A three-dimensional vertically porous composite alkali metal anode and its preparation method and application

Abstract

The present invention discloses a three-dimensional vertical porous composite alkali metal negative electrode and its preparation method and application. A polymer is mixed with an organic solvent, and a precursor solution is obtained after sufficient stirring; the precursor solution is thinly coated on the surface of the alkali metal in situ by a simple scraper coating method and dried at low temperature in an inert atmosphere, and after the organic solvent in the coating is completely volatilized, an alkali metal containing a composite polymer layer is obtained; holes are punched on the surface of the composite polymer layer by a mechanical punching method to obtain a three-dimensional vertical porous composite alkali metal negative electrode. The present invention has a simple preparation process, low cost, and is suitable for large-scale commercial production. By taking a different approach to control the growth mode of dendritic deposited alkali metal to obtain a densified deposition morphology, the battery cycle stability is greatly improved, and the application prospect is broad, which is conducive to the breakthrough of high safety of secondary alkali metal batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal battery preparation, and particularly relates to a three-dimensional vertical porous composite alkali metal negative electrode, a preparation method thereof, and an application thereof. Background Art

[0002] Traditional secondary batteries are gradually difficult to meet the high requirements for energy density and safety of rapidly developing large-scale energy storage devices such as electric vehicles and photovoltaic power stations. For example, for lithium-ion batteries based on ion insertion / extraction reactions, the negative electrode of which is graphite material with a specific capacity approaching its theoretical limit (372 mAh g -1 ), severely restricts the further breakthrough of the overall energy density of lithium-ion batteries. Therefore, it is the general trend to find high specific capacity negative electrode materials that can replace graphite.

[0003] Using alkali metal materials to directly replace graphite materials as the negative electrode of secondary batteries has many advantages. On the one hand, alkali metal resources such as lithium, sodium, and potassium are abundant in the earth's reserves, which can meet the requirements of large-scale applications. On the other hand, alkali metal negative electrodes generally have high specific capacity and low density, which can greatly improve the energy density of secondary batteries. For example, alkali metals have an extremely high theoretical specific capacity (3860 mAh g -1 ), an extremely low density (0.534 g cm -3 ), and a low electrochemical potential (-3.04 V vs standard hydrogen electrode), and are considered the "holy grail" of negative electrode materials.

[0004] However, directly using alkali metals as the negative electrode of secondary batteries will also bring many problems, severely restricting their commercial application prospects. These include:

[0005] (1) Due to reasons such as uneven surfaces of alkali metal negative electrodes, dendritic deposits are likely to occur during cycling, resulting in diaphragm puncture, and ultimately internal short circuit, causing serious safety problems such as fire and explosion.

[0006] (2) In addition, there are huge volume changes in alkali metal negative electrodes during cycling, which are likely to cause the rupture of the SEI film on the electrode surface, exposing the fresh alkali metal to continuously react with the electrolyte, thereby accelerating capacity decay.

[0007] (3) At the same time, alkali metal negative electrodes have relatively high chemical activity and poor compatibility with electrolytes or solid electrolytes. During long-term cycling, they are prone to corrosion or the formation of a passivation layer, resulting in a sudden increase in interfacial impedance and polarization, and ultimately battery failure.

[0008] Therefore, in order to suppress dendritic growth, limit the volume change of the alkali metal anode during deposition / stripping, and improve the safety performance of secondary batteries, a variety of modification methods have been proposed, including using electrolyte additives, solid electrolytes, metal deposition skeletons, and composite metal anodes, etc. However, most of these methods have complex processes, high costs, and cannot fundamentally prevent the generation of dendritic alkali metal deposition morphology. The above problems will still inevitably occur after long-term cycling. The main reasons include:

[0009] (1) The generation of dendritic alkali metal deposition is a complex, random, and uncontrollable process, affected by various factors such as temperature, pressure, electric field strength, ion concentration, and electrolyte performance.

[0010] (2) The introduced additives and interface layers will be exhausted or damaged after long-term cycling and become ineffective, making it difficult to continue to play a role.

[0011] (3) There are almost no methods that can completely suppress the side reactions between lithium metal and the electrolyte or solid electrolyte, and the products will eventually accumulate at the interface and affect the lithium deposition morphology.

