Composite current collector and preparation method thereof, negative pole piece and solid-state battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a composite current collector and a preparation method thereof, a negative pole piece and a solid-state battery. The composite current collector comprises a polymer layer and an alloy layer arranged on at least one side of the polymer layer; and the alloy layer is a CuN alloy layer. The composite current collector has the advantages of low cost, corrosion resistance and long service life, ensures the long-term service of the current collector in the sulfide solid-state battery, prolongs the service life of the battery, and solves the problem that the current collector is corroded by the sulfide solid-state electrolyte when the traditional composite copper foil is used in the solid-state battery. Meanwhile, compared with copper foil, stainless steel foil and the like used at present, the composite current collector structure has the advantage that the energy density of the battery is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to a composite current collector, a preparation method thereof, a negative electrode sheet, and a solid-state battery. Background Art

[0002] With the progress of technology, people have higher and higher requirements for the endurance time, endurance mileage, safety performance, etc. of new energy vehicles. The energy density of traditional liquid lithium-ion batteries has approached the limit, and there are risks of thermal runaway such as electrolyte leakage, battery fire, and explosion during collisions; the market has an increasingly strong demand for high-safety and high-energy-density solid-state batteries. The ionic conductivity of sulfide solid electrolytes is as high as 10 -3 -10 -2 S / cm, which is comparable to the ionic conductivity of electrolytes, and is one of the electrolyte materials that can most quickly achieve mass production of high-safety and high-energy-density solid-state batteries. Sulfide electrolytes have the problem of poor air stability. Even in a dry room with a dew point of -50°C, sulfide electrolytes will still react with trace amounts of water in the air to generate H2S gas. H2S will corrode copper foils, damage the mechanical properties of current collectors, increase the interfacial resistance, and then deteriorate the electrical performance of solid-state batteries, resulting in rapid battery failure and shortening the battery life

[0003] Currently, for traditional liquid batteries, copper foils or composite copper foils are used as negative current collectors. Compared with ordinary copper foils, composite copper foils have a lower areal density, so the energy density of the battery can be significantly improved. The copper foils or composite copper foils used in traditional liquid batteries are surface-treated by electrochemically depositing Cr,; or by organic antioxidant treatment. The main function of these two surface treatments is antioxidant, which can improve the ambient temperature storage performance of copper foils or composite copper foils. The corrosion resistance of copper foils or composite copper foils treated by these methods is generally poor and cannot be used in sulfide solid-state batteries, which limits the improvement of the energy density of solid-state batteries.

[0004] In the patent of CN118738405B, to avoid the possible generation of trace amounts of H2S in sulfide solid-state batteries from corroding the current collector, an anti-corrosion conductive layer is added outside the current collector. The material of the anti-corrosion conductive layer is selected from one or more of transition metals Ta, Pd, Ir, and Rh, and the thickness of the anti-corrosion conductive layer is 0.2 μm to 2 μm. Since Ta, Pd, Ir, and Rh are expensive, reaching several hundred to over a thousand yuan per gram, the high cost makes this technology difficult to be mass-produced and applied.

[0005] In addition to the above patent, to avoid the corrosion of copper foils by sulfide electrolytes, technicians will use stainless steel foils as negative current collectors. However, due to the limitations of stainless steel foil preparation technology, the thinnest stainless steel foil that can be mass-produced, has a moderate cost, and has processing performance that meets the requirements of negative electrode coating, rolling, slitting, etc. is 15 microns. Such a thickness affects the improvement of the energy density of solid-state batteries. Summary of the Invention

[0006] The object of the present invention is to overcome the shortcomings in the prior art and provide a composite current collector, a preparation method thereof, a negative electrode sheet and a solid-state battery.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A composite current collector includes a polymer layer and an alloy layer provided on at least one side of the polymer layer; the alloy layer is a CuNi alloy layer.

