A copper-aluminum composite foil for a sulfide solid-state battery and a method of manufacturing the same

Abstract

This invention discloses a copper-aluminum composite foil for sulfide solid-state batteries and its preparation method, relating to the field of copper-aluminum composite foil technology. The method includes the following steps: Step 1: Electroplating a copper layer on the surface of an aluminum foil to obtain a copper-plated aluminum foil; Step 2: Pre-drying the copper-plated aluminum foil, then heat-treating it in a sulfur-containing atmosphere to form a Cu-Li-S transition layer; inert encapsulation to obtain the copper-aluminum composite foil; the sulfur-containing atmosphere includes a mixture of H2S and an inert gas, wherein the volume percentage of H2S is 1-3%, and the remainder is inert gas. This invention, by forming a Cu-Li-S transition layer on the surface of the copper-plated aluminum foil, combined with optional plasma pretreatment and in-situ lithium source doping, results in a copper-aluminum composite foil with tight interfacial contact with the sulfide solid electrolyte, few side reactions, and good interfacial stability, which can significantly improve the cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of copper-aluminum composite foil technology, specifically a copper-aluminum composite foil for sulfide solid-state batteries and its preparation method. Background Technology

[0002] Copper and aluminum possess excellent electrical and thermal conductivity, as well as cost advantages, making them widely used in structural connections and electrochemical devices in various industrial products. In sulfide solid-state battery systems, copper and aluminum foils are commonly used current collector substrate materials, while sulfide electrolytes, with their high ionic conductivity and good compaction properties, have become key electrolyte materials in this type of battery.

[0003] However, in sulfide solid-state battery systems, copper foil is typically used as the negative electrode current collector, but the free sulfur and its reduction products, such as S, present in the sulfide electrolyte... 2- PS4 3- It can chemically react with the copper layer to generate corrosion products such as cuprous sulfide and copper sulfide, which have poor conductivity. This leads to a series of problems, such as a rapid increase in interfacial resistance, which hinders the current transmission inside the battery; migration and peeling of the copper layer, which damages the integrity of the electrode structure; and a decline in electrochemical cycle performance, which significantly shortens the battery's lifespan. At the same time, the battery's first-cycle coulombic efficiency decreases, affecting the battery's energy utilization efficiency. Therefore, in order to alleviate the above problems, the existing technology often uses a protective layer to modify the surface of the copper foil. However, there are still shortcomings: First, in terms of conductivity, some inert protective layers and organic self-assembled films can hinder electron transmission; second, in terms of continuity, it is difficult to achieve stable control of the coating thickness, which can easily lead to cracking or localized reactions; third, in terms of process cost, some preparation processes are complex, and the required equipment and material costs are high, which is not conducive to large-scale industrial production.

[0004] Therefore, in order to solve the above problems, it is of great significance to provide a copper-aluminum composite foil for sulfide solid-state batteries and its preparation method. Summary of the Invention

[0005] The present invention aims to provide a copper-aluminum composite foil for sulfide solid-state batteries and its preparation method. A reactive transition layer is set on the surface of the copper-aluminum composite foil, with a chemically stable and conductive Cu-Li-S ternary transition layer pre-generated as the core, which effectively inhibits the corrosion of the copper layer by sulfides, reduces the interfacial impedance, and thus improves the interfacial stability and cycle life of the all-solid-state battery, thereby solving the problems proposed in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing copper-aluminum composite foil for sulfide solid-state batteries includes the following steps: Step 1: Electroplat a copper layer on the surface of the aluminum foil to obtain copper-plated aluminum foil; Step 2: Pre-dry the copper-plated aluminum foil, then heat-treat it in a sulfur-containing atmosphere to form a Cu-Li-S transition layer; inertly encapsulate it to obtain a copper-aluminum composite foil.

[0007] The aluminum foil has a thickness of 15-20 μm, and the copper layer has a thickness of 1-2 μm.

[0008] Furthermore, the sulfur-containing atmosphere comprises a mixture of H2S and inert gas, wherein the volume percentage of H2S is 1-3%, and the remainder is inert gas.

[0009] The copper plating layer is formed in an electroplating solution, the formulation of which is: 72~88g / L copper sulfate pentahydrate, 180~220g / L concentrated sulfuric acid, 110~130g / L ammonium citrate, 0.1~0.2mL / L hydrochloric acid, 5~12g / L polyethylene glycol-6000, and 0.3~1.5g / L sodium polydisulfide dipropane sulfonate; the inert gas includes, but is not limited to, Ar gas.