[0012] Therefore, it is particularly important to find a simple process to regulate the growth behavior of dendrites and significantly delay the diaphragm piercing time when dendrites have already formed, in order to improve the safety of alkali metal batteries. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a three-dimensional vertically porous composite alkali metal anode and its preparation method and application in view of the above-mentioned deficiencies in the prior art, to solve the technical problems of low safety and poor cycle stability of alkali metal batteries. It can further regulate the growth behavior mode of dendritic metal deposition when it has already occurred, achieve densified deposition, and greatly reduce the probability of diaphragm piercing, so as to improve the cycle life and safety of metal batteries.

[0014] The present invention adopts the following technical solutions:

[0015] A three-dimensional vertically porous composite alkali metal anode includes an alkali metal. A composite polymer layer is provided on one side of the alkali metal, and three-dimensional vertical holes are arrayed on one side of the composite polymer layer. The three-dimensional vertical holes are micron-sized or sub-micron-sized.

[0016] Specifically, the thickness of the composite polymer layer is 1-10 μm.

[0017] Specifically, the diameter of the three-dimensional vertical holes is 50-150 μm, the hole depth of the three-dimensional vertical holes is 70%-90% of the thickness of the alkali metal anode, and the area ratio of the three-dimensional vertical holes on the composite polymer layer is 30%-70%.

[0018] Another technical solution of the present invention is a method for preparing a three-dimensional vertically porous composite alkali metal negative electrode, comprising the following steps:

[0019] In-situ thinly coat a polymer precursor solution on the surface of an alkali metal, and under an inert atmosphere, obtain an alkali metal containing a composite polymer layer after low-temperature drying; punch holes on one side surface of the composite polymer layer by a mechanical punching method to obtain a three-dimensional vertically porous composite alkali metal negative electrode.

[0020] Specifically, the mass fraction of the polymer precursor solution is 5% to 20%.

[0021] Further, mix a polymer and an organic solvent, and obtain a polymer precursor solution after sufficient stirring. The polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyamic acid, and polyimide, and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile.

[0022] Specifically, use a doctor blade coating method to in-situ thinly coat the polymer precursor solution on the surface of the alkali metal. The height of the doctor blade is 20 to 50 μm higher than the thickness of the alkali metal.

[0023] Specifically, the temperature of the low-temperature drying treatment is 40 to 50 °C, and the time is 3 to 5 h.

[0024] Specifically, the alkali metal is one or more of lithium, sodium, and potassium.

[0025] Another technical solution of the present invention is the application of a three-dimensional vertically porous composite alkali metal negative electrode in an alkali metal battery.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] A three-dimensional vertically porous composite alkali metal negative electrode. On the one hand, due to the electron-insulating property of the composite polymer coating, the deposition of the alkali metal is restricted to the holes. On the other hand, due to its ion-adsorbing property, the ion concentration at the outer edge of the holes is increased, which is beneficial to regulating the dendritic metal deposition on the inner wall of the holes to grow horizontally towards the center of the holes; the three-dimensional vertical holes arranged in an array can effectively regulate the electric field distribution of the negative electrode, making the electric field inside the holes turn vertically downward and deflect towards the surrounding hole walls, and the electric field at the outer edge of the holes turn vertically downward and deflect towards the inside of the holes. Therefore, the alkali metal will deposit vertically upward from the bottom of the holes and horizontally deposit towards the center of the holes until they contact and squeeze each other; under the dual action of the vertical array hole structure and the polymer coating, finally, the deposition morphology of the alkali metal inside the holes is dense and uniform, reducing the probability of dendrite piercing the separator and greatly improving the electrochemical stability and safety performance of the alkali metal secondary battery.

[0028] Furthermore, adjusting the height of the scraper so that the thickness of the final composite polymer layer is 1-10 μm can not only isolate electrons, prevent the deposition of lithium ions on the surface of the polymer layer, and confine them to the holes, but also minimize the impact on the energy density of the battery due to the ultra-thin thickness.

[0029] Furthermore, determine the surface deposition capacity required for the composite anode based on the surface capacity of the matched cathode material, and then select appropriate needle aperture, needle density, and punching depth; at the same needle density, increasing the aperture and depth appropriately can accommodate more surface deposition capacity of alkali metals in the holes, thus enabling the matching of cathode materials with a high active material surface loading; at the same aperture and depth, the greater and more uniform the needle density, the more surface deposition capacity of alkali metals can be accommodated in the holes, and it can also match cathode materials with a high active material surface loading.

