Ultra-light lithium-containing self-supporting foil, method for producing the same, and lithium secondary battery using the same as a negative electrode

Abstract

This invention discloses an ultralight lithium-containing self-supporting foil, its preparation method, and a lithium secondary battery using it as the negative electrode. The invention yields an ultralight lithium-containing self-supporting foil with excellent mechanical strength and ductility. This foil is a lithium-containing alloy with a dual-phase structure, consisting of a lithium solid solution phase and an intermetallic compound phase. The lithium solid solution phase uses lithium as a solvent and other elements A that are soluble in lithium as solutes. The intermetallic compound phase is a compound alloy formed by a second phase element B and lithium metal. This material can be cast and rolled into foil for use as a self-supporting electrode in a lithium secondary battery, eliminating the need for copper foil support and achieving a thickness as thin as less than 50 μm, with a weight of 6.5 g / m³. 2 Furthermore, this foil material can transform the lithium deposition mechanism into a reversible charge-discharge mechanism of lithium solid solution-deintercalation (solid solution-desolution), allowing it to replace pure lithium strips or lithium-copper composite strips as the negative electrode of secondary batteries, thus significantly improving battery cycle life and safety.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials, specifically relating to an ultralight lithium-containing self-supporting foil and its application in secondary batteries. Background Technology

[0002] my country has prioritized the development of high-energy-density lithium batteries. However, limited by graphite anodes, the energy density of lithium-ion batteries cannot exceed 300Wh / kg, making it increasingly difficult to meet the demands of mobile devices, electric vehicles, and electric aircraft. Lithium metal anodes (LMAs) have a theoretical capacity (3860mAh / g) nearly ten times that of graphite anodes and possess an extremely low standard hydrogen potential (-3.04V), which can significantly increase battery energy density to levels exceeding 400Wh / kg.

[0003] To match the capacity of the positive electrode and meet the design requirements of high-energy-density batteries, lithium foil with a thickness of <50μm is required as the negative electrode. However, lithium is soft and sticky with low mechanical strength, making it impossible to directly roll it thin. Current research mostly uses thick lithium strips >150μm or lithium-copper composite strips with lithium coated on the surface of copper foil as the negative electrode sheet. Using thick lithium strips or lithium-copper composite strips not only increases the cost but also makes the overall thickness or weight of the negative electrode larger (e.g., 8μm copper foil ≈ 72g / m). 2 This limitation restricts the volumetric / weight energy density of the battery. Furthermore, during battery charging and discharging, the lithium metal anode is prone to peeling / uneven deposition reactions, leading to battery capacity decay, dendrite growth, and even internal short circuits. Therefore, fabricating lightweight and thin anode sheets and improving their cycle life are key technologies for high-energy-density rechargeable batteries.

[0004] For the preparation of thin lithium anodes, existing technologies mainly fall into three categories: First, surface modification of metallic lithium during rolling. For example, patent CN 117080363A discloses a method of adding rolling mineral oil during rolling, which can form an organic-inorganic passivation layer on the lithium strip surface, thereby achieving thinning of lithium and improving its mechanical and electrochemical properties. However, achieving uniform distribution and good ion conduction of the rolling oil and its derived passivation layer remains a challenge. Second, lithium deposition or coating is performed after modifying the current collector. For example, patent CN 117393701A discloses a technique for electrodepositing lithium on copper foil coated with nano-silicon, which can prepare ultra-thin lithium metal anodes and improve their cycle life. Another example is Liu et al. coating a lithium-indium alloy layer on the surface of copper using vacuum vapor deposition, using the lithium-indium alloy to replace metallic lithium as the active material (S. Liu et al. Energy Storage). (Mater, 2020, 33, 423–431.), but such processes are complex and costly, and still rely on copper foil as a substrate, making it difficult to achieve lightweight large-area negative electrodes.

