the ion transference number is 0.47, the electrochemical window is only 4.2V, the Li||Li coin cell can only cycle for 477h, and the assembled solid-state lithium metal coin cell with NCM811 cathode has a capacity retention of 6.17% under 2C conditions at room temperature for 1200 cycles. Unprotonated carbon nitride cannot be uniformly dispersed in solution, resulting in agglomeration and poor electrochemical performance. Comparative Example 4 shows that melamine powder without thermal polymerization treatment cannot form a stable carbon nitride structure and cannot effectively play its role in the interfacial protective layer. Comparative Examples 5 and 6 show that too low a calcination temperature leads to insufficient crystallinity of carbon nitride, preventing the formation of a stable carbon nitride structure, while too high a calcination temperature leads to excessive decomposition or structural collapse of carbon nitride, causing changes in the pore structure of the material, affecting its ion conductivity and mechanical stability, and thus affecting the performance of solid-state batteries. Comparative Example 7 shows that a protonation treatment time of more than 4 hours leads to excessive protonation on the carbon nitride surface, significantly reducing the cycle performance of the solid-state battery. At room temperature and 2C, the capacity retention after 1200 cycles is only 11.96%. For Comparative Examples 8 and 9, if the coating is too thin (below 10 μm), it may not effectively protect the lithium metal anode, failing to achieve a uniform lithium-ion flux distribution and thus failing to effectively suppress lithium dendrite growth. If the coating is too thick (above 30 μm), it may increase the battery's internal resistance, resulting in an excessively long lithium-ion transport path and reduced ion transport efficiency. Comparative Example 10 shows that uniform coating on the solid electrolyte surface cannot guarantee the uniformity of the interface layer, thus affecting the ion transport path. Furthermore, the compatibility issues between the precursor and the polymer matrix lead to easy peeling of the interface layer, failing to provide effective protection. Comparative Example 11 shows that with carbon nitride-coated molten lithium, the uniformity and density of the carbon nitride coating affect the material's stability. Moreover, the high-temperature melting reaction must be carried out in a glove box, resulting in significant energy consumption costs and high process complexity, which is unfavorable for large-scale production.

[0117] In Example 1, by introducing protonated carbon nitride in synergy with the polymer, a carbon nitride-polymer composite layer is formed, exhibiting excellent mechanical stability and ion conductivity, and achieving a high ion transference number (t). Li + =0.68), a wide electrochemical window (4.8V), and a Li||Li coin cell achieved stable cycling for 2000h. A solid-state lithium metal coin cell with an assembled NCM811 cathode maintained 82.97% capacity after 1200 cycles at 2C at room temperature. Furthermore, a pouch cell assembled with lithium foil modified with a carbon nitride-polymer coating achieved stable cycling for 160 cycles at 0.2C. Example 2 shows that the calcination temperature should be controlled within a certain range to ensure the structural stability and specific surface area of ​​carbon nitride. Examples 3 and 4 show that the protonation time should be controlled within 1-3h to achieve H + Uniform insertion. Examples 5 and 6 show that the coating thickness should be controlled between 10 and 30 μm to balance ion transport efficiency and mechanical stability.

[0118] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing protonated carbon nitride, characterized in that, Includes the following steps: Carbon nitride is ground, soaked in an acidic solution, washed until neutral, and then sonicated, peeled, and dried to obtain protonated carbon nitride. The preparation method of the carbon nitride is: calcining melamine in stages under an inert atmosphere to obtain carbon nitride. The segmented calcination process is as follows: the first stage calcination temperature is 450-550℃, the heating rate is 5-10℃ / min, and the time is 1-3 h; the second stage calcination temperature is 650-750℃, the heating rate is 5-10℃ / min, and the time is 1-3 h. The porosity of protonated carbon nitride is 20%-30%; the diameter of the micropores in protonated carbon nitride is 0.5-1 nm. The acidic solution is hydrochloric acid; The ultrasonic process is as follows: 3-5 seconds of operation, 3-5 seconds of rest, and 1-3 hours of ultrasonic treatment.

2. The preparation method according to claim 1, characterized in that, The inert gas flow rate is 40~60 mL / min; the inert gas is argon, nitrogen or helium.

3. The preparation method according to claim 1, characterized in that, The hydrochloric acid concentration is 3-6 mol / L; the soaking time in the acidic solution is 1-2 h; the carbon nitride is ground to a particle size of 25-75 μm; the stripping process is as follows: the carbon nitride and salt are mixed and ball-milled at a speed of 400-700 r / min for 2-4 h; the salt is one or more of sodium chloride, ammonium sulfate, and potassium chloride.

4. Protonated carbon nitride prepared by the preparation method according to claims 1-3.

5. A polymer slurry, characterized in that, The polymer slurry contains the protonated carbon nitride as described in claim 4.

6. The polymer slurry according to claim 5, characterized in that, The polymer slurry contains 1-5 parts of the protonated carbon nitride as described in claim 4, 8-12 parts of an olefin polymer, and 3-8 parts of a lithium salt.

7. A lithium metal anode, characterized in that, The lithium metal anode is coated with the polymer slurry as described in claim 5 or 6.

8. A solid-state battery, characterized in that, The solid-state battery includes the lithium metal anode as described in claim 7.

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