High-capacity low-expansion composite negative electrode plate, current collector and preparation method and application of high-capacity low-expansion composite negative electrode plate

Abstract

The invention relates to a high-capacity low-expansion composite negative electrode plate, a current collector and a preparation method and application of the high-capacity low-expansion composite negative electrode plate. The negative pole piece comprises a composite metal foil current collector and an electrode active material carried on the composite metal foil current collector; the composite metal foil current collector comprises a multi-aperture composite laminated structure which is formed by hot-pressing and compounding two layers of porous copper foils serving as outer layers on two sides and at least one layer of porous metal foil serving as a middle layer; the porous copper foil and the porous metal foil have pore structures with different pore diameters; the electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and is in contact with the inner wall of the pore structure, so that the composite metal foil current collector forms a three-dimensional conductive skeleton structure for bearing the electrode active material, and the loading capacity of the electrode active material, the electrolyte permeability and the ion transmission performance are improved.

Description

Technical Field

[0001] This invention relates to the field of negative electrode material technology, and in particular to a high-capacity, low-expansion composite negative electrode sheet, current collector, its preparation method, and its application. Background Technology

[0002] With the rapid development of lithium-ion battery technology, the performance of the negative electrode plays a crucial role in the overall battery performance. Microporous copper foil, with its excellent conductivity, mechanical stability, and unique microporous structure, has always been an important choice for negative electrode current collectors. However, as market demands for battery energy density and cost become increasingly stringent, the limitations of single-pore-size microporous copper foil are gradually becoming apparent.

[0003] In terms of energy density, while traditional microporous copper foil can provide some channels for lithium-ion transport, its limited pore volume restricts the amount of active material it can hold. This means that, for the same volume or mass, the energy storage capacity of a battery is insufficient to meet the demands of long-range electric vehicles or extended use of portable electronic devices.

[0004] Several existing technologies have focused on this area. For example, CN213752758U discloses a composite current collector. By setting protrusions in the adhesive layer, the surface area of ​​contact between the adhesive layer and the conductive layer is increased, enhancing the adhesion between the adhesive layer and the conductive layer, thereby improving the bonding force between the adhesive layer and the conductive layer, effectively reducing the shedding of the conductive layer, and thus improving the cycle performance of the battery cell using this composite current collector. However, this technology still has some areas for improvement. The introduction of the adhesive layer may bring some potential problems, especially for high energy density negative electrodes. The polymer binder itself has low conductivity and can form non-conductive regions between active material particles, leading to an increase in the total internal resistance of the electrode; the binder covering the active material particles or the pore walls of the current collector can partially hinder electrolyte penetration and slow down the diffusion rate of lithium ions.

[0005] Therefore, existing technologies urgently need a negative electrode current collector and negative electrode sheet that can balance high active material loading, good ion transport performance, structural stability, and cost advantages to meet the needs of the next generation of high-performance batteries. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-capacity, low-expansion composite negative electrode, current collector, its preparation method, and its applications. By compositing porous metal foils with different pore structures with porous copper foils to form a multi-pore layered structure, the electrode active material fully fills the pore structure, increasing the active material loading, optimizing ion transport, and enhancing electrochemical performance. Simultaneously, hot-pressing composite enhances the mechanical strength and structural stability of the current collector, ensuring unobstructed electron channels and extending battery life.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a high-capacity, low-expansion composite negative electrode sheet, comprising: The composite metal foil current collector and the electrode active material carried on the composite metal foil current collector; The composite metal foil current collector includes: a multi-pore composite stacked structure formed by hot pressing two layers of porous copper foil as outer layers on both sides and at least one layer of porous metal foil as an intermediate layer; the porous copper foil and the porous metal foil have different pore sizes. The electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and in contact with the inner wall of the pore structure, so that the composite metal foil current collector forms a three-dimensional conductive skeleton structure for carrying the electrode active material, thereby improving the loading capacity, electrolyte permeability and ion transport performance of the electrode active material.

[0008] Preferably, the porous copper foil has a thickness of 0.01-10 mm, a pore size of 0.01-10 mm, and a porosity of 30-80%; the porous metal foil has a thickness of 0.01-10 mm, a pore size of 5 nm-100 μm, and a porosity of 40-90%. The metal foil includes one or more of aluminum foil, nickel foil, or titanium foil; preferably, the surface of the aluminum foil has an alloying inhibition layer for inhibiting the alloying reaction between aluminum and lithium, the alloying inhibition layer including a carbon coating and / or an aluminum oxide layer.