[0005] Despite the rapid development of lithium metal anodes recently, most lithium anode materials are either too thick or use heavy copper foil as a substrate, making it difficult to achieve further breakthroughs in the energy density of secondary batteries. Furthermore, the processing costs are high, and large-area fabrication is challenging. At the same time, using the deposition reaction of lithium metal as the anode's working mechanism makes it difficult to completely eliminate the shortened cycle life and safety hazards caused by dendrite growth and electrode pulverization. Therefore, developing a self-supporting, lightweight, and thin anode electrode technology, and improving its safety and cycle life, is of great significance for developing ultra-high specific energy lithium secondary batteries. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention provides an ultralight lithium-containing self-supporting foil, its preparation method, and a lithium secondary battery using it as the negative electrode. This yields an ultralight lithium-containing self-supporting foil with excellent mechanical strength and ductility. This material can be cast and rolled into a foil for use as a self-supporting electrode, eliminating the need for copper foil support and achieving a thickness as thin as less than 50 μm, with a weight of 6.5 g / m³. 2 The foil material of this invention can transform the lithium deposition mechanism into a reversible charge-discharge mechanism of lithium solid solution-deintercalation (solid solution-desolution), and replacing pure lithium strips or lithium-copper composite strips as the negative electrode of secondary batteries with this material can significantly improve battery cycle life and safety.

[0007] In this specification, "self-supporting" means that the material can be processed into foil and is suitable for battery manufacturing and charging / discharging requirements without the use of current collectors.

[0008] The ultralight lithium-containing self-supporting foil provided by this invention is a lithium-containing alloy with a dual-phase structure, consisting of a lithium solid solution phase and an intermetallic compound phase. The lithium solid solution phase uses lithium as a solvent and other elements A that can dissolve in lithium as solutes, forming a molar ratio of LiA. x The crystal is a BCC-type crystal (body-centered cubic structure). The intermetallic compound phase is a compound alloy formed by the second phase element B and lithium metal. The ultralight lithium-containing self-supporting foil material is designated LiA based on the molar ratio of Li, A, and B elements. x -LiB y LiA x With LiB y The two phases can have any molar ratio, where x is the solid solution phase LiA. x The molar ratio of element A to element Li (i.e., the molar ratio of element A to element Li); y represents the intermetallic compound phase LiB. yThe molar ratio of element B to element Li (i.e., the molar ratio of element B to element Li). Here, A is a solute element that can be dissolved in metallic lithium (limited or unlimited miscibility), including but not limited to silver (Ag) and magnesium (Mg); B is a second-phase element that can form intermetallic compounds with lithium, including but not limited to tin (Sn), indium (In), silicon (Si), germanium (Ge), aluminum (Al), and zinc (Zn).

[0009] Furthermore, when A is metallic magnesium, the solid solution phase LiMg of the ultralight lithium-containing self-supporting foil is... x In the case of 0 < x < 2.3, when A is metallic silver, the solid solution phase LiAg in the ultralight lithium-containing self-supporting foil is... x In the case of 0 < x < 0.1.

[0010] Furthermore, when B is tin, indium, silicon, or germanium, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y In the case of y = 0.23; when B is aluminum, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y In the case of y = 0.50; when B is zinc, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y In the given condition, y = 0.33. Preferably, the phase composition of the intermetallic compound in the dual-phase lithium-containing alloy is LiSn. 0.23 、LiAl 0.50 or LiIn 0.23 .

[0011] This invention also provides a self-supporting rolling method for the aforementioned ultralight lithium-containing self-supporting foil. Conventional lithium alloys are soft, have poor mechanical properties, and are highly viscous. Direct rolling of these alloys easily leads to adhesion to the roller surface (also known as "roller sticking"), making it difficult to prepare self-supporting foils. The alloy material described in this invention retains the characteristics of multiple BCC-type crystal slip systems and good ductility, and also possesses good plasticity and strength due to the presence of numerous "hard and strong" intermetallic compounds. Furthermore, the introduction of a supporting protective layer during the rolling process further prevents adhesion between the alloy foil and the rollers, and between alloy foils themselves, enabling continuous roll production of large-area foil strips. The thickness of the self-supporting lithium alloy foil prepared by this invention can be controlled between 20 and 150 μm, with a minimum weight of 2.6 g / cm³. 2 Preferably, the thickness of the obtained foil is 40–50 μm, and the weight is 5.2–6.5 g / cm³. 2 .

[0012] The thinning process of the ultralight lithium-containing self-supporting foil provided by the present invention includes one or more combinations of folding-rolling, rolling-hydraulic, and melting-rolling methods. During rolling, the alloy material is rolled directly or placed in two layers of rolling support protective layers, wherein the rolling support protective layers are PET, PP, or PI films.