[0010] Furthermore, the sulfur-containing atmosphere also includes CS2, wherein the volume percentage of CS2 is 0.5-1.5%.

[0011] Introducing CS2 can regulate the supply rate of sulfur and reduce local overreaction.

[0012] Furthermore, the heat treatment temperature is 100~220℃, and the time is 5~30 minutes.

[0013] Furthermore, the thickness of the Cu-Li-S transition layer is 5~50 nm.

[0014] The Cu-Li-S transition layer retains the electronic conductivity of Cu, ensuring smooth electron transport at the interface, and also forms a chemical barrier against sulfide corrosion, effectively preventing further chemical reactions between sulfides and the copper layer, thus achieving effective protection of the copper layer.

[0015] Furthermore, before electroplating the copper layer, the aluminum foil undergoes plasma pretreatment; the process parameters for the plasma pretreatment are: ion source power of 0.5~1.5kW and bombardment velocity of 1~2m / s.

[0016] Furthermore, the Cu-Li-S transition layer undergoes in-situ lithium source doping treatment; The method for in-situ lithium source doping is as follows: a lithium source dispersion is sprayed onto the surface of the Cu-Li-S transition layer; the lithium source includes one or both of lithium carbonate and lithium hydroxide.

[0017] Furthermore, the spraying is performed using a reciprocating spraying method, with the following process parameters: spraying amount of 0.1~0.5 mL / cm². 2 The actual lithium doping concentration is 0.01~0.05 mg / cm³. 2 The spraying pressure is 0.1~0.3MPa, the spraying distance is 15~25cm, and the spraying speed is 5~10cm / s.

[0018] The preferred spraying amount is 0.2~0.3 mL / cm. 2 .

[0019] A method for preparing copper-aluminum composite foil for sulfide solid-state batteries.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, after copper is electroplated onto an aluminum substrate, a Cu-Li-S transition layer is generated in situ on the surface of the electroplated copper through vapor phase treatment, forming an integrated current collector structure of "aluminum-copper-Cu-Li-S". The interface bonding is strong, avoiding the problem of increased interface impedance caused by traditional coating processes. Furthermore, by controlling the time and temperature of low-temperature heat treatment, the stoichiometry of the Cu-Li-S transition layer can be controlled with a precision of 5~50nm, thereby balancing electronic conductivity and chemical barrier performance. 2. This invention employs an in-situ lithium source doping process. By controlling the amount of lithium source doping, a gradient composition structure is formed on the surface of the Cu-Li-S transition layer, where the lithium content in the surface layer is higher than that in the inner layer. After the lithium source dispersion is sprayed onto the surface of the Cu-Li-S transition layer, lithium elements diffuse inward from the surface. Because the heat treatment is performed at a low temperature for a short time, the lithium elements do not achieve sufficient and uniform diffusion, thus forming a gradient composition distribution with high lithium content on the surface and decreasing lithium content in the interior. High-temperature heat treatment would significantly increase the lithium atom diffusion rate, making it impossible to form a gradient composition structure and easily leading to defects such as abnormal grain growth and grain boundary coarsening, thus damaging the transition layer structure. Therefore, using low-temperature heat treatment not only strengthens the barrier effect of the transition layer against sulfide corrosion but also further improves the interfacial compatibility between the transition layer and the copper layer and subsequent electrode materials. This gradient doping design solves the problem that traditional uniform transition layers struggle to balance protective performance and interfacial compatibility. 3. The lithium source of this invention is a stable lithium source such as lithium carbonate and lithium hydroxide, which is made into a low-concentration dispersion and uniformly sprayed onto the surface of the generated Cu-Li-S transition layer to ensure uniform lithium source coverage without damaging the transition layer structure; and the doping process is compatible with the original heat treatment process, without the need for additional complex equipment, thus reducing process costs. 4. This invention performs plasma pretreatment on the aluminum substrate before copper electroplating. Controllable plasma bombardment removes the oxide layer and impurities on the aluminum foil surface, while forming a micro-nano-level rough structure on the aluminum foil surface. This effectively improves the bonding strength between the subsequent copper layer and the aluminum substrate, prevents the copper layer from falling off during use, and further ensures the long-term stability of the current collector. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that there are no special restrictions on the suppliers of all raw materials involved in this invention; exemplary examples include: Electroplating solution: 82g / L copper sulfate pentahydrate, 200g / L concentrated sulfuric acid, 120g / L ammonium citrate, 0.15mL / L hydrochloric acid, 8.5g / L polyethylene glycol-6000, 0.9g / L sodium polydisulfide dipropane sulfonate.

