Lithium composite electrode and its preparation method and application

Abstract

The present invention provides a lithium composite electrode, a preparation method and application thereof. The lithium composite electrode of the present invention comprises: a porous carbon film formed by carbon nanotubes or carbon fibers; and metal lithium or lithium alloy layers pressure-compounded on two surfaces of the porous carbon film, wherein each of the two metal lithium or lithium alloy layers is partially embedded in the porous carbon film.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a lithium negative electrode for a lithium ion battery, and a preparation method and application thereof. Background Art

[0002] As society's requirements for the energy density of lithium-ion batteries are getting higher and higher. First of all, we need to use negative electrode materials with higher specific capacity. Metallic lithium is considered to be the best negative electrode material due to its capacity of 3860mAh / g and low potential of -3.04V. Secondly, we need to reduce the mass of inactive substances, for example, reduce the weight of the current collector and continuously reduce the thickness of the copper current collector. Finally, the battery needs a certain rate performance, and it is necessary to improve the contact between the negative electrode active layer and the current collector to ensure the battery's charge and discharge performance under high current density conditions.

[0003] The copper foil current collector of current lithium-ion batteries has reduced its thickness from 12 microns to 6 microns, and further reduced it to 5 microns, reaching the limit of copper foil processing. In order to achieve interface adhesion and conductivity, carbon coating is performed on the surface of the copper foil.

[0004] In addition, a method for preparing a metal lithium-skeleton material flexible electrode by hot melt coating or vacuum deposition has been proposed. (CN201610252135.6), which mainly adopts hot melt coating or vacuum deposition to fill metal lithium into a three-dimensional current collector. However, since metal lithium is very active, hot melt coating needs to be carried out in high-purity argon gas, and the amount of metal lithium filling and the thickness of the overall electrode cannot be effectively controlled. When using the vacuum deposition method, since the current collector has a three-dimensional skeleton and a huge specific surface area, it takes a long time to evacuate the vacuum to achieve the required vacuum degree, and the production efficiency is low. In addition, it is difficult for metal lithium molecules to enter the internal pores and they are only deposited on the surface of the electrode.

[0005] Therefore, the existing technology still cannot meet the requirements for the metallic lithium negative electrode of the lithium battery. Summary of the invention

[0006] The present invention proposes a special lithium electrode design, in which a metallic lithium layer is pressed on two surfaces of a porous carbon film so that the metallic lithium layer is partially embedded in the porous carbon film. In this way, a metallic lithium negative electrode suitable for a lithium-ion battery can be obtained in a simple, efficient and low-cost manner.

[0007] The present invention adopts the following technical solution:

[0008] One aspect of the present invention provides a lithium composite electrode, which includes: a porous carbon film formed by carbon nanotubes or carbon fibers; and metal lithium or lithium alloy layers pressure-compounded on both surfaces of the porous carbon film, wherein each of the two metal lithium or lithium alloy layers is partially embedded in the porous carbon film.

[0009] According to one embodiment, the embedding degree of the metallic lithium or lithium alloy layer into the porous carbon film is 10-50%.

[0010] According to one embodiment, the lithium alloy includes lithium aluminum, lithium magnesium, lithium boron, lithium zinc or lithium indium alloy.

[0011] According to one embodiment, the total thickness of the lithium composite electrode is in the range of 20-200 microns.

[0012] According to one embodiment, the thickness of the porous carbon film is in the range of 10-100 microns.

[0013] According to one embodiment, the carbon nanotubes or carbon fibers have a diameter of 3-15 nanometers and a length of 3-100 micrometers.

[0014] According to one embodiment, the porous carbon film is woven from the carbon nanotubes or carbon fibers.

[0015] According to one embodiment, the porous carbon film has a pore size of 50-2000 nm.

[0016] Another aspect of the present invention provides a method for preparing the above-mentioned lithium composite electrode, the method comprising: by pressure compounding, two metal lithium or lithium alloy films are compounded sequentially or simultaneously on two surfaces of a porous carbon film, so that each metal lithium or lithium alloy layer after pressure compounding is partially embedded in the porous carbon film.

[0017] According to one embodiment, the pressure bonding is performed in a roll-to-roll manner using a pressure roller.

[0018] According to one embodiment, partial embedding of metallic lithium or lithium alloy into the porous carbon film is achieved by changing the pressure and the roller gap.

[0019] Another aspect of the present invention provides use of the lithium composite electrode in a lithium ion battery. The lithium composite electrode can be used as a negative electrode of the lithium ion battery.

[0020] The present invention has at least one of the following advantages:

[0021] (1) The present invention overcomes the problem that the tensile strength of metallic lithium is low (tensile strength 11MPa), which is far lower than the tensile strength of the current collector used for the positive electrode of the current lithium-ion battery, and is not conducive to the winding of the positive and negative electrodes during the winding process of the positive and negative electrodes of the battery. The present invention adopts a lithium / porous carbon film / lithium structure. Since the tensile strength of the carbon film can be as high as 100MPa or more, and lithium or lithium alloy is also partially embedded in the carbon film (using the porosity of the porous carbon film), its tensile strength is greatly improved, which is convenient for high-speed winding and unwinding.