[0013] The above method further includes the following steps:

[0014] (1) After removing the surface oxide layer of lithium metal, metal A and metal B, place them in a melting equipment, heat them to a suitable melting temperature under a protective atmosphere so that they are fully melted and mixed, and then place them at room temperature to cool slowly and naturally to obtain an alloy ingot.

[0015] (2) The alloy ingot prepared in step (1) is extruded and rolled into foil under a dry atmosphere to obtain a lithium alloy sheet with a smooth surface.

[0016] (3) Adjust the speed of the twin-roll mill to 10-30 rpm, sandwich the lithium alloy sheet between the roll support protective layer, and perform cumulative stacking rolling (gradually reduce the gap between the rolls after each roll) or multi-roll continuous rolling (gradually reduce the gap between the front and rear rolls) at room temperature until the sheet thickness is reduced to the target thickness (any thickness below 50 μm). The reduction rate of a single rolling is 20%.

[0017] The thinned lithium alloy sheet forms a self-supporting foil with high mechanical strength. The solid solution phase in the foil can promote the solid solution diffusion of the lithium phase during battery charging and discharging, and inhibit the growth of lithium dendrites on the foil surface. At the same time, due to the sufficient and adjustable active lithium in the alloy, the battery cycle life and safety can be significantly improved.

[0018] In the above method, the final thickness of the lithium alloy sheet in step (3) can be adjusted by adjusting the foil spacing and reduction rate, and can be as thin as 20 μm.

[0019] This invention also provides the application of the aforementioned ultralight lithium-containing self-supporting foil in lithium secondary batteries, specifically as the negative electrode. The aforementioned ultralight lithium-containing self-supporting foil effectively suppresses lithium dendrite growth and electrode pulverization, achieving stable cycling and improving battery safety while maintaining thinness and light weight.

[0020] The present invention also provides a lithium secondary battery based on the above-mentioned ultralight lithium-containing self-supporting foil, wherein the lithium secondary battery uses the ultralight lithium-containing self-supporting foil LiA x -LiB y It serves as the negative electrode and also includes the positive electrode, a membrane, and an electrolyte.

[0021] The cathodes of the aforementioned lithium secondary batteries include, but are not limited to, lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), and NCM ternary cathode materials (LiNi). x Co y Mn z O2), NCA ternary cathode material (LiNi) x Co y Al z One of the following: O2, sulfur, or sulfides (SeS2, FeS2, Co9S8, etc.).

[0022] The aforementioned lithium secondary battery electrolyte is composed of a solute, a solvent, and electrolyte additives. The solvent includes, but is not limited to, one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), 1,3-epoxypentane (DOL), and dimethyl ethylene glycol (DME).

[0023] The solute is a lithium salt, including but not limited to one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluoroborate (LiBF6), and lithium difluorooxalate borate (LiDFOB);

[0024] The electrolyte additives include, but are not limited to, one or more of fluoroethylene carbonate (FEC), lithium nitrate (LiNO3), and tetrafluoroethyl tetrafluoropropyl ether (TTE).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention significantly improves the processing performance and mechanical strength of lithium alloys by designing an alloy structure in which a lithium solid solution phase and an intermetallic compound phase coexist. Combined with an innovative casting and rolling process, it enables the large-area fabrication of alloys as thin as ~20μm and as light as ~2.6g / cm³. 2 The self-supporting foil material significantly reduces the thickness and weight of the negative electrode material, thereby increasing the energy density of the battery.

[0027] 2. The ultralight lithium-containing self-supporting foil disclosed in this invention can induce uniform lithium-ion reaction and promote its solid solution into the foil bulk phase through an alloying reaction dominated by solid solution-desolution in the battery. This improves the stability of the electrode interface, inhibits lithium dendrite growth and electrolyte side reactions, improves battery cycle life and safety, and helps reduce the change in electrode thickness during charging and discharging. Attached Figure Description

[0028] Figure 1 The images shown are digital images and SEM cross-sectional images of the 20μm thick ultralight lithium-containing self-supporting foil material in Example 1.

[0029] Figure 2 The stress-strain curves are from tensile tests of Example 1, Comparative Example 1, and Comparative Example 2.

[0030] Figure 3 Example 2 ( Figure 3 b) and Comparative Example 2 Figure 3 a) Deposition 5mAh / cm 2 SEM image of the surface after the areal capacity.

[0031] Figure 4 For 50μm Example 2 (Figure b) and 50μm Comparative Example 2 (Figure a), at 0.1mA / cm 2 5mAh / cm 2 Cross-sectional SEM image of lithium deposition under the specified conditions.