[0023] Example 1: A method for preparing copper-aluminum composite foil for sulfide solid-state batteries, specifically including the following steps: Step 1: Place an 18μm thick aluminum foil in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained. Step 2: Place the copper-plated aluminum foil in an Ar atmosphere and pre-dry it at 80°C for 10 minutes. After the reaction is complete, place it in a reactor and introduce a 2 vol% H2S / Ar mixed gas into the reactor as the reaction atmosphere. Control the reaction temperature at 180°C and heat-treat for 15 minutes to form a 25 nm thick Cu-Li-S transition layer. Then continue to introduce Ar gas into the reactor to cool the aluminum foil to room temperature in an inert atmosphere and inertly encapsulate it to obtain a copper-aluminum composite foil.

[0024] Example 2: A method for preparing copper-aluminum composite foil for sulfide solid-state batteries, specifically including the following steps: Step 1: Place an 18μm thick aluminum foil in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1μm thick copper layer. After washing and drying, you will get copper-plated aluminum foil. Step 2: Place the copper-plated aluminum foil in an Ar atmosphere and pre-dry it at 80°C for 10 minutes. After the reaction is complete, place it in a reactor and introduce a 1 vol% H2S / 1 vol% CS2 / Ar mixture into the reactor as the reaction atmosphere. Control the reaction temperature at 200°C and heat-treat for 10 minutes to form a 25 nm thick Cu-Li-S transition layer. Then continue to introduce Ar gas into the reactor to cool the aluminum foil to room temperature in an inert atmosphere and inertly encapsulate it to obtain a copper-aluminum composite foil.

[0025] Example 3: Based on Example 1, aluminum foil undergoes plasma pretreatment followed by copper plating, specifically including the following steps: Step 1: Plasma pretreatment was performed on an 18μm thick aluminum foil in an Ar / O2 mixed atmosphere with a volume ratio of 9:1, with the ion source power controlled at 1kW and the bombardment velocity at 1.5m / s. Then, the foil was placed in an acetone solution and ultrasonically cleaned for 5 minutes to remove oil and impurities from the surface. After washing and drying, the foil was used as a cathode and placed in an electroplating solution to electroplat a copper layer, forming a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil was obtained. Step 2: Place the copper-plated aluminum foil in an Ar atmosphere and pre-dry it at 80°C for 10 minutes. After the reaction is complete, place it in a reactor and introduce a 2 vol% H2S / Ar mixture into the reactor as the reaction atmosphere. Control the reaction temperature at 180°C and heat-treat for 15 minutes to form a 25 nm thick Cu-Li-S transition layer. Then, continue to introduce Ar gas into the reactor to cool the aluminum foil to room temperature in an inert atmosphere and inertly encapsulate it to obtain a copper-aluminum composite foil.

[0026] Example 4: Based on Example 2, aluminum foil undergoes plasma pretreatment before copper plating, specifically including the following steps: Step 1: Place an 18μm thick aluminum foil in an Ar / O2 mixed atmosphere with a volume ratio of 9:1. Perform plasma pretreatment under the conditions of ion source power of 1kW and bombardment velocity of 1.5m / s. After treatment, place it in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained. Step 2: Place the copper-plated aluminum foil in an Ar atmosphere and pre-dry it at 80°C for 10 minutes. After the reaction is complete, place it in a reactor and introduce a 1 vol% H2S / 1 vol% CS2 / Ar mixture into the reactor as the reaction atmosphere. Control the reaction temperature at 180°C and heat-treat for 15 minutes to form a 25 nm thick Cu-Li-S transition layer. Then continue to introduce Ar gas into the reactor to cool the aluminum foil to room temperature in an inert atmosphere and inertly encapsulate it to obtain a copper-aluminum composite foil.