[0009] The CuNi alloy layer includes the following components in molar ratio: Cu 80-90%, Ni 10%-20%; preferably, the thickness of the CuNi alloy layer is 0.5 μm-2.5 μm.

[0010] Preferably, a transition layer is provided between the polymer layer and the alloy layer; preferably, the transition layer is one or a mixture of NiO, Al2O3, SiO2, TiO, Cr2O3, ZnO, SiC, Si3N4; preferably, the thickness of the transition layer is 10-100 nm.

[0011] A carbon-coated layer is provided on the outer surface of the CuNi alloy layer; preferably, the thickness of the carbon-coated layer is 0.5 μm-3 μm;

[0012] The carbon-coated layer includes a conductive agent and a binder; the mass ratio of the conductive agent to the binder is (1-3):1;

[0013] The conductive agent is one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, nano conductive agents, carbon nanofibers, flake graphite and graphene;

[0014] The binder is one or more of polyvinylidene fluoride or its modified binder, polyacrylic acid or its modified binder, isopropyl alcohol, modified acrylic resin, fluororubber, etc.

[0015] The present invention also includes a preparation method of the above composite current collector, and a CuNi alloy layer is prepared on the surface of the polymer layer by magnetron sputtering, pulse electroplating or direct current electroplating.

[0016] When preparing by magnetron sputtering, according to the designed molar ratio of Cu and Ni in the alloy layer, an alloy with the corresponding copper-nickel ratio is first prepared as the target for magnetron sputtering, and then a CuNi alloy layer with the required thickness is deposited on the surface of the polymer layer.

[0017] When using pulse electroplating or direct current electroplating, a seed layer is provided between the polymer layer and the alloy layer; preferably, a transition layer is first provided on the polymer surface, and then a seed layer is provided between the transition layer and the alloy layer.

[0018] The described seed layer includes one of Cu, Ni or CuNi alloy. Preferably, the thickness of the seed layer is 10 - 100 nm, and the preparation method of the seed layer is magnetron sputtering.

[0019] The present invention further includes a negative electrode sheet, which includes the composite current collector described above and a negative electrode active material layer disposed on the surface of the composite current collector.

[0020] The present invention further includes a solid-state battery, which includes the negative electrode sheet described above; the battery is a sulfide solid-state battery; the sulfide solid-state battery includes a positive electrode sheet, a negative electrode sheet, and a sulfide solid-state electrolyte membrane disposed between the positive electrode sheet and the negative electrode sheet.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] Since Cu will react with the sulfide solid-state electrolyte, resulting in the corrosion of the copper foil, the composite copper foil current collector used in traditional liquid batteries cannot be used in sulfide solid-state batteries. Currently, on sulfide solid-state batteries, stainless steel foil, nickel foil, etc. are used as negative current collectors. The thinnest mass-produced thickness of stainless steel foil is 15 μm, so the areal density is relatively high, which affects the improvement of the energy density of the solid-state battery; the price of electrolytic nickel foil is 1.5 - 3 times that of electrolytic copper foil. Therefore, using pure nickel foil will increase the battery cost. To solve the problem of copper foil being corroded by the electrolyte and avoid the influence of using stainless steel foil or electrolytic nickel foil on the energy density and cost of the battery, the present invention provides a composite current collector resistant to sulfide electrolyte corrosion, its preparation method, a negative electrode sheet, and a solid-state battery. A CuNi alloy layer is disposed on the surface of the polymer layer. The Ni element has excellent properties such as corrosion resistance and high-temperature resistance. The CuNi alloy can serve for a long time without being corroded in acidic, alkaline and other environments, and the price of nickel element is 124 yuan / kg. Compared with the prices of hundreds or thousands of yuan per gram of transition metals Ta, Pd, Ir, and Rh, the price of nickel metal is only one ten-thousandth to one-thousandth of these metals. Therefore, using a current collector with a CuNi alloy layer on the surface can achieve low cost, corrosion resistance, and long life at the same time, thereby ensuring the long-term service of the current collector in the sulfide solid-state battery, extending the battery life, and solving the problem of the sulfide solid-state electrolyte corroding the current collector when the traditional composite copper foil is used in the solid-state battery. At the same time, the structure of the composite current collector significantly improves the energy density of the battery compared with the currently used copper foil, stainless steel foil, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : Schematic diagram of the composite current collector of Example 1 of the present invention;

