Composite current collector, method for preparing the same and application thereof in a negative electrode-free lithium metal battery

Abstract

The application provides a composite current collector, a preparation method thereof and application of the composite current collector in a negative electrode-free lithium metal battery, and belongs to the technical field of battery materials. The composite current collector comprises a polymer support layer and a carbon-based composite material active layer arranged on at least one side surface of the polymer support layer; and the material in the carbon-based composite material active layer comprises carbon nanomaterial and fluorine-containing polymer material. The application takes the polymer support layer as a base material, prepares the carbon-based composite material active layer on at least one side surface of the base material, and obtains the composite current collector. Due to the introduction of the support layer and the synergistic cooperation of the carbon nanomaterial and the fluorine-containing polymer material, the mechanical property of the composite current collector is effectively improved, and the generation of defects in the battery processing and cycling process is avoided. The charge-discharge cycling performance of the negative electrode-free lithium metal battery prepared based on the composite current collector is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a composite current collector, a preparation method thereof and application of the composite current collector in a no-negative-electrode lithium metal battery. BACKGROUND

[0002] At present, lithium metal batteries, which are known for high energy density, continue to attract attention as a promising next-generation advanced energy storage technology. In particular, no-negative-electrode lithium metal batteries, which do not use initial negative active materials, can push the energy density of the full battery to the extreme, exceeding 450 Wh·kg -1 , which is considered the ultimate choice for high-energy-density lithium metal batteries. The application of a composite current collector to a no-negative-electrode lithium metal battery can further highlight the advantages of high energy density of the no-negative-electrode lithium metal battery. For a no-negative-electrode lithium metal battery, copper foil is used as a current collector. The current collector is easily corroded by air and electrolyte, resulting in unstable SEI film. In addition, the surface of the current collector is lithium-phobic, which easily leads to uneven lithium metal deposition during charging, resulting in lithium dendrites and continuous accumulation of dead lithium. The unstable SEI film and the continuous accumulation of dead lithium formed above will cause the cycle performance of the battery to deteriorate. In order to solve this problem, people began to use carbon-based current collectors to replace traditional copper foil.

[0003] However, the existing carbon-based current collector has the problem of poor mechanical properties, which leads to defects in the battery processing and charging and discharging cycles, resulting in poor charging and discharging performance of the prepared battery.

[0004] Therefore, how to solve the problems of poor mechanical properties, poor processing performance of the current collector used in the no-negative-electrode lithium metal battery, and poor charging and discharging cycle performance of the prepared battery is the focus of current research. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a composite current collector, a preparation method thereof and application of the composite current collector in a no-negative-electrode lithium metal battery. The present application takes a polymer support layer as a base material, and prepares a carbon-based composite material active layer on at least one side surface thereof to obtain a composite current collector. Due to the introduction of the support layer and the synergistic cooperation of the carbon nanomaterial and the fluorine-containing polymer material, the mechanical properties of the composite current collector are effectively improved, and the generation of defects in the battery processing and cycle process is avoided. The charging and discharging cycle performance of the no-negative-electrode lithium metal battery prepared based on the composite current collector is significantly improved.

[0006] To achieve the purpose of the present application, the following technical solutions are adopted:

[0007] In a first aspect, the present application provides a composite current collector, which comprises a polymer support layer, and a carbon-based composite material active layer arranged on at least one side surface of the polymer support layer.

[0008] The material in the carbon-based composite active layer includes carbon nanomaterial and fluorine-containing polymer material.

[0009] The present application takes a polymer support layer as a substrate, and a carbon-based composite active layer is prepared on at least one side surface of the substrate to obtain a composite current collector. Due to the introduction of the support layer and the synergistic effect of the carbon nanomaterial and the fluorine-containing polymer material, the mechanical properties of the composite current collector are effectively improved, and the generation of defects in the battery processing and cycling process is avoided. The charge-discharge cycling performance of the anode-free lithium metal battery based on the composite current collector is significantly improved.

