WO2023245960A1 - Lithium-magnesium composite negative electrode and preparation method therefor, and lithium-sulfur battery and all-solid-state battery prepared therefrom - Google Patents

Abstract

The present invention relates to the technical field of secondary batteries, and discloses a lithium-magnesium composite negative electrode and a preparation method therefor, and a lithium-sulfur battery and an all-solid-state battery prepared therefrom. The lithium-magnesium composite negative electrode comprises lithium metal, magnesium metal and an auxiliary metal element, wherein the content of the lithium metal is 50-65 wt%, the content of the magnesium metal is 35-50 wt%, and the content of the auxiliary metal element is 0.01-15 wt%; and the auxiliary metal element comprises one or any combination of Cu, Al, Zn, Fe, Ni, Zr or Y. The present invention has the following beneficial effects: the lithium-magnesium composite negative electrode of the present invention has good plastic processing formability, a small thickness and a low density, and improves the volume energy density and the weight energy density of a battery; during the charging and discharging process, lithium metal is continuously reduced to continuously replenish lost active lithium, which can greatly prolong the cycle life of a battery and improve the capacity retention rate under the premise of ensuring safety; and when the lithium-magnesium composite negative electrode is used in a lithium-sulfur battery and an all-solid-state metal battery, no additional current collector is required, such that the weight of the battery is greatly reduced.

Description

A lithium-magnesium composite negative electrode and its preparation method and the prepared lithium-sulfur battery and all-solid-state battery Technical field

The present invention relates to the technical field of secondary batteries, and in particular to a lithium-magnesium composite negative electrode and its preparation method, as well as the prepared lithium-sulfur battery and all-solid-state battery.

Background technique

Since their commercialization, lithium-ion batteries have been widely used in portable electronic devices such as mobile phones, digital cameras, and notebook computers. In recent years, the continuous improvement of the energy density of lithium-ion batteries and the continuous decline of their manufacturing costs have promoted their application in fields such as unmanned aircraft, electric bicycles, electric vehicles and energy storage. With the increasing depletion of non-renewable fossil energy, the gradual transformation of fuel vehicles into electric vehicles has become a future development trend. At present, the cruising range of electric vehicles is the focus of people's attention. In order to achieve a longer single cruising range, power batteries need to have higher energy density (>400Wh/kg). It is difficult for existing liquid lithium-ion batteries to meet this requirement, but lithium-sulfur batteries and all-solid-state batteries with higher energy density are expected to achieve this goal.

The traditional lithium-ion battery negative electrode is mainly composed of graphite negative active material and copper foil current collector. The theoretical discharge capacity of the graphite active material is only 360mAh/g, and the density of the copper foil is as high as 8.9g/cm ^3. It is high in density and heavy in mass. Limits the energy density of traditional lithium-ion batteries. The theoretical specific capacity of metallic lithium is as high as 3860mAh/g, and it has extremely low electrode potential and density. It is expected to be widely used in high-energy-density lithium-sulfur batteries and all-solid-state batteries.

The loss of active lithium during the charging and discharging process of the battery will not only cause the battery capacity to attenuate, but is one of the main factors affecting the battery cycle life. The current mainstream method to solve this problem is to use negative electrode prelithiation technology. The additional lithium source provided by negative electrode prelithiation technology can greatly improve the cycle life of lithium-ion batteries. There are two main methods: lithium powder lithium supplementation and lithium foil lithium supplementation. kind. Lithium supplementation with lithium powder can be directly applied to existing battery manufacturing processes, but the chemical properties of metallic lithium powder are active, which brings high safety risks. The method of replenishing lithium with lithium foil has high lithium replenishment efficiency. In the early stage of lithium replenishment, it is safe and has no side effects. However, in the later stage of lithium replenishment, the lithium foil will gradually pulverize to form lithium powder, which is very likely to cause the explosion of the battery. ; Moreover, lithium metal has poor mechanical processing performance and is difficult to process. It usually needs to be compounded on metal copper foil by rolling.

Currently, the Chinese invention patent with publication number CN107819104A discloses a method for preparing a lithium-copper composite negative electrode foil. The lithium metal foil is evenly adhered to the surface of the copper foil through an interval local pressure enhancement method to form a lithium-copper composite. negative electrode foil, but this will increase the density of the lithium negative electrode and reduce the energy density of the battery. The Chinese invention patent with publication number CN110085804A reports an ultra-lightweight composite anode, which is provided with a vacuum coating or lithium storage coating on a porous polymer film to form a lightweight composite anode. However, the conductivity of the porous polymer is poor. , will increase the internal resistance of the battery, thereby reducing the rate performance of the battery. The Chinese invention patent with publication number CN 106784770 A discloses a lithium-magnesium alloy negative electrode with a high magnesium content and is applied to lithium-sulfur batteries. However, the thickness of the lithium-magnesium alloy negative electrode is too large and excess lithium metal cannot be used in the battery. Use, increases the production cost of the battery, while also reducing the energy density and safety of the battery.

