Three-dimensional composite negative electrode, battery and preparation method thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a three-dimensional composite negative electrode, a battery and a preparation method thereof. The three-dimensional composite negative electrode comprises a three-dimensional current collector and lithium-silicon alloy filled in the pores of the three-dimensional current collector; wherein the lithium-silicon alloy is formed by being heated into a molten state and then being calendered into the pores of the three-dimensional current collector under external pressure. The three-dimensional composite negative electrode in the application is combined by the three-dimensional current collector and the lithium-silicon alloy filled in the pores of the three-dimensional current collector. The volume change of the three-dimensional composite negative electrode is limited in the three-dimensional current collector, and the volume change is less than that of a single metal lithium negative electrode. The volume change of the negative electrode can be effectively inhibited, and the lithium-silicon alloy has more growth orientations than pure lithium, so that the preferential growth of dendrites can be inhibited to a certain extent, and the application of the three-dimensional composite negative electrode in high-performance lithium ion batteries is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a three-dimensional composite negative electrode, a battery, and a method for preparing the same. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and large-scale energy storage systems, higher demands are being placed on the energy density, cycle life, and safety performance of lithium-ion batteries. Traditional graphite anode materials have a relatively low theoretical specific capacity (approximately 372 mAh / g), which is insufficient to meet the needs of next-generation high-energy-density batteries.

[0003] Lithium metal anodes are considered ideal anode materials due to their extremely high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, lithium metal suffers from significant volume changes and uncontrollable lithium dendrite growth during charge and discharge. Lithium dendrites can easily puncture the separator, causing battery short circuits and posing safety hazards. Simultaneously, volume expansion / contraction leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI), continuously consuming electrolyte and active lithium, reducing coulombic efficiency and cycle life.

[0004] To address the aforementioned issues, related technologies have attempted to employ three-dimensional porous current collectors to accommodate volume changes in the active material. While this can confine pure lithium metal within the porous structure of the current collector for deposition, effectively mitigating volume changes and the resulting stress, it cannot effectively further suppress the growth of lithium dendrites. Summary of the Invention

[0005] This application aims to overcome the shortcomings of the prior art and provide a three-dimensional composite anode, a battery, and a method for preparing the same. By pressing molten lithium-silicon alloy into the pores of a three-dimensional current collector, a structurally stable and tightly bonded three-dimensional composite anode is formed. Compared with pure lithium, the lithium-silicon alloy has more growth orientations, which can suppress the preferential growth of dendrites to a certain extent.

[0006] To achieve the above objectives, a first aspect of this application provides a three-dimensional composite negative electrode, comprising: a three-dimensional current collector and a lithium-silicon alloy filling the pores of the three-dimensional current collector; wherein the lithium-silicon alloy is formed by heating to a molten state and then rolling it into the pores of the three-dimensional current collector under external pressure.

[0007] A further technical solution is that the silicon in the lithium-silicon alloy is in the form of nanocrystalline, amorphous, Li2Si, or Li 13 At least one form of the Si4 alloy phase exists.

[0008] A further technical solution is that the thickness of the lithium-silicon alloy is 15-45μm.

[0009] A further technical solution is that the silicon content of the lithium-silicon alloy is 15-35 wt%.

[0010] A further technical solution is that the particle size of the lithium silicon alloy is 1-20μm, and the particle size distribution D50 is 5-15μm, and D90≤30μm.

[0011] A further technical solution is that the melting point of the lithium-silicon alloy is 180-600℃, and its melt viscosity is higher than that of pure lithium.

[0012] A further technical solution is that the thickness of the three-dimensional current collector is 40-80μm and the porosity is 65-85%.

[0013] A second aspect of this application provides a method for preparing a three-dimensional composite anode, the method comprising the following steps: S1: In an inert atmosphere, a lithium-silicon alloy is stacked on top of a three-dimensional current collector; S2: Apply ultrasonic waves to the stacked lithium-silicon alloy and the three-dimensional current collector, and use the energy generated by the ultrasonic waves to rapidly raise the temperature of the lithium-silicon alloy to above its melting point, thereby melting the lithium-silicon alloy. S3: During or after ultrasonic heating, external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional current collector to roll the molten lithium-silicon alloy and force it to penetrate into the pores of the three-dimensional current collector below. Then, it is cooled to obtain a three-dimensional composite negative electrode.

[0014] A further technical solution is that, in S1, the lithium-silicon alloy is prepared by high-energy ball milling, melt spinning, or vapor deposition.

[0015] A further technical solution is that, in S2, the ultrasonic heating temperature is 300-550℃, the time is 5-15s, and the frequency is 40-80kHz.

[0016] A further technical solution is that, in step S3, the calendering time is 20-100 s and the pressure is 0.05-0.8 MPa.

[0017] A third aspect of this application provides a battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte; wherein the negative electrode is the three-dimensional composite negative electrode described above or a three-dimensional composite negative electrode prepared by the method described above.

