A lithium metal anode, its preparation method and secondary battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a lithium metal negative electrode, a preparation method thereof and a secondary battery. The preparation method of the lithium metal negative electrode comprises the following steps: under weak alkaline conditions, a mixed solution of a soluble transition metal salt, vanillin and a carbon material is subjected to heating treatment, and the carbon material loaded with the soluble transition metal salt is separated; the carbon material loaded with the soluble transition metal salt is uniformly mixed with a binder and an organic solvent, is coated on the surface of a negative electrode current collector, is dried, and a base material is obtained; and metal lithium is deposited on the surface of the base material, and the lithium metal negative electrode is obtained. The lithium metal negative electrode can effectively form a uniform and dense lithium-philic layer on the current collector, and can induce the uniform deposition of metal lithium on the copper foil, so that the problem of dendrite growth of lithium metal is solved, and the stability of the lithium metal as a negative electrode is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a lithium metal anode, its preparation method, and a secondary battery. Background Technology

[0002] In recent years, to improve the development and utilization efficiency of traditional energy sources such as fossil fuels, it is even more necessary to change the energy structure and promote its diversification and clean energy development. Therefore, the development and utilization of clean energy, such as wind, solar, geothermal, tidal, and biomass energy, has become an inevitable choice. However, due to the intermittent nature and uneven geographical distribution of these energy sources, energy storage devices are needed to store excess energy and release it on demand. Electrochemical energy storage devices, represented by rechargeable batteries, are considered one of the most important strategies for solving energy problems due to their high energy conversion efficiency, environmental friendliness, and ease of use. Among them, lithium-ion batteries have attracted great attention from academia and industry worldwide due to their high rate capability, long lifespan, and low cost. Since their commercialization in the early 1990s, they have been widely used in various electronic products, electric vehicles, and power systems, and are considered a significant milestone in the development of electrochemical energy storage systems. However, with the rapid development of modern technology, higher requirements have been placed on the various technical indicators of batteries, while the energy density of lithium-ion batteries with carbon-based materials as negative electrodes can only reach ~250Wh / kg. -1 The current level of rechargeable batteries can no longer meet the requirements of various fields for high-energy-density energy storage systems. Therefore, there is an urgent need to develop a new generation of rechargeable batteries to meet and support the long-term development of related industries.

[0003] Lithium metal anodes have an extremely high theoretical specific capacity (3860 mAh g). -1 With its low redox potential (-3.04V vs. SHE), lithium metal anodes are ideal anode materials for next-generation rechargeable batteries. However, lithium metal anodes suffer from severe dendrite growth and volume expansion during battery cycling, limiting the further widespread application of lithium metal batteries.

[0004] Therefore, solving the problem of lithium metal dendrite growth and improving its stability as a negative electrode are important issues in current lithium battery system research. Summary of the Invention

[0005] The present invention aims to solve the above problems and provides a lithium metal anode, its preparation method and secondary battery. The lithium metal anode can effectively form a uniform and dense lithiophilic layer on the current collector and induce uniform deposition of lithium metal on the copper foil, thereby solving the problem of lithium metal dendrite growth and improving its stability as an anode.

[0006] According to the technical solution of the present invention, the method for preparing the lithium metal anode includes the following steps:

[0007] S1: Under weakly alkaline conditions, a mixed solution of soluble transition metal salt, vanillin and carbon material is heated to separate carbon material loaded with soluble transition metal salt.

[0008] The carbon material has a three-dimensional porous layered structure;

[0009] S2: The carbon material loaded with soluble transition metal salt is mixed with binder and organic solvent, coated on the surface of negative electrode current collector, and dried to obtain substrate material;

[0010] S3: Deposit metallic lithium on the surface of the substrate material to obtain the lithium metal anode.

[0011] Furthermore, in step S1, the pH of the weakly alkaline condition is 7.2-8.7. Specifically, the pH can be adjusted to 7.2-8.7 using a weak base, such as sodium citrate, ammonia, or sodium bicarbonate, with the addition amount and the mass ratio of the added amount to the soluble transition metal salt being 1-2:1-2.