[0010] In the present application, the carbon nanomaterial serves as a conductor, the fluorine-containing polymer material serves as a binder for the carbon nanomaterial, provides flexibility, and can create a lower Fermi level for the active layer, create a lithium-friendly surface, and provide a fluorine source for the formation of an SEI film, thereby forming a fluorine-containing SEI film with a lower Fermi level, a lithium-friendly surface, and a lower Fermi level SEI film that together hinders the transfer of electrons to the electrolyte to reduce the electrolyte, realizes the compatibility and stability of the composite current collector and the electrolyte interface, and improves the performance of the battery. Moreover, the formed fluorine-containing SEI film can promote the uniform passage of lithium ions and uniform deposition on the surface of the composite current collector, inhibit the generation of dendrites, and improve the performance of the battery. The carbon nanomaterial and the fluorine-containing polymer material synergistically cooperate to form a carbon-based composite active layer with good conductivity and a more stable structure, and form a stable SEI film during the battery cycling and discharging process, ensuring the stability of the cycling performance.

[0011] As a preferred technical solution of the present application, the thickness of the polymer support layer is 1-10 μm, for example, it can be 1 μm, 3 μm, 5 μm, 7 μm or 9 μm, etc.

[0012] In the present application, considering the application requirements of the composite current collector, the difficulty and cost of the preparation process are also taken into account, and the thickness of the polymer film support layer is limited to 1-10 μm.

[0013] Preferably, the material of the polymer support layer includes any 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), or a combination of at least two of them.

[0014] As a preferred technical solution of the present application, the carbon nanomaterials include any one or a combination of at least two of graphene, carbon nanotubes, carbon nanofibers, or multi-layer graphene-nanodiamond composite materials.

[0015] Preferably, the fluorine-containing polymer material includes any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, poly(vinylidene fluoride-co-hexafluoropropylene), or ethylene-tetrafluoroethylene copolymer.

[0016] Preferably, the mass ratio of the carbon nanomaterials and the fluorine-containing polymer material is 1:(0.1-10), which may be 1:0.1, 1:0.5, 1:1, 1:3, 1:5, 1:7, or 1:9, etc.

[0017] In the present application, if the mass ratio of the carbon nanomaterials and the fluorine-containing polymer material is too small, the prepared active layer has poor conductivity, resulting in poor cycle charge-discharge performance of the battery prepared therefrom; if the mass ratio of the carbon nanomaterials and the fluorine-containing polymer material is too large, the prepared active layer has poor structural stability, and cannot form a surface with a lower Fermi level and SEI film, resulting in poor cycle charge-discharge performance of the battery prepared therefrom. As a preferred technical solution of the present application, the carbon nanomaterials include any one of a combination of graphene and carbon nanotubes, a combination of graphene and carbon nanofibers, a combination of multi-layer graphene-nanodiamond composite material and carbon nanotubes, or a combination of multi-layer graphene-nanodiamond composite material and carbon nanofibers.

[0018] In the present application, the combination of the above materials can form a conductive network, improving the conductivity and mechanical properties.

[0019] Preferably, the mass ratio of the carbon nanomaterials and the fluorine-containing polymer material is 1:(1-8), which may be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8, etc.

[0020] As a preferred technical solution of the present application, the thickness of the single-sided carbon-based composite material active layer is ≥1 μm, which may be 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 20 μm, 25 μm, or 30 μm, etc., preferably 5-15 μm.

[0021] In the present application, if the thickness of the single-sided carbon-based composite material active layer is too thin, the resistance is high, which may result in reduced charge-discharge cycle performance of the battery.

[0022] In the present application, considering the performance and energy density of the battery, the thickness of the single-sided carbon-based composite material active layer is preferably 5-15 μm.