[0009] Secondly, embodiments of the present invention provide a composite metal foil current collector, comprising: a multi-pore composite stacked structure formed by hot pressing of two layers of porous copper foil as outer layers on both sides and at least one layer of porous metal foil as an intermediate layer; wherein the porous copper foil and the porous metal foil have pore structures with different pore sizes; The electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and in contact with the inner wall of the pore structure, so that the composite metal foil current collector forms a three-dimensional conductive skeleton structure for carrying the electrode active material, thereby improving the loading capacity, electrolyte permeability and ion transport performance of the electrode active material.

[0010] Preferably, the porous copper foil has a thickness of 0.01-10 mm, a pore size of 0.01-10 mm, and a porosity of 30-80%; the porous metal foil has a thickness of 0.01-10 mm, a pore size of 5 nm-100 μm, and a porosity of 40-90%. The metal foil includes one or more of aluminum foil, nickel foil, or titanium foil; preferably, the surface of the aluminum foil has an alloying inhibition layer for inhibiting the alloying reaction between aluminum and lithium, the alloying inhibition layer including a carbon coating and / or an aluminum oxide layer.

[0011] Thirdly, embodiments of the present invention provide a method for preparing the composite metal foil current collector described in the second aspect above, comprising: The copper foil and metal foil are subjected to pore-forming treatment to obtain porous copper foil and porous metal foil with pore structures of different pore sizes; After surface cleaning and drying, the porous copper foil and porous metal foil are cut to the required size. The cut porous copper foil and porous metal foil are stacked in the hot press mold of the hot press machine with the porous copper foil on both sides and the porous metal foil in the middle, and the composite metal foil current collector is obtained by hot pressing.

[0012] Preferably, the hot pressing process includes: The hot press is evacuated to remove air. During the heating phase, the internal temperature of the hot press is gradually increased to a set hot pressing temperature of 300-900℃. At the same time, the mechanical pressure applied by the hot press is gradually increased to 10-30 MPa. The mechanical pressure applied by the hot press is transmitted to the porous copper foil and porous metal foil through the hot pressing mold. The set hot pressing temperature does not exceed the melting point temperature of the metal foil. After the hot pressing temperature and mechanical pressure reach the set values, the hot pressing and holding stage is entered, and the temperature is stabilized for 30-60 minutes, so that the porous copper foil and porous metal foil can be combined under the action of thermoplastic deformation and atomic diffusion to form a composite laminated structure. After the hot pressing and holding stage is completed, heating is stopped, and the material is gradually cooled to room temperature while the hot pressing mold is kept closed, in order to eliminate thermal stress in the composite laminate structure and avoid interlayer peeling or warping.

[0013] Fourthly, the present invention provides a method for preparing the negative electrode sheet described in the first aspect above, the method comprising: A composite metal foil current collector is prepared according to the preparation method described in the third aspect above; The negative electrode sheet is obtained by loading a negative electrode material containing electrode active material onto the surface and pore structure of the composite metal foil current collector.

[0014] Fifthly, the present invention provides a negative electrode, comprising the negative electrode sheet described in the first aspect above, or comprising the composite metal foil current collector described in the second aspect above.

[0015] In a sixth aspect, the present invention provides a lithium battery comprising the negative electrode described in the fifth aspect above.

[0016] The high-capacity, low-expansion composite negative electrode sheet provided in this invention achieves a multi-pore composite laminate structure by hot-pressing porous metal foils with different pore structures and porous copper foils. This broadens the pore structure of the current collector, avoiding the problem of limited active material loading in traditional single-pore copper foils. This allows the electrode active material to fully fill the pore structure and make tight contact with the inner wall, forming a three-dimensional conductive network structure. This effectively increases the active material loading, improves electrolyte permeability, and accelerates ion migration, thereby enhancing the electrochemical performance and rate performance of the electrode sheet. The hot-pressing composite of the porous metal foil and porous copper foil creates a tight bond, giving the current collector higher mechanical strength and structural stability, enhancing tensile and compressive strength, reducing damage caused by external forces, extending battery life, and ensuring smooth electron transport channels. Attached Figure Description

[0017] Figure 1 A flowchart illustrating the preparation method of the composite metal foil current collector provided in this embodiment of the invention. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] This invention provides a high-capacity, low-expansion composite negative electrode sheet, comprising: a composite metal foil current collector and an electrode active material supported on the composite metal foil current collector.