Contents of the invention

The technical problem to be solved by the present invention is how to provide a lithium-magnesium composite negative electrode, which has good formability, can be rolled to a thinner thickness, contains a higher lithium element, and can provide a high specific capacity for the battery. This solves the problems of low energy density and poor safety of batteries in the prior art.

The present invention solves the above technical problems through the following technical means:

A first aspect of the present invention proposes a lithium-magnesium composite negative electrode, including metallic lithium, metallic magnesium and auxiliary metal elements. The content of the metallic lithium is 50-65wt%, and the content of the metallic magnesium is 35-50wt%. The content of the auxiliary metal element is 0.01-15wt%; the auxiliary metal element includes one or any combination of Cu, Al, Zn, Fe, Ni, Zr or Y.

Beneficial effects: The present invention combines lithium, magnesium and auxiliary metal elements to obtain an alloy material that exhibits good plastic processing formability due to grain refinement and can be rolled to ultra-thin lithium-magnesium alloy, which can be used as a negative electrode. An appropriate amount of lithium can effectively improve the volume energy density and weight energy density of the battery; at the same time, lithium-magnesium alloy materials can be mass-produced using rolling, stamping and other technologies, which solves the problem of difficult processing of lithium metal and supports large-scale production.

In the lithium-magnesium composite negative electrode of the present invention, during the charging and discharging process of the lithium-ion battery, due to the low reduction potential of lithium, the lithium metal in the lithium-magnesium alloy can be continuously reduced, and the lost active lithium can be continuously replenished while ensuring safety. Under the premise, it can greatly extend the battery cycle life and improve the capacity retention rate.

Preferably, the thickness of the lithium-magnesium composite negative electrode is 10-200 μm.

Preferably, the density of the lithium-magnesium composite negative electrode is 0.6-1.5g/cm ³ .

Preferably, the room temperature elongation of the lithium-magnesium composite negative electrode is 10 to 30%.

Preferably, the conductivity of the lithium-magnesium composite negative electrode is 5×10 ⁶ to 18×10 ⁶ S/m.

Preferably, the roughness Ra of the lithium-magnesium composite negative electrode is 0.09-0.5 μm, and the roughness Rz is 0.8-3 μm.

A second aspect of the present invention proposes a method for preparing the above-mentioned lithium-magnesium composite negative electrode, which includes the following steps:

(1) Weigh the calculated metallic lithium, metallic magnesium and auxiliary metal according to the proportion of lithium-magnesium alloy and set aside;

(2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 220-230℃ at 5-15℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir as follows Raise the temperature to 350~600°C at a heating rate of 5~15°C/min, and continue stirring for 0.5~10h;

(3) After the lithium-magnesium alloy is completely melted, add auxiliary metal and continue stirring for 2.5 to 3.5 hours;

(4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand for 2 to 10 hours at 300 to 500°C for homogenization treatment;

(5) Under the protection of inert gas, roll the homogenized ingot multiple times at 150-280°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 10-200 μm.

A third aspect of the present invention provides a lithium-sulfur battery made of the above-mentioned lithium-magnesium composite negative electrode.

Preferably, the lithium-sulfur battery includes a lithium-magnesium composite negative electrode, a sulfur positive electrode, a separator, and an electrolyte. The sulfur positive electrode includes a sulfur-carbon composite, CNT conductive slurry, PVDF and carbon-coated aluminum foil, and the sulfur-carbon composite The mass ratio of CNT conductive slurry and PVDF is 70:25:5, and the mass ratio of elemental sulfur and graphene in the sulfur-carbon composite is 70:30.

A fourth aspect of the present invention proposes an all-solid-state battery made of the above-mentioned lithium-magnesium composite negative electrode.

Preferably, the all-solid-state battery includes a lithium-magnesium composite negative electrode, a positive electrode, and an electrolyte membrane. The positive electrode includes a ternary positive electrode with a mass ratio of 70:27:3, solid electrolyte powder, and conductive agent.

Beneficial effects: The lithium-magnesium composite negative electrode of the present invention can be directly used in lithium-sulfur batteries and all-solid-state metal batteries. It does not require additional current collectors, greatly reducing the weight of the battery. Under the same conditions, the battery energy density using the lithium-magnesium composite negative electrode is higher. It can be significantly improved; at the same time, the negative electrode also has good electrochemical performance and anti-oxidation performance.

