CN115377356A - Three-dimensional vertical porous composite alkali metal cathode and preparation method and application thereof - Google Patents

Three-dimensional vertical porous composite alkali metal cathode and preparation method and application thereof Download PDF

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CN115377356A
CN115377356A CN202211202425.1A CN202211202425A CN115377356A CN 115377356 A CN115377356 A CN 115377356A CN 202211202425 A CN202211202425 A CN 202211202425A CN 115377356 A CN115377356 A CN 115377356A
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alkali metal
dimensional vertical
porous composite
composite
polymer
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王凯铭
沈飞
张亮
陈逸菲
苏毅宁
韩晓刚
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Xian Jiaotong University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract

The invention discloses a three-dimensional vertical porous composite alkali metal cathode and a preparation method and application thereof, wherein a polymer and an organic solvent are mixed and fully stirred to obtain a precursor solution; coating the precursor solution on the surface of alkali metal in situ by a simple scraper blade coating method, drying at low temperature in an inert atmosphere, and obtaining the alkali metal containing the composite polymer layer after the organic solvent in the coating is completely volatilized; and punching the surface of the composite polymer layer by a mechanical punching method to obtain the three-dimensional vertical porous composite alkali metal cathode. The preparation method is simple in preparation process, low in cost and suitable for large-scale commercial production, and the densified deposition morphology is obtained by adjusting and controlling the growth mode of the dendritic deposition alkali metal through another method, so that the cycling stability of the battery is greatly improved, the application prospect is wide, and the breakthrough of high safety of the secondary alkali metal battery is facilitated.

Description

Three-dimensional vertical porous composite alkali metal cathode and preparation method and application thereof
Technical Field
The invention belongs to the technical field of metal battery preparation, and particularly relates to a three-dimensional vertical porous composite alkali metal cathode and a preparation method and application thereof.
Background
The traditional secondary battery is gradually difficult to meet the high requirements of large energy storage devices such as rapidly developed electric vehicles, photovoltaic power stations and the like on energy density and safety. For example, the specific capacity of the negative electrode of a lithium ion battery based on ion intercalation/deintercalation reaction approaches the theoretical limit (372 mAh g) -1 ) The graphite material seriously limits the further breakthrough of the overall energy density of the lithium ion battery, so that the search for a high-specific-capacity negative electrode material capable of replacing graphite is great tendency.
The alkali metal material is used for replacing the graphite material to directly serve as the cathode of the secondary battery, so that the advantages are achieved. On one hand, the earth reserves of alkali metal resources such as lithium, sodium, potassium and the like are abundant, and the requirements of large-scale application can be met. On the other hand, the alkali metal cathode generally has high specific capacity and low density, and the energy density of the secondary battery can be greatly improved. For example, alkali metals have extremely high theoretical specific capacities (3860 mAh g) -1 ) Very low density (0.534 g cm) -3 ) And low electrochemical potential (-3.04V vs standard hydrogen electrode), considered as "holy grail" of the negative electrode material.
However, the direct use of alkali metal as the negative electrode of the secondary battery also brings many problems, which severely limits the commercial application prospect. The method comprises the following steps:
(1) Due to the reason that the surface of the alkali metal cathode is uneven and the like, dendritic deposition is easy to occur in the circulating process to cause the piercing of a diaphragm, and finally, serious safety problems such as fire explosion and the like caused by internal short circuit occur.
(2) In addition, the alkali metal cathode has huge volume change in the circulation process, so that an SEI film on the surface of the electrode is easy to break, and the exposed fresh alkali metal continuously reacts with the electrolyte, thereby exacerbating capacity fading.
(3) Meanwhile, the alkali metal negative electrode has high chemical activity, is poor in matching with an electrolyte or a solid electrolyte, is easy to corrode or form a passivation layer in a long-circulating process, causes interface impedance and polarization surge, and finally fails.
Therefore, in order to suppress dendrite growth, limit the volume change of the alkali metal negative electrode during the deposition/stripping process, and improve the safety performance of the secondary battery, various modification methods are proposed, including the use of electrolyte additives, solid electrolytes, metal deposition frameworks, and composite metal negative electrodes, etc. However, most of these methods are complicated and costly, and cannot fundamentally prevent the formation of dendritic alkali metal deposit morphology, and the above problems still occur after long cycles, mainly because of the following reasons:
(1) The generation of dendritic alkali metal deposition is a complex random uncontrolled process, influenced by a number of factors such as temperature, pressure, electric field strength, ion concentration and electrolyte properties.