[0020] The composite metal foil current collector includes: a multi-pore composite stacked structure formed by hot pressing two layers of porous copper foil as outer layers on both sides and at least one layer of porous metal foil as the middle layer; the metal foil may specifically include one or more of aluminum foil, nickel foil or titanium foil; preferably, the surface of the aluminum foil has an alloying inhibition layer for inhibiting the alloying reaction between aluminum and lithium, and the alloying inhibition layer may specifically include a carbon coating and / or an aluminum oxide layer.

[0021] Porous copper foil and porous metal foil have pore structures with different pore sizes. The thickness of porous copper foil can be 0.01-10 mm, the pore size can be 0.01-10 mm, and the porosity can be 30-80%; the thickness of porous metal foil can be 0.01-10 mm, the pore size can be 5 nm-100 μm, and the porosity can be 40-90%. Porosity refers to the ratio of pore volume to the total volume of the material. Preferably, the pores in porous copper foil are through-holes, while the pores in porous metal foil can be through-holes or blind holes. When blind holes are used, they are preferably located on both sides of the metal foil.

[0022] In this invention, the pore size and porosity of the porous metal foil and porous copper foil are independently configured. The main purpose of using composite porous copper foil and porous metal foil with different pore sizes and porosities is to broaden the pore size distribution. The above descriptions of the material of the porous metal foil, the foil layer thickness of the copper foil and metal foil, and the specific numerical ranges of the pore size and porosity are merely preferred examples of some achievable solutions of this invention. Those skilled in the art can select the required materials and parameters according to the design concept of this invention in actual implementation.

[0023] In the negative electrode sheet, the electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and in contact with the inner wall of the pore structure. This allows the composite metal foil current collector to form a three-dimensional conductive framework structure for supporting the electrode active material, thereby improving the loading capacity, electrolyte permeability, and ion transport performance of the electrode active material. It is understandable that some of the electrode active material may be loaded onto the outermost surface of the current collector, similar to conventional loading methods.

[0024] Optionally, the porous metal foil layer as the intermediate layer can be one or more layers, and the metal foil materials, pore sizes, and porosities of the layers can be different. However, regardless of which specific materials are used for the porous metal foil intermediate layer, the outer surface of the composite metal foil current collector is still copper foil, which ensures good compatibility and stability between the current collector and the negative electrode active material.

[0025] Figure 1 The composite metal foil current collector provided in the embodiments of the present invention is described below in conjunction with... Figure 1 The preparation method of the composite metal foil current collector of the present invention will be described.

[0026] The main preparation method includes the following steps: Step 110: Perform hole-forming treatment on the copper foil and the metal foil respectively to obtain porous copper foil and porous metal foil with different pore sizes.

[0027] Specifically, through-holes can be formed on the surface of copper foil and through-holes and / or blind holes on the surface of metal foil using methods such as laser drilling, chemical etching, electrochemical etching, mechanical punching, or template etching. By adjusting process parameters such as laser power, etching time, etching solution concentration, or template size, the pore size, porosity, and blind hole depth can be controllably adjusted, thereby obtaining porous copper foil and porous metal foil with different pore size distributions. These are then combined to form a hierarchical porous structure with a wide pore size distribution. Through this differentiated pore size design, ion transport channels of different sizes can be constructed within the composite current collector composed of porous copper foil and porous metal foil, reducing ion diffusion resistance and increasing the ion transport rate within the current collector structure.

[0028] Step 120: After cleaning and drying the porous copper foil and porous metal foil, cut them to the required size.

[0029] Specifically, the porous copper foil and porous metal foil are cleaned with organic solvents (such as acetone or alcohol), followed by rinsing with deionized water to remove residual oil, etching byproducts, and particulate impurities from the pore-forming process. Then, residual solvents on the surface are removed through vacuum drying, inert atmosphere drying, or hot air drying to ensure the internal structure of the pores is clean and free of residual liquid. Afterward, the porous copper foil and porous metal foil are cut to predetermined sizes for use, depending on the needs of subsequent battery fabrication or experiments.