[0018] Compared with the prior art, this application has the following beneficial effects: This application provides a three-dimensional composite negative electrode. A lithium-silicon alloy is heated to a molten state and then rolled and infiltrated into the pores of a three-dimensional current collector under external pressure to form the three-dimensional composite negative electrode. By filling and confining the lithium-silicon alloy within the pore network of the three-dimensional current collector, the volume expansion / contraction of the alloy material during charging and discharging is constrained within the three-dimensional framework structure, significantly reducing the overall macroscopic volume change of the negative electrode, improving structural stability, and helping to maintain a stable SEI film. Furthermore, the lithium-silicon alloy material itself has more crystal growth orientations than pure metallic lithium, making it less prone to the formation of directional dendrites. Filling it within the three-dimensional conductive framework further homogenizes the current distribution and lithium-ion flow. The three-dimensional space also provides ample reaction sites and accommodation space for lithium deposition / dissolution, thereby suppressing lithium dendrite growth from both material intrinsic and structural design perspectives, and improving battery safety. Attached Figure Description

[0019] Figure 1 This is a cross-sectional scanning electron microscope image of the three-dimensional composite negative electrode processed in Example 1; Figure 2 Cycling curve at 0.33 C for a semi-solid-state battery assembled from a three-dimensional composite negative electrode treated in Example 1. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] For the sake of brevity, this document only discloses a few specific numerical ranges for a given parameter. However, any lower limit can be combined with any upper limit to form an unspecified range, and any lower limit can be combined with other lower limits to form an unspecified range; similarly, any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit, combined with any other point or single value, or with other lower or upper limits, to form an unspecified range. It should be understood that this disclosure is not limited to the specific methods, schemes, and reagents described herein, and is itself subject to variation. The terminology used herein is for the purpose of describing specific embodiments or aspects only and is not intended to limit the scope of this disclosure.

[0022] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application). Unless otherwise expressly stated, all reagents used in this application are commonly used reagents for chemical analysis or experiments and are derived from conventional commercial suppliers in the art.

[0023] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0024] This embodiment provides a three-dimensional composite negative electrode, comprising: a three-dimensional current collector and a lithium-silicon alloy filling the pores of the three-dimensional current collector; wherein the lithium-silicon alloy is formed by heating to a molten state and then rolling it into the pores of the three-dimensional current collector under external pressure.

[0025] In this embodiment, a three-dimensional current collector, such as a three-dimensional copper current collector, forms a continuous conductive framework network, providing a pathway for electron transport. Its internal pores are used to accommodate the active material (lithium-silicon alloy). The lithium-silicon alloy is heated to a molten state and then rolled and infiltrated into the pores of the three-dimensional current collector under external pressure, thus obtaining a three-dimensional composite anode. This structure, where the lithium-silicon alloy is within the framework, physically confines the volume change of the active material within the framework pores, greatly alleviating the overall expansion / contraction of the electrode. Furthermore, the volume change of the selected lithium-silicon alloy is smaller than that of a single metallic lithium anode in existing technologies, effectively suppressing the volume change of the anode. Simultaneously, the lithium-silicon alloy material has more growth orientations than pure lithium, making it less prone to dendrite growth compared to metallic lithium anodes, thus effectively suppressing lithium dendrite growth.

[0026] In this embodiment, it should be noted that the three-dimensional current collector can be obtained by means of, for example, copper foam, copper nanowire / fiber networks, 3D printed copper structures, or porous copper foil prepared by template methods (such as dealloying, electrodeposition, etc.). The thickness of the three-dimensional current collector is 40-80 μm, for example, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 70 μm, 80 μm, etc. The porosity is 65-85%, for example, 65%, 70%, 75%, 80%, 85%, etc. It should be noted that the thickness range of the three-dimensional current collector ensures that the negative electrode has suitable areal capacity and mechanical strength. When the thickness of the three-dimensional current collector is less than the selected range, it cannot fully compensate for the loss of active lithium; when it is greater than the selected range, it will lead to a decrease in battery energy density. Within this porosity range, it can provide enough space to accommodate active materials to ensure high capacity, while also ensuring that the framework has sufficient strength and conductivity. When the porosity is below the selected range, the mechanical strength of the current collector is insufficient; when it is above the selected range, it will lead to a decrease in battery energy density.

[0027] In this embodiment, it should be noted that the thickness of the filled lithium-silicon alloy (referring to the original foil thickness before filling the pores or the equivalent thickness after filling) is 15-45 μm, for example, 15 μm, 20 μm, 30 μm, 35 μm, 40 μm, 45 μm, etc. The silicon content in the lithium-silicon alloy is 15-35 wt% (mass percentage), for example, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, etc. It should be noted that within this silicon content range, the melting temperature of the lithium-silicon alloy is lower than or equal to the melting point of pure lithium, which is beneficial for the implementation of the ultrasonic heating process. At the same time, the lithium-silicon alloy has good electrochemical performance and dendrite suppression ability. When the silicon content and thickness are lower than the selected range, the affinity between the lithium-silicon alloy and the three-dimensional current collector is insufficient, and the dendrite suppression effect is weakened. When the silicon content and thickness are higher than the selected range, the hardness of the lithium-silicon alloy will increase, making it difficult to roll, and may make the lithium-silicon alloy too brittle or deteriorate its electrochemical performance.

[0028] Furthermore, the silicon in the lithium-silicon alloy is in the form of nanocrystalline, amorphous, Li₂Si, or Li₂Si. 13 At least one form of the Si4 alloy phase is required to obtain preferred electrochemical activity. It should be noted that silicon undergoes a large volume change (>300%) during charge and discharge, and may be in nanocrystalline, amorphous, or specific alloy phases (such as Li2Si or Li). 13Si₄ can provide a more uniform stress distribution, avoiding electrode pulverization or detachment from the current collector due to localized excessive expansion. Amorphous or nanocrystalline lithium-silicon alloys have higher structural flexibility and lithium-ion transport channels, reducing the risk of lithium being trapped in the silicon lattice and forming "dead lithium" during cycling. Simultaneously, these phases are less prone to severe side reactions with the electrolyte than coarse-grained silicon, which is beneficial for forming a stable solid-state electrolyte interface (SEI) film. Li₂Si or Li 13 Si4 itself is a typical discharge / charge product phase of lithium-silicon alloys. Pre-forming these phases (or amorphous states with similar local structures) can shorten the lithium diffusion path, reduce the electrochemical activation energy barrier, and thus improve the initial coulombic efficiency and long-term cycling stability.

