Composite current collector, preparation method therefor, and use thereof

Abstract

A composite current collector, a preparation method therefor, and a use thereof. The composite current collector comprises a polymer layer, and a conductive layer located on at least one side surface of the polymer layer. The conductive layer comprises at least one metal layer and at least one transition layer which are alternately stacked, and the material of the transition layer is an inorganic-organic hybrid material. When the composite current collector is used in a battery, the charging / discharging cycle performance and the safety performance of the battery can be significantly improved.

Description

Composite current collector and its preparation method and application Technical Field

[0001] The present application belongs to the field of battery technology and relates to a composite current collector and its preparation method and application. Background Art

[0002] At present, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation of this composite current collector usually adopts the method of physical vapor deposition (PVD) to deposit a layer of metal on a polymer film (such as polyester, polyolefin, etc.), thereby preparing a composite current collector with good conductivity. Compared with traditional current collectors, composite current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0003] There are two main issues with composite copper current collectors: ① Because the copper layer of composite copper current collectors is relatively thin and is continuously corroded by the electrolyte during the battery's charge and discharge cycles, its performance degrades significantly, resulting in poor battery charge and discharge cycle performance; ② Current composite current collectors primarily rely on the insulation and flame retardant properties of the intermediate layer, the polymer film layer, to improve battery safety. However, while this improves battery safety, the improvement is limited. Composite copper current collectors, in particular, do not significantly improve battery safety due to the structural limitations of the metal layer under current processes.

[0004] Therefore, in order to further improve the charge-discharge cycle and safety performance of batteries based on composite copper current collectors, it is necessary to develop a new composite copper current collector to promote the application and promotion of composite copper current collectors in batteries.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] In response to the above problems in the prior art, the present application aims to provide a composite current collector and its preparation method and application. The composite current collector of the present application is applied to batteries, which can significantly improve the charge-discharge cycle performance and safety performance of the batteries.

[0008] To achieve the above objectives, this application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a composite current collector, which includes a polymer layer and a conductive layer located on the surface of at least one side of the polymer layer; the conductive layer includes at least one metal layer and at least one transition layer alternately stacked, and the material of the transition layer is an inorganic-organic hybrid.

[0010] The present application creates a multilayer structure in which a transition layer and a metal layer are alternately arranged in the conductive layer of the composite current collector. Due to the material properties of the transition layer, it has good barrier and tolerance to the electrolyte, which can protect the metal layer, thereby promoting the improvement of the cycle charge and discharge performance of the battery based on the composite current collector. In addition, due to the inorganic-organic hybrid structure of the transition layer, it can achieve: 1. Blocking the penetration of metal layer grains; 2. Providing nucleation sites for the growth of metal grains in different layers, promoting the generation of grains with uniform particle size distribution and small size; the generated metal layer composed of non-penetrating, uniform particle size distribution and small size grains will produce microcracks after a certain deformation during the battery needle puncture process, and quickly spread to the surrounding area, causing large-scale fracture and fragmentation of the metal layer, thereby achieving separation of the metal layer from the steel needle, avoiding the formation of a closed circuit by the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0011] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. Through the following optional technical solutions, the technical objectives and beneficial effects of this application can be better achieved and realized.

[0012] In one embodiment, in the conductive layer, the inorganic-organic hybrid comprises at least one of basic chromium chromate, copper chromate, and copper chromite, and an organic acid-copper ion complex.

[0013] In one embodiment, in the conductive layer, the material of the metal layer includes at least one of copper and a copper alloy.

[0014] In one embodiment, the outermost layer of the conductive layer on the side closest to the polymer layer is a metal layer, and the outermost layer on the side away from the polymer layer is a transition layer. In this embodiment, the final transition layer can protect the prepared composite current collector and act as a protective layer to prevent it from oxidation.

[0015] In one embodiment, in the conductive layer, the number of metal layers is n, and the number of transition layers is n, where n is an integer greater than 2, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, and further, 5 ≤ n ≤ 15. If the number of metal layers is too large, the efficiency of preparing the composite current collector is too low, and if the number of metal layers is too small, the composite current collector has a poor effect on improving battery safety performance.