The advantages of the present invention are:

1. The present invention combines lithium, magnesium and auxiliary metal elements to obtain an alloy material that exhibits good plastic processing formability due to grain refinement and can be rolled to ultra-thin lithium-magnesium alloy. It can provide an appropriate amount of lithium-magnesium alloy as a negative electrode. The lithium effectively improves the volume energy density and weight energy density of the battery; at the same time, lithium-magnesium alloy materials can be mass-produced using rolling, stamping and other technologies, which solves problems such as difficulty in processing lithium metal and supports large-scale production;

2. In the lithium-magnesium composite negative electrode of the present invention, during the charging and discharging process of the lithium-ion battery, due to the low reduction potential of lithium, the lithium metal in the lithium-magnesium alloy can be continuously reduced, and the lost active lithium can be continuously replenished, while ensuring Under the premise of safety, it can greatly extend the battery cycle life and improve the capacity retention rate;

3. The lithium-magnesium composite negative electrode of the present invention can be directly used in lithium-sulfur batteries and all-solid-state metal batteries, without the need for additional current collectors, greatly reducing the weight of the battery. Under the same conditions, the energy density of the battery using the lithium-magnesium composite negative electrode can be The improvement is obvious; at the same time, the negative electrode also has good electrochemical performance and anti-oxidation performance.

Description of the drawings

Figure 1 is a schematic structural diagram of a lithium-sulfur battery prepared in Example 1 of the present application.

Figure 2 is a schematic structural diagram of an all-solid-state battery prepared in Example 1 of the present application.

Explanation of reference signs: 1. Lithium-magnesium composite negative electrode; 2. Separator; 3. Sulfur positive electrode; 4. Electrolyte; 5. Electrolyte membrane; 6. Positive electrode.

Detailed ways

In order to make the purpose, 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 embodiments of the present invention. Obviously, the described embodiments are part of the present invention. Examples, not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The test materials and reagents used in the following examples can all be obtained from commercial sources unless otherwise specified.

If no specific techniques or conditions are specified in the examples, the techniques or conditions described in literature in the field can be followed or the product instructions can be followed.

The first aspect of this application discloses a method for preparing a lithium-magnesium composite negative electrode, which includes the following steps:

(1) Weigh 50-65wt% lithium metal, 35-50wt% magnesium metal and 0.01-15wt% auxiliary metal respectively according to mass ratio for later use. The auxiliary metal includes one or any combination of Cu, Al, Zn, Fe, Ni, Zr or Y.

(2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 220-230℃ at 5-15℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir as follows Raise the temperature to 350~600°C at a heating rate of 5~15°C/min, and continue stirring for 0.5~10h;

(3) After the lithium-magnesium alloy is completely melted, add auxiliary metal and continue stirring for 2.5 to 3.5 hours;

(4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand for 2 to 10 hours at 300 to 500°C for homogenization treatment;

(5) Under the protection of inert gas, roll the homogenized ingot multiple times at 150-280°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 10-200 μm.

It has been measured that the density of the lithium-magnesium composite negative electrode foil is 0.6~1.5g/ ^cm3 , the room temperature elongation is 10~30%, the conductivity is 5× ¹⁰⁶ ~18× ^106S /m, and the roughness Ra is 0.09 ~0.5μm, Rz is 0.8~3μm.

The second aspect of this application discloses a lithium-sulfur battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a sulfur positive electrode, a separator, and an electrolyte. The sulfur positive electrode includes a sulfur-carbon composite, CNT conductive slurry, PVDF and Carbon-coated aluminum foil, and the mass ratio of sulfur-carbon composite, CNT conductive slurry, and PVDF is 70:25:5, and the mass ratio of elemental sulfur and graphene in the sulfur-carbon composite is 70:30.

The preparation method of the lithium-sulfur battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Weigh elemental sulfur and graphene according to a mass ratio of 70:30, dissolve elemental sulfur in carbon disulfide, then add graphene, stir evenly, and volatilize the solvent at 60°C to obtain a sulfur-carbon composite.

(3) Mix the sulfur-carbon composite, CNT conductive slurry and PVDF according to the mass ratio of 70:25:5, use NMP as the solvent, mix the above materials in a 400r/min ball mill for 5 hours to obtain a uniform slurry; then use The slurry is evenly transferred to the carbon-coated aluminum foil by scraper coating, and then vacuum dried at 80°C for 12 hours to obtain a positive electrode sheet, which is then punched into a disc with a diameter of 10 mm to obtain a sulfur positive electrode.

(4) Using a PP film with a thickness of 16um as a separator, dissolve 1M lithium bistrifluoromethanesulfonimide (LiTFSI) in an equal volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane. The resulting mixed solution is used as the electrolyte; the lithium-magnesium composite negative electrode, separator, and sulfur positive electrode are stacked in sequence, and then the electrolyte is filled in to assemble a lithium-sulfur battery.