[0032] Figure 5 Example 2 uses 0.1 mA / cm 2 5mAh / cm 2 SEM images of lithium after deposition under the specified conditions (Figure a) and elemental mapping diagrams of Sn (Figure b), O (Figure c), and Mg (Figure d).

[0033] Figure 6 The full cells of Example 2 and Comparative Example 2 were charged at 0.5C (1C = 2 mA / cm). 2 Charge-discharge cycle data under current Detailed Implementation

[0034] The present invention will be further illustrated below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described content, and these improvements and adjustments will still fall within the scope of protection of the invention.

[0035] In the following embodiments, the application of ultralight lithium-containing self-supporting foil in secondary batteries includes the design and construction of the battery system and the corresponding battery testing conditions. The electrolyte, positive electrode, separator, etc., used in the embodiments are all commercially available.

[0036] Assembly of button cell full cells: using commercial lithium alloy foil LiA x And self-made ultralight lithium-containing self-supporting foil material LiA x -LiB y They were used as negative electrodes, with a loading of 21.8 mg / cm³. 2 It matches the NCA cathode, namely LiA x ||NCA and LiA x -LiB y||NCA, manufactured into CR2025 full cells (hereinafter referred to as button cells).

[0037] Among them, the aforementioned commercial lithium alloy foil LiA x The thickness is 100μm, and the thickness of the ultralight lithium-containing self-supporting foil is 20-150μm.

[0038] The separator material used in the assembled batteries is polypropylene or polyethylene, the gaskets and springs are all made of 316 stainless steel, and the electrolyte is 2M LiFSI+DME / TTE (volume ratio 1:1).

[0039] The assembly of the above-mentioned lithium secondary batteries was carried out in a glove box filled with argon gas, with an oxygen content of <0.1ppm and a water content of <0.1ppm.

[0040] The full-cell test conditions are as follows: first, at 0.05C (1C = 2mA / cm). 2 After activating the device with a current for 3 cycles, it is then charged and discharged with a constant current of 0.5C, and the test voltage window is 2.8 to 4.2V.

[0041] All the above tests were performed at room temperature and pressure using a blue electric current tester.

[0042] Mechanical property testing: Pure lithium strip, conventional lithium alloy foil and the foil described in this invention were cut into "dumbbell-shaped" mechanical strips. Under the protection of an inert atmosphere, their stress-strain curves were measured using an automatic tensile tester at a tensile speed of approximately 0.8 mm / s.

[0043] Example 1

[0044] After cleaning the surfaces of lithium, magnesium, and metallic tin inside the glove box, proceed according to the LiMg... x -LiSn y A mixture with a molar ratio of x = 0.13 and y = 0.23 was placed in a crucible, heated to 250°C and held for 30 minutes in a melting furnace, and then cooled to room temperature to obtain an alloy ingot. The alloy ingot was pressed into an alloy sheet using a hydraulic press. The alloy sheet was then placed between two PET films, and the speed of the two-roll mill was adjusted to 10–30 rpm. The rolls were repeatedly stacked and the gap between the two rolls was gradually reduced, finally yielding a large-area, ultralight, lithium-containing self-supporting foil with a diameter of 20 μm.

[0045] Example 2

[0046] After cleaning the surfaces of lithium, magnesium, and metallic tin inside the glove box, proceed according to the LiMg... x -LiSn yThe alloy ingots were mixed in a molar ratio of x = 0.13 and y = 0.23 in a crucible, placed in a melting furnace, heated to 250°C and held for 30 minutes, and then cooled to room temperature. The alloy ingots were then pressed into alloy sheets using a hydraulic press. The alloy sheets were then placed between two PET films, and the speed of the twin-roll mill was adjusted to 10–30 rpm. The sheets were repeatedly stacked and rolled using a twin-roll mill, with the gap between the two rolls gradually decreasing. The roller spacing was adjusted to roll the alloy foil to a thickness of 50 μm, resulting in a self-supporting foil.

[0047] The area and thickness of the foil were measured using a micrometer inside a glove box. The cross-section of the foil was then subjected to argon ion polishing and transferred to a SEM for further verification of its thickness.

[0048] The prepared foil was cut into dumbbell-shaped samples, and its tensile properties were measured inside a glove box.