[0016] In one embodiment, the total thickness of the conductive layer is 500 nm - 2000 nm, such as 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm or 2000 nm, etc., and it is preferably 800 nm - 1200 nm. If the total thickness of the conductive layer is too thin, the conductivity of the composite current collector will be poor; if the total thickness of the conductive layer is too thick, it is not conducive to improving the energy density of the battery. Considering both good conductivity and the improvement of energy density, the total thickness of the conductive layer is selected within the above range.

[0017] In one embodiment, in the conductive layer, the single-layer thickness d1 of the metal layer satisfies: 0 < d1 ≤ 200 nm, such as 0.5 nm, 1 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm or 200 nm, etc., and the further preferred range is 50 ≤ d1 ≤ 150 nm. If the single-layer thickness of the metal layer is too thick, it is not conducive to improving the safety performance of the battery; if the single-layer thickness of the metal layer is too thin, it will affect the preparation efficiency of the composite current collector.

[0018] In one embodiment, in the conductive layer, the single-layer thickness d2 of the transition layer satisfies: 2 nm ≤ d2 ≤ 20 nm, such as 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 10 nm, 11 nm, 13 nm, 15 nm, 16 nm, 17 nm, 18 nm or 20 nm, etc., and the further preferred range is 5 ≤ d2 ≤ 20 nm. If the single-layer thickness of the transition layer is too thin, the improvement of battery performance is not obvious; if the single-layer thickness of the transition layer is too thick, it will affect the conductivity of the composite current collector.

[0019] In one embodiment, the material of the polymer layer includes at least one of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) or polyimide (PI). However, it is not limited to the above-listed substances, and other commonly used polymers in the art are also applicable to this application.

[0020] In one embodiment, the thickness of the polymer layer is 1 μm-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc. Taking into account the application requirements of the composite current collector and the difficulty and cost of the preparation process (such as biaxial stretching), the thickness of the polymer layer is selected within the above range.

[0021] In one embodiment, a primer layer is further provided between the polymer layer and the conductive layer.

[0022] In one embodiment, the primer layer comprises at least one of aluminum oxide, silicon oxide, titanium oxide, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide, or polyurethane. However, the primer layer is not limited to the aforementioned materials, and other common primer materials in the art are also suitable for use in this application.

[0023] In the present application, by providing a primer layer between the polymer layer and the conductive layer, the bonding force between the polymer layer and the conductive layer can be improved.

[0024] In a second aspect, the present application provides a method for preparing a composite current collector, comprising the following steps:

[0025] (1) providing a polymer film;

[0026] (2) Alternately forming at least one metal layer and at least one transition layer on the surface of the polymer film to obtain a composite current collector.

[0027] The method of the present application is simple and easy to implement and can be easily scaled up for production.

[0028] In one embodiment, the metal layer is prepared by at least one of electroplating, chemical plating or physical vapor deposition.

[0029] In one embodiment, the transition layer is prepared by using an in-situ dip coating method using a dip coating solution.

[0030] In one embodiment, the dipping solution includes chromic anhydride and an organic acid.

[0031] In one embodiment, in the dipping solution, the concentration of chromic anhydride is 0.2 g / L-1.0 g / L, such as 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L or 1.0 g / L; the concentration of the organic acid is 2 g / L-10 g / L, such as 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L or 10 g / L.

[0032] In one embodiment, the organic acid substance includes at least one of sodium gluconate, diacetone-D-glucose, sodium citrate, β-D-glucose pentaacetate, 5-thio-D-glucose, sodium lactobionate, glucaric acid, sodium chromotropic acid, sodium hyaluronate, lithium D-xylonic acid, lithium 2-deoxy-D-ribonate, lithium gluconate, lithium citrate, or lithium tartrate, and may further optionally include a lithium salt containing an organic acid. The lithium salt containing an organic acid can replenish lithium salt to the battery system during the battery's charge and discharge cycle, thereby improving the battery's cycle performance.

[0033] In one embodiment, the lithium salt containing an organic acid includes at least one of lithium D-xylonate, lithium 2-deoxy-D-ribonate, lithium gluconate, lithium citrate, or lithium tartrate.