[0029] Furthermore, the particle size of the lithium-silicon alloy is 1-20 μm, for example, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, etc., preferably 1-10 μm. The particle size distribution D50 is 5-15 μm, for example, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, etc., preferably 5-10 μm, and D90 ≤ 30 μm, preferably D90 ≤ 15 μm.

[0030] Furthermore, the melting point of lithium-silicon alloys is 180-600℃, for example, 180℃, 185℃, 200℃, 210℃, 250℃, 300℃, 380℃, 450℃, 500℃, 560℃, 585℃, 600℃, etc., and its melt viscosity is higher than that of pure lithium. It should be noted here that the melting point of pure lithium is 180℃, while the melting point of lithium-silicon alloys can be controlled within the range of 180–600℃ (by changing the silicon content). Higher melting points allow operation on certain polymer-based current collectors or special coatings that cannot withstand high temperatures, but in this embodiment, the design selects 180–600℃ and "viscosity higher than that of pure lithium" mainly to utilize a slightly higher temperature range (such as 300–500℃) to optimize flowability and avoid incomplete filling caused by melt rush or rapid solidification at excessively low temperatures. Secondly, pure lithium melt has a high surface tension and poor wettability on most current collectors (such as copper and carbon materials), making it difficult to press into micro- and nano-pores. Although the viscosity of lithium-silicon alloy melt is "higher than that of pure lithium," its interfacial reactivity with the current collector is stronger (e.g., silicon forms intermetallic compounds with copper and nickel), resulting in superior dynamic wetting behavior. Combined with external pressure, it can be forced to penetrate complex pores, achieving uniform filling. In the actual rolling process, appropriate ultrasonic heating parameters and external pressure need to be applied based on the specific alloy composition and melting point to ensure that the molten lithium-silicon alloy can fully penetrate into the pores of the three-dimensional current collector.

[0031] This embodiment also provides a method for preparing a three-dimensional composite anode, the method comprising the following steps: S1: In an inert atmosphere, a lithium-silicon alloy is stacked on top of a three-dimensional current collector; S2: Apply ultrasonic waves to the stacked lithium-silicon alloy and the three-dimensional current collector. Use the energy generated by the ultrasonic waves to rapidly raise the temperature of the lithium-silicon alloy to above its melting point, thereby melting the lithium-silicon alloy. S3: During or after ultrasonic heating, external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional current collector, rolling the molten lithium-silicon alloy and forcing it to penetrate into the pores of the three-dimensional current collector below. After cooling, a three-dimensional composite negative electrode is obtained.

[0032] In this embodiment, a lithium-silicon alloy is stacked on top of a three-dimensional current collector. The lithium-silicon alloy stacked on top of the three-dimensional current collector is heated to its melting point and melted using ultrasonic heating. Simultaneously or after ultrasonic heating, external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional current collector, rolling the molten lithium-silicon alloy and forcing it to penetrate into the pores of the underlying three-dimensional current collector. After cooling, a porous copper self-supporting three-dimensional composite negative electrode is obtained. Furthermore, by utilizing the frictional heat generated within the material by ultrasonic waves, the lithium-silicon alloy can be rapidly and uniformly heated to a molten state with a short heating time (on the order of seconds) and high energy utilization. This avoids the problems of long heating times, high energy consumption, and the tendency for alloy oxidation or side reactions with the current collector associated with traditional furnace heating. It also allows for precise control of the microstructure and composition distribution of the lithium-silicon alloy. Simultaneously, by precisely controlling the ultrasonic heating temperature (above the melting point of the lithium-silicon alloy but far below the melting point of copper) and time, it is ensured that the lithium-silicon alloy melts rapidly without unnecessary alloying reactions with the three-dimensional current collector, thus maintaining the conductive framework function of the three-dimensional current collector. This structure not only provides abundant conductive pathways, but also effectively constrains the volume expansion of lithium silicon alloy during charging and discharging, suppresses electrode pulverization and repeated rupture of the SEI film, thereby significantly improving the structural stability and cycle life of the electrode.

[0033] Each step is explained in detail below: Before S1, the process also includes: the preparation of lithium-silicon alloys, which are prepared by high-energy ball milling, melt spinning, or vapor deposition, so that the silicon in them is in the form of nanocrystalline, amorphous, or Li2Si or Li 13 The presence of Si4 and other alloy phases allows for the acquisition of preferred electrochemical activity.

[0034] High-energy ball milling is a simple and efficient solid-state reaction method that uses the mechanical force of a ball mill to alloy lithium and silicon at room temperature. Specifically, silicon powder and lithium metal (usually in granular or shaving form) are mixed according to the stoichiometric ratio of the target alloy. Because lithium is extremely reactive, the entire process must be carried out under an inert atmosphere (such as a glove box) to prevent oxygen buildup. The mixed raw materials are then loaded into a sealed ball mill jar along with cemented carbide or stainless steel balls. Under the high-speed operation of the high-energy ball mill, the grinding balls collide violently with the jar wall, generating enormous impact, shearing, and grinding forces. These forces continuously break, cold-weld, and re-break the lithium and silicon powder particles, causing atoms to diffuse into each other at fresh contact interfaces, thus forming a lithium-silicon alloy.