[0030] A method for preparing a three-dimensional vertically porous composite alkali metal anode. The alkali metal anode with an organic interface layer has strong mechanical properties even after punching to form a three-dimensional deposition structure, making it an ideal choice for the deposition support structure of the alkali metal anode. The preparation method steps of first coating and drying to form an organic polymer coating can first increase the mechanical strength of the alkali metal anode, making it less likely to be damaged during subsequent mechanical punching.

[0031] Furthermore, to avoid the continuous side reaction between the alkali metal and the solvent due to slow solvent evaporation, determine the concentration of the precursor solution according to the required scraper height and coating thickness. If the scraper height and coating thickness are small, the concentration of the precursor solution can be appropriately reduced, that is, the proportion of the organic solvent can be higher; conversely, the concentration of the precursor solution should be appropriately increased, that is, the proportion of the organic solvent should be reduced.

[0032] Furthermore, by dissolving the polymer in an organic solvent and then scraping it, not only can the adhesion between the polymer and the alkali metal be increased, but also an organic polymer coating with more uniform and consistent thickness and other characteristics and a smooth surface can be obtained.

[0033] Furthermore, applying the organic polymer solution to the surface of the alkali metal by scraping with a scraper can not only more conveniently change the scraper height to obtain the required coating thickness, but also reduce the amount of solvent on the surface of the alkali metal and increase the evaporation area to inhibit the continuous occurrence of side reactions.

[0034] Furthermore, completely volatilize the organic solvent by thinly coating the polymer solution and quickly drying it at a low temperature to avoid its continuous side reaction with the alkali metal. When the coating thickness is constant, the lower the low-temperature drying temperature, the longer the time should be appropriately increased; when the low-temperature drying temperature is constant, the thicker the coating thickness, the longer the time should be appropriately increased; when the low-temperature drying time is constant, the thicker the coating thickness, the higher the low-temperature drying temperature should be appropriately increased, ultimately enabling the full volatilization of the organic solvent.

[0035] Furthermore, alkali metals (such as lithium, sodium, potassium, etc.) are abundant in the earth's resources, easy to obtain, generally have high theoretical capacity, low density and relatively low electrochemical potential, and are expected to replace commercial graphite anodes to improve the energy density of batteries.

[0036] In summary, the preparation process of the present invention is simple and has low cost, suitable for large-scale commercial production. By taking a different approach to regulate the growth mode of dendritic deposited alkali metals to obtain a densified deposition morphology, the cycle stability of the battery is greatly improved, with broad application prospects, contributing to the breakthrough of high safety of secondary alkali metal batteries.

[0037] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments. Description of the Drawings

[0038] Figure 1 ; Optical image of the alkali metal anode prepared in Example 1, where (a) is the surface morphology of the alkali metal anode with only a polymer coating, and (b) is the surface morphology of the alkali metal anode with both a vertical array of hole structures and a polymer coating;

[0039] Figure 2 is the mechanical punching tool with a 100 μm diameter needle head in Example 1, where (a) is the front view of the tool and (b) is the side view of the tool;

[0040] Figure 3 is the surface and cross-section scanning electron microscope images of the novel alkali metal anode with a vertical array of hole structures and a polymer coating prepared in Example 1, where (a) is the surface morphology of the novel alkali metal anode and (b) is the cross-section morphology of the novel alkali metal anode;

[0041] Figure 4 is the result diagram of the Comsol simulation of the negative electrode electric field distribution of the ternary full cell assembled with the novel alkali metal anode with a vertical array of hole structures and a polymer coating;

[0042] Figure 5 is the comparison diagram of the cycle performance of the ternary full cells assembled with the alkali metal anode with only an insulating polymer coating and the novel alkali metal anode with an insulating polymer coating and a vertical array of holes respectively;

[0043] Figure 6 At a current density of 0.5 mA cm -2 and different deposition capacities, scanning electron microscope images of alkali metal deposition on the electrode surface in the lithium-lithium symmetric cell assembled with the novel alkali metal anode with a vertical array of hole structures and a polymer coating prepared in Example 1, where (a) is the image of alkali metal deposition at 0.1 mAh cm -2Morphology of the electrode surface after deposition of alkali metal, (b) is the electrode surface morphology after deposition of 0.3 mAh cm -2 Morphology of the electrode surface after deposition of alkali metal, (c) is the electrode surface morphology after deposition of 0.5 mAh cm -2 Morphology of the electrode surface after deposition of alkali metal, (d) is the electrode surface morphology after deposition of 0.75 mAh cm -2 Morphology of the electrode surface after deposition of alkali metal;