[0030] When aluminum foil is used as the metal foil, an alloying inhibition layer can be further constructed on its surface to suppress the alloying reaction between aluminum and lithium. The alloying inhibition layer can be formed through chemical vapor deposition, sol-gel coating, in-situ oxidation, or coating heat treatment, and its materials include a carbon coating and / or an alumina layer. By forming the aforementioned alloying inhibition layer on the aluminum foil surface, a stable interfacial barrier layer can be constructed between the aluminum substrate and lithium, thereby reducing the possibility of an alloying reaction between aluminum and lithium and improving the structural and electrochemical stability of the composite current collector during battery cycling.

[0031] Step 130: The cut porous copper foil and porous metal foil are stacked in the hot press mold of the hot press machine in the order of placing the porous copper foil on both sides and the porous metal foil in the middle, and the composite metal foil current collector is obtained by hot pressing.

[0032] Specifically, hot pressing can include: Step 131: Vacuum the hot press to remove air.

[0033] A vacuum pump can be connected to evacuate the internal cavity of the hot press, removing air, moisture, and other gaseous impurities. This prevents oxidation reactions or gas retention that could lead to interface defects during subsequent heating and hot pressing processes. The evacuation time and vacuum level can be set according to conventional hot pressing processes, for example, evacuating to 10... -1 ~10 -3 Pa, and maintain for 1 to 15 minutes to create a stable low-oxygen environment inside the hot-pressing chamber.

[0034] Step 132: Enter the heating stage. Gradually increase the internal temperature of the hot press to a set hot pressing temperature of 300-900℃. At the same time, gradually increase the mechanical pressure applied by the hot press to 10-30 MPa. The mechanical pressure applied by the hot press is transmitted to the porous copper foil and porous metal foil through the hot pressing mold.

[0035] Mechanical pressure is applied uniformly to the foil stack structure through a hot pressing mold, which makes the porous copper foil and the porous metal foil form a tight contact, providing conditions for subsequent interfacial diffusion bonding.

[0036] The hot pressing temperature is set to not exceed the melting point of the metal foil; for example, when aluminum foil is used, the hot pressing temperature can be controlled below 600 ℃, preferably between 300 ℃ and 400 ℃.

[0037] Step 133: After the hot pressing temperature and mechanical pressure reach the set values, enter the hot pressing and holding stage, stabilize for 30-60 minutes, so that the porous copper foil and porous metal foil can combine under the action of thermoplastic deformation and atomic diffusion to form a composite laminated structure.

[0038] During this stage, under the set temperature and pressure conditions, the contact interface between each two adjacent foil layers is further bonded under the action of thermoplastic deformation, and a certain degree of atomic diffusion occurs, forming a stable metallurgical bonding interface between the two metal materials, thereby improving the bonding strength and structural stability of the composite laminate structure.

[0039] Step 134: After the hot pressing and holding stage is completed, stop heating and gradually cool to room temperature while keeping the hot pressing mold closed, so as to eliminate thermal stress in the composite laminate structure and avoid interlayer peeling or warping.

[0040] In this step, the composite structure can be gradually cooled by natural cooling or by controlling the cooling rate. During the cooling process, the hot pressing mold is kept in a closed state, so that the composite laminate structure can complete stress release under pressure constraint, thereby reducing residual stress caused by the difference in thermal expansion coefficients and improving the flatness and interlayer bonding stability of the composite current collector structure.

[0041] Furthermore, on the composite metal foil current collector prepared above, a negative electrode material containing electrode active material is loaded onto the surface and pore structure of the composite metal foil current collector to obtain the negative electrode sheet of the present invention. The loading method of the negative electrode material can be as follows: the electrode active material, conductive agent and binder are dispersed in a solvent to prepare a negative electrode slurry, and the negative electrode slurry is applied to the surface of the composite metal foil current collector by means of coating, spraying, scraping or impregnation, so that the negative electrode slurry penetrates into the pore structure. Subsequently, after drying and rolling treatment, the negative electrode material is stably attached to the surface and pore structure of the composite metal foil current collector, thereby forming a negative electrode sheet.

[0042] The composite metal foil current collector and negative electrode sheet proposed in this invention can be applied to lithium battery secondary battery systems.

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0044] Example 1 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0045] Step 1: Use alcohol to treat the porous aluminum foil and porous copper foil with carbon coating on their surfaces to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous aluminum foil and porous copper foil is 1 mm. The pore size of the porous aluminum foil is about 5 nm and the porosity is about 60%, while the pore size of the porous copper foil is about 0.5 mm and the porosity is about 50%.