[0034] In one embodiment, the organic acid material comprises at least two materials, including a lithium salt containing an organic acid. In this embodiment, the improvement in battery cycling performance and charge-discharge performance is more significant, which is caused by the change in the transition layer structure and its change in the structure of the adjacent metal layer.

[0035] In one embodiment, the in-situ dip coating method comprises the following steps: placing the polymer film in a dip coating solution for dip coating, and after the dip coating is completed, squeezing out the liquid, and drying.

[0036] In one embodiment, the dipping time is 5s-150s, for example, 5s, 8s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s, 120s, 125s, 130s, 135s, 140s or 150s, etc.

[0037] In one embodiment, the drying method is oven drying, and the oven drying temperature is 50°C-80°C, such as 50°C, 55°C, 65°C, 70°C, 75°C or 80°C.

[0038] In one embodiment, the polymer film is prepared by a melt-extrusion-biaxial stretching method.

[0039] As an optional technical solution for the preparation method of the composite current collector described in the present application, the method further includes preparing a base layer on the surface of the polymer film, and the polymer film with the base layer on the surface is used for the preparation of step (2).

[0040] In one embodiment, the preparation method of the primer layer includes at least one of magnetron sputtering, evaporation or coating.

[0041] In a third aspect, the present application provides a battery, comprising the composite current collector described in the first aspect.

[0042] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0043] Compared with the existing technology, this application has the following beneficial effects:

[0044] (1) The present application proposes a new composite current collector, which comprises a multilayer structure in which transition layers and metal layers are alternately arranged. Due to the material properties of the transition layer and the unique conductive layer structure, the cycle charge and discharge performance and safety performance of the battery based on the composite copper current collector can be improved. Moreover, the last layer of the conductive layer is set as a transition layer, which can protect the prepared composite current collector and prevent it from being oxidized.

[0045] (2) The preparation method of the present application is simple and easy to implement and can be easily scaled up for production.

[0046] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0048] FIG1 is a schematic structural diagram of a composite current collector provided in one embodiment of the present application. DETAILED DESCRIPTION

[0049] The technical solution of the present application will be further explained below with reference to the accompanying drawings and through specific implementation methods.

[0050] The specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0051] Example 1

[0052] This embodiment provides a composite current collector, a structural schematic diagram of which is shown in Figure 1, comprising a first conductive layer 1, a first primer layer 2, a polymer layer 3, a second primer layer 4 and a second conductive layer 5 stacked in sequence; wherein, the first conductive layer 1 is 10 layers of copper layers (single layer thickness is 100 nm) and 10 layers of transition layers (single layer thickness is 5 nm) alternately stacked, wherein the first conductive layer 1 is in contact with the first primer layer 2 through the copper layer, the first primer layer 2 is a 5nm thick nickel-chromium alloy, the polymer layer 3 is a 4.5μm thick polyethylene terephthalate (PET), the second primer layer 4 is a 5nm thick nickel-chromium alloy, and the second conductive layer 5 is 10 layers of copper layers (single layer thickness is 100 nm) and 10 layers of transition layers (single layer thickness is 5 nm) alternately stacked, wherein the second conductive layer 5 is in contact with the second primer layer 4 through the copper layer.

[0053] The preparation method of the composite current collector provided in this embodiment includes the following steps:

[0054] First, a base layer was prepared. A biaxially oriented PET film with a thickness of 4.5 μm was placed in a magnetron sputtering machine. A nickel-chromium alloy target was used as the target material to deposit a 5 nm layer of base layer on each side of the PET film. The specific process conditions were: a nickel-chromium alloy target (purity: 99.99%) was used as the target material, a target power of 5.0 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.08 Pa, a coating time of 1 s, and a temperature of the main roller of 2°C during the coating process. Thus, a PET composite film with a surface containing a base layer was prepared.