[0023] In a second aspect, the present application provides a preparation method of the composite current collector as described in the first aspect, and the preparation method comprises the following steps:

[0024] (1) preparing a coating solution of the carbon-based composite material active layer;

[0025] (2) coating the coating solution on at least one side surface of the polymer support layer, drying, and then hot pressing to obtain the composite current collector.

[0026] The present application does not limit the preparation method of the polymer support layer, and examples include a melt-extrusion-biaxial stretching method.

[0027] As a preferred technical solution of the present application, the preparation method of the coating solution in step (1) comprises:

[0028] mixing the carbon nanomaterial, the fluorine-containing polymer material, and the organic solvent to obtain the coating solution.

[0029] The present application does not limit the type of the organic solvent, and examples include N-methylpyrrolidone, dichloromethane, N,N-dimethylformamide, or N,N-dimethylacetamide, etc.

[0030] Preferably, the solid content of the coating solution is 5-30%, for example, 5%, 10%, 15%, 20%, 25%, or 30%, etc.

[0031] Preferably, the temperature of the mixing is 40-90℃, for example, 40℃, 50℃, 60℃, 70℃, 80℃, or 90℃, etc.

[0032] As a preferred technical solution of the present application, the coating method in step (2) comprises a coating method.

[0033] Preferably, the temperature of the drying in step (2) is 50-100℃, for example, 50℃, 60℃, 70℃, 80℃, 90℃, or 100℃, etc.

[0034] In the present application, due to the swelling effect of the solvent on the polymer support layer during the drying process, the polymer support layer and the active layer can be closely attached to each other, thereby improving the adhesion.

[0035] Preferably, the temperature of the hot pressing in step (2) is 50-120℃, for example, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, or 120℃, etc., the pressure is 0.1-1MPa, for example, 0.1MPa, 0.3MPa, 0.5MPa, 0.7MPa, or 0.9MPa, etc., and the time is 5-60s, for example, 5s, 10s, 20s, 30s, 40s, 50s, or 60s, etc.

[0036] In the present application, if the temperature, pressure or time of hot pressing is too high, it is easy to cause film breakage, and the compaction degree is too high, the porosity of the active layer material is low, which is not conducive to the embedding and deposition of lithium ions; if the temperature, pressure or time of hot pressing is too low, it will cause the combination of the active layer and the polymer support layer to be not firm, easy to fall off, poor mechanical properties, leading to poor cycle performance of the battery.

[0037] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0038] (1) adding carbon nanomaterial into an organic solvent and uniformly dispersing by ultrasonic with a power of 200-1000W, then adding fluoropolymer material and mixing by heating to 40-90℃ to obtain a coating liquid;

[0039] (2) coating the above-mentioned coating liquid on at least one side surface of the polymer support layer by using a slit extrusion coating or doctor blade coating device, then drying in an oven at 50-100℃, and then placing the dried sample in a hot roller pressing device for hot roller pressing, the hot pressing conditions are: temperature of 50-120℃, pressure of 0.2-1.0MPa, and hot pressing time of 5-60s, and the composite current collector is obtained after hot pressing.

[0040] In a third aspect, the present application provides a use of the composite current collector according to the first aspect in a negative electrode-free lithium metal battery.

[0041] The numerical range of the present application includes not only the point values listed above, but also any point values between the above-mentioned numerical ranges, which are not listed due to space limitations and for the sake of simplicity. The present application does not list the specific point values included in the range.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] (1) The present application uses a polymer support layer as a substrate to prepare a carbon-based composite material active layer on at least one side surface of the support layer to obtain a composite current collector. Due to the introduction of the support layer and the synergistic effect of the carbon nanomaterial and the fluoropolymer material, the mechanical properties of the composite current collector are effectively improved, and the generation of defects during the processing and cycling of the battery is avoided. The charge-discharge cycle performance of the negative electrode-free lithium metal battery based on the composite current collector is significantly improved.

[0044] (2) The preparation method provided by the present application is simple and easy to operate, and is suitable for large-scale promotion. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 FIG. 1 is a schematic diagram of the structure of the composite current collector prepared in Example 1 of the present application.