The third aspect of this application discloses an all-solid-state battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a positive electrode, and an electrolyte membrane. The positive electrode includes a ternary positive electrode and solid electrolyte powder with a mass ratio of 70:27:3. , conductive agent.

The preparation method of the all-solid-state battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Press the electrolyte powder into thin sheets under a pressure of 300MPa to serve as an electrolyte membrane.

(3) Using VCGF as the conductive agent, mix the ternary positive electrode, solid electrolyte powder, and conductive agent in a mass ratio of 70:27:3, and then stir and mix with a mortar in a glove box with an oxygen and water content of less than 0.1 ppm. Uniformly; then use a scraper coating method to evenly transfer the slurry to the carbon-coated aluminum foil, vacuum dry it at 80°C for 12 hours to obtain a positive electrode sheet, and impact it into a disc with a diameter of 10mm to obtain a positive electrode.

(4) Stack the lithium-magnesium composite negative electrode, electrolyte membrane, and positive electrode in sequence, and assemble them to obtain an all-solid-state battery.

Example 1

The first aspect of this embodiment discloses a method for preparing a lithium-magnesium composite negative electrode, which includes the following steps:

(1) Weigh 0.6kg metal lithium, 0.35kg metal magnesium, 0.02kg metal Al powder, 0.02kg metal Zn powder, and 0.01kg metal Fe powder respectively for later use.

(2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 220℃ at 10℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir at 10℃/min. The heating rate is increased to 500°C, and stirring is continued for 2 hours;

(3) After the lithium-magnesium alloy is completely melted, add Al powder, Zn powder, and Fe powder, and continue stirring for 3 hours;

(4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand at 350°C for 3 hours for homogenization treatment;

(5) Under the protection of inert gas, roll the homogenized ingot multiple times at 250°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 20 μm.

It was measured that the density of the lithium-magnesium composite negative electrode foil was 0.93g/cm ³ , the elongation at room temperature was 14.6%, the conductivity was 7.91×10 ⁶ S/m, and the roughness Ra was 0.35 μm and Rz was 2.1 μm.

The second aspect of this embodiment discloses a lithium-sulfur battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode 1, a sulfur positive electrode 3, a separator 2, and an electrolyte 4. The sulfur positive electrode 3 includes a sulfur-carbon composite, CNT Conductive slurry, PVDF and carbon-coated aluminum foil, and the mass ratio of sulfur-carbon composite, CNT conductive slurry, PVDF is 70:25:5, and the mass ratio of elemental sulfur and graphene in the sulfur-carbon composite is 70:30.

The preparation method of the lithium-sulfur battery includes the following steps:

(1) In a glove box with oxygen and water contents both less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm to serve as lithium-magnesium composite negative electrode 1.

(2) Weigh elemental sulfur and graphene according to a mass ratio of 70:30, dissolve elemental sulfur in carbon disulfide, then add graphene, stir evenly, and volatilize the solvent at 60°C to obtain a sulfur-carbon composite.

(3) Mix the sulfur-carbon composite, CNT conductive slurry and PVDF according to the mass ratio of 70:25:5, use NMP as the solvent, mix the above materials in a 400r/min ball mill for 5 hours to obtain a uniform slurry; then use The slurry was evenly transferred to the carbon-coated aluminum foil by scraper coating, and then vacuum dried at 80°C for 12 hours to obtain a positive electrode sheet, which was then punched into discs with a diameter of 10 mm to obtain sulfur positive electrode 3.

(4) Using a PP film with a thickness of 16um as separator 2, dissolve 1M lithium bistrifluoromethanesulfonyl imide (LiTFSI) in an equal volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane. , the mixed solution obtained is used as the electrolyte 4; as shown in Figure 1, the lithium-magnesium composite negative electrode 1, the separator 2, and the sulfur positive electrode 3 are stacked in sequence, and then the electrolyte 4 is charged, thereby assembling a lithium-sulfur battery.

The third aspect of this embodiment discloses an all-solid-state battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode 1, a positive electrode 6, and an electrolyte membrane 5. The positive electrode includes a ternary positive electrode with a mass ratio of 70:27:3. , solid electrolyte powder, conductive agent.

The preparation method of the all-solid-state battery includes the following steps:

(1) In a glove box with oxygen and water contents both less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm to serve as lithium-magnesium composite negative electrode 1.

(2) Press the electrolyte powder into thin sheets under a pressure of 300MPa to prepare the electrolyte membrane 5.