(2) The introduced additives and interface layers are consumed or destroyed after a long cycle to fail, and thus it is difficult to continue their functions.
(3) Almost no method can completely inhibit the side reaction of lithium metal and electrolyte or solid electrolyte, and the product can be accumulated at the interface to influence the lithium deposition appearance.
Therefore, finding a simple process to regulate the growth behavior of dendrites under the condition that the dendrites are generated and greatly delay the piercing time of the diaphragm is very important for improving the safety of the alkali metal battery.
Disclosure of Invention
The invention aims to solve the technical problems in the prior art, and provides a three-dimensional vertical porous composite alkali metal cathode, a preparation method and application thereof, which are used for solving the technical problems of low safety and poor cycle stability of an alkali metal battery, can further regulate and control the growth behavior mode of the alkali metal battery under the condition that dendritic metal deposition is generated, realize densification deposition, greatly reduce the probability of puncturing a diaphragm and achieve the purpose of improving the cycle life and the safety of the metal battery.
The invention adopts the following technical scheme:
a three-dimensional vertical porous composite alkali metal cathode comprises an alkali metal, wherein a composite polymer layer is arranged on one side of the alkali metal, three-dimensional vertical holes are arranged on one side of the composite polymer layer in an array mode, and the three-dimensional vertical holes are in a micron-sized or submicron-sized mode.
Specifically, the thickness of the composite polymer layer is 1 to 10 μm.
Specifically, the diameter of the three-dimensional vertical hole is 50-150 μm, the hole depth of the three-dimensional vertical hole is 70-90% of the thickness of the alkali metal cathode, and the area of the three-dimensional vertical hole on the composite polymer layer is 30-70%.
The invention also provides a method for preparing the three-dimensional vertical porous composite alkali metal cathode, which comprises the following steps:
in-situ thin coating the polymer precursor solution on the surface of alkali metal, and drying at low temperature in an inert atmosphere to obtain the alkali metal containing the composite polymer layer; and punching the surface of one side of the composite polymer layer by a mechanical punching method to obtain the three-dimensional vertical porous composite alkali metal cathode.
Specifically, the mass fraction of the polymer precursor solution is 5-20%.
Further, mixing a polymer and an organic solvent, and fully stirring to obtain a polymer precursor solution, wherein 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.
Specifically, a scraper blade coating method is adopted to thinly coat the polymer precursor solution on the surface of the alkali metal in situ, and the height of the scraper is 20-50 μm higher than the thickness of the alkali metal.
Specifically, the temperature of the low-temperature drying treatment is 40-50 ℃, and the time is 3-5 h.
Specifically, the alkali metal is one or more of lithium, sodium and potassium.
The other technical scheme of the invention is the application of the three-dimensional vertical porous composite alkali metal cathode in an alkali metal battery.
Compared with the prior art, the invention has at least the following beneficial effects:
a three-dimensional vertical porous composite alkali metal cathode is characterized in that a composite polymer coating limits alkali metal deposition to be carried out in a hole due to the electronic insulation characteristic, and improves the ion concentration at the outer edge of the hole due to the ion adsorption characteristic, so that dendritic metal deposition on the inner wall of the hole can be regulated and controlled to grow towards the center of the hole along the horizontal direction; three-dimensional vertical holes arranged in an array can effectively regulate and control the distribution of a negative electrode electric field, so that an electric field in the holes is converted into a vertical downward electric field and deflects towards the peripheral hole walls, and an electric field at the outer edges of the holes is converted into a vertical downward electric field and deflects towards the inner parts of the holes, therefore, alkali metal can grow from the bottom of the holes vertically and upwards and from the horizontal deposition of the hole walls towards the center of the holes at the same time until the alkali metal and the hole walls are in contact with each other and extruded; under the dual action of the vertical array hole structure and the polymer coating, the final alkali metal deposition morphology in the hole is compact and uniform, the probability that the dendrite pierces the diaphragm is reduced, and the electrochemical stability and safety performance of the alkali metal secondary battery are greatly improved.