[0055] Secondly, a conductive layer was prepared. The PET composite film with a base layer prepared above was placed in a magnetron sputtering machine, and a metal layer and a transition layer were sequentially deposited on the surface of the composite film, wherein: ① The metal layer was a copper layer with a thickness of 100 nm and 10 layers. The preparation conditions for each layer were: a copper target (purity: 99.99%) was used as the target material, a target power of 12 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.08 Pa, a coating time of 10 s, and a coating process of 10 s. The temperature of the main roller during the process is 2°C; ② The transition layer is basic chromium chromate, (Cr(OH)CrO4), copper chromate (CuCrO4), copper chromite (CuCr2O4) and D-xylonate lithium-copper complex, with a thickness of 5nm and 10 layers. The preparation conditions of each layer are: prepared by in-situ dip coating. The specific process is: after the metal layer is prepared, the composite film is placed in a dip coating solution, the solute components of the dip coating solution are 0.5g / L chromic anhydride and 5g / L D-xylonate lithium, the solvent is water, and the dip coating time is 25s. After the dip coating is completed, the liquid is squeezed out and then placed in a 60°C oven for drying to prepare a conductive layer with a thickness of 1050nm, that is, a composite copper current collector is obtained.

[0056] Example 2

[0057] The method is basically the same as Example 1, except that the lithium D-xylonic acid in the dipping solution during the preparation of the transition layer is replaced by lithium gluconate.

[0058] Example 3

[0059] The method is basically the same as Example 1, except that the lithium D-xylonic acid in the dipping solution during the preparation of the transition layer is replaced by sodium lactobionate.

[0060] Example 4

[0061] The method is basically the same as Example 1, except that the lithium D-xylonate in the dipping solution during the preparation of the transition layer is replaced with diacetone-D-glucose.

[0062] Example 5

[0063] The method is basically the same as Example 1, except that the lithium D-xylonic acid in the dipping solution during the preparation of the transition layer is replaced with glucaric acid.

[0064] Example 6

[0065] The method is basically the same as Example 1, except that the lithium D-xylonate in the dipping solution during the preparation of the transition layer is replaced by a mixture of lithium D-xylonate and lithium gluconate, and the mass ratio of the two is 1:1.

[0066] Example 7

[0067] The method is basically the same as Example 1, except that the lithium D-xylonate in the dipping solution during the preparation of the transition layer is replaced by a mixture of lithium D-xylonate and sodium lactobionate, and the mass ratio of the two is 1:1.

[0068] Example 8

[0069] The method is basically the same as Example 1, except that the lithium D-xylonate in the dipping solution during the preparation of the transition layer is replaced by a mixture of lithium D-xylonate and sodium hyaluronate, and the mass ratio of the two is 1:1.

[0070] Example 9

[0071] It is basically the same as Example 1, except that: the single layer thickness of the metal layer is 50nm, the preparation conditions are: copper target (purity: 99.99%) is used as the target material, the target power is 12kW, the argon flow rate is 50mL / min, the coating vacuum is 0.08Pa, the coating time is 5s, and the temperature of the main roller during the coating process is 2°C.

[0072] Example 10

[0073] It is basically the same as Example 1, except that: the single layer thickness of the metal layer is 150nm, the preparation conditions are: copper target (purity: 99.99%) is used as the target material, the target power is 12kW, the argon flow rate is 50mL / min, the coating vacuum is 0.08Pa, the coating time is 15s, and the temperature of the main roller during the coating process is 2°C.

[0074] Example 11

[0075] It is basically the same as Example 1, except that: the single layer thickness of the metal layer is 200nm, the preparation conditions are: copper target (purity: 99.99%) is used as the target material, the target power is 12kW, the argon flow rate is 50mL / min, the coating vacuum is 0.08Pa, the coating time is 20s, and the temperature of the main roller during the coating process is 2°C.