[0012] Furthermore, in step S1, the mass ratio of the soluble transition metal salt, vanillin, and carbon material is 1:(0.05-0.5):(1-3). Specifically, the mass ratio of the soluble transition metal salt to the carbon material can be (1-2):(2-3), and the amount of vanillin added is 0.05-0.5 of the mass of the soluble transition metal salt.

[0013] Furthermore, in step S1, the heating treatment temperature is 60-120℃ and the time is 10-18h.

[0014] Furthermore, the transition metal in the soluble transition metal salt is a lithiophilic element, and the soluble transition metal salt is selected from one or more of tin salts, titanium salts, zinc salts and aluminum salts, such as sulfates, chlorides, nitrates, etc. of transition metals.

[0015] Furthermore, the carbon material is obtained by calcining activated biomass material.

[0016] Furthermore, the activation includes the following steps: mixing biomass materials with a strong alkali and heating them, then washing, drying, grinding, and then soaking them in a strong alkali.

[0017] Furthermore, the biomass material is selected from one or more of cellulose, bamboo fiber, coconut shell, rice straw, cotton stalk bark, and sugarcane bagasse; the strong alkali can be KOH solution, NaOH solution, etc.; the heating treatment temperature is 120-200℃, the heating treatment time is 8-24h; the strong alkali soaking time is 8-20h.

[0018] Furthermore, the calcination temperature after activation is 600-1000℃, and the calcination time is 2-5 hours.

[0019] Furthermore, in step S2, the mass ratio of the carbon material loaded with soluble transition metal salt to the binder is (7-9):(1-3); the organic solvent is N-methyl-2-pyrrolidone, or other commonly used solvents in battery preparation processes.

[0020] Furthermore, in step S2, the coating thickness is 40-60 μm.

[0021] Furthermore, in step S3, lithium metal is deposited by magnetron sputtering or melting.

[0022] Furthermore, in step S3, the amount of lithium deposited can be (0.1-0.4g) / 1540.25cm³. 2 .

[0023] A second aspect of the present invention provides a lithium metal anode prepared by the above-described preparation method.

[0024] Furthermore, the lithium metal anode includes an anode current collector, a carbon layer, and lithium metal. The carbon layer includes carbon material and a transition metal element (lithophile element). The carbon material has a three-dimensional porous layered structure, the transition metal element is loaded in the pores of the carbon material, and the lithium metal is loaded in the pores of the carbon material through the transition metal element.

[0025] Furthermore, the thickness of the carbon layer is 30-50 μm; the loading of the transition metal element is (0.5-1 g) / 15.4025 cm³. 2 Some of the lithium metal forms an alloy with the transition metal element.

[0026] A third aspect of the present invention provides a secondary battery comprising the aforementioned lithium metal anode.

[0027] The technical solution of the present invention has the following advantages compared with the prior art:

[0028] The lithium metal anode of this invention can effectively form a uniform and dense lithiophilic layer on the current collector, inducing uniform deposition of metallic lithium on the copper foil;

[0029] Among them, porous layered carbon can provide more sites for lithium deposition, slow down the formation of lithium dendrites, and enable the prepared lithium metal anode to have good cycle stability.

[0030] The lithium storage mechanism of alloying with lithiophilic elements (transition metals) can achieve rapid ion transfer kinetics, while simultaneously enhancing lithium adsorption, providing abundant nucleation sites, and promoting uniform lithium nucleation and deposition. Specifically, taking tin as an example, the reaction equation is as follows: Sn + xLi = Li x Sn (22≥x≥2) alloy, Li x Sn alloys have low Li + The diffusion barrier enables rapid ion transfer kinetics. Its adsorption of lithium is mainly manifested in good deposition kinetics. Due to the huge difference in electronegativity between Sn and Li, Li can rapidly diffuse into each other. Furthermore, the voltage difference between the alloy phase and the lithium layer is extremely small, which allows the adsorbed lithium to be rapidly deposited on the alloy layer, forming a dense SEI film and improving its cycle performance.