[0046] 1-polymer support layer, 21-first carbon-based composite active layer; 22-second carbon-based composite active layer; 2-active layer. DETAILED DESCRIPTION

[0047] The technical solutions of the present application are further illustrated below by means of specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0048] Embodiment 1

[0049] This embodiment provides a composite current collector, a schematic structural diagram of which is shown in Figure 1 The composite current collector includes a polymer support layer 1 and an active layer 2 arranged on both sides of the polymer support layer 1, which are a first carbon-based composite active layer 21 and a second carbon-based composite active layer 22, respectively.

[0050] The material in the active layer 2 includes carbon nanomaterial and fluorine-containing polymer material, the carbon nanomaterial is graphene with a sheet diameter of 2 μm, and the fluorine-containing polymer material is polyvinylidene fluoride (Solef 5120), and the mass ratio of the carbon nanomaterial and the fluorine-containing polymer material is 1:0.1.

[0051] The thickness of the first carbon-based composite active layer 21 and the second carbon-based composite active layer 22 is 1 μm.

[0052] The thickness of the polymer support layer 1 is 4.5 μm, and the material of the polymer support layer 1 is PET.

[0053] This embodiment also provides a preparation method of the above-mentioned composite current collector, which includes the following steps:

[0054] (1) A certain amount of graphene (sheet diameter 2 μm) is added to N-methylpyrrolidone, and is uniformly dispersed by using 500 W ultrasonic, then polyvinylidene fluoride (Solef 5120) is added, and is mixed by heating to 70℃, and is stirred until completely dissolved, to obtain a coating liquid with a solid content of 20%;

[0055] The mass ratio of graphene and polyvinylidene fluoride is 1:0.1.

[0056] (2) The above-mentioned coating liquid is coated on both sides of the surface of the PET film by using a slot extrusion coater, and then is dried in a 70℃ oven, and the sample after drying is placed in a hot roller pressing device for hot roller pressing, the hot pressing conditions are: temperature is 90℃, pressure is 0.5 MPa, and hot pressing time is 20 s, and the composite current collector with a thickness of 6.5 μm is obtained after hot pressing.

[0057] Embodiment 2

[0058] The difference between this embodiment and embodiment 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating liquid is 1:1.

[0059] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0060] Embodiment 3

[0061] The difference between this embodiment and embodiment 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating liquid is 1:4.

[0062] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0063] Embodiment 4

[0064] The difference between this embodiment and embodiment 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating liquid is 1:8.

[0065] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0066] Embodiment 5

[0067] The difference between this embodiment and embodiment 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating liquid is 1:10.

[0068] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0069] Embodiment 6

[0070] The difference between this embodiment and embodiment 1 is that the parameters of coating are adjusted so that the thickness of the first carbon-based composite active layer and the second carbon-based composite active layer are both 5 μm.

[0071] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0072] Embodiment 7

[0073] The difference between this embodiment and embodiment 1 is that the parameters of coating are adjusted so that the thickness of the first carbon-based composite active layer and the second carbon-based composite active layer are both 10 μm.

[0074] The rest of the preparation method and parameters remain consistent with embodiment 1.

[0075] Embodiment 8

[0076] The difference between this embodiment and embodiment 1 is that the parameters of coating are adjusted so that the thickness of the first carbon-based composite active layer and the second carbon-based composite active layer are both 15 μm.

[0077] The rest of the preparation method and parameters are consistent with Example 1.

[0078] Example 9

[0079] The difference between this example and Example 3 is that in step (1), graphene is replaced by a mixture of graphene and carbon nanotubes with a mass ratio of 1:1.

[0080] The rest of the preparation method and parameters are consistent with Example 3.

[0081] Example 10

[0082] The difference between this example and Example 3 is that in step (1), graphene is replaced by a mixture of graphene and carbon nanofibers with a mass ratio of 1:1.