[0044] Figure 7 At a current density of 1 mA cm -2 And a deposition capacity of 0.5 mAh cm -2 Optical photograph of the electrode surface in a lithium-lithium symmetric battery assembled with the novel alkali metal negative electrode containing a vertical array of hole structures and a polymer coating prepared in Example 1;

[0045] Figure 8 Is a comparative diagram of the cycle stability at a 1C rate of a lithium-NCM811 ternary cathode full battery assembled with the novel alkali metal containing a vertical array of hole structures and a polymer coating prepared in Example 1 and a commercial lithium sheet respectively;

[0046] Figure 9 Is a comparative diagram of the voltage-capacity curves of the assembled lithium-ternary cathode full battery at a 2C rate, where (a) is the voltage-capacity curve of the lithium-NCM811 ternary cathode full battery assembled with a commercial lithium sheet at a 2C rate, and (b) is the voltage-capacity curve of the lithium-NCM811 ternary cathode full battery assembled with the novel alkali metal negative electrode containing a vertical array of hole structures and a polymer coating prepared in Example 1 at a 2C rate;

[0047] Figure 10 Schematic diagram for the preparation of the novel alkali metal negative electrode containing a vertical array of hole structures and a polymer coating of the present invention.

[0048] Among them, 1. Lithium sheet; 2. Polymer precursor solution; 3. Scraper; 4. Mechanical punching tool. Detailed implementation manners

[0049] Next, the technical solutions of the present invention will be described clearly and completely. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] In the present invention, if there is no special description, all the implementation manners and preferred implementation methods mentioned in this article can be combined with each other to form a new technical solution.

[0051] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form new technical solutions.

[0052] In the present invention, unless otherwise specified, the percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0053] In the present invention, unless otherwise specified, the various components or their preferred components involved can be combined with each other to form new technical solutions.

[0054] In the present invention, unless otherwise stated, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "6 to 22" means that all real numbers between "6 and 22" are fully listed herein, and "6 to 22" is only an abbreviated representation of these numerical combinations.

[0055] The "range" disclosed in the present invention can be in the form of one or more lower limits and one or more upper limits, respectively.

[0056] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0057] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in order. Preferably, the reaction methods herein are carried out sequentially.

[0058] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the recorded content can also be applied to the present invention.

[0059] The present invention provides a three-dimensional vertically porous composite alkali metal negative electrode and a preparation method thereof. A prepared polymer precursor solution is thinly coated on the surface of one side of the alkali metal and dried at a low temperature. According to the surface capacity of the positive electrode material to be matched, the surface capacity of the alkali metal deposition in the required negative electrode holes is determined, and then the needle diameter, needle density and punching depth of the punching tool are determined. Under an inert atmosphere, micron-sized or sub-micron-sized holes with uniform distribution are mechanically punched on the surface of the composite polymer layer to obtain a novel alkali metal negative electrode containing a vertically arrayed hole structure and a polymer coating. The use of uniformly vertically arrayed holes can effectively regulate the distribution of the negative electrode electric field intensity. On the one hand, due to its electron insulation characteristics, the composite polymer layer confines the alkali metal deposition in the holes. On the other hand, due to its ion adsorption characteristics, it is beneficial to regulate the ion concentration at the hole edge. Finally, under the combined action of the vertical hole structure and the composite polymer layer, dendrites will grow vertically upward from the bottom of the hole and horizontally towards the center of the hole from the hole wall until they come into contact and squeeze each other to become dense and uniform, achieving the purpose of improving the cycle life and safety of the metal battery.

[0060] Please refer to Figure 10 , a three-dimensional vertically porous composite alkali metal negative electrode of the present invention includes a composite polymer layer provided on the alkali metal. The thickness of the composite polymer layer is 1-10 μm. A number of uniformly distributed micron-sized or sub-micron-sized holes (the holes account for 30%-70% of the total surface area) are opened on the composite polymer layer. The micron-sized or sub-micron-sized holes are three-dimensional vertical holes. The diameter of the three-dimensional vertical holes is 50-150 μm, and the hole depth of the three-dimensional vertical holes is 70%-90% of the thickness of the alkali metal.