[0024] Figure 2 : Schematic diagram of the composite current collector of Example 6 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0026] Currently, copper foil and composite copper foil are commonly used as current collectors for lithium battery negative electrodes. To address corrosion issues, some battery manufacturers have experimented with using nickel foil or stainless steel foil. Using these commonly used current collectors as comparative examples and the composite current collector of the present invention as an example, we investigated the corrosion resistance of the current collector and its impact on battery energy density.

[0027] Comparative Example 1: 8μm copper foil, surface density 71.2g / m 2 Currently widely used in liquid battery products, it has good conductivity, but high surface density and poor corrosion resistance. Although 6μm or even 5μm copper foil can be used in liquid batteries, its poor corrosion resistance requires thicker current collectors in solid-state batteries to prevent corrosion that can cause short-term mechanical failure of the current collector, thereby preventing short-term battery failure.

[0028] Comparative Example 2: Using 316 stainless steel foil, the thinnest currently in mass production is 15 μm, with good corrosion resistance. However, due to processing difficulties, the thickness is much thicker than the current copper foil, thus affecting the energy density of the battery.

[0029] Comparative Example 3: 2+4.5+2μm composite copper foil, the middle layer is 4.5μm thick PET material, and both sides of the polymer layer are 2μm metal Cu. The composite copper foil surface density is 25.5g / m 2 , significantly lower than the surface density of 8μm copper foil, which can significantly increase the energy density of the entire battery. Currently widely used in liquid battery products, but its poor corrosion resistance makes it unsuitable for use in sulfide all-solid-state batteries. Although 1+4.5+1μm composite copper foil can be used in liquid batteries, due to the poor corrosion resistance of Cu, when used in solid-state batteries, a thicker metal layer is required to extend its service life.

[0030] In order to improve the energy density of all-solid-state batteries while ensuring that the current collector material is not corroded by the electrolyte and maintaining the mechanical properties of the current collector, a corrosion-resistant composite current collector is developed that takes into account the low surface density and corrosion resistance of the current collector, ensuring that the energy density of the all-solid-state battery is improved while the battery life is not shortened due to current collector failure.

[0031] Embodiment 1:

[0032] like Figure 1A composite current collector is shown, comprising a polymer layer 110 and an alloy layer 121 arranged on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; in this embodiment, the polymer layer 110 is PET with a thickness of 4.5 μm; the alloy layer 121 has a thickness of 2 μm, and the Cu content in the alloy layer is 80% and the Ni content is 20%.

[0033] The composite current collector is prepared in the following manner:

[0034] A CuNi alloy layer 121 is deposited on each side of the polymer layer 110 using magnetron sputtering. The Cu content of the CuNi alloy layer 121 is 80% and the Ni content is 20%. In this embodiment, a copper-nickel alloy with a molar ratio of Cu:Ni = 80:20 is used as the magnetron sputtering target. CuNi alloy layers 121 of a designed thickness are deposited on both surfaces of the polymer layer 110. The resulting CuNi alloy layer 121 has a composition of 80% Cu and 20% Ni.

[0035] Example 2

[0036] A composite current collector includes a polymer layer 110 and alloy layers 121 arranged on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; in this embodiment, the polymer layer 110 is PET with a thickness of 3μm, and the alloy layer 121 has a thickness of 2μm.