(3) Using VCGF as the conductive agent, mix the ternary positive electrode, solid electrolyte powder, and conductive agent in a mass ratio of 70:27:3, and then stir and mix with a mortar in a glove box with an oxygen and water content of less than 0.1 ppm. Uniformly; then use a scraper coating method to evenly transfer the slurry to the carbon-coated aluminum foil, vacuum dry it at 80°C for 12 hours to obtain a positive electrode sheet, and impact it into a disc with a diameter of 10mm to obtain positive electrode 6.

(4) As shown in Figure 2, the lithium-magnesium composite negative electrode 1, electrolyte membrane 5, and positive electrode 6 are stacked in sequence and assembled to obtain an all-solid-state battery.

Example 2

This embodiment discloses a lithium-magnesium composite negative electrode and a preparation method thereof, a lithium-sulfur battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, an all-solid-state battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, and The difference between Example 1 is that in the preparation of the lithium-magnesium composite negative electrode, the thickness of the prepared lithium-magnesium composite negative electrode foil is 30 μm.

Example 3

This embodiment discloses a lithium-magnesium composite negative electrode and a preparation method thereof, a lithium-sulfur battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, an all-solid-state battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, and The difference between Example 1 is that in the preparation of the lithium-magnesium composite negative electrode, the thickness of the prepared lithium-magnesium composite negative electrode foil is 40 μm.

Example 4

This embodiment discloses a lithium-magnesium composite negative electrode and a preparation method thereof, a lithium-sulfur battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, an all-solid-state battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, and The difference between Example 1 is that in the preparation of the lithium-magnesium composite negative electrode, the thickness of the prepared lithium-magnesium composite negative electrode foil is 50 μm.

Example 5

This embodiment discloses a lithium-magnesium composite negative electrode and a preparation method thereof, a lithium-sulfur battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, an all-solid-state battery made of the lithium-magnesium composite negative electrode and a preparation method thereof, and The difference between Example 1 is that in the preparation of the lithium-magnesium composite negative electrode, the thickness of the prepared lithium-magnesium composite negative electrode foil is 60 μm.

Example 6

The first aspect of this embodiment discloses a method for preparing a lithium-magnesium composite negative electrode, which includes the following steps:

(1) Weigh 0.50kg metal lithium, 0.45kg metal magnesium, 0.03kg metal Al powder, 0.01kg metal Fe powder, and 0.1kg metal Ni powder respectively for later use.

(2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 225℃ at 5℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir at 5℃/min. The heating rate is increased to 350°C, and stirring is continued for 10 hours;

(3) After the lithium-magnesium alloy is completely melted, add Al powder, Fe powder, and Ni powder, and continue stirring for 3.5 hours;

(4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand at 500°C for 2 hours for homogenization treatment;

(5) Under the protection of inert gas, roll the homogenized ingot multiple times at 280°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 20 μm.

It has been measured that the density of the lithium-magnesium composite negative electrode foil is 1.05g/cm ³ , the elongation at room temperature is 12.6%, the conductivity is 10.17×10 ⁶ S/m, and the roughness Ra is 0.29 μm and Rz is 1.8 μm.

The second aspect of this embodiment discloses a lithium-sulfur battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a sulfur positive electrode, a separator, and an electrolyte. The sulfur positive electrode includes a sulfur-carbon composite, CNT conductive slurry, and PVDF and carbon-coated aluminum foil, and the mass ratio of sulfur-carbon composite, CNT conductive slurry, and PVDF is 70:25:5, and the mass ratio of elemental sulfur and graphene in the sulfur-carbon composite is 70:30.

The preparation method of the lithium-sulfur battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Weigh elemental sulfur and graphene according to a mass ratio of 70:30, dissolve elemental sulfur in carbon disulfide, then add graphene, stir evenly, and volatilize the solvent at 60°C to obtain a sulfur-carbon composite.

(3) Mix the sulfur-carbon composite, CNT conductive slurry and PVDF according to the mass ratio of 70:25:5, use NMP as the solvent, mix the above materials in a 400r/min ball mill for 5 hours to obtain a uniform slurry; then use The slurry is evenly transferred to the carbon-coated aluminum foil by scraper coating, and then vacuum dried at 80°C for 12 hours to obtain a positive electrode sheet, which is then punched into a disc with a diameter of 10 mm to obtain a sulfur positive electrode.

(4) Using a PP film with a thickness of 16um as a separator, dissolve 1M lithium bistrifluoromethanesulfonimide (LiTFSI) in an equal volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane. The resulting mixed solution is used as the electrolyte; the lithium-magnesium composite negative electrode, separator, and sulfur positive electrode are stacked in sequence, and then the electrolyte is filled in to assemble a lithium-sulfur battery.