[0035] Melt spinning is a method for preparing alloys using rapid solidification technology, particularly suitable for preparing thin strip materials with special microstructures (such as nanostructures). Lithium and silicon are mixed in a specific ratio and melted into a homogeneous alloy melt under an inert atmosphere via induction heating or other methods. The alloy melt is then loaded into a quartz tube with a fine nozzle at the bottom. A high-pressure inert gas (such as argon) is applied above the melt, which is then sprayed onto the surface of a high-speed rotating cooling roller (usually made of copper or copper alloy, internally water-cooled). Upon contact with the high-speed rotating cooling roller, the melt is cooled at an extremely high rate (up to 10⁻⁶). 5 -10 6 K / s) rapidly solidified into a continuous thin band.

[0036] Vapor deposition is a method in which lithium and silicon sources are evaporated into gaseous atoms under high vacuum, and then co-deposited on a substrate to form a lithium-silicon alloy thin film.

[0037] The specific preparation method used is not limited in this embodiment.

[0038] S1: In an inert atmosphere, a lithium-silicon alloy is stacked on top of a three-dimensional current collector; In this embodiment, it should be noted that a lithium-silicon alloy of predetermined thickness is laminated with a three-dimensional copper current collector of predetermined specifications. During lamination, the lithium-silicon alloy is placed on top of the three-dimensional copper current collector. It is preferable to operate in an inert atmosphere (such as argon) or a dry environment to prevent the lithium or alloy from being oxidized or reacting with moisture.

[0039] Furthermore, the thickness of the three-dimensional copper current collector is 40-80 μm, and the porosity is 65-85%. The thickness of the lithium-silicon alloy is 15-45 μm, and the silicon content is 15-35 wt%.

[0040] S2: Apply ultrasonic waves to the stacked lithium-silicon alloy and the three-dimensional current collector. Use the energy generated by the ultrasonic waves to rapidly raise the temperature of the lithium-silicon alloy to above its melting point, thereby melting the lithium-silicon alloy. In this embodiment, it should be noted that ultrasonic waves are applied to the stacked materials using an ultrasonic generator. When the ultrasonic waves act on the materials, their energy is rapidly absorbed and converted into heat energy. Since the melting point of lithium-silicon alloy is significantly lower than that of pure copper, selective rapid heating can be achieved by controlling ultrasonic parameters (such as power and time), causing the upper lithium-silicon alloy to melt rapidly into a liquid state, while the lower three-dimensional current collector, such as a three-dimensional copper current collector, maintains a basically solid skeleton shape due to its high melting point.

[0041] Furthermore, the ultrasonic heating temperature is 300-550℃, for example, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, etc. The ultrasonic heating time is 5-15s, for example, 5s, 6s, 8s, 10s, 12s, 14s, 15s, etc. The ultrasonic heating frequency is 40-80kHz, for example, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, etc. It should be noted that if the ultrasonic heating temperature, time, or frequency is below the selected range, the lithium-silicon alloy may not melt; if it is above the selected range, the lithium-silicon alloy may react with metallic copper.

[0042] S3: During or after ultrasonic heating, external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional current collector, rolling the molten lithium-silicon alloy and forcing it to penetrate into the pores of the three-dimensional current collector below. After cooling, a three-dimensional composite negative electrode is obtained.

[0043] In this embodiment, it should be noted that external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional copper current collector simultaneously with or immediately after ultrasonic heating. The applied pressure rolls the molten lithium-silicon alloy, forcing it to penetrate downwards and fill deep into the pores of the three-dimensional copper current collector under the combined action of capillary force and external pressure. After penetration and filling are complete, heating and pressurization are stopped, allowing the composite to cool naturally or by forced cooling. The molten lithium-silicon alloy solidifies within the pores, tightly bonding with the three-dimensional copper current collector framework, thus obtaining a structurally stable three-dimensional composite negative electrode.

[0044] Furthermore, the rolling time is 20-100 seconds, for example, 20 seconds, 40 seconds, 50 seconds, 55 seconds, 75 seconds, 100 seconds, etc. The pressure is 0.05-0.8 MPa, for example, 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.5 MPa, 0.7 MPa, 0.8 MPa, etc. It should be noted that appropriate pressure and duration ensure that the molten alloy fully fills the pores, eliminates air bubbles, and forms good contact with the copper skeleton; if the pressure is below the selected range, the lithium-silicon alloy will not be able to penetrate; if it is above the selected range, it will cause unnecessary deformation.

[0045] This embodiment also provides a battery, including a negative electrode, a positive electrode, a separator, and an electrolyte; the negative electrode is the aforementioned three-dimensional composite negative electrode or a three-dimensional composite negative electrode prepared by the aforementioned method. This battery can be a conventional liquid lithium-ion battery, a lithium metal battery, or a battery using a solid-state or gel electrolyte. The positive electrode can be lithium cobalt oxide, lithium iron phosphate, ternary materials, lithium-rich manganese-based materials, etc. The electrolyte is selected based on the appropriate lithium salt and solvent according to the battery system.

[0046] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0047] Example 1 A method for preparing a three-dimensional composite anode, the method comprising the following steps: S1. Prepare a piece of copper foam with a thickness of 80μm and a porosity of 70% as a three-dimensional copper current collector.

[0048] S2. A lithium-silicon alloy with a thickness of 45 μm and a silicon content of 30 wt% was prepared by high-energy ball milling. The particle size distribution was D50 = 2 μm and D90 = 12 μm. The silicon in the lithium-silicon alloy mainly existed in the form of Li2Si alloy phase.