[0049] The above alloy materials were matched and assembled with pure lithium to form LiMg 0.13 -LiSn 0.23 ||Li half-cell, at 1mA / cm 2 5mAh / cm 2 Under the specified conditions, the battery was charged. After charging was completed, the battery was disassembled, the alloy material was washed with DMC, dried, and its surface morphology was characterized by scanning electron microscopy (SEM).

[0050] The above alloy material was cut into discs using a handheld chip cutter. The alloy negative electrode discs were then matched with NCA positive electrode discs to form a coin cell (LiMg). 0.13 -LiSn 0.23 ||NCA).

[0051] Under charge / discharge conditions of 2.8V-4.2V cutoff voltage and 0.5C, LiMg 0.13 -LiSn 0.23 ||After 450 stable NCA cycles, the capacity retention rate is 90.64%.

[0052] Example 3

[0053] After cleaning the surfaces of lithium, magnesium, and indium metals inside the glove box, they were then mixed in a molar ratio of x = 0.13 and y = 0.23 (LiMg 0.13 -LiIn 0.23 The specific preparation steps are the same as in Example 2. Finally, the thickness of the alloy foil is rolled to 50 μm by adjusting the roller spacing to obtain an ultralight lithium-containing self-supporting foil.

[0054] The mechanical properties and battery performance of the ultralight lithium-containing self-supporting foil prepared above were also measured according to the methods described in Examples 1 and 2.

[0055] Example 4

[0056] After cleaning the surfaces of lithium, silver, and tin metals inside the glove box, they were mixed in a molar ratio of x = 0.10 and y = 0.23 (LiAg... 0.10 -LiSn 0.23 The specific preparation steps are the same as in Example 2. Finally, the thickness of the alloy foil is rolled to 50 μm by adjusting the roller spacing to obtain an ultralight lithium-containing self-supporting foil.

[0057] The mechanical properties and battery performance of the ultralight lithium-containing self-supporting foil prepared above were also measured according to the methods described in Examples 1 and 2.

[0058] Comparative Example 1

[0059] After cleaning the surface of pure 50μm lithium metal foil, it was cut into dumbbell-shaped mechanical strips and disc electrodes. Its mechanical properties and battery performance were measured. The specific preparation and testing steps were the same as in Examples 1 and 2.

[0060] Comparative Example 2

[0061] 50μm lithium-magnesium alloy foil (Li-Mg) 0.13 After surface cleaning, it is cut into dumbbell-shaped mechanical strips and disc electrodes, and its mechanical properties and battery performance are measured. The specific preparation and testing steps are the same as in Examples 1 and 2.

[0062] Under charge / discharge conditions of 2.8V-4.2V cutoff voltage and 0.5C, Li-Mg 0.13 ||After 295 cycles, the capacity of an NCA button cell decreases to less than 80% of its initial capacity.

[0063] Lithium-magnesium composite foil was matched and assembled with pure lithium to form LiMg 0.13 ||Li half-cell, after standing for 2 hours, at 1mA / cm 2 5mAh / cm 2 Under the specified conditions, the battery was charged. After charging was completed, the battery was disassembled, and the lithium-magnesium composite foil was washed with DMC. After the solvent evaporated, its surface morphology was characterized by SEM.

[0064] Figure 1 The figures show digital photographs (Figure a) and SEM cross-sectional photographs (Figure b) of the 20 μm thick alloy foil from Example 1. As can be seen from the figures, the thinning process described in this invention can produce large-area, ultralight, lithium-containing self-supporting foils.

[0065] Figure 2 Figure a shows the stress-strain curves of tensile tests for Example 1 and Comparative Examples 1 and 2, and Figure b shows the tensile strength and tensile force histograms for Example 1, Comparative Examples 1 and 2, and commercial copper foil and commercial lithium-copper composite strip. Figure a shows that the ultralight lithium-containing self-supporting foil LiMg provided by this invention...0.13 -LiSn 0.23 The maximum stress is 10.98 MPa, while for the same thickness, LiMg 0.13 The maximum stresses of the lithium band are only 1.74 MPa and 1.29 MPa, respectively; as shown in Figure b, the 150 μm LiMg... 0.13 -LiSn 0.23 The fact that it can withstand almost the same tensile force as commercial lithium-copper composite strips without copper foil indicates that the dual-phase lithium-rich alloy material has higher tensile strength, while also giving it good machinability and self-supporting properties without copper foil. This provides a new approach to solving the problem of thinning lithium anodes and improving energy density in the field of secondary batteries.