[0027] Example 5: Based on Example 4, lithium source dispersion was sprayed onto the surface of the Cu-Li-S transition layer for in-situ lithium source doping treatment, with the rest remaining the same as in Example 4; specifically, the following steps were included: Step 1: Place an 18μm thick aluminum foil in an Ar / O2 mixed atmosphere with a volume ratio of 9:1. Perform plasma pretreatment under the conditions of ion source power of 1kW and bombardment velocity of 1.5m / s. After treatment, place it in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained. Step 2: Place the copper-plated aluminum foil in an Ar atmosphere and pre-dry it at 80℃ for 10 minutes. After the reaction, place it in a reactor and introduce a 1 vol% H2S / 1 vol% CS2 / Ar mixture into the reactor as the reaction atmosphere. Control the reaction temperature at 180℃ and heat-treat for 15 minutes to form a 25 nm thick Cu-Li-S transition layer. Then, under a spraying pressure of 0.2 MPa, at a distance of 20 cm from the Cu-Li-S transition layer, perform reciprocating spraying at a speed of 7 cm / s, with a spraying rate of 0.25 mL / cm. 2 The lithium source dispersion has an actual lithium source doping concentration of 0.3 mg / cm³. 2 Then, Ar gas is continuously introduced into the reactor to cool the aluminum foil to room temperature under an inert atmosphere, and it is then inertly encapsulated to obtain a copper-aluminum composite foil.

[0028] Comparative Example 1: Based on Example 1, the subsequent heat treatment and inert packaging operations in a sulfur-containing atmosphere were not performed; the rest remained the same as in Example 1. The specific steps are as follows: An 18μm thick aluminum foil is placed in an acetone solution and ultrasonically cleaned for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, it is used as a cathode and placed in an electroplating solution to electroplat a copper layer, forming a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained; that is, copper-aluminum composite foil.

[0029] Comparative Example 2: Based on Example 1, after electroplating a copper layer, an aluminum foil was coated with an aluminum oxide layer with a thickness of 10 nm using atomic layer deposition, with the rest remaining the same as in Example 1; the specific steps are as follows: Step 1: Place an 18μm thick aluminum foil in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained. Step 2: Place the copper-plated aluminum foil in an atomic deposition chamber at 115℃. Under nitrogen carrier gas, trimethylaluminum is introduced as the aluminum source for 0.02s, followed by 8s of exposure and 25s of nitrogen purging. Then, deionized water is introduced as the oxygen source, introduced into the chamber for 0.1s, exposed for 8s, and purged with nitrogen for 40s. This completes the atomic layer deposition cycle. Repeat the above cycle 100 times to form an aluminum oxide coating with a thickness of 10nm. Then, the foil is cooled to room temperature with the furnace to obtain the copper-aluminum composite foil.

[0030] Comparative Example 3: Based on Example 1, after the aluminum foil was electroplated with a copper layer, it was immersed in an organophosphate solution to form an organophosphate self-assembled film on the copper surface. The rest of the steps were the same as in Example 1. The specific steps are as follows: Step 1: Place an 18μm thick aluminum foil in an acetone solution and ultrasonically clean it for 5 minutes to remove oil and impurities from the surface of the aluminum foil. After washing and drying, use it as a cathode and place it in an electroplating solution to electroplat a copper layer to form a 1.5μm thick copper layer. After washing and drying, copper-plated aluminum foil is obtained. Step 2: Place the copper-plated aluminum foil in an organophosphate solution with a concentration of 1 mmol / L. The organophosphate is octadecylphosphonic acid, and the solvent is a 3:1 volume ratio of ethanol-toluene mixture. Soak in a water bath at 50°C for 40 min, cool naturally to room temperature, rinse with a 3:1 volume ratio of ethanol-toluene mixture, and dry to obtain copper-aluminum composite foil.

[0031] Comparative Example 4: Based on Example 5, the content of sulfur-containing atmosphere was adjusted, the volume percentage of CS2 was 2%, and the rest remained the same as in Example 1.

[0032] Comparative Example 5: Based on Example 5, the heat treatment temperature was adjusted to 300°C, while the rest remained the same as in Example 1.

[0033] Performance testing: The copper-aluminum composite foils prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to the following performance tests: (1) Tensile strength: According to GB / T3880.2-2024, the copper-aluminum composite foil was cut into dumbbell-shaped standard specimens and tested at room temperature using a universal tensile testing machine with a gauge length of 50 mm and a tensile rate of 10 mm / min. (2) Interfacial impedance: A symmetrical blocking battery was assembled using a copper-aluminum composite foil as the working electrode, a lithium metal sheet as the counter electrode and reference electrode, and a sulfide solid electrolyte as the ion conduction layer. AC impedance was measured using an electrochemical workstation within a test frequency range of 1 MHz to 0.01 Hz, with the AC amplitude controlled at 5 mV. The interfacial impedance value was calculated. (3) Battery first-cycle efficiency: A solid-state coin cell was assembled using copper-aluminum composite foil as the current collector, sulfide solid electrolyte, and positive electrode active material; constant current charge-discharge test was performed, and the first charge capacity and first discharge capacity were recorded at 25℃ and 0.1C~0.2C charge-discharge current density. The first-cycle coulombic efficiency was calculated according to the following formula: First-cycle coulombic efficiency (%) = First discharge capacity / First charge capacity × 100%.