[0061] A preparation method of a three-dimensional vertically porous composite alkali metal negative electrode of the present invention includes the following steps:

[0062] S1. Mix the polymer and the organic solvent, and fully stir to obtain a polymer precursor solution with a mass fraction of 5%-20%;

[0063] Among them, the polymer selects a polymer material with electron insulation and certain ion adsorption properties, which is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyamic acid and polyimide. The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile.

[0064] S2. In-situ thinly coat the polymer precursor solution on the surface of the alkali metal by a doctor blade coating method, and dry it at a low temperature of 40-50 °C for 3-5 h under an inert atmosphere. After the organic solvent has completely volatilized, an alkali metal containing a composite polymer layer is obtained;

[0065] The height of the doctor blade is 20-50 μm higher than the thickness of the alkali metal, and the thickness of the composite polymer layer is 1-10 μm.

[0066] Among them, the alkali metal is one or more of lithium, sodium and potassium.

[0067] S3. Use a punching tool with a micron or sub-micron needle to punch holes on the surface of the composite polymer layer by mechanical punching to obtain a three-dimensional vertically porous composite alkali metal negative electrode.

[0068] The diameter of the needle used in the mechanical punching method is 50-150 μm, the density of the needle is 30%-70% (area ratio), and the punching depth is 70%-90% of the thickness of the alkali metal negative electrode.

[0069] Among them, the surface capacity of the alkali metal deposited in the hole required for the negative electrode is determined according to the surface capacity of the matching positive electrode material, and then the diameter, density and punching depth of the needle on the surface of the mechanical punching tool are determined according to the surface capacity of the alkali metal deposited in the hole required for the negative electrode. Under the same punching density, the larger the pore diameter and the hole depth, the more surface capacity of the alkali metal deposited in the hole can be accommodated; under the same pore diameter and hole depth, the greater and more uniform the punching density, the more surface capacity of the alkali metal deposited in the hole can be accommodated.

[0070] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0071] Example 1

[0072] 4,4'-Diaminodiphenyl ether (ODA) was added to the organic solvent N,N-dimethylacetamide (DMAC) and stirred until it was clear and transparent, and then an equal number of moles of pyromellitic dianhydride (PMDA) was added and stirred. After sufficient in-situ polymerization, a pale yellow clear polyamic acid (PAA) precursor solution was obtained, in which the mass percentage content of the PAA polymer was 20%.

[0073] The polymer precursor solution 2 was in-situ blade-coated on the metal surface of a commercial lithium sheet 1 with a thickness of 100 μm. The height of the blade 3 was 50 μm higher than the thickness of the alkali metal, and it was dried for 5 h at a low temperature of 40 °C in an inert gas atmosphere to obtain Figure 1 The alkali metal negative electrode shown in (a) containing only a polymer coating.

[0074] The front and side optical photos of the selected mechanical punching tool 4 are respectively as Figure 2 (a) and Figure 2 (b) shown. It has a needle with a diameter of 80 μm, a punching depth of 70 μm (70% of the alkali metal thickness), and a needle density of 30% (area ratio).

[0075] The new alkali metal negative electrode with vertical array holes and polymer coating obtained after mechanical punching is subjected to electron scanning microscope testing and optical observation, respectively as Figure 3 and Figure 1 (b) shown. The hole diameter is 80 μm, the hole density is 30% (area ratio), the PAA polymer coating is smooth and flat without cracks, and the thickness is 10 μm.

[0076] Comsol electric field simulation is carried out on the ternary full cell assembled based on the new alkali metal negative electrode with vertical array holes and polymer coating. The results are as Figure 4 shown. The electric field inside the hole turns vertically downward and deflects towards the surrounding hole walls, and the electric field at the outer edge of the hole turns vertically downward and deflects into the hole. Therefore, alkali metal will deposit and grow vertically upward at the bottom of the hole and horizontally towards the center of the hole on the hole walls simultaneously until they contact and squeeze each other to become dense and uniform.