[0066] Figure 3 For Example 2 (Figure b) and Comparative Example 2 (Figure a), the input current is 1 mA / cm. 2 5mAh / cm 2 SEM images of lithium deposition under the specified conditions. Figure a shows the LiMg deposition conditions. 0.13 The deposited surface is rough and porous, with numerous bent lithium dendrites; while Figure b shows LiMg 0.13 -LiSn 0.23 The deposited surface is smooth and dense, mainly consisting of granular solid solution deposition of lithium ions. This result demonstrates that the ultralight lithium-containing self-supporting foil of this invention, when applied to the negative electrode of a lithium battery, completes charge-discharge cycles through a reversible charge-discharge mechanism of solid solution-desolution, which differs from conventional lithium surface deposition mechanisms. This mechanism facilitates the diffusion of deposited lithium ions into the bulk phase of the electrode, suppresses dendrite growth and side reactions, and improves battery cycle life.

[0067] Figure 4 For 50μm Example 2 (Figure b) and 50μm Comparative Example 2 (Figure a), at 0.1mA / cm 2 5mAh / cm 2 Cross-sectional SEM images of LiMg after deposition under the specified conditions. Figure a shows the LiMg... 0.13 The cross-section after deposition is rough and porous, and the thickness control is poor. The thickness increases by 18 μm after lithium deposition, and the volume expansion is severe; while Figure b shows LiMg 0.13 -LiSn 0.23 The deposited cross-section is smooth and dense, with better volume control and a thickness increase of only 7 μm. This result indicates that the ultralight lithium-containing self-supporting foil of this invention, when applied to the negative electrode of a lithium battery, can effectively control the change in electrode thickness during charging and discharging through a reversible charge-discharge mechanism of solid solution-desolution.

[0068] Figure 5 Example 2 uses 0.1 mA / cm 2 5mAh / cm 2SEM images of Li after deposition under the specified conditions (Figure a) and elemental mapping diagrams of Sn (Figure b), O (Figure c), and Mg (Figure d). Figure a shows the LiMg... 0.13 -LiSn 0.23 The surface after deposition is smooth and dense, mainly composed of granular solid solution deposition of lithium ions. Figure b shows that Sn is absent in the newly deposited lithium, while figures c and d show the signal of Mg in the newly deposited Li and the original LiMg. 0.13 -LiSn 0.23 The presence of these components on both surfaces indicates that LiMg is involved in the lithium-ion deposition process. 0.13 -LiSn 0.23 The Mg in the solution dissolves into the newly deposited Li. This demonstrates that the ultralight lithium-containing self-supporting foil of the present invention, when applied to the negative electrode of a lithium battery, represents a reversible charge-discharge mechanism of solution-desolution.

[0069] Figure 6 For Example 2 and Comparative Example 2, the button cell was charged at 0.5C (1C = 2mA / cm). 2 Charge-discharge cycle diagram under current. LiMg 0.13 -LiSn 0.23 || NCA coin cell retains less than 80% of its capacity after 300 cycles, while LiMg 0.13 -LiSn 0.23 After 500 NCA cycles, the capacity retention rate reached as high as 90%. The experimental results demonstrate that, compared with the lithium deposition mechanism in conventional lithium metal anodes, the ultralight lithium-containing self-supporting foil material of this invention, as an anode, exhibits a reversible charge-discharge mechanism of lithium solid solution-desolution, which inhibits the formation of lithium dendrites, alleviates electrode volume expansion, and thus improves the safety and cycle life of the secondary battery.