[0046] Step 2: Place the layers into the hot press mold of the hot press in the following order: first layer is porous copper foil, second layer is porous aluminum foil, and third layer is porous copper foil. Then, evacuate the mold to 1×10⁻⁶. -3 MPa.

[0047] Step 3: Set the hot pressing temperature to 350℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 350℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 350℃±5℃ and a pressure of 30MPa±2MPa.

[0048] Step 4: After the pressure holding stage is completed, stop heating, gradually cool the hot pressing mold to room temperature, remove the mold, take out the composite metal foil current collector, clean the surface residue, rinse it with deionized water, and then place the obtained composite metal foil current collector in a vacuum oven at 60–80 ℃ for 4–8 h to remove residual moisture on the surface.

[0049] Step 5: Active material graphite, conductive agent conductive carbon black, and binder sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are ground in a mortar at a mass ratio of 8:1:1 for 30 minutes. Then, deionized water is added to adjust the solid content to 50 wt%. The mixture is then stirred in a pulper at 1200 rpm for 30 minutes to form a uniform slurry. This slurry is then coated onto the composite metal foil current collector using a doctor blade coating method. The wet film thickness is controlled to 200 μm, allowing the slurry to partially penetrate the porous structure. Afterward, it is dried in a vacuum oven at 80℃ for 12 hours to remove the solvent, yielding the negative electrode sheet.

[0050] Step 6: After connecting the negative electrode to the negative terminal via a nickel sheet, it is sequentially stacked with the polyethylene (PE) separator and the positive electrode (active material is NCM811), and wound along the long side to form a cylindrical cell. Electrolyte is then injected to complete battery assembly. The electrolyte is 1 M LiPF6 dissolved in ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate (EC:DMC:EMC) = 1:1:1 (volume ratio), with an injection volume of approximately 100 μL / cell. After assembly, the cells are allowed to stand for 2 hours to fully wet the electrodes.

[0051] Step 7: After the battery has settled, perform initial charge-discharge activation. In a 25°C constant temperature chamber, charge at 0.05 C to a cutoff voltage of 4.2 V for the first time, and discharge at 0.05 C to a cutoff voltage of 2.8 V for the first time. Perform 2–3 activation cycles to ensure that the electrodes are fully wetted and stable.

[0052] Step 8, Ratio Performance Test: Test instrument: LAND CT2001A battery test system; Test temperature: 25 ℃; Cyclic current ratio settings: 1C, 2C, 3C; Charging cutoff voltage: 4.2 V; Discharging cutoff voltage: 2.8 V. Each rate was cycled 5 times, and the average capacity retention rate at each rate was recorded in Table 1.

[0053] Example 2 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0054] Step 1: Surface-treat the porous aluminum foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous aluminum foil and porous copper foil is 1 mm. The pore size of the porous aluminum foil is approximately 1 μm with a porosity of approximately 60%, while the pore size of the porous copper foil is approximately 0.5 mm with a porosity of approximately 50%.

[0055] Steps 2-8 are the same as in Example 1.

[0056] Example 3 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0057] Step 1: Surface-treat the porous aluminum foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous aluminum foil and porous copper foil is 1 mm. The pore size of the porous aluminum foil is approximately 50 μm, and the porosity is approximately 60%. The pore size of the porous copper foil is approximately 0.5 mm, and the porosity is approximately 50%.

[0058] Steps 2-8 are the same as in Example 1.

[0059] Example 4 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0060] Step 1: Use alcohol to treat the porous nickel foil and porous copper foil with carbon coating on their surfaces to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous nickel foil and porous copper foil is 1 mm. The pore size of the porous nickel foil is about 5 nm and the porosity is about 60%, while the pore size of the porous copper foil is about 0.5 mm and the porosity is about 50%.

[0061] Step 2 is the same as in Example 1.

[0062] Step 3: Set the hot pressing temperature to 550℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 550℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 550℃±5℃ and a pressure of 30MPa±2MPa.

[0063] Steps 4-8 are the same as in Example 1.

[0064] Example 5 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0065] Step 1: Surface-treat the porous nickel foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. Both the porous nickel foil and porous copper foil are 1 mm thick. The porous nickel foil has a pore size of approximately 1 μm and a porosity of approximately 60%, while the porous copper foil has a pore size of approximately 0.5 mm and a porosity of approximately 50%.

[0066] Step 2 is the same as in Example 1.

[0067] Step 3: Set the hot pressing temperature to 550℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 550℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 550℃±5℃ and a pressure of 30MPa±2MPa.

