Artificial SEI film and preparation method thereof

Abstract

The invention relates to an artificial SEI film and a preparation method thereof, and belongs to the technical field of metal batteries. The artificial SEI film is composed of polytetrafluoroethylene, a dispersant, deionized water, a conductive agent and a binder, and the specific preparation method comprises the following steps: coating the surface of a copper foil with a layer of polytetrafluoroethylene-containing prime coat slurry, drying, cutting the coated copper foil into a specific shape, assembling into a battery, and carrying out pre-charging treatment. And the formed SEI film has dual effects of promoting uniform deposition of lithium metal and preventing reaction of the lithium metal and electrolyte, so that the stability of the negative-electrode-free lithium metal battery is greatly improved. In addition, the conductive agent is also added into the prime coat slurry, so that the rate capability of the battery is greatly improved. The SEI membrane constructed by adopting the method disclosed by the invention has very important significance for realizing the commercial value of the negative-electrode-free lithium metal battery.

Description

Technical Field

[0001] The invention belongs to the technical field of metal batteries and relates to an artificial SEI film and a preparation method thereof. Background Art

[0002] Traditional lithium-ion batteries use graphite as the negative electrode material, but because the theoretical gram capacity of graphite is only 372mAh / g, the energy density of commercial lithium-ion batteries using graphite as the negative electrode is difficult to exceed 300Wh / kg, making it difficult for current commercial lithium-ion batteries to meet the requirements of high energy density in special application scenarios, especially in the field of electric aviation. Compared with graphite, the gram capacity of lithium metal is more than ten times that of graphite. Using lithium metal as the negative electrode material, the energy density of the battery can reach 400Wh / kg or even 500Wh / kg. In addition, in order to further improve the energy density of the battery, a negative electrode-free design can also be adopted, that is, lithium ions are directly deposited on copper foil. Compared with lithium metal batteries, negative electrode-free lithium metal batteries have higher energy density, lower manufacturing cost and better safety. However, both lithium metal batteries and negative electrode-free lithium metal batteries face a series of problems. On the one hand, uneven deposition of lithium metal will form lithium dendrites, which not only consume active lithium and reduce the cycle life of the battery, but also cause internal short circuits, posing serious safety risks. On the other hand, direct contact between lithium metal and electrolyte will cause side reactions, which will continue to consume lithium metal and further reduce the stability of lithium metal batteries. For lithium metal batteries without negative electrodes, since all of their lithium ions come from the positive electrode, side reactions will continue to consume a large amount of active lithium, which will lead to worse cycle stability of the battery.

[0003] Constructing a SEI mainly composed of inorganic components LiF and Li2O on the surface of the negative electrode can promote the uniform deposition of lithium metal and avoid corrosion caused by direct contact between lithium metal and the electrolyte. At present, the regulation of SEI is achieved through electrolyte engineering, that is, adding F-containing solvents or additives to the electrolyte to generate inorganic components mainly composed of LiF or Li2O on the surface of the negative electrode. The SEI obtained by electrolyte engineering regulation often has inorganic and organic components mixed together, which has limited improvement in cycle life and cannot meet the needs of actual commercial batteries. Therefore, the development of a simple and scalable inorganic SEI film construction method is of great significance for realizing the commercial value of negative electrode-free lithium metal batteries. Summary of the invention

[0004] In view of this, one of the objects of the present invention is to provide an artificial SEI film; a second object of the present invention is to provide a method for preparing an artificial SEI film; a third object of the present invention is to provide a negative electrode sheet for a negative electrode-free lithium metal battery; a fourth object of the present invention is to provide a negative electrode-free lithium metal battery.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The invention provides an artificial SEI membrane. The artificial SEI membrane consists of polytetrafluoroethylene, a dispersant, deionized water, a conductive agent and a binder, and the mass ratio is 120:1:80:100:50. The dispersant is polyoxyethylene, the conductive agent consists of any one or more of conductive carbon, carbon nanotubes or graphene, and the binder consists of one or more of CMC, SBR and PEO.