[0031] Vanillin is added during the preparation of lithium metal anodes. Taking tin as an example, when Sn undergoes an alloying reaction, vanillin will preferentially adsorb onto the protrusions of deposited Sn, preventing further deposition of metallic lithium. This can effectively inhibit the growth of lithium dendrites, ultimately resulting in a uniform and dense morphology of lithium and improving the stability of lithium metal anodes. Attached Figure Description

[0032] Figure 1 The discharge rate performance diagram of the coin cell prepared from the material obtained in the example is shown. Detailed Implementation

[0033] This invention provides a lithium metal anode, comprising an anode current collector, a carbon layer, and lithium metal, wherein the carbon layer comprises carbon material and a transition metal element (lithophile element). Specifically, the carbon material has a three-dimensional porous layered structure, the transition metal element is loaded within the pores of the carbon material, and the lithium metal is loaded within the pores of the carbon material through the transition metal element.

[0034] Specifically, the soluble transition metal salt is selected from one or more of tin, titanium, zinc, and aluminum salts, such as sulfates, chlorides, and nitrates of transition metals. Taking tin salts as an example, the soluble transition metal salt can be selected from one or more of tin sulfate, tin chloride, and tin nitrate.

[0035] In some preferred embodiments, the carbon material is obtained by calcining activated biomass material (selected from one or more of cellulose, bamboo fiber, coconut shell, rice straw, cotton stalk bark, and sugarcane bagasse).

[0036] Specifically, the carbon material of this invention uses low-cost biomass materials as the carbon source. Three-dimensional layered porous carbon is prepared by hydrothermal reaction with strong alkali and high-temperature carbonization reaction. The strong alkali, as an activator, can react violently with the fiber to release gases (CO, CO2, H2O and H2). During the reaction, the fiber is destroyed and reorganized, some pore structures collapse, and some pore structures are retained and expanded.

[0037] The specific preparation method can be as follows:

[0038] A mixed solution is obtained by using biomass materials as a carbon source and stirring with a strong alkali (such as KOH solution, NaOH solution, etc.) at 25-60℃ for 0.5-2 hours.

[0039] The mixed solution is transferred to a reaction vessel and reacted at 120-200℃ for 8-24 hours. After removal, it is washed with water and ethanol (or other organic solvents) alternately. The washed sample is placed in a forced-air drying oven and dried at 60-100℃ for 8-18 hours. After removal, it is ground and sieved to obtain biomass material samples.

[0040] The biomass material sample is then soaked in a strong alkali (such as KOH solution, NaOH solution, etc.) for 8-20 hours, dried, and placed in a high-temperature tube furnace. The temperature is raised to 600-1000℃ at 5-10℃ / min and held for 2-5 hours. After cooling to room temperature (25±5℃) with the furnace, the sample is removed, ground, and sieved to obtain a carbon material with a three-dimensional porous layered structure.

[0041] In some preferred embodiments, the carbon layer has a thickness of 30-50 μm, and the loading of transition metal elements is 0.5-1 g / 15.4025 cm². 2 Some lithium metal forms alloys with transition metal elements in the carbon layer. Taking tin as an example, the Sn alloy formed by Sn and lithium metal acts as a lithiophilic layer, which can effectively solve the problem of large contact angle between lithium metal and copper foil, allowing lithium metal and copper foil to bond better.

[0042] This lithium metal anode can be prepared by the following method:

[0043] S1: Under weakly alkaline conditions, a mixed solution of soluble transition metal salt, vanillin and carbon material is heated to separate carbon material loaded with soluble transition metal salt.

[0044] S2: The obtained carbon material loaded with soluble transition metal salt is mixed with binder and organic solvent (such as N-methyl-2-pyrrolidone), coated on the surface of negative electrode current collector, and dried to obtain substrate material;

[0045] S3: Deposit metallic lithium on the surface of the substrate material to obtain a lithium metal anode.