Furthermore, the height of the scraper is adjusted to enable the thickness of the final composite polymer layer to be 1-10 microns, so that the scraper not only can play a role in isolating electrons and prevent lithium ions from depositing on the surface of the polymer layer and limiting the lithium ions in holes, but also can keep the energy density of the battery from being influenced by the ultrathin thickness as far as possible.
Further, determining the surface deposition capacity required by the composite cathode according to the surface capacity of the matched cathode material, and selecting proper needle aperture, needle density and punching depth; under the same needle density, the aperture and the depth of the hole are properly increased, and the more the alkali metal deposition surface capacity in the hole can be accommodated, the more the anode material with high active substance surface loading can be matched; under the same aperture and depth, the density of the needles is more uniform, the capacity of the alkali metal deposition surface in the hole is more, and the positive electrode material with high active substance surface loading can be matched.
The preparation method of the three-dimensional vertical porous composite alkali metal cathode is characterized in that the alkali metal cathode with the organic interface layer has strong mechanical property even after a three-dimensional deposition structure is formed by punching, and is an ideal choice for a deposition support structure of the alkali metal cathode.
Further, in order to avoid the continuous side reaction between the alkali metal and the solvent caused by slow volatilization of the solvent, the concentration of the precursor solution is determined according to the required height of the scraper and the required thickness of the scraper. If the height of the scraper and the scraping thickness are smaller, the concentration of the precursor solution can be properly reduced, namely the organic solvent proportion can be higher; on the contrary, the concentration of the precursor solution is increased properly, i.e. the organic solvent ratio is decreased.
Furthermore, the method of dissolving the polymer in the organic solvent and then scraping the polymer can not only increase the cohesiveness of the polymer and the alkali metal, but also obtain an organic polymer coating with more uniform and consistent thickness and other characteristics and smooth surface.
Further, the organic polymer solution is applied to the alkali metal surface by a doctor blade method, not only can the height of the doctor blade be changed more conveniently to obtain a desired coating thickness, but also the amount of the alkali metal surface solvent can be reduced and the volatilization area can be increased to suppress the continuous occurrence of side reactions.
Furthermore, the organic solvent is completely volatilized through thin coating of a polymer solution and rapid low-temperature drying treatment, so that the continuous side reaction between the organic solvent and alkali metal is avoided. Under the condition of certain coating thickness, the time is properly increased when the low-temperature drying temperature is lower; under the condition of a certain low-temperature drying temperature, the thicker the coating thickness is, the time is properly increased; under the condition of a certain low-temperature drying time, the thicker the coating thickness is, the higher the low-temperature drying temperature is, and finally, the organic solvent is fully volatilized.
Furthermore, the earth resources of alkali metals (such as lithium, sodium, potassium and the like) are abundant and easy to obtain, and the alkali metals generally have high theoretical capacity, low density and lower electrochemical potential, and are expected to replace commercial graphite negative electrodes to improve the energy density of the battery.
In conclusion, the preparation process is simple, the cost is low, the preparation method is suitable for large-scale commercial production, and the growth mode of dendritic deposition alkali metal is regulated and controlled through another method to obtain the densified deposition morphology, so that the battery cycle stability is greatly improved, the application prospect is wide, and the breakthrough of high safety of secondary alkali metal batteries is facilitated.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic view; the optical image of the alkali metal cathode prepared in example 1, wherein (a) is the surface topography of the alkali metal cathode containing only the polymer coating, and (b) is the surface topography of the alkali metal cathode containing both the vertical array hole structure and the polymer coating;
FIG. 2 is a mechanical perforating tool with a 100 μm diameter needle of example 1, wherein (a) is a front view of the tool and (b) is a side view of the tool;
FIG. 3 is a scanning electron microscope image of the surface and cross-section of the novel alkali metal anode with a vertical array pore structure and a polymer coating prepared in example 1, wherein (a) is the surface morphology of the novel alkali metal anode and (b) is the cross-sectional morphology of the novel alkali metal anode;
FIG. 4 is a diagram showing the results of a Comsol simulation of the cathode electric field distribution of a novel alkali metal cathode assembled ternary full cell containing a vertical array hole structure and a polymer coating;