[0049] S3. In an argon glove box, stack the lithium-silicon alloy on top of the foam copper.

[0050] S4. Transfer the stacked materials to the ultrasonic-calendering integrated device. Apply ultrasonic waves at a frequency of 40 kHz and heat for 10 seconds to melt the lithium-silicon alloy (temperature approximately 200°C).

[0051] S5. Immediately starting in the last second of ultrasonic heating, using a copper plate as a rolling head, apply an external pressure of 0.5 MPa to the surface of the molten lithium-silicon alloy, and continue rolling for 50 seconds. Under pressure, the molten lithium-silicon alloy is squeezed and rapidly penetrates into all the pores of the underlying three-dimensional porous copper current collector.

[0052] S6. Remove the pressure and ultrasound, and allow the composite to cool naturally to room temperature to obtain a three-dimensional composite negative electrode.

[0053] Example 2 The difference between Example 2 and Example 1 is that Example 2 uses a lithium-silicon alloy with a thickness of 30 μm, a three-dimensional copper current collector with a thickness of 50 μm, and a porosity of 70%. Other steps and parameters are exactly the same as in Example 1.

[0054] Example 3 The difference from Example 1 is that the lithium-silicon alloy in Example 3 was prepared by melt spinning. In the lithium-silicon alloy, silicon mainly exists in the form of Li2Si alloy phase, and its particle size distribution is D50=10μm and D90=18μm.

[0055] Example 4 The difference from Example 1 is that the lithium-silicon alloy in Example 4 was prepared by vapor deposition. In the lithium-silicon alloy, silicon mainly exists in an amorphous form, and its particle size distribution is D50=7μm and D90=15μm.

[0056] Example 5 The difference from Example 1 is that the lithium-silicon alloy in Example 5 was prepared by high-energy ball milling, and in the lithium-silicon alloy, silicon is mainly in the form of Li. 13 The Si4 exists in the form of an alloy phase, with a particle size distribution of D50=8μm and D90=20μm.

[0057] Example 6 The difference from Example 1 is that the lithium-silicon alloy in Example 6 was prepared by melt spinning. In the lithium-silicon alloy, silicon mainly exists in the form of nanocrystals (internal grain size <100nm), and its particle size distribution is D50=12μm, D90=22μm.

[0058] Example 7 The difference from Example 1 is that the lithium-silicon alloy in Example 7 was prepared by high-energy ball milling. In the lithium-silicon alloy, silicon mainly exists in the form of Li2Si alloy phase, and its particle size distribution is D50=6μm and D90=13μm.

[0059] Comparative Example 1 The difference from Example 1 is that lithium metal was used in Comparative Example 1, and the molten lithium metal was squeezed and rapidly penetrated into all the pores of the three-dimensional porous copper current collector below.

[0060] Comparative Example 2 The difference from Example 1 is that Comparative Example 2 uses a lithium-tin alloy, and the molten lithium-tin alloy is squeezed and rapidly penetrates into all the pores of the three-dimensional porous copper current collector below.

[0061] Comparative Example 3 The difference from Example 1 is that Comparative Example 3 uses a lithium-zinc alloy, in which the molten lithium-zinc alloy is squeezed and rapidly penetrates into all the pores of the underlying three-dimensional porous copper current collector.

[0062] Comparative Example 4 The difference from Example 1 is that the thickness of the three-dimensional copper current collector is selected as 25 μm (lower than the lower limit of the preferred range of 40-80 μm in this invention), and the other conditions are the same as in Example 1.

[0063] Comparative Example 5 The difference from Example 1 is that the thickness of the three-dimensional copper current collector is selected as 110 μm (higher than the upper limit of the preferred range of 40-80 μm in this invention), and the other conditions are the same as in Example 1.

[0064] Comparative Example 6 The difference from Example 1 is that the thickness of the lithium-silicon alloy is selected as 5 μm (lower than the lower limit of the preferred range of 15-45 μm in this invention), while the other conditions are the same as in Example 1.

[0065] Comparative Example 7 The difference from Example 1 is that the thickness of the lithium-silicon alloy is selected as 60 μm (higher than the upper limit of the preferred range of 15-45 μm in this invention), while the other conditions are the same as in Example 1.

[0066] Comparative Example 8 The difference from Example 1 is that the silicon content of the lithium-silicon alloy is selected as 5 wt% (lower than the lower limit of the preferred range of 15-35 wt% in this invention), and the other conditions are the same as in Example 1.

[0067] Comparative Example 9 The difference from Example 1 is that the silicon content of the lithium-silicon alloy is selected as 50 wt% (higher than the upper limit of the preferred range of 15-35 wt% in this invention), while the other conditions are the same as in Example 1. Its melting point is higher and the melt viscosity is too high, making effective penetration impossible under the same ultrasonic heating conditions.

[0068] Comparative Example 10 The difference from Example 1 is that the particle size of the lithium silicon alloy is 50 μm (D50=45 μm, D90=60 μm), which exceeds the preferred particle size range of 1-20 μm in this application. The other conditions are the same as in Example 1.

[0069] Comparative Example 11 The difference from Example 1 is that the ultrasonic heating temperature is selected as 150℃ (lower than the lower limit of the preferred range of 300-550℃ of the present invention), and the other conditions are the same as in Example 1.

[0070] Comparative Example 12 The difference from Example 1 is that the ultrasonic heating temperature is selected as 650℃ (higher than the upper limit of the preferred range of 300-550℃ of the present invention), and the other conditions are the same as in Example 1.