[0037] The composite current collector is prepared in the following manner:

[0038] 1) A seed layer is deposited on both sides of the polymer layer 110 by magnetron sputtering. The seed layer 120 is one of Cu, Ni or CuNi alloy, and its thickness is 10-100nm, specifically 10nm, 30nm, 40nm, 50nm, 100nm; in this embodiment, the seed layer 120 uses a Ni layer with a thickness of 40nm.

[0039] 2) CuNi alloy layers 121 are deposited on both sides of the seed layer away from the polymer layer, with a Cu content of 85% and a Ni content of 15%. The thickness of the CuNi alloy layer 121 is 2 μm.

[0040] The CuNi alloy layer was deposited by pulse electrochemical deposition. The electrolyte for CuNi pulse electrochemical deposition was 0.475Mol / L NiSO4·7H2O, 0.125Mol / L CuSO4·5H2O and 0.20Mol / L sodium citrate additive, with a pH of 9.0. Pulse electrodeposition was used with a peak current of 5A / dm 2 , the average current is 2A / dm 2, the pulse frequency is 100 Hz, the duty cycle is 10%, and finally the composition of the CuNi alloy layer 121 obtained is 85% Cu content; 15% Ni content.

[0041] Using the method of this embodiment, by upgrading PET to a thinner material, the thickness and areal density of the current collector decrease, and the energy density of the battery can be further improved. At the same time, the CuNi alloy layer is prepared by pulse electroplating, and the cost is lower than that of magnetron sputtering.

[0042] Example 3:

[0043] A composite current collector includes a polymer layer 110 and alloy layers 121 provided on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; in this embodiment, the polymer layer 110 is PET with a thickness of 4.5 μm; the alloy layer 121 has a thickness of 1.5 μm, and the Cu content in the alloy layer is 80% and the Ni content is 20%.

[0044] The composite current collector is prepared by the following method:

[0045] 1) Deposit a seed layer on both sides of the polymer layer 110. The deposition method is magnetron sputtering. The seed layer uses a Ni layer with a thickness of 40 nm.

[0046] 2) Deposit CuNi alloy layers 121 on both sides of the seed layer away from the polymer layer. The thickness of the CuNi alloy layer 121 is 1.5 μm.

[0047] The deposition method of the CuNi alloy layer is pulse electrochemistry deposition. The electrolyte for CuNi pulse electrochemistry deposition is 0.475 Mol / L NiSO4·7H2O, 0.125 Mol / L CuSO4·5H2O and 0.20 Mol / L sodium citrate additive, and the pH is 9.0. Pulse electroplating is used, the peak current is 20 A / dm 2 , the average current is 2 A / dm 2 , the pulse frequency is 100 Hz, the duty cycle is 10%, and finally the composition of the CuNi alloy layer 121 obtained is 80% Cu content; 20% Ni content.

[0048] Using the method of this embodiment, by thinning the alloy layer on the surface of the polymer layer, the thickness and areal density of the current collector decrease, and the energy density of the battery can be further improved.

[0049] Example 4

[0050] A composite current collector includes a polymer layer 110 and alloy layers 121 disposed on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; a transition layer is provided between the alloy layer and the polymer; in this embodiment, the polymer layer 110 is PET with a thickness of 4.5 μm; the alloy layer 121 has a thickness of 1.5 μm, the Cu content in the alloy layer is 80%, and the Ni content is 20%. The transition layer uses a NiO layer with a thickness of 40 nm;

[0051] The preparation method is as follows:

[0052] 1) Deposit a transition layer on each side of the polymer layer 110. The transition layer is one of NiO, Al2O3, SiO2, TiO, Cr2O3, ZnO, SiC, Si3N4, etc., with a thickness of 30 - 50 nm, specifically 30 nm, 40 nm, or 50 nm. The transition layer plays a connecting role between the polymer layer and the metal layer, enhancing the bonding strength between the polymer layer and the metal layer. In this embodiment, the NiO layer with a thickness of 40 nm is used as a preferred example for illustration.