FIG. 5 is a graph comparing the cycling performance of a ternary full cell based on the separate assembly of an alkali metal cathode containing only an insulating polymer coating and a novel alkali metal cathode containing an insulating polymer coating and a vertical array of holes;
FIG. 6 at 0.5mA cm -2 At different current densities and different deposition capacities, scanning electron microscope images of alkali metal deposition on the electrode surface in the novel alkali metal negative assembled lithium-lithium symmetric cell containing the vertical array pore structure and the polymer coating prepared in example 1, where (a) is deposition of 0.1mAh cm -2 The surface appearance of the electrode after the alkali metal is obtained, and (b) is 0.3mAh cm of deposition -2 The surface appearance of the electrode after the alkali metal is obtained, and (c) is 0.5mAh cm of deposition -2 Alkali of (2)The surface appearance of the electrode after metal deposition, and (d) 0.75mAh cm -2 The surface morphology of the electrode after alkali metal treatment;
FIG. 7 at 1mA cm -2 Current density of 0.5mAh cm -2 In the novel lithium-lithium symmetric battery assembled with the alkali metal cathode containing the vertical array pore structure and the polymer coating prepared in example 1, an optical photograph of the electrode surface;
fig. 8 is a graph comparing the cycle stability at 1C rate of a lithium-NCM 811 ternary positive electrode full cell assembled with a commercial lithium plate separately based on the novel alkali metal containing vertical array pore structure and polymer coating prepared in example 1;
fig. 9 is a graph comparing voltage-capacity curves at 2C rate for an assembled lithium-ternary positive full cell, wherein (a) is the voltage-capacity curve at 2C rate for a lithium-NCM 811 ternary positive full cell assembled based on a commercial lithium plate, and (b) is the voltage-capacity curve at 2C rate for a lithium-NCM 811 ternary positive full cell assembled based on a novel alkali metal negative electrode containing a vertical array pore structure and a polymer coating prepared in example 1;
FIG. 10 is a schematic diagram of the preparation of the novel alkali metal anode with a vertical array pore structure and a polymer coating according to the present invention.
Wherein, 1, lithium sheet; 2. a polymer precursor solution; 3. a scraper; 4. a mechanical punching tool.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, all embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified.
In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated.
In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "6 to 22" indicates that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is only a shorthand representation of the combination of these numbers.
The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits.
As used herein, the term "and/or" refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.
In the present invention, unless otherwise specified, each reaction or operation step may be performed sequentially or in an order. Preferably, the reaction processes herein are carried out sequentially.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.
The invention provides a three-dimensional vertical porous composite alkali metal cathode and a preparation method thereof, wherein a prepared polymer precursor solution is thinly coated on the surface of one side of an alkali metal and dried at a low temperature, the volume of an alkali metal deposition surface in a required cathode hole is determined according to the volume of a positive electrode material to be matched, the diameter of a punching tool needle, the density of a pillow and the punching depth are further determined, and in an inert atmosphere, mechanical punching is carried out on the surface of a composite polymer layer to obtain uniformly distributed micron-sized or submicron-sized holes, so that the novel alkali metal cathode containing a vertical array hole structure and a polymer coating is obtained. The uniform vertical array holes can effectively regulate and control the intensity distribution of the negative electric field, and the composite polymer layer limits the alkali metal deposition in the holes due to the electronic insulation property on one hand and is favorable for regulating and controlling the concentration of ions at the edges of the holes due to the ion adsorption property on the other hand; finally, under the combined action of the vertical hole structure and the composite polymer layer, the dendritic crystal grows vertically upwards from the hole bottom deposition and grows horizontally to the hole center until the dendritic crystal is mutually contacted and extruded to become compact and uniform, and the purposes of prolonging the cycle life and improving the safety of the metal battery are achieved.
Referring to fig. 10, the three-dimensional vertical porous composite alkali metal cathode of the present invention includes a composite polymer layer disposed on an alkali metal, the thickness of the composite polymer layer is 1-10 μm, the composite polymer layer is provided with a plurality of uniformly distributed micron-sized or submicron-sized holes (the holes account for 30% -70% of the total surface area), the micron-sized or submicron-sized holes are three-dimensional vertical holes, the diameter of the three-dimensional vertical holes is 50-150 μm, and the depth of the three-dimensional vertical holes is 70% -90% of the thickness of the alkali metal.