[0076] Example 12

[0077] The method is basically the same as Example 1, except that the single layer thickness of the transition layer is 2 nm, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic anhydride and 5 g / L lithium D-xylonate as the solute components, and the solvent is water. The dipping time is 10 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0078] Example 13

[0079] The method is basically the same as Example 1, except that the single layer thickness of the transition layer is 10 nm, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic anhydride and 5 g / L lithium D-xylonate as the solute components, and the solvent is water. The dipping time is 50 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0080] Example 14

[0081] The method is basically the same as Example 1, except that the single layer thickness of the transition layer is 20 nm, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic anhydride and 5 g / L lithium D-xylonate as the solute components, and the solvent is water. The dipping time is 100 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0082] Example 15

[0083] The embodiment is basically the same as that in Example 1, except that the number of metal layers and transition layers in the conductive layer is 5.

[0084] Example 16

[0085] The embodiment is basically the same as that in Example 1, except that the number of metal layers and transition layers in the conductive layer is 15.

[0086] Example 17

[0087] It is basically the same as Example 11, except that the number of metal layers and transition layers in the conductive layer are both 3.

[0088] Example 18

[0089] Basically the same as Example 11, except that the PET film is replaced by a PP film.

[0090] Example 19

[0091] The method is basically the same as Example 1, except that the transition layer is a mixture of basic chromium chromate and lithium D-xylonate-copper complex, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic acid, 5 g / L lithium D-xylonate as the solute component, and water as the solvent. The pH of the solution is adjusted to 3, and the dipping time is 25 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0092] Example 20

[0093] The method is basically the same as Example 1, except that the transition layer is a mixture of copper chromate and lithium D-xylonate-copper complex, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic acid, 5 g / L lithium D-xylonate, and 1 g / L copper sulfate as the solute components, and the solvent is water. The pH of the solution is adjusted to 6, and the dipping time is 25 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0094] Example 21

[0095] The method is basically the same as Example 1, except that the transition layer is a mixture of copper chromite and lithium D-xylonate-copper complex, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L copper chromite, 5 g / L lithium D-xylonate, 1 g / L copper sulfate, and 5 g / L sulfuric acid. The solvent is water, and the dipping time is 25 s. After the dipping is completed, the liquid is removed by squeezing, and then the membrane is dried in an oven at 60°C.

[0096] Comparative Example 1

[0097] It is basically the same as Example 1, except that: the conductive layer does not contain a transition layer, that is, the metal layer is one layer, the thickness of the metal layer is 1000 nm, and the preparation conditions are: using a copper target (purity: 99.99%) as the target material, the target power is 12 kW, the argon flow rate is 50 mL / min, the coating vacuum is 0.08 Pa, the coating time is 100 s, and the temperature of the main roller during the coating process is 2°C.

[0098] Comparative Example 2

[0099] The embodiment is basically the same as that in Example 1, except that the number of metal layers and transition layers in the conductive layer are both 2.

[0100] Comparative Example 3

[0101] It is basically the same as Example 1, except that: the thickness of the metal layer is 220nm, the preparation conditions are: using a copper target (purity: 99.99%) as the target material, the target power is 12kW, the argon flow rate is 50mL / min, the coating vacuum is 0.08Pa, the coating time is 22s, and the temperature of the main roller during the coating process is 2°C.

[0102] Comparative Example 4

[0103] The same as Example 1, except that the thickness of the transition layer is 1 nm, and the preparation conditions are as follows: after the metal layer is prepared, the composite membrane is placed in a dipping solution containing 0.5 g / L chromic anhydride and 5 g / L lithium D-xylonate as the solute components, and the solvent is water. The dipping time is 5 s. After the dipping is completed, the liquid is squeezed out and then placed in a 60°C oven for drying.

[0104] Test evaluation:

[0105] Here, the charge-discharge cycle performance and safety performance of the battery assembled with the prepared composite current collector are tested. The specific test methods are as follows:

[0106] ①Battery assembly: For the positive electrode, the positive electrode current collector uses a traditional aluminum current collector (thickness is 13 microns), and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622); for the negative electrode: the negative electrode current collector adopts the composite copper current collector prepared in this application, and the negative electrode material adopts artificial graphite; for the diaphragm, a polyethylene diaphragm coated with alumina ceramic (thickness of 25 microns) is adopted; for the electrolyte, 1 mol·L -1 A carbonate solution of LiPF6, wherein the carbonates are propylene carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1; the above materials are used to assemble a lithium-ion battery according to the relevant process.