[0046] Specifically, in step S1, the pH of the mixed solution can be adjusted to 7.2-8.7 using a weak alkali (selected from one or more of sodium citrate, ammonia, sodium bicarbonate, etc.); the temperature for heating the mixed solution is 60-120℃, and the time is 10-18h.

[0047] In some preferred embodiments, the mass ratio of the soluble transition metal salt to the carbon material is (1-2):(2-3), and the amount of vanillin added is 0.05-0.5 of the mass of the soluble transition metal salt, for example, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.

[0048] In some preferred embodiments, in step S2, the mass ratio of the carbon material loaded with soluble transition metal salt to the binder is (7-9):(1-3); after the carbon material and the binder are mixed, they are ground for 30-60 minutes to form a slurry, which is then coated on the surface of the negative electrode current collector (such as copper foil) with a coating thickness of 40-60 μm. After vacuum drying, the substrate material is obtained.

[0049] In some preferred embodiments, lithium metal is deposited using magnetron sputtering or molten deposition, and the amount of lithium deposited can be (0.1-0.4 g) / 1540.25 cm⁻¹. 2 For example, it could be 0.218g / 1540.25cm. 2 .

[0050] The resulting lithium metal anode can be used to prepare secondary batteries.

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0052] Example 1

[0053] (1) Bundle 20 chopsticks (wooden chopsticks) into a bundle and shorten them to a length of 3cm. Soak them in a 0.1mol / L KOH solution and stir them in a heated magnetic stirrer at 45℃ for 0.5h to obtain a mixed solution. Transfer the mixed solution to a reaction vessel and place it in a forced-air drying oven at 180℃ for 12h. After taking it out, wash it alternately with water and ethanol. Place the sample in a drying oven at 80℃ to dry it and then grind and sieve it to obtain fiber material.

[0054] (2) Soak the fiber material in KOH for 15 hours, dry it, and then place it in a high-temperature tube furnace. The temperature is raised to 800℃ at 5℃ / min and kept for 3 hours. Then, the furnace is cooled to room temperature. After taking out the sample, it is ground and sieved to obtain a carbon material with a three-dimensional porous layered structure.

[0055] (3) Dissolve SnSO4, sodium citrate, vanillin and carbon material in a distilled aqueous solution in a ratio of 1:1:0.25:2, and stir for 2 hours to obtain a mixed solution;

[0056] (4) The mixed solution was transferred to the reaction vessel and placed in a forced-air drying oven for hydrothermal reaction at 120°C for 12 hours. After the reaction was completed, the mixture was washed and dried to obtain Sn@porous layered carbon sample.

[0057] (5) Mix Sn@ porous layered carbon with binder at a ratio of 7:2, use N-methyl-2-pyrrolidone as solvent, grind for 40 min after mixing evenly to make a slurry with a solid content of 50%, then coat it on copper foil with a coating thickness of 50 μm, and vacuum dry to obtain Sn@ porous layered carbon substrate material.

[0058] (6) A Sn@porous layered carbon modified lithium metal composite anode was obtained by uniformly spraying lithium metal onto the surface of Sn@porous layered carbon substrate material using magnetron sputtering.

[0059] Example 2

[0060] This embodiment provides a Sn@porous layered carbon-modified lithium metal composite anode, the preparation method of which is basically the same as that of Example 1, except that in step (3), the mass ratio of SnSO4, sodium citrate and vanillin to carbon material is adjusted to 1:1:0.05:2.

[0061] Example 3

[0062] This embodiment provides a Sn@porous layered carbon-modified lithium metal composite anode, the preparation method of which is basically the same as that of Example 1, except that in step (3), the mass ratio of SnSO4, sodium citrate and vanillin to carbon material is adjusted to 1:1:0.15:2.

[0063] Example 4

[0064] This embodiment provides a Sn@porous layered carbon-modified lithium metal composite anode, the preparation method of which is basically the same as that of Example 1, except that in step (3), the mass ratio of SnSO4, sodium citrate and vanillin to carbon material is adjusted to 1:1:0.5:2.