The invention discloses a preparation method of a three-dimensional vertical porous composite alkali metal cathode, which comprises the following steps:
s1, mixing a polymer and an organic solvent, and fully stirring to obtain a polymer precursor solution with the mass fraction of 5-20%;
wherein, the polymer is selected from polymer materials with electronic insulation and certain ion adsorption, and is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyamide acid and polyimide, and the organic solvent is one or more of N, N-dimethylformamide, N, N-dimethylacetamide and acetonitrile.
S2, coating the polymer precursor solution on the surface of alkali metal in situ by a scraper blade coating method, drying at the low temperature of 40-50 ℃ for 3-5 h in an inert atmosphere, and obtaining the alkali metal containing the composite polymer layer after the organic solvent is completely volatilized;
the height of the scraper is 20-50 μm higher than the thickness of the alkali metal, and the thickness of the composite polymer layer is 1-10 μm.
Wherein the alkali metal is one or more of lithium, sodium and potassium.
And S3, punching the surface of the composite polymer layer by using a punching tool with a micron or submicron needle head through a mechanical punching method to obtain the three-dimensional vertical porous composite alkali metal cathode.
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 cathode.
The method comprises the following steps of determining the capacity of an alkali metal surface deposited in a hole required by a negative electrode according to the surface capacity of a matched positive electrode material, and determining the diameter, density and punching depth of a needle head on the surface of a mechanical punching tool according to the capacity of the alkali metal surface deposited in the hole required by the negative electrode, wherein under the same punching density, the aperture and the hole depth are properly increased, and the more the capacity of the alkali metal deposited surface in the hole can be accommodated; under the same aperture and depth, the higher and more uniform the perforation density, the more the capacity of the alkali metal deposition surface in the hole can be accommodated.
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
Example 1
Adding 4,4' -diaminodiphenyl ether (ODA) into an organic solvent N, N-Dimethylacetamide (DMAC), stirring until the mixture is transparent and clear, adding pyromellitic dianhydride (PMDA) with the same mole number, stirring, and fully polymerizing in situ to obtain a light yellow clear polyamic acid (PAA) precursor solution, wherein the PAA polymer accounts for 20% by mass.
The polymer precursor solution 2 was in-situ coated on the metal surface of a commercial lithium plate 1 having a thickness of 100 μm with a doctor blade 3 having a height of 50 μm higher than the thickness of the alkali metal, and dried at a low temperature of 40 ℃ in an inert gas atmosphere for 5 hours to obtain an alkali metal negative electrode containing only the polymer coating as shown in fig. 1 (a).
The front and side optical photographs of the mechanical punching tool 4 were taken as shown in FIG. 2 (a) and FIG. 2 (b), respectively, and had a 80 μm-diameter needle punching depth of 70 μm (70% of the alkali metal thickness) and a needle density of 30% (area ratio).
The novel alkali metal cathode containing the vertical array of holes and the polymer coating obtained after mechanical punching is subjected to electron scanning microscope test and optical observation, as shown in fig. 3 and fig. 1 (b), respectively, the hole diameter is 80 μm, the hole density is 30% (area ratio), the PAA polymer coating is smooth, flat and crack-free, and the thickness is 10 μm.
Comsol electric field simulation is carried out on the ternary full cell assembled based on the novel alkali metal cathode containing the vertical array holes and the polymer coating, and the result is shown in figure 4, the electric field in the hole is changed to be vertical and downward and deflected towards the peripheral hole wall, and the electric field at the outer edge of the hole is changed to be vertical and downward and deflected towards the hole, so that the alkali metal can be deposited and vertically grow upwards at the bottom of the hole and horizontally grow towards the hole center at the bottom of the hole at the same time until the alkali metal is contacted and extruded mutually and becomes compact and uniform.
Using alkali metal containing insulating polymer coating and novel alkali metal containing insulating polymer coating and vertical array holes as negative electrode, using NCM811 material as positive electrode, using Polyethylene (PE) microporous diaphragm as diaphragm, dripping 70 μ L commercial LiPF 6 The electrolyte is assembled into a full battery, a charge-discharge cycle test is carried out under the multiplying power of 1C, the specific capacity change of an active substance is shown in figure 5, and the discharge specific capacity of full electric Chi Shoujuan assembled by a novel alkali metal cathode containing vertical array holes and a polymer coating is 148.9mAh g -1 Can stably run for more than 600 circles, and the discharge specific capacity is the first circle after 600 circles of circulation82.13% of discharge specific capacity, while the full cell assembled by the alkali metal cathode only containing the insulating polymer coating has no discharge specific capacity, which proves that the PAA coating has electronic insulation property, and alkali metal cannot be deposited on the surface of the PAA coating.