The third aspect of this embodiment discloses an all-solid-state battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a positive electrode, and an electrolyte membrane. The positive electrode includes a ternary positive electrode and a solid electrolyte with a mass ratio of 70:27:3. Powder, conductive agent.

The preparation method of the all-solid-state battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Press the electrolyte powder into thin sheets under a pressure of 300MPa to serve as an electrolyte membrane.

(3) Using VCGF as the conductive agent, mix the ternary positive electrode, solid electrolyte powder, and conductive agent in a mass ratio of 70:27:3, and then stir and mix with a mortar in a glove box with an oxygen and water content of less than 0.1 ppm. Uniformly; then use a scraper coating method to evenly transfer the slurry to the carbon-coated aluminum foil, vacuum dry it at 80°C for 12 hours to obtain a positive electrode sheet, and impact it into a disc with a diameter of 10mm to obtain a positive electrode.

(4) Stack the lithium-magnesium composite negative electrode, electrolyte membrane, and positive electrode in sequence, and assemble them to obtain an all-solid-state battery.

Example 7

The first aspect of this embodiment discloses a method for preparing a lithium-magnesium composite negative electrode, which includes the following steps:

(1) Weigh 0.64kg metal lithium, 0.35kg metal magnesium, 0.007kg metal Al powder, 0.002kg metal Fe powder, and 0.001kg metal Ni powder respectively for later use.

(2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 230℃ at 15℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir at 15℃/min. The heating rate is increased to 600°C, and stirring is continued for 0.5h;

(3) After the lithium-magnesium alloy is completely melted, add Al powder, Fe powder, and Ni powder, and continue stirring for 2.5 hours;

(4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand at 300°C for 10 hours for homogenization treatment;

(5) Under the protection of inert gas, roll the homogenized ingot multiple times at 150°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 20 μm.

It was measured that the density of the lithium-magnesium composite negative electrode foil was 0.95g/cm ³ , the elongation at room temperature was 14.7%, the conductivity was 7.91×10 ⁶ S/m, and the roughness Ra was 0.34 μm and Rz was 2.1 μm.

The second aspect of this embodiment discloses a lithium-sulfur battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a sulfur positive electrode, a separator, and an electrolyte. The sulfur positive electrode includes a sulfur-carbon composite, CNT conductive slurry, and PVDF and carbon-coated aluminum foil, and the mass ratio of sulfur-carbon composite, CNT conductive slurry, and PVDF is 70:25:5, and the mass ratio of elemental sulfur and graphene in the sulfur-carbon composite is 70:30.

The preparation method of the lithium-sulfur battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Weigh elemental sulfur and graphene according to a mass ratio of 70:30, dissolve elemental sulfur in carbon disulfide, then add graphene, stir evenly, and volatilize the solvent at 60°C to obtain a sulfur-carbon composite.

(3) Mix the sulfur-carbon composite, CNT conductive slurry and PVDF according to the mass ratio of 70:25:5, use NMP as the solvent, mix the above materials in a 400r/min ball mill for 5 hours to obtain a uniform slurry; then use The slurry is evenly transferred to the carbon-coated aluminum foil by scraper coating, and then vacuum dried at 80°C for 12 hours to obtain a positive electrode sheet, which is then punched into a disc with a diameter of 10 mm to obtain a sulfur positive electrode.

(4) Using a PP film with a thickness of 16um as a separator, dissolve 1M lithium bistrifluoromethanesulfonimide (LiTFSI) in an equal volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane. The resulting mixed solution is used as the electrolyte; the lithium-magnesium composite negative electrode, separator, and sulfur positive electrode are stacked in sequence, and then the electrolyte is filled in to assemble a lithium-sulfur battery.

The third aspect of this embodiment discloses an all-solid-state battery made of the above-mentioned lithium-magnesium composite negative electrode, including a lithium-magnesium composite negative electrode, a positive electrode, and an electrolyte membrane. The positive electrode includes a ternary positive electrode and a solid electrolyte with a mass ratio of 70:27:3. Powder, conductive agent.

The preparation method of the all-solid-state battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact the above lithium-magnesium composite negative electrode foil into discs with a diameter of 16 mm as a lithium-magnesium composite negative electrode.

(2) Press the electrolyte powder into thin sheets under a pressure of 300MPa to serve as an electrolyte membrane.

(3) Using VCGF as the conductive agent, mix the ternary positive electrode, solid electrolyte powder, and conductive agent in a mass ratio of 70:27:3, and then stir and mix with a mortar in a glove box with an oxygen and water content of less than 0.1 ppm. Uniformly; then use a scraper coating method to evenly transfer the slurry to the carbon-coated aluminum foil, vacuum dry it at 80°C for 12 hours to obtain a positive electrode sheet, and impact it into a disc with a diameter of 10mm to obtain a positive electrode.