[0107] ② Charge and discharge cycle performance: The battery is charged and discharged 2000 times at a charge and discharge rate of 1C, and the battery capacity retention rate after 2000 cycles is recorded, that is, the battery capacity after 2000 cycles / the initial capacity of the battery × 100%.

[0108] ③ Safety performance test: A needle puncture test is used to verify the safety performance of the battery, as follows: 100 batteries prepared as described above are taken and placed in a needle puncture test device, wherein the diameter of the steel needle is 3 mm and the puncture speed is 10 mm / s. The battery passes if it does not explode, catch fire, or emit smoke during the puncture process, otherwise it fails. The number of batteries that pass and fail is recorded, and the battery puncture pass rate can be obtained, that is, the number of batteries that pass / the total number of batteries × 100%.

[0109] The test results are shown in Table 1.

[0110] Table 1

[0111] From the table above we can see that:

[0112] ① It can be seen from Examples 1-17 and Comparative Example 1 that compared with the traditional composite copper current collector, due to the introduction of the transition layer, the prepared composite current collector can improve the capacity retention rate and needle puncture rate of the battery, that is, improve the cycle charge and discharge performance and safety performance of the battery.

[0113] ② From Examples 1-8, it can be seen that during the preparation of the transition layer, the composite copper current collector prepared with a lithium salt containing an organic acid in the dipping solution significantly improves the battery's capacity retention, that is, it significantly improves the battery's cyclic charge and discharge performance. This is because the introduction of a lithium salt containing an organic acid into the transition layer can replenish lithium ions during the battery's cyclic charge and discharge process, thereby improving the battery's cyclic charge and discharge performance. Moreover, during the preparation of the transition layer, the inclusion of two combinations of organic acid substances in the dipping solution significantly improves the battery's cyclic performance and charge and discharge performance. This is due to the changes in the transition layer structure and the changes it causes to the adjacent metal layer structure.

[0114] ③ From Examples 1, 9-11, and Comparative Example 3, it can be seen that increasing the thickness of the metal layer leads to an increase in the cyclic charge-discharge performance and safety performance of the battery based on the composite copper current collector, followed by a decrease. This may be because changes in the thickness of the metal layer affect the normal particle size of the metal layer's grains, which in turn affects the fracture behavior of the metal layer during needle penetration, resulting in changes in safety performance. At the same time, changes in the normal particle size of the grains also affect the resistance to current flow during the battery's charge and discharge process, thereby affecting the battery's cyclic charge-discharge performance.

[0115] ④ From Examples 1, 12-14 and Comparative Example 4, it can be seen that by increasing the thickness of the transition layer, the cyclic charge and discharge performance of the battery based on the composite copper current collector shows an improving trend. This may be because increasing the thickness of the transition layer can improve the barrier and tolerance of the transition layer to the electrolyte, thereby promoting the improvement of the cyclic charge and discharge performance of the battery based on the composite copper current collector. Increasing the thickness of the transition layer also shows an improving trend in the safety performance of the battery based on the composite copper current collector. This may be because increasing the thickness of the transition layer can promote large-scale fission of the conductive layer during the needle puncture process, causing the conductive layer to be more easily disconnected from the steel needle, thereby promoting the improvement of the safety performance of the battery based on the composite copper current collector.

[0116] ⑤ From Examples 1, 15-17 and Comparative Examples 1 and 2, it can be seen that increasing the number of metal layers and transition layers improves the cyclic charge-discharge performance and safety performance of batteries based on composite copper current collectors. This may be because increasing the number of layers can, on the one hand, improve the multi-layer alternating structure of transition layers and metal layers, promote layer-by-layer protection of the metal layers, and thus promote the improvement of battery cyclic charge-discharge performance; on the other hand, increasing the number of layers can promote large-scale fission of the conductive layer during the needle puncture process, causing the conductive layer to be more easily disconnected from the steel needle, thereby promoting the improvement of the safety performance of batteries based on this composite copper current collector.