[0068] Steps 4-8 are the same as in Example 1.

[0069] Example 6 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0070] Step 1: Surface-treat the porous nickel foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous nickel foil and porous copper foil is 1 mm. The pore size of the porous nickel foil is approximately 50 μm, and the porosity is approximately 60%. The pore size of the porous copper foil is approximately 0.5 mm, and the porosity is approximately 50%.

[0071] Step 2 is the same as in Example 1.

[0072] Step 3: Set the hot pressing temperature to 550℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 550℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 550℃±5℃ and a pressure of 30MPa±2MPa.

[0073] Steps 4-8 are the same as in Example 1.

[0074] Example 7 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0075] Step 1: Surface-treat the porous titanium foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous titanium foil and porous copper foil is 1 mm. The pore size of the porous titanium foil is approximately 5 nm, and the porosity is approximately 60%. The pore size of the porous copper foil is approximately 0.5 mm, and the porosity is approximately 50%.

[0076] Step 2 is the same as in Example 1.

[0077] Step 3: Set the hot pressing temperature to 850℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 850℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 850℃±5℃ and a pressure of 30MPa±2MPa.

[0078] Steps 4-8 are the same as in Example 1.

[0079] Example 8 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0080] Step 1: Surface-treat the porous titanium foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous titanium foil and porous copper foil is 1 mm. The pore size of the porous titanium foil is approximately 1 μm with a porosity of approximately 60%, while the pore size of the porous copper foil is approximately 0.5 mm with a porosity of approximately 50%.

[0081] Step 2 is the same as in Example 1.

[0082] Step 3: Set the hot pressing temperature to 850℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 850℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 850℃±5℃ and a pressure of 30MPa±2MPa.

[0083] Steps 4-8 are the same as in Example 1.

[0084] Example 9 This embodiment provides a method for preparing a negative electrode sheet containing a composite metal foil current collector, as well as for battery assembly and testing.

[0085] Step 1: Surface-treat the porous titanium foil and porous copper foil with carbon coating using alcohol to remove oil and impurities, then rinse with deionized water and dry. The thickness of both the porous titanium foil and porous copper foil is 1 mm. The porous titanium foil has a pore size of approximately 50 μm and a porosity of approximately 60%, while the porous copper foil has a pore size of approximately 0.5 μm and a porosity of approximately 50%.

[0086] Step 2 is the same as in Example 1.

[0087] Step 3: Set the hot pressing temperature to 850℃ and the target pressure to 30MPa. Increase the temperature of the hot pressing mold from room temperature to 850℃, gradually increasing the applied pressure during the heating process. Once the pressure reaches 30MPa, maintain a constant pressure for 30 minutes. During the pressure holding stage, maintain a temperature of 850℃±5℃ and a pressure of 30MPa±2MPa.

[0088] Steps 4-8 are the same as in Example 1.

[0089] Comparative Example 1 Step 1: The porous copper foil is surface-treated with alcohol to remove oil and impurities, then rinsed with deionized water and dried to form a current collector. The porous copper foil is 1 mm thick, with a pore size of approximately 0.5 μm and a porosity of approximately 50%.

[0090] Step 2: Active material graphite, conductive agent conductive carbon black, and binder sodium carboxymethyl cellulose (CMC) in a mass ratio of 8:1:1, along with styrene-butadiene rubber (SBR), are ground in a mortar for 30 minutes. Then, deionized water is added to adjust the solid content to 50 wt%. The mixture is then stirred in a pulper at 1200 rpm for 30 minutes to form a uniform slurry. This slurry is then coated onto the current collector using a doctor blade. The wet film thickness is controlled to 200 μm, allowing the slurry to partially penetrate the porous structure. Afterward, it is dried in a vacuum oven at 80℃ for 12 hours to remove the solvent, yielding the negative electrode sheet.

[0091] Steps 6-8 are the same as in Example 1.

[0092] Table 1 As can be seen from the comparison between Comparative Example 1 and Examples 1-9, compared with the conventional single-material copper foil current collector, the copper foil composite metal foil current collector proposed in this invention can improve the cycle rate performance of lithium-ion batteries to a certain extent.