[0053] 2) Use magnetron sputtering to deposit a CuNi alloy layer 121 on the side of the transition layer away from the polymer layer. The proportion of Cu in the CuNi alloy layer 121 is 80%, and the proportion of Ni is 20%. In this embodiment, an alloy with a copper - nickel ratio of Cu:Ni = 80:20 in molar ratio is used as the target for magnetron sputtering, and CuNi alloy layers 121 with a designed thickness are deposited on the two surfaces of the polymer layer 110. Finally, the composition of the obtained CuNi alloy layer 121 is 80% Cu content; 20% Ni content.

[0054] Example 5:

[0055] A composite current collector includes a polymer layer 110 and alloy layers 121 disposed on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; a transition layer is provided between the alloy layer and the polymer; in this embodiment, the polymer layer 110 is PET with a thickness of 4.5 μm, the alloy layer 121 has a thickness of 1.5 μm, the Cu content is 90%; the Ni content is 10%. The transition layer uses a NiO layer with a thickness of 40 nm;

[0056] The preparation method is as follows:

[0057] 1) Deposit a transition layer on each side of the polymer layer 110. In this embodiment, the NiO layer with a thickness of 40 nm is used as the transition layer.

[0058] 2) Deposit a seed layer on the surfaces of the transition layer away from the polymer layer on both sides. The deposition method is magnetron sputtering; in this embodiment, the Ni layer with a thickness of 40 nm is used as the seed layer.

[0059] 3) On both sides of the seed layer away from the polymer layer, CuNi alloy layers 121 are respectively deposited, and the thickness of the CuNi alloy layer 121 is 1.5 μm.

[0060] The deposition method of the CuNi alloy layer is direct current electrochemcial deposition. The electrolyte for CuNi direct current electrochemcial deposition is 0.5 Mol / L of NiSO4·7H2O, 0.1 Mol / L of CuSO4·5H2O, 0.35 Mol / L of sodium citrate, 0.001 Mol / L of trisodium citrate dihydrate additive, pH is 7.0, and the current is 3 A / dm 2 The obtained metal layer 121 has a composition of 80% Cu content and 20% Ni content.

[0061] Example 6:

[0062] Figure 2 A composite current collector is shown, including a polymer layer 110 and alloy layers provided on both sides of the polymer layer; the alloy layer is a CuNi alloy layer 121; a carbon-coated layer 122 is provided on one side of the alloy layer away from the polymer layer. The polymer layer is made of PET material with a thickness of 3 μm;

[0063] The preparation method is as follows:

[0064] 1) A seed layer 120 is deposited on both sides of the polymer layer 110. The seed layer is a magnetron sputtered Cu layer with a thickness of 50 nm;

[0065] 2) On both sides of the seed layer 120 away from the polymer layer, CuNi alloy layers 121 are respectively deposited, and the thickness of the CuNi alloy layer 121 is 1 μm.

[0066] The deposition method of the CuNi alloy layer is pulse electrochemcial deposition. The electrolyte for CuNi pulse electrochemcial deposition is 0.475 Mol / L of NiSO4·7H2O, 0.125 Mol / L of CuSO4·5H2O and 0.20 Mol / L of sodium citrate additive, pH is 9.0. Pulse electro-deposition is used, the peak current is 5 A / dm 2 and the average current is 2 A / dm 2 , the pulse frequency is 100 Hz, the duty cycle is 10%, and finally the obtained CuNi alloy layer 121 has a composition of 85% Cu content and 15% Ni content.

[0067] 3) On the outer side of the CuNi alloy layer 121 away from the seed layer, a carbon-coated layer 122 is prepared. The conductive agent material in the carbon-coated layer is graphene, and the binder is polyvinylidene fluoride. The mass ratio of the two is 2:1 (which can be adjusted to 1:1 or 3:1 at the same time. In this example, 2:1 is used as an exemplary illustration), and the thickness of the carbon-coated layer 122 is 1.5 μm.