[0083] The rest of the preparation method and parameters are consistent with Example 3.

[0084] Example 11

[0085] The difference between this example and Example 3 is that in step (1), graphene is replaced by a mixture of multi-layer graphene-nanodiamond composite and carbon nanotubes with a mass ratio of 1:1.

[0086] The rest of the preparation method and parameters are consistent with Example 3.

[0087] Example 12

[0088] The difference between this example and Example 3 is that in step (1), graphene is replaced by a mixture of multi-layer graphene-nanodiamond composite and carbon nanofibers with a mass ratio of 1:1.

[0089] The rest of the preparation method and parameters are consistent with Example 3.

[0090] Example 13

[0091] The difference between this example and Example 3 is that in step (1), polyvinylidene fluoride is replaced by poly(vinylidene fluoride-co-hexafluoropropylene).

[0092] The rest of the preparation method and parameters are consistent with Example 3.

[0093] Example 14

[0094] The difference between this example and Example 3 is that in step (2), the PET film is replaced by a PP film.

[0095] The rest of the preparation method and parameters are consistent with Example 3.

[0096] Example 15

[0097] The difference between this example and Example 3 is that the PET film in step (2) is replaced by a PPS film.

[0098] The rest of the preparation method and parameters remain the same as in Example 3.

[0099] Example 16

[0100] The difference between this example and Example 1 is that the temperature of hot pressing in step (2) is 50°C.

[0101] The rest of the preparation method and parameters remain the same as in Example 1.

[0102] Example 17

[0103] The difference between this example and Example 1 is that the temperature of hot pressing in step (2) is 120°C.

[0104] The rest of the preparation method and parameters remain the same as in Example 1.

[0105] Example 18

[0106] The difference between this example and Example 1 is that the pressure of hot pressing in step (2) is 0.2 MPa.

[0107] The rest of the preparation method and parameters remain the same as in Example 1.

[0108] Example 19

[0109] The difference between this example and Example 1 is that the pressure of hot pressing in step (2) is 1.0 MPa.

[0110] The rest of the preparation method and parameters remain the same as in Example 1.

[0111] Example 20

[0112] The difference between this example and Example 1 is that the time of hot pressing in step (2) is 5 s.

[0113] The rest of the preparation method and parameters remain the same as in Example 1.

[0114] Example 21

[0115] The difference between this example and Example 1 is that the time of hot pressing in step (2) is 60 s.

[0116] The rest of the preparation method and parameters remain the same as in Example 1.

[0117] Example 22

[0118] The difference between this example and Example 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating solution is 1:11.

[0119] The remaining preparation method and parameters are consistent with Example 1.

[0120] Example 23

[0121] The difference between this example and Example 1 is that the mass ratio of graphene and polyvinylidene fluoride in the coating liquid is 1:0.05.

[0122] The remaining preparation method and parameters are consistent with Example 1.

[0123] Example 24

[0124] The difference between this example and Example 1 is that the parameters of coating are adjusted so that the thickness of the first carbon-based composite active layer and the second carbon-based composite active layer is 0.5 μm.

[0125] The remaining preparation method and parameters are consistent with Example 1.

[0126] Example 25

[0127] The difference between this example and Example 1 is that the parameters of coating are adjusted so that the thickness of the first carbon-based composite active layer and the second carbon-based composite active layer is 16 μm.

[0128] The remaining preparation method and parameters are consistent with Example 1.

[0129] Example 26

[0130] The difference between this example and Example 1 is that the temperature of hot pressing in step (2) is 40°C.

[0131] The remaining preparation method and parameters are consistent with Example 1.

[0132] Example 27

[0133] The difference between this example and Example 1 is that the temperature of hot pressing in step (2) is 130°C.

[0134] The remaining preparation method and parameters are consistent with Example 1.

[0135] Example 28

[0136] The difference between this example and Example 1 is that the pressure of hot pressing in step (2) is 0.1 MPa.