[0007] A method for preparing an artificial SEI film, the preparation method being as follows:

[0008] (1) adding polytetrafluoroethylene powder and dispersant into deionized water, wherein the mass ratio of polytetrafluoroethylene powder to dispersant is 120:80, to prepare a PTFE dispersion;

[0009] (2) Adding a conductive agent and a binder to the PTFE dispersion in step (1) at a mass ratio of 100:50, with a solid content of the binder of 50%, and mixing them thoroughly to form a primer slurry.

[0010] (3) coating the primer slurry in step (2) on the surface of the negative electrode of a lithium metal battery, and drying to obtain a coated negative electrode, wherein the negative electrode is any one of copper foil and lithium metal,

[0011] (4) Assembling the negative electrode sheet in step (3) into a battery, and then precharging, so as to obtain an artificial SEI film on the surface of the negative electrode sheet;

[0012] Furthermore, the dispersant in step (1) is polyoxyethylene;

[0013] Furthermore, the conductive agent in step (2) includes any one or more of conductive carbon, carbon nanotubes or graphene;

[0014] Furthermore, the binder in step (2) includes one or more of CMC (sodium carboxymethyl cellulose), SBR (styrene-butadiene rubber), and PEO (polyethylene oxide);

[0015] The content of the PTFE dispersion in the primer slurry is 10-90%;

[0016] The coating thickness in step (2) is 200 to 3000 nm;

[0017] Further, a negative electrode sheet for a lithium metal battery comprising the artificial SEI film;

[0018] Furthermore, a lithium metal battery comprising the negative electrode sheet for lithium metal battery.

[0019] The beneficial effects of the present invention are as follows: the present invention provides an artificial SEI membrane and a preparation method and application thereof. The artificial SEI membrane is prepared by coating a layer of primer slurry containing polytetrafluoroethylene (PTFE) on the surface of a copper foil current collector, assembling the coated copper foil current collector into a battery after drying, and then precharging. The thickness of the membrane can be precisely controlled by the content of the primer slurry and PTFE. During the first charging of the battery, since PTFE has a lower LUMO, it is easy to obtain electrons to be reduced and react with lithium ions to generate dense LiF. Compared with the traditional SEI membrane of electrolyte engineering components, the artificial SEI membrane constructed by the preparation method of the present invention is mainly composed of LIF, which has the dual effects of promoting uniform deposition of lithium metal, slowing down the growth of lithium dendrites and preventing the reaction of lithium metal and electrolyte, greatly improving the stability of negative electrode-free lithium metal batteries. The conductive agent added to the primer slurry also increases the conductivity, reduces the resistance of the battery, and improves the rate performance of the battery.

[0020] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0022] Example 1

[0023] A method for preparing an artificial SEI film, the specific preparation process is as follows:

[0024] (1) 6 g of polytetrafluoroethylene powder and 0.05 g of polyoxyethylene were placed in 4 g of deionized water to form a polytetrafluoroethylene dispersion with a solid content of 60%, and then 1 g of conductive carbon black and 0.5 g of SBR adhesive with a solid content of 50% were added to the dispersion and stirred thoroughly to form a primer slurry;

[0025] (2) coating the primer slurry obtained in step (1) with a gravure coater, controlling the thickness of the coating layer to be 1000 nm, and obtaining a coated negative electrode;

[0026] (3) cutting the coated copper foil obtained in step (2) into a negative electrode sheet;

[0027] (4) The negative electrode sheet obtained in step (3) is assembled with the NMC positive electrode sheet and the lithium battery separator into a bare cell, and then the electrolyte is injected and packaged to obtain a single cell. The single cell is then placed under the conditions of 0.05CC / 0.2DC (charging rate 0.05C, discharge rate 0.2C) for the first cycle of charge and discharge, and an artificial SEI film can be obtained on the surface of the negative electrode.