[0117] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed methods of the present application, the present application is not limited to the above-mentioned detailed methods, which does not mean that the present application must rely on the above-mentioned detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A composite current collector, comprising a polymer layer and a conductive layer located on at least one surface of the polymer layer; The conductive layer includes at least one metal layer and at least one transition layer that are alternately laminated, and the material of the transition layer is an inorganic-organic hybrid.

2. The composite current collector according to claim 1, wherein, In the conductive layer, the inorganic-organic hybrid includes at least one of basic chromium chromate, copper chromate, and cuprous chromite, and an organic acid-copper ion complex.

3. The composite current collector according to claim 1 or 2, wherein In the conductive layer, the material of the metal layer includes at least one of copper and copper alloys; Optionally, in the conductive layer, the outermost layer close to the polymer layer is a metal layer, and the outermost layer far from the polymer layer is a transition layer; Optionally, in the conductive layer, the number of metal layers is n, and the number of transition layers is n, where n is an integer greater than 2, and further optionally 5 ≤ n ≤ 15; Optionally, the total thickness of the conductive layer is 500 nm - 2000 nm, and further optionally 800 nm - 1200 nm; Optionally, in the conductive layer, the single-layer thickness d1 of the metal layer satisfies: 0 < d1 ≤ 200 nm, and the further optional range is 50 ≤ d1 ≤ 150 nm; Optionally, in the conductive layer, the single-layer thickness d2 of the transition layer satisfies: 2 nm ≤ d2 ≤ 20 nm, and the further optional range is 5 ≤ d2 ≤ 20 nm.

4. The composite current collector according to any one of claims 1-3, wherein, The material of the polymer layer includes at least one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polystyrene, or polyimide; Optionally, the thickness of the polymer layer is 1 μm - 10 μm.

5. The composite current collector according to any one of claims 1-4, wherein, An underlayer is further provided between the polymer layer and the conductive layer; Optionally, the material of the underlayer includes at least one of alumina, silica, titania, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide, or polyurethane.

6. A method for preparing a composite current collector according to any one of claims 1 - 5, comprising the following steps: (1) Provide a polymer film; (2) Alternately form at least one metal layer and at least one transition layer on the surface of the polymer film to obtain a composite current collector.

7. The method for preparing the composite current collector according to claim 6, wherein, The metal layer is prepared by at least one of electroplating, electroless plating, or physical vapor deposition; Optionally, the transition layer is prepared by an in-situ dip coating method using a dip coating solution; Optionally, the dip coating solution includes chromic anhydride and organic acid substances; Optionally, in the dip coating solution, the concentration of chromic anhydride is 0.2 g / L - 1.0 g / L, and the concentration of organic acid substances is 2 g / L - 10 g / L; Optionally, the organic acid substances include at least one of sodium gluconate, diacetone-D-glucose, sodium citrate, β-D-glucose pentaacetate, 5-thio-D-glucose, sodium lactobionate, glucaric acid, sodium chromotropate, sodium hyaluronate, lithium D-xylonate, lithium 2-deoxy-D-ribonate, lithium gluconate, lithium citrate, or lithium tartrate, and further optionally include lithium salts containing organic acids; Optionally, the lithium salt containing an organic acid includes at least one of lithium D-xylonate, lithium 2-deoxy-D-ribonate, lithium gluconate, lithium citrate, or lithium tartrate; Optionally, the organic acid substances include at least two substances and include a lithium salt containing an organic acid.

8. The method for preparing a composite current collector according to claim 6 or 7, wherein, The method of in-situ dip coating includes the following steps: placing the polymer film in a dip coating solution for dip coating, after the dip coating is completed, squeezing out the liquid, and drying; Optionally, the time of dip coating is 5 s - 150 s; Optionally, the drying method is drying by baking, and the baking temperature is 50°C - 80°C.

9. The preparation method of the composite current collector according to any one of claims 6-8, wherein, The method further includes preparing a primer layer on the surface of the polymer film, and applying the polymer film with the primer layer on the surface to the preparation in step (2); Optionally, the preparation method of the primer layer includes at least one of magnetron sputtering, evaporation coating, or coating.

10. A battery comprising the composite current collector according to any one of claims 1 - 5.

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