[0065] Example 5

[0066] This embodiment provides an Al@porous layered carbon modified lithium metal composite anode, the preparation method of which is basically the same as that of Example 1, except that AlCl3 is used in step (3). Specifically, the mass ratio of AlCl3, sodium citrate, vanillin and carbon material is 1:1:0.25:2. Step (4) yields Al@porous layered carbon, and step (5) yields Al@porous layered carbon substrate material.

[0067] Example 6

[0068] This embodiment provides a Sn@ porous layered carbon modified lithium metal composite anode, the preparation method of which is basically the same as that of Embodiment 1, except that in step (6), lithium metal is injected onto the surface of the Sn@ porous layered carbon substrate material to obtain the Sn@ porous layered carbon modified lithium metal composite anode.

[0069] Example 7

[0070] This embodiment provides a Sn@ porous layered carbon modified lithium metal composite anode, the preparation method of which is basically the same as that of Embodiment 1, except that bamboo is used in step (1).

[0071] Comparative Example 1

[0072] This embodiment provides a Sn@ porous layered carbon modified lithium metal composite anode, the preparation method of which is basically the same as that of Embodiment 1, except that vanillin is not added in step (3).

[0073] Comparative Example 2

[0074] This embodiment provides a Sn@ porous layered carbon substrate material, which is prepared by the same method as steps (1)-(5) in Example 1, except that step (6) is not included.

[0075] Comparative Example 3

[0076] This embodiment provides a Sn@ porous layered carbon modified lithium metal composite anode, the preparation method of which is basically the same as that of embodiment 1, except that steps (1) and (2) are not included, and carbon black is directly used as the carbon material (in step (3)).

[0077] Results Analysis

[0078] The negative electrodes obtained in the examples (including Sn@porous layered carbon modified lithium metal composite negative electrode, Al@porous layered carbon modified lithium metal composite negative electrode and Sn@porous layered carbon substrate material) were cut into 12mm diameter discs as working electrodes, and NCM613 was used as the counter electrode. They were assembled into 2025 coin cells using a double-sided ceramic separator and lithium metal electrolyte.

[0079] The obtained button cells were connected to a charging cabinet for rate performance and cycle performance testing. The rate performance testing method was as follows: First, discharge to 2.8V using a constant current of 0.1C, let stand for 5 minutes, then charge to 4.2V using a constant current of 0.1C, let stand for 5 minutes, then discharge to 2.8V using a constant current of 1C, then fully discharge using a constant current and voltage of 0.1C, let stand for 5 minutes, then charge to 4.2V using a constant current of 0.2C, let stand for 5 minutes, then discharge to 2.8V using a constant current of 1C, then fully discharge using a constant current and voltage of 0.1C, and so on. Discharge rate tests were conducted at 0.5C, 1C, 2C, 3C, and 5C respectively. The measured specific capacity was 30mAh / cm³. 2 The result is as follows Figure 1 As shown in Table 1, the cycle performance test was performed by constant current charging at 0.2C and constant current discharging at 0.5C until the capacity was 80% of the initial capacity. The number of cycles was recorded.

[0080] Table 1

[0081]

[0082]

[0083] like Figure 1 As shown in Table 1, the rate performance and cycle performance of the Sn@porous layered carbon modified lithium metal anode material treated with vanillin are superior to those of the untreated lithium metal battery (Comparative Example 1). The rate performance and cycle performance also differed depending on the amount of vanillin added. The performance of the battery with 25% vanillin (Example 1) was better than the other groups. This is because the addition of a certain amount of vanillin can effectively inhibit the growth of lithium dendrites and ensure uniform deposition at the interface of the modified layer. Too little vanillin has an insufficient inhibitory effect on lithium dendrite growth, while too much vanillin occupies part of the internal space of the porous layered carbon, preventing lithium from depositing into the internal space and having the opposite effect on the rate performance and cycle performance of the battery.