Claims

1. An ultralight lithium-containing self-supporting foil, characterized in that, This is a lithium-containing alloy with a dual-phase structure, consisting of a lithium solid solution phase and an intermetallic compound phase. The lithium solid solution phase uses lithium as a solvent and reacts with element A, which is dissolved in lithium, as a solute, to form a chemical formula LiA expressed in molar ratio. x The BCC-type crystal, with a body-centered cubic structure, is denoted as LiA. x The intermetallic compound phase is a compound alloy formed by the second-phase element B and lithium metal, denoted as LiB. y The ultralight lithium-containing self-supporting foil material is denoted as LiA based on the molar ratio of Li, A, and B elements. x -LiB y LiA x With LiB y The two phases have any molar ratio, and x is the lithium solid solution phase LiA. x A represents the molar ratio of Li; y represents the intermetallic compound phase LiB. y In the context of element B: the molar ratio of Li; where A is a solute element that can be dissolved in metallic lithium, including one of silver and magnesium; and B is a second-phase element that can form intermetallic compounds with lithium, including one of tin, indium, silicon, germanium, aluminum, and zinc. When A is metallic magnesium, the solid solution phase LiMg of the ultralight lithium-containing self-supporting foil is... x In the case of x = 0.13; when A is metallic silver, the solid solution phase LiAg in the ultralight lithium-containing self-supporting foil is... x In the middle, x = 0.10; When B is tin, indium, silicon, or germanium, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y In the case of y=0.23; when B is aluminum, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y In the case of y=0.50; when B is zinc, the intermetallic compound phase LiB of the ultralight lithium-containing self-supporting foil is... y in y=0.33; The ultralight lithium-containing self-supporting foil is prepared by one or more combinations of folding-rolling, rolling-hydraulic, and melt-rolling methods. During rolling, the alloy material is placed in two layers of rolling support protective layers, which are PET, PP, or PI films. The specific steps include: (1) After removing the surface oxide layer of lithium metal, metal A and metal B, place them in a melting equipment, heat them to 250°C under a protective atmosphere to fully melt and mix them, and then place them at room temperature to cool slowly and naturally to obtain an alloy ingot. (2) The alloy ingot prepared in step (1) is extruded and rolled into foil under a dry atmosphere to obtain a lithium alloy sheet with a smooth surface. (3) Adjust the speed of the twin-roll mill to 10~30 rpm, sandwich the lithium alloy sheet between the roll support protective layer, and perform cumulative stacking rolling at room temperature, or multi-roll continuous rolling, until the sheet thickness is reduced to less than 50 μm, and the reduction rate of a single rolling is 20%.

2. The self-supporting rolling process of the ultralight lithium-containing self-supporting foil as described in claim 1, characterized in that, The preparation method includes one or more combinations of folding-rolling, rolling-hydraulic, and melting-rolling methods; during rolling, the alloy material is placed in two layers of rolling support protective layer for rolling, wherein the rolling support protective layer is PET, PP or PI film; Specifically, the following steps are included: (1) After removing the surface oxide layer of lithium metal, metal A and metal B, place them in a melting equipment, heat them to 250°C under a protective atmosphere to fully melt and mix them, and then place them at room temperature to cool slowly and naturally to obtain an alloy ingot. (2) The alloy ingot prepared in step (1) is extruded and rolled into foil under a dry atmosphere to obtain a lithium alloy sheet with a smooth surface. (3) Adjust the speed of the twin-roll mill to 10~30 rpm, sandwich the lithium alloy sheet between the roll support protective layer, and perform cumulative stacking rolling at room temperature, or multi-roll continuous rolling, until the sheet thickness is reduced to less than 50 μm, and the reduction rate of a single rolling is 20%; the final thickness of the lithium alloy sheet is adjusted by adjusting the foil spacing and reduction rate, and the thinnest is 20 μm.

3. The application of the ultralight lithium-containing self-supporting foil as described in claim 1 in lithium secondary batteries.

4. The application according to claim 3, characterized in that, The application is as the negative electrode of a lithium secondary battery.

5. A lithium secondary battery based on the ultralight lithium-containing self-supporting foil material as described in claim 1, characterized in that, The lithium secondary battery uses the ultralight lithium-containing self-supporting foil LiA as described in claim 1. x -LiB y It serves as the negative electrode and also includes the positive electrode, a membrane, and an electrolyte.

6. The lithium secondary battery according to claim 5, characterized in that, The cathode includes one of lithium iron phosphate, lithium cobalt oxide, NCM ternary cathode material, NCA ternary cathode material, sulfur, and sulfides.

7. The lithium secondary battery according to claim 5, characterized in that, The electrolyte is composed of a solute, a solvent, and electrolyte additives; the solvent includes one or more of diethyl carbonate, dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, 1,3-epoxypentane, and dimethyl ethylene glycol. The solute is a lithium salt, including one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluoroborate, and lithium difluorooxalateborate. The electrolyte additives include one or more of fluoroethylene carbonate, lithium nitrate, and tetrafluoroethyltetrafluoropropyl ether.

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