[0028] Example 2

[0029] A method for preparing an artificial SEI film, the specific preparation process is as follows:

[0030] (1) 6 g of polytetrafluoroethylene powder and 0.05 g of polyoxyethylene were placed in 4 g of deionized water to form a polytetrafluoroethylene dispersion with a solid content of 60%, and then 1 g of carbon nanotube powder and 0.5 g of CMC adhesive with a solid content of 50% were added to the dispersion and stirred thoroughly to form a primer slurry;

[0031] (2) coating the primer slurry obtained in step (1) with a gravure coater, controlling the thickness of the coating layer to be 1000 nm, and obtaining a coated negative electrode;

[0032] (3) cutting the coated negative electrode obtained in step (2) into negative electrode sheets;

[0033] (4) The negative electrode sheet, the positive electrode sheet and the separator obtained in step (3) are assembled into a bare cell by lamination, and then the electrolyte is injected and packaged to obtain a single cell. The single cell is then placed under the conditions of 0.05CC / 0.2DC for the first cycle of charge and discharge, and an artificial SEI film can be obtained on the surface of the negative electrode.

[0034] Example 3

[0035] A method for preparing an artificial SEI film, the specific preparation process is as follows:

[0036] (1) 6 g of polytetrafluoroethylene powder and 0.05 g of polyoxyethylene were placed in 4 g of deionized water to form a polytetrafluoroethylene dispersion with a solid content of 60%, and then 2 g of carbon nanotubes and 0.5 g of a PEO adhesive with a solid content of 50% were added to the dispersion and stirred thoroughly to form a primer slurry;

[0037] (2) coating the primer slurry obtained in step (1) with a gravure coater, controlling the thickness of the coating layer to be 1000 nm, and obtaining a coated negative electrode;

[0038] (3) cutting the coated negative electrode obtained in step (2) into negative electrode sheets;

[0039] (4) The negative electrode sheet, the positive electrode sheet and the separator obtained in step (3) are assembled into a bare cell by lamination, and then the electrolyte is injected and packaged to obtain a single cell. The single cell is then placed under the conditions of 0.05CC / 0.2DC for the first cycle of charge and discharge, and an artificial SEI film can be obtained on the surface of the negative electrode.

[0040] Example 4

[0041] A method for preparing an artificial SEI film, the specific preparation process is as follows:

[0042] (1) 6 g of polytetrafluoroethylene powder and 0.05 g of polyoxyethylene were placed in 4 g of deionized water to form a polytetrafluoroethylene dispersion with a solid content of 60%, and then 0.5 g of SBR adhesive with a solid content of 50% was added to the dispersion and stirred thoroughly to form a primer slurry;

[0043] (2) coating the primer slurry obtained in step (1) with a gravure coater, controlling the thickness of the coating layer to be 1000 nm, and obtaining a coated negative electrode;

[0044] (3) cutting the coated copper foil obtained in step (2) into a negative electrode sheet;

[0045] (4) The negative electrode sheet, the positive electrode sheet and the separator obtained in step (3) are assembled into a bare cell through a lamination process, and then the electrolyte is injected and packaged to obtain a single cell. The single cell is then placed under the conditions of 0.05CC / 0.2DC for the first cycle of charge and discharge, and an artificial SEI film can be obtained on the surface of the negative electrode.

[0046] Example 5

[0047] A method for preparing an artificial SEI film, the specific preparation process is as follows:

[0048] (1) 6 g of polytetrafluoroethylene powder and 0.05 g of polyoxyethylene were placed in 4 g of deionized water to form a polytetrafluoroethylene dispersion with a solid content of 60%, and then 1 g of carbon nanotubes and 0.5 g of SBR adhesive with a solid content of 50% were added to the dispersion and stirred thoroughly to form a primer slurry;

[0049] (2) coating the primer slurry obtained in step (1) with a gravure coater, controlling the thickness of the coating layer to be 2000 nm, and obtaining a coated negative electrode;

[0050] (3) cutting the coated copper foil obtained in step (2) into a negative electrode sheet;

[0051] (4) Assembling the negative electrode sheet obtained in step (3) with the positive electrode sheet and the separator into a bare cell, and then injecting the electrolyte to encapsulate to obtain a single cell, and then placing the single cell under the conditions of 0.05CC / 0.2DC for the first cycle of charge and discharge, thereby obtaining an artificial SEI film on the surface of the negative electrode.