(4) Stack the lithium-magnesium composite negative electrode, electrolyte membrane, and positive electrode in sequence, and assemble them to obtain an all-solid-state battery.

Comparative example 1

This comparative example discloses a lithium-sulfur battery made of commercial lithium metal negative electrode, including commercial lithium metal negative electrode, sulfur positive electrode, separator, and electrolyte. The commercial lithium metal anode was purchased from Tianjin Zhongneng Lithium Co., Ltd. It is a metal lithium disc with a thickness of 200 μm. The subsequent commercial lithium metal anodes all use this kind of lithium metal anode. The sulfur cathode includes a sulfur-carbon composite, CNT conductive slurry, PVDF and carbon-coated aluminum foil, and the mass ratio of the sulfur-carbon composite, CNT conductive slurry, and PVDF is 70:25:5. The elemental sulfur and graphite in the sulfur-carbon composite The mass ratio of alkene is 70:30.

The preparation method of the lithium-sulfur battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact a commercial lithium metal anode with a thickness of 30 μm into a disc with a diameter of 16 mm as the anode.

(2) Weigh elemental sulfur and graphene according to a mass ratio of 70:30, dissolve elemental sulfur in carbon disulfide, then add graphene, stir evenly, and evaporate the solvent at 60°C to obtain a sulfur-carbon composite.

(3) Mix the sulfur-carbon composite, CNT conductive slurry and PVDF according to the mass ratio of 70:25:5, use NMP as the solvent, mix the above materials in a 400r/min ball mill for 5 hours to obtain a uniform slurry; then use The slurry is evenly transferred to the carbon-coated aluminum foil by scraper coating, and then vacuum dried at 80°C for 12 hours to obtain a positive electrode sheet, which is then punched into a disc with a diameter of 10 mm to obtain a sulfur positive electrode.

(4) Using a PP film with a thickness of 16um as a separator, dissolve 1M lithium bistrifluoromethanesulfonimide (LiTFSI) in an equal volume ratio of ethylene glycol dimethyl ether and 1,3-dioxolane. The resulting mixed solution is used as the electrolyte; the commercial lithium metal negative electrode, separator, and sulfur positive electrode are stacked in sequence, and then filled with the electrolyte to assemble a lithium-sulfur battery.

Comparative example 2

This comparative example discloses an all-solid-state battery made of a commercial lithium metal negative electrode, including a commercial lithium metal negative electrode, a positive electrode, and an electrolyte membrane. The positive electrode includes a ternary positive electrode with a mass ratio of 70:27:3, solid electrolyte powder, Conductive agent.

The preparation method of the all-solid-state battery includes the following steps:

(1) In a glove box with an oxygen and water content of less than 0.1 ppm, impact a commercial lithium metal anode with a thickness of 30 μm into a disc with a diameter of 16 mm as a lithium-magnesium composite anode.

(2) Press the electrolyte powder into thin sheets under a pressure of 300MPa to serve as an electrolyte membrane.

(3) Using VCGF as the conductive agent, mix the ternary positive electrode, solid electrolyte powder, and conductive agent in a mass ratio of 70:27:3, and then stir and mix with a mortar in a glove box with an oxygen and water content of less than 0.1 ppm. Uniformly; then use a scraper coating method to evenly transfer the slurry to the carbon-coated aluminum foil, vacuum dry it at 80°C for 12 hours to obtain a positive electrode sheet, and impact it into a disc with a diameter of 10mm to obtain a positive electrode.

(4) Stack the commercial lithium metal negative electrode, electrolyte membrane, and positive electrode in sequence, and assemble them to obtain an all-solid-state battery.

Test example 1

The charge and discharge performance of the lithium-sulfur battery prepared in Example 1-5 was tested at 25°C and 0.2C, and the voltage range was 1.7V-2.8V; the all-solid-state battery prepared in Example 1-5 was tested at 45°C and 0.2C. Charge and discharge performance tests were conducted at 50MPa and 0.1C, with a voltage range of 2V-4.3V. The first discharge capacity and capacity retention rate after 100 cycles of all batteries were measured. The results are shown in Table 1.

Table 1 Battery performance test results

It can be seen from Table 1 that both lithium-sulfur batteries and all-solid-state batteries show similar discharge capacities. Compared with the comparative example, the battery using the lithium-magnesium composite negative electrode prepared by the present invention has a higher capacity retention rate, which is significantly higher than that of the comparative example. Improved battery cycle performance.