[0071] Comparative Example 13 The difference from Example 1 is that the ultrasonic heating time is selected as 3s (lower than the lower limit of the preferred range of 5-15s of the present invention), and the other conditions are the same as in Example 1.

[0072] Comparative Example 14 The difference from Example 1 is that the ultrasonic heating time is selected as 30s (higher than the upper limit of the preferred range of 5-15s in this invention), and the other conditions are the same as in Example 1.

[0073] Comparative Example 15 The difference from Example 1 is that the rolling pressure is selected as 0.02 MPa (lower than the lower limit of the preferred range of 0.05-0.8 MPa of the present invention), and the other conditions are the same as in Example 1.

[0074] Comparative Example 16 The difference from Example 1 is that the rolling pressure is selected as 1.5 MPa (higher than the upper limit of the preferred range of 0.05-0.8 MPa of the present invention), and the other conditions are the same as in Example 1.

[0075] Comparative Example 17 The difference from Example 1 is that the calendering time is selected as 10s (lower than the lower limit of the preferred range of 20-100s in this invention).

[0076] Comparative Example 18 The difference from Example 1 is that the calendering time is selected as 110s (higher than the upper limit of the preferred range of 20-100s in this invention), and the other conditions are the same as in Example 1.

[0077] Table 1 shows the differences between the parameters in embodiments 1-7 of this application: Table 1

[0078] Performance testing and characterization Morphological characterization: The negative electrode prepared in Example 1 was observed by cross-sectional SEM, and the results are as follows. Figure 1 As shown. Figure 1 (Example 1) shows that the bright area is a three-dimensional copper current collector and the dark area is a lithium-silicon alloy. It can be seen that the lithium-silicon alloy can fully fill the gaps in the three-dimensional copper current collector and the two are tightly bonded.

[0079] Electrochemical performance testing: Battery assembly: A ternary cathode material (nickel-cobalt-manganese 622) is used as the positive electrode active material, Super-P as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. The materials are mixed in a mass ratio of 18:1:1 to form a slurry and then coated to form the positive electrode sheet. Polyethylene oxide (PEO) and lithium lanthanum zirconium oxide (Li7La3Zr2O) are used. 12 A composite solid electrolyte membrane was prepared by mass ratio of lithium salt (LiTFSI) to lithium oxide (LLZO) at 3:1, with a lithium-oxygen atomic ratio of 1:15. Three-dimensional lithium-silicon alloys prepared in the various examples and comparative examples were used as the negative electrode. A small amount of LB302 electrolyte (accounting for 10% of the total cell mass) was injected, and the cells were assembled into a semi-solid-state simulated battery with an assembly external pressure of 200 kPa.

[0080] Test conditions: The battery was left to stand for 4 hours after assembly. A constant current charge-discharge test was conducted at 0.33C at room temperature (25°C) (the voltage range is set according to the specific positive and negative electrode materials, e.g., 2.8-4.3V vs. Li / Li). + ).

[0081] Test results: The performance comparison of the negative electrodes obtained in each embodiment and the comparative example in the semi-solid battery is shown in Tables 2 and 3 below.

[0082] Table 2

[0083] Table 3

[0084] The first-cycle discharge specific capacity, first-cycle coulombic efficiency, and capacity retention rate after 400 cycles of the semi-solid-state batteries assembled from the three-dimensional lithium-silicon alloys treated in Examples 1-7 and Comparative Examples 1-18 are shown in Tables 2 and 3 above.

[0085] It can be seen that all embodiments show little difference in first-cycle discharge specific capacity and first-cycle coulombic efficiency, indicating that the active material is effectively utilized. Furthermore, the embodiments of this application significantly outperform the comparative examples in terms of long-term cycle stability.

[0086] The capacity retention rates of Examples 1-7 after 400 cycles all exceeded 83%, with the highest reaching 86.7%. This is attributed to the molten lithium-silicon alloy being pressed into the pores of the three-dimensional current collector, forming a structurally stable and tightly bonded three-dimensional composite negative electrode, which greatly buffers the volume effect. Moreover, the lithium-silicon alloy has more growth orientations than pure lithium, which can suppress the preferential growth of dendrites to a certain extent.

[0087] Figure 2 The figure shows the 0.33 C cycling curve of the semi-solid battery assembled with the three-dimensional composite negative electrode treated in Example 1. After 400 cycles, its capacity retention rate can reach 85.8%. When the lithium silicon alloy is fully filled in the pores of the three-dimensional copper current collector, its volume change rate is suppressed to the maximum extent, thus exhibiting good electrochemical stability.

[0088] Comparative Example 1 uses metallic lithium to fill the pores of a three-dimensional copper current collector. Pure metallic lithium undergoes significant volume changes during cycling (repeated deposition / stripping during charge / discharge), easily leading to the destruction of the pore structure of the three-dimensional copper current collector and repeated rupture and regeneration of the SEI film, thus rapidly consuming the electrolyte and active lithium. Its capacity retention after 400 cycles is only 45.4%, far lower than the 85.8% of Example 1. Lithium-silicon alloys, due to the alloying reaction mechanism of silicon, exhibit large volume expansion, but this is effectively constrained by the three-dimensional pores, and the alloy state itself is more resistant to structural fatigue than pure lithium.