[0084] When bamboo fiber is used as the carbon material (Example 7), the carbon nanotubes within the bamboo fiber are more easily damaged than chopsticks, resulting in an incomplete three-dimensional porous layered carbon structure, which affects the electrical performance of the battery cell. While lithium infusion (Example 6) allows more lithium to enter the three-dimensional material, the uniformity of the surface cannot be controlled during infusion. When the surface is uneven, lithium dendrites are more likely to form in thicker areas, leading to a decrease in battery cycle performance. When tin salts are replaced with aluminum salts (Example 5), since both are lithophilic elements, the cycle performance of the cells is not significantly different. The minor differences mainly stem from the different electronegativity of tin and aluminum, leading to different lithium deposition rates and thus affecting the cycle performance of the lithium metal battery. Furthermore, in the later stages of rate testing, because aluminum atoms are less stable than tin atoms, the products of the side reactions between aluminum atoms and the electrolyte continue to react, reducing the lithophilic effect of aluminum atoms. This results in lithium atoms being unable to deposit on the negative electrode surface through aluminum atoms at high rates, leading to uneven lithium deposition on the negative electrode surface and the formation of lithium dendrites, affecting the rate stability of the battery. When carbon black is used as the carbon material (Comparative Example 3), its large specific surface area (10-150 m²) provides a significant advantage. 2 The larger surface area ( / g) leads to an increase in the electrode resistance of the prepared negative electrode. In addition, the larger surface area also causes the cell to generate a larger solid electrolyte membrane (SEI), which consumes more electrolyte and reduces the cell's initial efficiency and cycle life.

[0085] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a lithium metal negative electrode, characterized by, The method comprises the following steps: S1: heating a mixed solution of a soluble metal salt, vanillin and a carbon material under weak alkaline conditions to obtain a carbon material loaded with the soluble metal salt; the soluble metal salt is selected from one or more of a soluble tin salt, a soluble titanium salt, a soluble zinc salt and a soluble aluminum salt; the mass ratio of the soluble metal salt, vanillin and the carbon material is 1:(0.05-0.5):(1-3); The carbon material has a three-dimensional porous layered structure; S2: uniformly mixing the carbon material loaded with the soluble metal salt with a binder and an organic solvent, coating the mixture on the surface of a negative current collector, and drying to obtain a base material; S3: depositing lithium metal on the surface of the base material to obtain the lithium metal negative electrode.

2. The production method according to claim 1, wherein The step S1 satisfies at least one of the following conditions: The pH of the weak alkaline condition is 7.2-8.7; The heating treatment is performed at a temperature of 60-120℃ for 10-18 h.

3. The production method according to claim 2, wherein The pH is adjusted to 7.2-8.7 by a weak base selected from one or more of sodium citrate, ammonia and sodium bicarbonate.

4. The production method according to claim 1, wherein The carbon material is obtained by calcining an activated biomass material; The activation comprises the following steps: heating a mixed solution of a biomass material and a strong base, washing, drying, grinding, and then soaking in a strong base.

5. The production method according to claim 4, wherein At least one of the following conditions is satisfied: The biomass material is selected from one or more of cellulose, bamboo fiber, coconut shell, rice straw, cotton stalk skin and sugarcane residue; The strong base is selected from KOH solution and / or NaOH solution; The heating treatment is performed at a temperature of 120-200℃ for 8-24 h; The soaking in the strong base is performed for 8-20 h; The calcination after the activation is performed at a temperature of 600-1000℃ for 2-5 h.

6. The production method according to claim 1, wherein In the step S2, the mass ratio of the carbon material loaded with the soluble metal salt to the binder is (7-9):(1-3).

7. The production method according to claim 1, wherein In the step S3, the lithium metal is deposited by magnetron sputtering or melting.

8. A lithium metal negative electrode prepared by the preparation method of any one of claims 1-7.

9. A secondary battery characterized by comprising: The lithium metal negative electrode of claim 8.

Images