The implementation principle of this application is: the present invention combines lithium, magnesium and auxiliary metal elements to obtain an alloy material that exhibits good plastic processing formability due to grain refinement and can be rolled to ultra-thin lithium-magnesium alloy. As the negative electrode, it can provide an appropriate amount of lithium, effectively improving the volumetric energy density and gravimetric energy density of the battery. At the same time, lithium-magnesium alloy materials can be mass-produced using rolling, stamping and other technologies, solving problems such as difficulty in processing lithium metal and supporting large-scale production. Production.

In the lithium-magnesium composite negative electrode of the present invention, during the charging and discharging process of the lithium-ion battery, due to the low reduction potential of lithium, the lithium metal in the lithium-magnesium alloy can be continuously reduced, and the lost active lithium can be continuously replenished while ensuring safety. Under the premise, it can greatly extend the battery cycle life and improve the capacity retention rate.

The lithium-magnesium composite negative electrode of the present invention can be directly used in lithium-sulfur batteries and all-solid-state metal batteries, without the need for additional current collectors, greatly reducing the weight of the battery. Under the same conditions, the energy density of batteries using the lithium-magnesium composite negative electrode can be significantly improved. ; At the same time, the negative electrode also has good electrochemical performance and anti-oxidation performance.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not 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 of the foregoing embodiments. The recorded technical solutions may be modified, or some of the technical features thereof may be equivalently replaced; however, these modifications or substitutions shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims (10)

1. A lithium-magnesium composite negative electrode, characterized by: including metal lithium, metal magnesium and auxiliary metal elements. The content of the metal lithium is 50-65wt%, the content of the metal magnesium is 35-50wt%, and the auxiliary metal The content of the element is 0.01-15wt%; the auxiliary metal element includes one or any combination of Cu, Al, Zn, Fe, Ni, Zr or Y.
2. The lithium-magnesium composite negative electrode according to claim 1, wherein the thickness of the lithium-magnesium composite negative electrode is 10 to 200 μm.
3. The lithium-magnesium composite negative electrode according to claim 1, characterized in that: the density of the lithium-magnesium composite negative electrode is 0.6-1.5g/cm ³ .
4. A lithium-magnesium composite negative electrode according to claim 1, characterized in that the room temperature elongation of the lithium-magnesium composite negative electrode is 10-30% and the electrical conductivity is 5×10 ⁶ -18×10 ⁶ S/m.
5. The lithium-magnesium composite negative electrode according to claim 1, characterized in that the roughness Ra of the lithium-magnesium composite negative electrode is 0.09-0.5 μm, and Rz is 0.8-3 μm.
6. A method for preparing a lithium-magnesium composite negative electrode according to any one of claims 1 to 5, characterized in that it includes the following steps:

   (1) Weigh the calculated metallic lithium, metallic magnesium and auxiliary metal according to the proportion of lithium-magnesium alloy and set aside;

   (2) Pour metallic lithium into the vacuum smelting furnace first, raise the temperature to 220-230℃ at 5-15℃/min, and then start mechanical stirring; after the metallic lithium is completely melted, add metallic magnesium into the vacuum smelting furnace, and stir as follows Raise the temperature to 350~600°C at a heating rate of 5~15°C/min, and continue stirring for 0.5~10h;

   (3) After the lithium-magnesium alloy is completely melted, add auxiliary metal and continue stirring for 2.5 to 3.5 hours;

   (4) After all the metals are completely melted and mixed evenly, pour them into ingots under the protection of inert gas, and let them stand for 2 to 10 hours at 300 to 500°C for homogenization treatment;

   (5) Under the protection of inert gas, roll the homogenized ingot multiple times at 150-280°C to obtain a lithium-magnesium composite negative electrode foil with a thickness of 10-200 μm.
7. A lithium-sulfur battery made of the lithium-magnesium composite negative electrode described in any one of claims 1-5.
8. A lithium-sulfur battery made of a lithium-magnesium composite negative electrode according to claim 7, characterized in that: the lithium-sulfur battery includes a lithium-magnesium composite negative electrode, a sulfur positive electrode, a separator, and an electrolyte, and the sulfur positive electrode includes sulfur carbon composite, CNT conductive slurry, PVDF and carbon-coated aluminum foil, and the mass ratio of the sulfur-carbon composite, CNT conductive slurry, and PVDF is 70:25:5, and the elemental sulfur and graphene in the sulfur-carbon composite The mass ratio is 70:30.
9. An all-solid-state battery made of the lithium-magnesium composite negative electrode described in any one of claims 1-5.
10. A lithium-sulfur battery made of a lithium-magnesium composite negative electrode according to claim 9, characterized in that: the all-solid-state battery includes a lithium-magnesium composite negative electrode, a positive electrode, and an electrolyte membrane, and the positive electrode includes a mass ratio of 70:27 : 3 ternary cathode, solid electrolyte powder, conductive agent.

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