[0089] Comparative Example 2 used a lithium-tin alloy to fill the pores of the three-dimensional copper current collector. The lithium-tin alloy could also alleviate volume changes, but its ability to suppress volume expansion was weaker than that of the lithium-silicon alloy (silicon has a higher theoretical lithium intercalation capacity, and the alloy phase formed with lithium is denser and has higher mechanical strength). Therefore, the retention rate of Comparative Example 2 after 400 cycles was 72.6%, which was still lower than that of Example 1.

[0090] Comparative Example 3 used a lithium-tin alloy to fill the pores of a three-dimensional copper current collector. The first-cycle discharge capacity of Comparative Example 3 was only 130.9 mAh / g, indicating that its initial active material utilization rate was low or the pore filling was uneven / insufficient. At the same time, its 400-cycle retention rate of 81.3% was also lower than that of Example 1. This indicates that its alloy composition leads to poor electrochemical activity and poor internal contact. Even though its cycle stability is slightly better than that of Comparative Example 2, its overall energy density and cycle life are not as good as those of Example 1.

[0091] Basis for parameter range selection: Regarding the thickness of the current collector, the difference between Comparative Examples 4 and 5 and Example 1 lies in that the thickness of the three-dimensional copper current collector is selected outside the preferred range of 40-80 μm, thus allowing for comparison with Example 1 and verifying the influence of the thickness of the three-dimensional copper current collector. As can be seen from Tables 2 and 3, the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability are all inferior to Example 1. A current collector that is too thin (25 μm) results in poor structural strength; a current collector that is too thick (110 μm) results in low energy density and deteriorated cycle performance.

[0092] The difference between Comparative Examples 6 and 7 and Example 1 lies in the thickness of the lithium-silicon alloy: the thickness of the lithium-silicon alloy was selected outside the preferred range of 15-45 μm, thus allowing for comparison with Example 1 and verifying the effect of the lithium-silicon alloy thickness. Tables 2 and 3 show that the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability are all inferior to Example 1. A lithium-silicon alloy that is too thin (5 μm) results in low capacity; an alloy that is too thick (60 μm) results in severe hardening, uneven rolling, and unstable SEI.

[0093] The difference between Comparative Examples 8 and 9 and Example 1 lies in the silicon content: the silicon content of the lithium-silicon alloy was selected outside the preferred range of 15-35 wt%, thus allowing for comparison with Example 1 and verifying the influence of silicon content in the lithium-silicon alloy. Tables 2 and 3 show that when the silicon content of the lithium-silicon alloy in Comparative Example 8 was below the selected range, or when the silicon content of the lithium-silicon alloy in Comparative Example 9 was above the selected range, a good three-dimensional composite anode could not be prepared for testing. This was mainly because if the silicon content was too low (5 wt%), the alloy melting point was too high or difficult to form; if the silicon content was too high (50 wt%), the alloy melt viscosity was too high, preventing effective penetration (Comparative Example 9). This verifies the crucial role of the synergistic effect of silicon content and process parameters. In other words, Comparative Example 9, by adjusting the silicon content to change the melting point and viscosity of the alloy, found that under the same ultrasonic heating and rolling parameters, the alloy with an excessively high silicon content (>35 wt%) could not effectively penetrate due to excessive viscosity. This further verifies the crucial role of the synergistic effect of the lithium-silicon alloy characteristics (silicon content, corresponding melting point, and viscosity) and process parameters as defined in this application.

[0094] Comparative Example 10 used a lithium-silicon alloy with an excessively large particle size (50 μm), which made it difficult for the molten lithium-silicon alloy to completely penetrate into the fine pores of the three-dimensional current collector. The cycle life of the assembled battery was significantly lower than that of Example 1, demonstrating the necessity of controlling the lithium-silicon alloy particle size within the range of 1-20 μm.

[0095] The ultrasonic heating temperature differs from that of Example 1 in that Comparative Examples 11 and 12 are selected outside the range of 300-550℃, allowing for comparison with Example 1 and verification of the effect of ultrasonic heating temperature. Tables 2 and 3 show that when the ultrasonic heating temperature of Comparative Example 11 is below the selected range, the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability are all inferior to Example 1. The ultrasonic temperature is too low (150℃), resulting in incomplete melting of the lithium-silicon alloy and poor penetration. When the ultrasonic heating temperature of Comparative Example 12 is above the selected range, a good three-dimensional composite anode cannot be prepared for testing, mainly because the ultrasonic temperature is too high (650℃), leading to severe alloy oxidation, volatilization, or reaction with copper.

[0096] The ultrasonic heating time differs between Comparative Examples 13 and 14 and Example 1 in that the ultrasonic heating time is selected outside the range of 5-15 s, allowing for comparison with Example 1 and verification of the effect of ultrasonic heating time. Tables 2 and 3 show that when the ultrasonic heating time of Comparative Example 13 is lower than the selected range, the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability are all inferior to Example 1, indicating insufficient melting due to the short ultrasonic time (3 s). When the ultrasonic heating time of Comparative Example 14 is higher than the selected range, a good three-dimensional composite anode cannot be prepared for testing, mainly because the ultrasonic time is too long (30 s), resulting in severe thermal damage.

[0097] The difference between Comparative Examples 15 and 16 and Example 1 lies in the rolling pressure: the rolling pressure was selected outside the range of 0.05-0.8 MPa, allowing for comparison with Example 1 and verification of the effect of rolling pressure. Tables 2 and 3 show that when the rolling pressure of Comparative Example 15 was lower than the selected range, the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability were all inferior to Example 1. The rolling pressure was too low (0.02 MPa), resulting in insufficient penetration. When the rolling pressure of Comparative Example 16 was higher than the selected range, a good three-dimensional composite anode could not be prepared for testing, mainly because the rolling pressure was too high (1.5 MPa), causing the current collector structure to collapse.