Taking a novel alkali metal electrode containing vertical array holes and a polymer coating as a negative electrode, taking a commercial lithium sheet 1 as a positive electrode, adopting a Polyethylene (PE) microporous diaphragm as the diaphragm, and dropwise adding 70 mu L of commercial LiPF 6 Assembling the symmetrical battery with the electrolyte at 0.5mA cm -2 The cell was disassembled for electron scanning microscope testing after charging at the current density for different times, and the results are shown in fig. 6, with increasing time, the deposited alkali metal gradually and densely filled the entire hole. At 1mA cm -2 The cell was disassembled after charging for 0.5h at the current density of (1), and an optical photograph of the negative electrode is shown in fig. 7, which proves that alkali metal cannot be deposited on the surface of the polymer layer and can only be deposited and grown in the holes.
Respectively using prepared novel alkali metal containing vertical array holes and polymer coating and commercial lithium sheet 1 as a negative electrode, using NCM811 ternary material as a positive electrode, using Polyethylene (PE) microporous diaphragm as the diaphragm, and dropwise adding 70 mu L of commercial LiPF 6 The electrolyte is assembled into a full battery, the change trend of the specific capacity of the positive active material is shown in figure 8 by a charge-discharge cycle test under the multiplying power of 1C, and the discharge specific capacity of the full battery Chi Shoujuan assembled by the novel alkali metal negative electrode containing the vertical array holes and the polymer coating is 148.9mAh g -1 The lithium ion battery can stably run for more than 700 circles, the discharge specific capacity is 75.49% of the discharge specific capacity of the first circle after 700 circles of circulation, and the discharge specific capacity of a full battery assembled by taking a commercial lithium sheet as a negative electrode is only 56.14% of the discharge specific capacity of the first circle after 700 circles of circulation. The result shows that under the combined action of the vertical hole structure and the polymer interface layer, the dendritic crystal can grow vertically upwards from the hole bottom deposition and horizontally grow towards the hole center until the dendritic crystal is mutually contacted and extruded to become compact and uniform, so that the battery has better cycle performance. In a charge-discharge cycle test under the multiplying power of 2C, a voltage-capacity curve comparison graph is shown in fig. 9, and the fact that the composite alkali metal cathode with the novel structure can greatly improve the cycle stability and the capacity retention rate of the battery can be proved.
Example 2
Polyvinylidene fluoride (PVDF) is added into an organic solvent N, N-Dimethylacetamide (DMAC) and stirred until the mixture is transparent and clear, and a polymer precursor solution 2 is obtained, wherein the mass percentage of the PVDF polymer is 5%.
And (3) carrying out in-situ blade coating on the surface of commercial sodium metal 1 with the thickness of 80 microns by using a scraper 3, wherein the height of the scraper 3 is 20 microns higher than the thickness of the sodium metal, and after drying for 3 hours at the low temperature of 50 ℃ in an inert gas atmosphere, the thickness of the PVDF coating is 1 micron, so as to finally obtain the sodium metal cathode containing the polymer coating.
The mechanical punching tool 4 is selected to have a needle with a diameter of 100 μm, the punching depth is 60 μm (75% of the thickness of the sodium metal cathode), the needle density is 50% (area ratio), and the novel sodium metal cathode containing the vertical array holes and the polymer coating is finally obtained.
Example 3
Adding polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) into an organic solvent anhydrous acetonitrile, stirring until the mixture is transparent and clear, and obtaining a polymer precursor solution 2, wherein the mass percentage content of the PVDF-HFP polymer is 10%.
And (3) in-situ blade-coating the polymer precursor solution 2 on the alkali metal surface of a commercial lithium sheet 1 with the thickness of 100 microns by using a scraper 3, wherein the height of the scraper 3 is 50 microns higher than the thickness of the alkali metal, and after drying for 3 hours at the low temperature of 50 ℃ in an inert gas atmosphere, the thickness of the PVDF-HFP coating is 5 microns, so that the alkali metal cathode containing the polymer coating is finally obtained.