[0068] The carbon-coated layer can not only increase the contact area between the active material and the current collector, reduce the interfacial resistance, but also physically isolate the sulfide electrolyte and the current collector to avoid the electrolyte from corroding the current collector.

[0069] Example 7:

[0070] A composite current collector includes a polymer layer 110 and alloy layers 121 provided on both sides of the polymer layer; the alloy layer is a CuNi alloy layer; in this example, the polymer layer 110 is PET with a thickness of 4.5 μm, the thickness of the alloy layer 121 is 2 μm, the Cu content is 95%; the Ni content is 5%.

[0071] The preparation method is as follows:

[0072] 1) Deposit a layer of CuNi alloy layer 121 on each side of the polymer layer 110, and the thickness of the CuNi alloy layer 121 is 2 μm.

[0073] Use magnetron sputtering to deposit a layer of CuNi alloy layer 121 on each side of the polymer layer 110. The proportion of Cu in the CuNi alloy layer 121 is 95%, and the proportion of Ni is 5%.

[0074] In this example, an alloy with a copper-nickel ratio of Cu:Ni = 95:5 in molar ratio is used as the target for magnetron sputtering, and a CuNi alloy layer 121 with a designed thickness is deposited on two surfaces of the polymer layer 110. Finally, the composition of the obtained CuNi alloy layer 121 is Cu content of 95%; Ni content of 5%.

[0075] Coat the current collectors of the above comparative examples and examples with an SiC negative electrode, match with a 9-series high-nickel positive electrode, use a sulfide electrolyte, assemble a soft-pack battery, and test the energy density of the battery.

[0076] For the test of the corrosion performance of the current collector, take the electrode sheet with both the negative electrode active material layer and the exposed current collector. In a drying room with a dew point of -50°C, evenly sprinkle the sulfide electrolyte powder on the negative electrode active material layer, and place it in the drying room for 48 h to observe whether the current collector is corroded. Table 1 shows the energy density and corrosion resistance results of different current collector batteries;

[0077] Table 1

[0078] <![CDATA[Areal density of current collector (g / m 2 )]]> Battery energy density (Wh / kg) Corrosion condition Comparative example 1 71.36 340.1 Corrosion Comparative example 2 119.70 326.4 No corrosion Comparative example 3 41.73 349.1 Corrosion Example 1 41.71 349.1 No corrosion Example 2 39.62 349.7 No corrosion Example 3 32.80 351.9 No corrosion Example 4 32.74 351.9 No corrosion Example 5 32.75 351.9 No corrosion Example 6 24.18 354.6 No corrosion Example 7 41.73 349.1 Corrosion

[0079] As can be seen from the above table: Compared with Example 1, in Comparative Examples 1-3, the copper foil in Comparative Example 1 is corroded, and the energy density is 9 Wh / kg lower than that in Example 1; in Comparative Example 2, the areal density of the current collector is too high, resulting in the energy density of the battery being 22.7 Wh / kg lower than that in Example 1; in Comparative Example 3, the energy density is relatively high, but the corrosion of the composite copper foil affects the service life of the battery.