[0034] (4) Capacity retention rate test: At 25℃, the circuit is repeatedly cyclically charged and discharged at a current density of 1C. The discharge capacity is recorded for each cycle. The cycle is repeated for 50, 100, and 200 cycles respectively until the capacity decays to 80% of the initial capacity or the specified number of cycles is reached. The discharge capacity of each cycle is recorded. The stable discharge capacity of the first cycle is used as the reference capacity. The cycle capacity retention rate is calculated according to the following formula: Capacity retention rate (%) = discharge capacity in the Nth cycle / discharge capacity in the first cycle × 100%.

[0035] The experimental data are shown in Table 1 below: Table 1

[0036] Conclusion: Based on the data in the table, it can be seen that the copper-aluminum composite foil in Example 1, heat-treated in a single H2S atmosphere, resulted in a Cu-Li-S transition layer with limited uniformity, thus exhibiting an interfacial impedance of 12.4 Ω·cm. 2 The initial efficiency was 95.1%, but interfacial side reactions continued to occur during long-term cycling, leading to a gradual decrease in capacity retention. In Example 2, the copper-aluminum composite foil underwent CS2-assisted heat treatment. The controlled release of sulfur optimized the density and stoichiometry of the transition layer, suppressed the side reactions between the copper foil and the sulfide electrolyte, and reduced the interfacial impedance to 10.8 Ω·cm. 2 The efficiency of the first pass was improved to 96.3%, and the improved interface stability enhanced capacity retention. However, due to the lack of plasma pretreatment, there was still room for improvement in the adhesion between the copper and aluminum interfaces, and the tensile strength was slightly reduced to 118 MPa. In Example 3, Ar / O2 plasma pretreatment was added to the copper-aluminum composite foil of Example 2. The aluminum foil surface was etched to form a micro-rough structure, which significantly enhanced the interfacial bonding between the copper layer and the aluminum foil, increasing the tensile strength to 126 MPa. At the same time, the clean and uniform surface provided an ideal substrate for the growth of the transition layer, further reducing the interface impedance to 9.2 Ω·cm. 2The first-cycle efficiency was improved to 96.8%, and the uniformity and stability of the interface structure were enhanced, thus increasing the capacity retention. In Examples 4 and 5, the copper-aluminum composite foils underwent in-situ lithium source doping based on plasma pretreatment. Example 4 used an H2S atmosphere and lithium source spraying, while Example 5 used an H2S / CS2 mixed atmosphere and lithium source spraying. The lithium source participated in the interface reaction during heat treatment, forming lithium-rich sulfides with high ionic conductivity, and simultaneously filling microscopic defects in the transition layer. Therefore, the interface impedance of the copper-aluminum composite foils in Examples 4 and 5 decreased to 8.5 Ω·cm, respectively. 2 and 7.8Ω·cm 2 The efficiency of the first cycle was increased to 97.2% and 97.5% respectively, and the mechanical properties were improved in conjunction with the plasma pretreatment, resulting in a significant increase in tensile strength.