[0098] The difference between Comparative Examples 17 and 18 and Example 1 lies in the calendering time: the calendering time was selected outside the range of 20-100s to compare with Example 1 and verify the effect of calendering time. Tables 2 and 3 show that when the calendering time of Comparative Example 17 was lower than the selected range, the first-cycle discharge specific capacity, first-cycle coulombic efficiency, and long-term cycle stability were all inferior to Example 1. The calendering time was too short (10s), resulting in insufficient penetration. When the calendering pressure of Comparative Example 18 was higher than the selected range, a good three-dimensional composite anode could not be prepared for testing, mainly because the calendering time was too long (110s), leading to low production efficiency or overheating.

[0099] In summary, Comparative Examples 1-3 investigated the performance of negative electrodes obtained by rolling and infiltrating three different materials—lithium metal, lithium-tin alloy, and lithium-zinc alloy—into the pores of a three-dimensional current collector after they were in a molten state in a semi-solid-state battery.

[0100] Comparative Examples 4-18 systematically investigated the effects of various parameters exceeding the preferred range of this invention when a three-dimensional composite negative electrode was formed by rolling and infiltrating a lithium-silicon alloy in a molten state into the pores of a three-dimensional current collector. The results showed that when the thickness of the three-dimensional current collector (Comparative Examples 4 and 5), the thickness and silicon content of the lithium-silicon alloy (Comparative Examples 6-9), the particle size of the lithium-silicon alloy (Comparative Example 10), the ultrasonic heating temperature and time (Comparative Examples 11-14), and the rolling pressure and time (Comparative Examples 15-18) were below or exceeded the preferred range defined by this invention, it would lead to battery fabrication failure, first-cycle performance degradation, or a sharp decline in cycle life. This powerfully demonstrates, from the opposite perspective, that the selected combination of parameters—40-80 μm thickness and 65-85% porosity of the three-dimensional current collector; 15-35 wt% silicon content and 15-45 μm thickness of the lithium-silicon alloy; ultrasonic heating temperature of 300-550℃, time of 5-15 s, and frequency of 40-80 kHz; and rolling pressure of 0.05-0.8 MPa and time of 20-100 s—is the optimal and necessary process window for achieving high-performance three-dimensional lithium-silicon alloy anodes by rolling and infiltrating the lithium-silicon alloy into the pores of the three-dimensional current collector after it has reached a molten state. Compared to a wider range of parameters, the narrower range preferred by this invention brings significant and unexpected improvements in technical performance.

[0101] The embodiments described in this application are merely illustrative examples. The embodiments of this application are not limited to the above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A three-dimensional composite negative electrode, characterized in that, include: A three-dimensional current collector and a lithium-silicon alloy filling the pores of the three-dimensional current collector; The lithium-silicon alloy is formed by heating it to a molten state and then rolling it into the pores of the three-dimensional current collector under external pressure.

2. The three-dimensional composite negative electrode as described in claim 1, characterized in that, The silicon in the lithium-silicon alloy is in the form of nanocrystalline, amorphous, Li₂Si, or Li. 13 At least one form of the Si4 alloy phase exists.

3. The three-dimensional composite negative electrode as described in claim 1 or 2, characterized in that, The thickness of the lithium-silicon alloy is 15-45 μm.

4. The three-dimensional composite negative electrode as described in claim 3, characterized in that, The silicon content of the lithium-silicon alloy is 15-35 wt%.

5. The three-dimensional composite negative electrode as described in claim 1, characterized in that, The lithium-silicon alloy has a particle size of 1-20 μm, and a particle size distribution D50 of 5-15 μm and D90 ≤ 30 μm.

6. The three-dimensional composite negative electrode as described in claim 1, characterized in that, The lithium-silicon alloy has a melting point of 180-600℃ and a melt viscosity higher than that of pure lithium.

7. The three-dimensional composite negative electrode as described in claim 1, characterized in that, The thickness of the three-dimensional current collector is 40-80 μm, and the porosity is 65-85%.

8. A method for preparing a three-dimensional composite negative electrode as described in any one of claims 1-7, characterized in that, The method includes the following steps: S1: In an inert atmosphere, a lithium-silicon alloy is stacked on top of a three-dimensional current collector; S2: Apply ultrasonic waves to the stacked lithium-silicon alloy and the three-dimensional current collector, and use the energy generated by the ultrasonic waves to rapidly raise the temperature of the lithium-silicon alloy to above its melting point, thereby melting the lithium-silicon alloy. S3: During or after ultrasonic heating, external pressure is applied to the molten lithium-silicon alloy on the surface of the three-dimensional current collector to roll the molten lithium-silicon alloy and force it to penetrate into the pores of the three-dimensional current collector below. Then, it is cooled to obtain a three-dimensional composite negative electrode.

9. The method as described in claim 8, characterized in that, In S1, the lithium-silicon alloy is prepared by high-energy ball milling, melt spinning, or vapor deposition. And / or, In S2, the ultrasonic heating temperature is 300-550℃, the time is 5-15 s, and the frequency is 40-80kHz; And / or, In step S3, the calendering time is 20-100 s and the pressure is 0.05-0.8 MPa.

10. A battery, characterized in that, It includes a negative electrode, a positive electrode, a separator, and an electrolyte; the negative electrode is a three-dimensional composite negative electrode according to any one of claims 1-7 or a three-dimensional composite negative electrode prepared by the method according to any one of claims 8-9.

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