[0077] Using the alkali metal with only an insulating polymer coating and the new alkali metal with an insulating polymer coating and vertical array holes as the negative electrode, NCM811 material as the positive electrode, and polyethylene (PE) microporous membrane as the separator, 70 μL of commercial LiPF6 electrolyte is dropped to assemble a full cell. Charge-discharge cycle testing is carried out at a 1C rate. The change in specific capacity of the active material is as Figure 5 shown. The first-cycle discharge specific capacity of the full cell assembled with the new alkali metal negative electrode with vertical array holes and polymer coating is 148.9 mAh g -1 , and it can stably operate for more than 600 cycles. After 600 cycles, the discharge specific capacity is 82.13% of the first-cycle discharge specific capacity. While the full cell assembled with the alkali metal negative electrode with only an insulating polymer coating has no discharge specific capacity, which proves that the PAA coating has electron insulation and alkali metal cannot deposit on its surface.

[0078] Using the new alkali metal electrode with vertical array holes and polymer coating as the negative electrode, commercial lithium sheet 1 as the positive electrode, and polyethylene (PE) microporous membrane as the separator, 70 μL of commercial LiPF6 electrolyte is dropped to assemble a symmetric cell. After charging for different times at a current density of 0.5 mA cm -2 , the battery is disassembled for electron scanning microscope testing. The results are as Figure 6 shown. As time increases, the deposited alkali metal gradually becomes dense and fills the entire hole. At 1 mA cm -2After charging for 0.5 h at a current density of Figure 7 as shown, it is proved that alkali metals cannot be deposited on the surface of the polymer layer and can only be deposited and grown in the holes.

[0079] Using the prepared novel alkali metal with vertical array holes and polymer coating and commercial lithium sheet 1 as the negative electrode, NCM811 ternary material as the positive electrode, polyethylene (PE) microporous diaphragm as the separator, and dropping 70 μL of commercial LiPF6 electrolyte to assemble a full cell, and performing charge and discharge cycle tests at a rate of 1C. The change trend of the specific capacity of the positive electrode active material is as Figure 8 shown. The initial discharge specific capacity of the full cell assembled with the novel alkali metal negative electrode with vertical array holes and polymer coating is 148.9 mAh g -1 , and it can stably operate for more than 700 cycles. After 700 cycles, the discharge specific capacity is 75.49% of the initial discharge specific capacity. While for the full cell assembled with commercial lithium sheet as the negative electrode, the discharge specific capacity after 700 cycles is only 56.14% of the initial discharge specific capacity. It shows that under the combined action of the vertical hole structure and the polymer interface layer, dendrites will grow vertically upward from the bottom of the hole and horizontally from the hole wall towards the center of the hole until they contact and squeeze each other to become dense and uniform, making the battery have better cycle performance. When performing charge and discharge cycle tests at a rate of 2C, the voltage-capacity curve comparison diagram is as Figure 9 shown, which can prove that the novel composite alkali metal negative electrode with the new structure can greatly improve the cycle stability and capacity retention rate of the battery.

[0080] Example 2

[0081] Polyvinylidene fluoride (PVDF) was added to the organic solvent N,N-dimethylacetamide (DMAC) and stirred until it became transparent and clear to obtain polymer precursor solution 2, in which the mass percentage content of PVDF polymer was 5%.

[0082] The polymer precursor solution 2 was in-situ blade-coated on the surface of commercial sodium metal 1 with a thickness of 80 μm. The height of the blade 3 was 20 μm higher than the thickness of the sodium metal. After drying for 3 h at 50 °C under a low temperature and inert gas atmosphere, the PVDF coating thickness was 1 μm, and finally a sodium metal negative electrode with a polymer coating was obtained.

[0083] The selected mechanical punching tool 4 had a needle with a diameter of 100 μm, a punching depth of 60 μm (75% of the thickness of the sodium metal negative electrode), and a needle density of 50% (area ratio), and finally a novel sodium metal negative electrode with vertical array holes and polymer coating was obtained.

[0084] Example 3

[0085] Polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP) was added to anhydrous acetonitrile, an organic solvent, and stirred until it became transparent and clear, obtaining a polymer precursor solution 2, where the mass percentage content of the PVDF - HFP polymer was 10%.