[0037] In Comparative Example 1, the copper-aluminum composite foil was not subjected to heat treatment in a sulfur-containing atmosphere, resulting in direct exposure of the copper-aluminum composite foil surface to the sulfide electrolyte. This led to severe interfacial side reactions and the formation of a high-impedance byproduct layer, resulting in an interfacial impedance as high as 10⁵ Ω·cm. 2 Irreversible lithium consumption increased significantly, resulting in a marked decrease in first-cycle efficiency to only 79%. Furthermore, interfacial side reactions intensified during battery charge-discharge cycles, leading to continuous consumption of active lithium and electrolyte, and consequently, a decrease in capacity retention. Although the tensile strength was 120 MPa, comparable to Example 1, the interfacial stability was completely unacceptable for solid-state batteries. Comparative Example 2 used an alumina coating instead of the Cu-Li-S transition layer. However, the alumina had poor interfacial compatibility with the sulfide electrolyte, hindering ion conduction, and the interfacial impedance remained as high as 45 Ω·cm. 2 Furthermore, the adhesion between the alumina coating and the copper layer is weak, making it prone to cracking and peeling during cycling, leading to deteriorated interfacial contact, accelerated capacity decay, and a tensile strength reduction to 105 MPa. The first-cycle efficiency is only 88%, making long-term stable cycling impossible. Comparative Example 3 uses an organophosphate self-assembled film. However, because the organophosphate self-assembled film is prone to decomposition or peeling under the high voltage and high stress environment of solid-state batteries, the interfacial impedance drops to 28 Ω·cm. 2However, the performance was still significantly higher than that of the embodiments of the present invention. At the same time, the adhesion between the organophosphate self-assembled film and the copper foil was insufficient, and interface peeling was prone to occur during cycling, resulting in rapid capacity decay. The tensile strength was only 112 MPa, and the first-cycle efficiency was only 85%, which could not balance interface stability and mechanical properties. Comparative Example 4 introduced a high CS2 content, which resulted in coarse grains and loose grain boundaries in the generated transition layer. The loose transition layer would form interface defects between the copper layer and the sulfide electrolyte, reducing the overall tensile strength and increasing the interface impedance, further reducing the first-cycle efficiency. Comparative Example 5 was heat-treated at 300°C. The high temperature caused abnormal growth of copper layer grains and weakening of grain boundaries, resulting in a decrease in the density of the transition layer and a decrease in the bonding force. Therefore, the tensile strength was greatly reduced, and the lithium element diffused excessively, failing to form a gradient structure. At the same time, the defects generated by thermal decomposition would form high-resistance compounds at the interface, increasing the interface impedance and thus leading to a significant decrease in the first-cycle efficiency. In summary, the embodiments show significant and consistent performance improvements in interfacial impedance, first-cycle efficiency, and capacity retention compared to the comparative examples. Therefore, the process differences and corresponding performance changes confirm that the process of the present invention can form a continuous and dense Cu-Li-S transition layer on the surface of the copper-aluminum composite foil and form an interfacial structure with a stepped gradient distribution of lithium components. The differences in process conditions and electrochemical and mechanical properties fully demonstrate its effectiveness in improving the interfacial stability and cycle durability of the current collector in sulfide solid-state batteries.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing copper-aluminum composite foil for sulfide solid-state batteries, characterized in that: Includes the following steps: Step 1: Electroplat a copper layer on the surface of the aluminum foil to obtain copper-plated aluminum foil; Step 2: Pre-dry the copper-plated aluminum foil, and then heat-treat it in a sulfur-containing atmosphere to form a Cu-Li-S transition layer; Inert encapsulation yields copper-aluminum composite foil.

2. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 1, characterized in that: The sulfur-containing atmosphere comprises a mixture of H2S and inert gas, wherein the volume percentage of H2S is 1-3%, and the remainder is inert gas.

3. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 2, characterized in that: The sulfur-containing atmosphere also includes CS2, wherein the volume percentage of CS2 is 0.5-1.5%.

4. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 1, characterized in that: The heat treatment temperature is 100~220℃, and the time is 5~30 minutes.

5. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 1, characterized in that: The thickness of the Cu-Li-S transition layer is 5~50 nm.

6. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 1, characterized in that: Before the copper layer is electroplated, the aluminum foil undergoes plasma pretreatment. The process parameters for the plasma pretreatment are: ion source power of 0.5~1.5kW and bombardment velocity of 1~2m / s.

7. The method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 1, characterized in that: The Cu-Li-S transition layer is further treated with in-situ lithium source doping and inert encapsulation to obtain a copper-aluminum composite foil; The method for in-situ lithium source doping is as follows: a lithium source dispersion is sprayed onto the surface of the Cu-Li-S transition layer; the lithium source includes one or both of lithium carbonate and lithium hydroxide.

8. A method for preparing a copper-aluminum composite foil for a sulfide solid-state battery according to claim 7, characterized in that: The spraying process employs a reciprocating spraying method, with the following parameters: spraying amount of 0.1~0.5 mL / cm². 2 The actual lithium doping concentration is 0.01~0.05 mg / cm³. 2 The spraying pressure is 0.1~0.3MPa, the spraying distance is 15~25cm, and the spraying speed is 5~10cm / s.

9. The copper-aluminum composite foil prepared by the method for preparing copper-aluminum composite foil for sulfide solid-state batteries according to any one of claims 1 to 8.

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