[0080] Compared with Comparative Examples 1-3, the composite current collector with a CuNi alloy layer deposited on both surfaces of PET in Example 1 can meet the requirements of corrosion resistance and high energy density simultaneously. Compared with Example 1, in Example 2, by upgrading PET to a thinner material, the thickness and density of the current collector decrease, and the energy density of the battery is further increased by 0.6 Wh / kg. At the same time, pulse electroplating is used to prepare the CuNi alloy layer, and the cost is lower than that of magnetron sputtering. In Example 3, by reducing the thickness of the alloy layer, the areal density of the current collector decreases, and the energy density of the battery is further increased by 2.8 Wh / kg compared with Example 1. In Example 4, a transition layer is added, and the transition layer improves the adhesion between the alloy layer and the polymer layer; both of these two composite current collectors can also meet the requirements of corrosion resistance and high energy density. In Example 6, by preparing a carbon-coated layer on the surface of the composite current collector, the carbon-coated layer can physically isolate the contact between the sulfide electrolyte and the alloy layer on the surface of the composite current collector, so the thickness of the alloy layer can be reduced. Since the density of the carbon-coated layer is much lower than that of the alloy layer, the areal density of the composite carbon-coated current collector is further reduced to 24.18 g / m 2 , and the energy density of the battery is further increased to 354.6 Wh / kg, which is increased by 14.5 Wh / kg, 28.2 Wh / kg and 5.6 Wh / kg respectively compared with Comparative Examples 1-3, and the effect of corrosion resistance is achieved at the same time.

[0081] In Example 7, when the Ni content in the alloy layer of the composite current collector is too low, the energy density of the battery is normal, but the current collector is not corrosion-resistant, so it is not applicable.

[0082] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that, It includes a polymer layer and an alloy layer provided on at least one side of the polymer layer; the alloy layer is a CuNi alloy layer.

2. The composite current collector according to claim 1, wherein The CuNi alloy layer includes the following components in molar ratio: Cu 80 - 90%, Ni 10% - 20%; preferably, the thickness of the CuNi alloy layer is 0.5 μm - 2.5 μm.

3. The composite current collector according to claim 2, wherein A transition layer is provided between the polymer layer and the alloy layer; preferably, the transition layer is one or a mixture of NiO, Al2O3, SiO2, TiO, Cr2O3, ZnO, SiC, Si3N4; preferably, the thickness of the transition layer is 10 - 100 nm, preferably 30 - 50 nm.

4. The composite current collector according to any one of claims 1 to 3, characterized in that, A carbon-coated layer is provided on the outer surface of the CuNi alloy layer; preferably, the thickness of the carbon-coated layer is 0.5 μm - 3 μm; The carbon-coated layer includes a conductive agent and a binder; the mass ratio of the conductive agent to the binder is (1 - 3):1; The conductive agent is one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, nano conductive agents, carbon nanofibers, flake graphite, or graphene; The binder is one or more of polyvinylidene fluoride or its modified binder, polyacrylic acid or its modified binder, isopropyl alcohol, modified acrylic resin, fluororubber.

5. A method for preparing the composite current collector according to any one of claims 1-4, characterized in that, The CuNi alloy layer is prepared on the surface of the polymer layer by magnetron sputtering, pulsed electrodeposition, or direct current electrodeposition.

6. The preparation method of the composite current collector according to claim 5, wherein When prepared by magnetron sputtering, according to the designed molar ratio of Cu and Ni in the alloy layer, an alloy with the corresponding copper-nickel ratio is first prepared as the target for magnetron sputtering, and then a CuNi alloy layer with the required thickness is deposited on the surface of the polymer layer.

7. The preparation method of the composite current collector according to claim 5, wherein, When pulsed electrodeposition or direct current electrodeposition is used, a seed layer is provided between the polymer layer and the alloy layer; preferably, a seed layer is provided between the transition layer and the alloy layer.

8. The preparation method of the composite current collector according to claim 7, wherein The seed layer includes one of Cu, Ni, or CuNi alloy; preferably, the thickness of the seed layer is 10 - 100 nm, and the preparation method of the seed layer is magnetron sputtering.

9. A negative electrode sheet, characterized in that, It includes the composite current collector according to any one of claims 1 - 4 and a negative electrode active material layer provided on the surface of the composite current collector.

10. A solid-state battery, characterized in that, It includes the negative electrode sheet according to claim 9; the battery is a sulfide solid-state battery; the sulfide solid-state battery includes a positive electrode sheet, a negative electrode sheet, and a sulfide solid electrolyte membrane provided between the positive electrode sheet and the negative electrode sheet.

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