[0086] The polymer precursor solution 2 was in - situ scrape - coated on the alkali - metal surface of a commercial lithium foil 1 with a thickness of 100 μm using a doctor blade 3. The height of the doctor blade 3 was 50 μm higher than the thickness of the alkali - metal. After drying for 3 h at a low temperature of 50 °C under an inert gas atmosphere, the thickness of the PVDF - HFP coating was 5 μm, and finally, an alkali - metal negative electrode with a polymer coating was obtained.

[0087] The selected mechanical punching tool 4 had a needle with a diameter of 50 μm, a punching depth of 90 μm (90% of the thickness of the alkali - metal negative electrode), and a needle density of 70% (area ratio). Finally, a novel alkali - metal negative electrode with vertical - array holes and a polymer coating was obtained.

[0088] Example 4

[0089] Polyacrylonitrile (PAN) was added to N, N - dimethylformamide (DMF), an organic solvent, and stirred until it became transparent and clear, obtaining a polymer precursor solution 2, where the mass percentage content of the PAN polymer was 15%.

[0090] The polymer precursor solution 2 was in - situ scrape - coated on the alkali - metal surface of a commercial lithium foil 1 with a thickness of 100 μm using a doctor blade 3. The height of the doctor blade 3 was 30 μm higher than the thickness of the alkali - metal. After drying for 3 h at a low temperature of 40 °C under an inert gas atmosphere, the thickness of the PAN coating was 10 μm, and finally, an alkali - metal negative electrode with a polymer coating was obtained.

[0091] The selected mechanical punching tool 4 had a needle with a diameter of 150 μm, a punching depth of 90 μm (90% of the thickness of the alkali - metal negative electrode), and a needle density of approximately 70% (area ratio). Finally, a novel alkali - metal negative electrode with vertical - array holes and a polymer coating was obtained.

[0092] In summary, a three - dimensional vertically porous composite alkali - metal negative electrode of the present invention, its preparation method and application are suitable for large - scale production. The introduced polymer coating not only does not significantly affect the energy density of the battery, but also combines with the vertical - array hole structure to regulate the deposition and growth behavior of alkali metals. Finally, the deposition and growth of alkali metals are restricted in the holes and the morphology is dense and uniform. This not only delays the diaphragm piercing time and improves the safety performance, but also greatly improves the cycle stability and capacity retention rate of the metal battery.

[0093] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a three-dimensional vertically porous composite alkali metal negative electrode, characterized in that It includes the following steps: Mix a polymer and an organic solvent, and obtain a polymer precursor solution through sufficient stirring. The polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyacrylonitrile, polyamic acid, and polyimide, and the organic solvent is one or more of N,N - dimethylformamide, N,N - dimethylacetamide, and acetonitrile. In - situ thinly coat the polymer precursor solution on the surface of an alkali metal, and under an inert atmosphere, obtain an alkali metal containing a composite polymer layer through low - temperature drying. The alkali metal is one or more of lithium, sodium, and potassium; perform punching on one side surface of the composite polymer layer by a mechanical punching method to obtain a three - dimensional vertically porous composite alkali metal negative electrode; The three - dimensional vertically porous composite alkali metal negative electrode includes an alkali metal, with a composite polymer layer provided on one side of the alkali metal. Three - dimensional vertical holes are arranged in an array on one side of the composite polymer layer. The three - dimensional vertical holes are of micron - level or sub - micron - level. The thickness of the composite polymer layer is 1 - 10 μm, the diameter of the three - dimensional vertical holes is 50 - 150 μm, the hole depth of the three - dimensional vertical holes is 70% - 90% of the thickness of the alkali metal negative electrode, and the area ratio of the three - dimensional vertical holes on the composite polymer layer is 30% - 70%; Adopt a doctor - blade coating method to in - situ thinly coat the polymer precursor solution on the surface of the alkali metal. The height of the doctor - blade is 20 - 50 μm higher than the thickness of the alkali metal.

2. The preparation method of the three-dimensional vertically porous composite alkali metal negative electrode according to claim 1, characterized in that, The mass fraction of the polymer precursor solution is 5% - 20%.

3. The preparation method of the three-dimensional vertically porous composite alkali metal negative electrode according to claim 1, characterized in that, The temperature of the low - temperature drying treatment is 40 - 50 °C, and the time is 3 - 5 h.

4. Application of the three - dimensional vertically porous composite alkali metal negative electrode prepared by the method according to claim 1 or 2 or 3 in an alkali metal battery.

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