The mechanical punching tool 4 is selected to have a needle with the diameter of 50 microns, the punching depth is 90 microns (90% of the thickness of the alkali metal cathode), the needle density is 70% (area ratio), and the novel alkali metal cathode containing the vertical array holes and the polymer coating is finally obtained.
Example 4
Adding Polyacrylonitrile (PAN) into an organic solvent N, N-Dimethylformamide (DMF), and stirring until the mixture is transparent and clear to obtain a polymer precursor solution 2, wherein the mass percent of the PAN polymer is 15%.
And (3) in-situ blade-coating the polymer precursor solution 2 on the alkali metal surface of a commercial lithium sheet 1 with the thickness of 100 microns by using a scraper 3, wherein the height of the scraper 3 is 30 microns higher than the thickness of the alkali metal, and after drying for 3 hours at the low temperature of 40 ℃ in an inert gas atmosphere, the thickness of the PAN coating is 10 microns, so that the alkali metal cathode containing the polymer coating is finally obtained.
The mechanical punching tool 4 is selected to have a 150 μm diameter needle with a punching depth of 90 μm (90% of the thickness of the alkali metal cathode) and a needle density of about 70% (area ratio), and the novel alkali metal cathode containing the vertical array of holes and the polymer coating is finally obtained.
In conclusion, the three-dimensional vertical porous composite alkali metal cathode, the preparation method and the application thereof are suitable for large-scale production, the introduced polymer coating does not greatly influence the energy density of the battery, the alkali metal deposition growth behavior can be regulated and controlled by combining with the vertical array hole structure, the alkali metal deposition growth is limited in the hole and the appearance is compact and uniform, the piercing time of the diaphragm is delayed, the safety performance is improved, and the cycle stability and the capacity retention rate of the metal battery are greatly improved.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The three-dimensional vertical porous composite alkali metal cathode is characterized by comprising an alkali metal, wherein a composite polymer layer is arranged on one side of the alkali metal, three-dimensional vertical holes are arranged on one side of the composite polymer layer in an array mode, and the three-dimensional vertical holes are in a micron-sized or submicron-sized mode.
2. The three-dimensional vertical porous composite alkali metal anode according to claim 1, wherein the composite polymer layer has a thickness of 1 to 10 μm.
3. The three-dimensional vertical porous composite alkali metal anode according to claim 1, wherein the diameter of the three-dimensional vertical pores is 50-150 μm, the depth of the three-dimensional vertical pores is 70-90% of the thickness of the alkali metal anode, and the area of the three-dimensional vertical pores on the composite polymer layer is 30-70%.
4. A method of making the three-dimensional vertical porous composite alkali metal anode of claim 1, 2 or 3 comprising the steps of:
in-situ thin coating the polymer precursor solution on the surface of alkali metal, and drying at low temperature in an inert atmosphere to obtain the alkali metal containing the composite polymer layer; and punching the surface of one side of the composite polymer layer by a mechanical punching method to obtain the three-dimensional vertical porous composite alkali metal cathode.
5. The preparation method of the three-dimensional vertical porous composite alkali metal cathode as claimed in claim 4, wherein the mass fraction of the polymer precursor solution is 5-20%.
6. The preparation method of the three-dimensional vertical porous composite alkali metal cathode according to claim 5, wherein a polymer and an organic solvent are mixed and fully stirred to obtain a polymer precursor solution, 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.
7. The method for preparing the three-dimensional vertical porous composite alkali metal cathode according to claim 4, wherein the polymer precursor solution is in-situ thinly coated on the surface of the alkali metal by using a doctor blade coating method, and the height of the doctor blade is 20-50 μm higher than the thickness of the alkali metal.
8. The preparation method of the three-dimensional vertical porous composite alkali metal cathode according to claim 4, wherein the temperature of the low-temperature drying treatment is 40-50 ℃ and the time is 3-5 h.
9. The method for preparing the three-dimensional vertical porous composite alkali metal cathode according to claim 4, wherein the alkali metal is one or more of lithium, sodium and potassium.
10. Use of the three-dimensional vertical porous composite alkali metal anode of any one of claims 1 to 3 in an alkali metal battery.
CN202211202425.1A 2022-09-29 2022-09-29 Three-dimensional vertical porous composite alkali metal cathode and preparation method and application thereof Pending CN115377356A (en)

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