[0093] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-capacity, low-expansion composite negative electrode, characterized in that, The negative electrode sheet includes: a composite metal foil current collector and an electrode active material carried on the composite metal foil current collector; The composite metal foil current collector includes: a multi-pore composite stacked structure formed by hot pressing two layers of porous copper foil as outer layers on both sides and at least one layer of porous metal foil as an intermediate layer; the porous copper foil and the porous metal foil have different pore sizes. The electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and in contact with the inner wall of the pore structure, so that the composite metal foil current collector forms a three-dimensional conductive skeleton structure for carrying the electrode active material, thereby improving the loading capacity, electrolyte permeability and ion transport performance of the electrode active material.

2. The high-capacity, low-expansion composite negative electrode sheet according to claim 1, characterized in that, The porous copper foil has a thickness of 0.01-10 mm, a pore size of 0.01-10 mm, and a porosity of 30-80%; the porous metal foil has a thickness of 0.01-10 mm, a pore size of 5 nm-100 μm, and a porosity of 40-90%. The metal foil includes one or more of aluminum foil, nickel foil, or titanium foil; preferably, the surface of the aluminum foil has an alloying inhibition layer for inhibiting the alloying reaction between aluminum and lithium, the alloying inhibition layer including a carbon coating and / or an aluminum oxide layer.

3. A composite metal foil current collector, characterized in that, The composite metal foil current collector includes: a multi-pore composite stacked structure formed by hot pressing two layers of porous copper foil as outer layers on both sides and at least one layer of porous metal foil as an intermediate layer; the porous copper foil and the porous metal foil have different pore sizes. The electrode active material is at least partially filled in the pore structure of the composite metal foil current collector and in contact with the inner wall of the pore structure, so that the composite metal foil current collector forms a three-dimensional conductive skeleton structure for carrying the electrode active material, thereby improving the loading capacity, electrolyte permeability and ion transport performance of the electrode active material.

4. The composite metal foil current collector according to claim 3, characterized in that, The porous copper foil has a thickness of 0.01-10 mm, a pore size of 0.01-10 mm, and a porosity of 30-80%; the porous metal foil has a thickness of 0.01-10 mm, a pore size of 5 nm-100 μm, and a porosity of 40-90%. The metal foil includes one or more of aluminum foil, nickel foil, or titanium foil; preferably, the surface of the aluminum foil has an alloying inhibition layer for inhibiting the alloying reaction between aluminum and lithium, the alloying inhibition layer including a carbon coating and / or an aluminum oxide layer.

5. A method for preparing the composite metal foil current collector according to claim 3 or 4, characterized in that, The preparation method includes: The copper foil and metal foil are subjected to pore-forming treatment to obtain porous copper foil and porous metal foil with pore structures of different pore sizes; After surface cleaning and drying, the porous copper foil and porous metal foil are cut to the required size. The cut porous copper foil and porous metal foil are stacked in the hot press mold of the hot press machine with the porous copper foil on both sides and the porous metal foil in the middle, and the composite metal foil current collector is obtained by hot pressing.

6. The preparation method according to claim 5, characterized in that, The hot pressing process includes: The hot press is evacuated to remove air. During the heating phase, the internal temperature of the hot press is gradually increased to a set hot pressing temperature of 300-900℃. At the same time, the mechanical pressure applied by the hot press is gradually increased to 10-30 MPa. The mechanical pressure applied by the hot press is transmitted to the porous copper foil and porous metal foil through the hot pressing mold. The set hot pressing temperature does not exceed the melting point temperature of the metal foil. After the hot pressing temperature and mechanical pressure reach the set values, the hot pressing and holding stage is entered, and the temperature is stabilized for 30-60 minutes, so that the porous copper foil and porous metal foil can be combined under the action of thermoplastic deformation and atomic diffusion to form a composite laminated structure. After the hot pressing and holding stage is completed, heating is stopped, and the material is gradually cooled to room temperature while the hot pressing mold is kept closed, in order to eliminate thermal stress in the composite laminate structure and avoid interlayer peeling or warping.

7. A method for preparing the negative electrode sheet according to claim 1 or 2, characterized in that, The preparation method includes: The composite metal foil current collector is prepared according to the preparation method of claim 5 or 6 above; The negative electrode sheet is obtained by loading a negative electrode material containing electrode active material onto the surface and pore structure of the composite metal foil current collector.

8. A negative electrode, characterized in that, The negative electrode includes the negative electrode sheet as described in claim 1 or 2, or the composite metal foil current collector as described in claim 3 or 4.

9. A lithium battery, characterized in that, The lithium battery includes the negative electrode as described in claim 8.

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