[0022] (2) Metallic lithium or lithium alloy is embedded in the carbon film, which has better contact and the electronic conductivity of the carbon film is as high as 10 5 S / cm, forming a three-dimensional electron path, ensuring the electrochemical performance under high current density conditions. It overcomes the problem of reduced conductivity of the electrode when using an insulating material skeleton.

[0023] (3) During the preparation process, the present invention only requires pressure compounding, without the need for hot melting or high vacuum, resulting in lower production costs and higher efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of the lithium composite electrode of the present invention.

[0025] Figure 2 FIG. 1 is a SEM image of a side cross section of the lithium composite electrode of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] Furthermore, the various product structural parameters, various reaction participants and process conditions used in the following embodiments are all relatively typical examples. However, after a large number of experiments and verifications by the inventors of this case, other different structural parameters, other types of reaction participants and other process conditions listed above are also applicable and can also achieve the technical effects claimed in the present invention.

[0028] Figure 1 The figure shows a schematic diagram of the structure of a lithium composite electrode of the present invention. The lithium composite electrode has a laminated structure of a metal lithium or lithium alloy layer 1-a porous carbon film 2-a metal lithium or lithium alloy layer 1, and the metal lithium or lithium alloy layer 1 on both sides is partially embedded in the porous carbon film 2 to form an embedded portion 3.

[0029] Figure 2 This is a SEM image of a side cross section of the lithium composite electrode of the present invention, in which the portion where lithium is embedded in the porous carbon film can be clearly seen.

[0030] In the above-mentioned lithium composite electrode, the metal lithium / lithium alloy on both sides is the active material of the electrode. Due to the embedded part, the metal lithium / lithium alloy and the porous carbon film (carbon film) have a closer contact. Therefore, the carbon film can not only be used as a current collector, but also enhance the tensile strength of the composite electrode. The composite electrode can use high-purity metal lithium, or lithium alloys such as lithium aluminum, lithium magnesium, lithium boron, lithium zinc, and lithium indium. The carbon film is formed by interweaving carbon nanotubes or carbon fibers, has a certain porosity, and has the ability to conduct electrons in three dimensions.

[0031] The composite electrode of the above-mentioned laminated structure can be prepared by the following method: the three layers of lithium-carbon film-lithium are placed in sequence, and then pressure composited by a roller pressing device. The composite electrode of different thicknesses and the degree of lithium embedding in the carbon film can be achieved by adjusting the size of the roller gap and the roller pressure.

[0032] Example 1

[0033] A 10um thick carbon nanotube film (Suzhou JEDI Nanotechnology Co., Ltd.; pore size: 200nm) and two 20um thick metal lithium films were used. The roller gap of the pressure roller was controlled to be 40um and the pressure was 1MPa. The two metal lithium films were pressure-compounded on the two surfaces of the porous carbon film to obtain a 45um thick lithium composite electrode. The tensile strength of the lithium metal of the lithium composite electrode when it was tensile broken was 120MPa.

[0034] Example 2

[0035] Similar to Example 1, the carbon nanotube film was replaced with a carbon fiber film (trade name: Beijing Jinglong Special Carbon Technology Co., Ltd.; thickness: 40um; pore size: 50nm), and two metal lithium films with a thickness of 50 microns were composited. The roller gap of the pressure roller was controlled to be 85um and the pressure was 1MPa. The thickness of the obtained lithium composite electrode was 90um, and the tensile strength of the lithium metal when it was tensile fractured was 2000MPa.

[0036] Example 3

[0037] The lithium composite electrode of Example 1 was used to carry out the winding process of the positive and negative electrodes of the battery, and the winding speed was 100m / min. It was observed that there was no stretching and breaking of the lithium negative electrode. The positive electrode was made of lithium nickel cobalt manganese oxide (Beijing Dangsheng Technology Co., Ltd.) and composed into a 20Ah soft-pack battery, and its energy density can reach 320wh / kg. It was cycled 200 times at a rate of 0.1C without obvious attenuation.

[0038] It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium composite electrode, characterized in that The lithium composite electrode comprises: A porous carbon film woven from carbon nanotubes or carbon fibers as a current collector, wherein the carbon nanotubes or carbon fibers have a diameter of 3-15 nanometers and a length of 3-100 micrometers, and the porous carbon film has a pore size of 50-2000 nm and a thickness of 10-40 micrometers; and The metal lithium or lithium alloy layers are pressure-compounded on the two surfaces of the porous carbon film, and the two metal lithium or lithium alloy layers are partially embedded in the porous carbon film. The embedding degree of the metal lithium or lithium alloy layer in the porous carbon film is 10-50%.

2. The lithium composite electrode according to claim 1, characterized in that The lithium alloy includes lithium aluminum, lithium magnesium, lithium boron, lithium zinc or lithium indium alloy.

3. The lithium composite electrode according to claim 1, characterized in that The total thickness of the lithium composite electrode is in the range of 20-200 microns.

4. A method for preparing the lithium composite electrode according to any one of claims 1 to 3, characterized in that: The method comprises: By pressure lamination, two metal lithium or lithium alloy films are laminated on two surfaces of the porous carbon film in sequence or simultaneously, so that each metal lithium or lithium alloy layer after pressure lamination is partially embedded in the porous carbon film.

5. The method according to claim 4, characterized in that The pressure bonding is performed by using a pressure roller in a roll-to-roll manner.

6. Use of the lithium composite electrode according to any one of claims 1 to 3 in a lithium ion battery.

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