[0052] Comparative Example 1

[0053] The preparation process of traditional SEI film is as follows:

[0054] The copper foil, the positive electrode sheet and the separator are assembled into a bare cell by stacking, and then the electrolyte is injected and packaged to obtain a single cell. Subsequently, the single cell is placed under the conditions of 0.05CC / 0.2DC for the first cycle of charge and discharge, and the SEI film can be prepared on the copper foil.

[0055] The single cells in Examples 1 to 5 and Comparative Example 1 were placed under 0.05CC / 0.2DC conditions for the first cycle of charge and discharge, and then subsequently subjected to a cycle test at 0.2CC / 0.5DC. The experimental results are shown in Table 1.

[0056] Table 1 Comparison of electrochemical performance of the single cells in Examples 1 to 5 and Comparative Example 1

[0057] project Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 First effect 82.9％ 84.8％ 86.7％ 83.3％ 85.8％ 83.5％ 50-cycle capacity retention rate 21％ 47％ 63％ 28％ 55％ 58％

[0058] It can be seen from Table 1 that the type of conductive agent in the base coating, the content of the conductive agent and the thickness of the base coating have a significant impact on the performance of the battery cell. In the implemented example, the best effect was achieved when Example 2 used carbon nanotubes as the conductive agent, 1g of the conductive agent was used and the base coating thickness was 1000nm.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. Artificial SEI membrane, characterized in that: The artificial SEI film is composed of polytetrafluoroethylene, a dispersant, a conductive agent, and a binder. The dispersant is polyoxyethylene with a mass ratio of 0.05-1%. The conductive agent is composed of any one or more of conductive carbon, carbon nanotubes or graphene with a mass ratio of 5-50%. The binder is composed of one or more of CMC, SBR, and PEO with a mass ratio of 1-5%.

2. The method for preparing the artificial SEI film according to claim 1, characterized in that: The following steps are involved: (1) dissolving polytetrafluoroethylene powder and a dispersant in deionized water, wherein the mass ratio of the polytetrafluoroethylene powder to the dispersant is 120:80, to prepare a PTFE dispersion; (2) adding a conductive agent and a binder to the PTFE dispersion prepared in step (1) at a mass ratio of 100:50, with the solid content of the binder being 50%, and mixing them thoroughly to form a primer slurry; (3) coating the primer slurry in step (2) on the surface of the negative electrode of a lithium metal battery, and drying to obtain a coated negative electrode, wherein the negative electrode is any one of copper foil and lithium metal; (4) Assembling the negative electrode sheets in step (3) into a battery and then precharging the battery to obtain an artificial SEI film on the surface of the negative electrode sheets.

3. The preparation method according to claim 2, characterized in that: The dispersant in step (1) is polyoxyethylene.

4. The preparation method according to claim 2, characterized in that: The conductive agent in step (2) includes any one or more of conductive carbon, carbon nanotubes or graphene.

5. The preparation method according to claim 2, characterized in that: The binder in step (2) includes one or more of CMC, SBR, and PEO.

6. The preparation method according to claim 2, characterized in that: The content of PTFE in the primer slurry is 10-90%.

7. The preparation method according to claim 2, characterized in that: The coating thickness in step (2) is 200 to 3000 nm.

8. A negative electrode sheet for a lithium metal battery, characterized in that: The negative electrode sheet for a lithium metal battery comprises the artificial SEI film according to claim 1.

9. A lithium metal battery, characterized in that: The lithium metal battery comprises the negative electrode sheet for a lithium metal battery according to claim 8.