[0137] The remaining preparation method and parameters are consistent with Example 1.

[0138] Example 29

[0139] The difference between this example and Example 1 is that the pressure of hot pressing in step (2) is 1.2 MPa.

[0140] The rest of the preparation method and parameters are consistent with Example 1.

[0141] Example 30

[0142] The difference between this example and Example 1 is that the hot-pressing time in step (2) is 3 s.

[0143] The rest of the preparation method and parameters are consistent with Example 1.

[0144] Example 31

[0145] The difference between this example and Example 1 is that the hot-pressing time in step (2) is 65 s.

[0146] The rest of the preparation method and parameters are consistent with Example 1.

[0147] Comparative Example 1

[0148] The difference between this comparative example and Example 1 is that the composite current collector does not contain a PET film.

[0149] The rest of the preparation method and parameters are consistent with Example 1.

[0150] Comparative Example 2

[0151] The difference between this comparative example and Example 1 is that the material in the active layer is only a carbon nanomaterial.

[0152] The rest of the preparation method and parameters are consistent with Example 1.

[0153] Comparative Example 3

[0154] The difference between this comparative example and Example 1 is that the material in the active layer is only a fluoropolymer material.

[0155] The rest of the preparation method and parameters are consistent with Example 1.

[0156] Performance Test

[0157] The tensile strength of the composite current collector prepared in the above examples and comparative examples and the cycle performance of the battery prepared are tested, and the specific test method is as follows:

[0158] (1) Tensile strength: test according to GB / T 1040.3-2006.

[0159] (2) Performance evaluation of assembled battery:

[0160] ① Assemble the lithium metal battery without negative electrode:

[0161] For the positive electrode, the positive electrode current collector adopts aluminum foil (12 pm), and the positive electrode material adopts lithium iron phosphate;

[0162] For the negative electrode: the negative electrode adopts the composite current collector prepared by the application; for the separator, a polypropylene separator (thickness of 20 pm) is adopted;

[0163] For the electrolyte, the electrolyte is lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and lithium nitrate (LiNO3), and the contents are 1 mol·L -1 , 2 wt.%, and the electrolyte is 1,2-dimethoxy methane (DME) and 1,3-dioxolane (DOL), and the volume ratio of the two is 1:1; a 1M LiPF6 carbonate solution is adopted, and the carbonate is a combination of propylene carbonate, vinyl carbonate and methyl ethyl carbonate, and the mass ratio of the three is 1:1:1;

[0164] Using the above materials, a negative electrode-free lithium metal battery is assembled according to the related process, and the battery capacity is 1 Ah.

[0165] 2. Cycle performance test: the battery prepared above is placed in a cycle performance test device, and the battery capacity retention rate after 100 cycles is recorded.

[0166] The above test results are shown in Table 1.

[0167] Table 1

[0168]

[0169] Analysis:

[0170] As can be seen from the above table, the tensile strength of the composite current collector prepared by the application is obviously higher than that of the carbon-based current collector, and the capacity retention rate of the negative electrode-free lithium metal battery prepared by the composite current collector after 100 cycles is higher than that of the negative electrode-free lithium metal battery prepared by the carbon-based current collector after 100 cycles, that is, the cycle performance is improved.

[0171] As can be seen from Examples 1-5 and Examples 22-23, reducing the mass ratio of graphene and polyvinylidene fluoride, the tensile strength of the composite current collector prepared presents a trend of improvement, and the capacity retention rate of the corresponding battery after 100 cycles first increases and then decreases, which is because as the mass ratio of graphene and polyvinylidene fluoride decreases, the polyvinylidene fluoride in the active layer forms a stronger spatial network structure with graphene, thereby promoting the improvement of the tensile strength of the composite current collector, and the improvement of the tensile strength promotes the increase of the capacity retention rate of the corresponding battery after 100 cycles, but if the mass ratio of the two is too high or too low, the conductivity of the active layer will be poor, which will cause the capacity retention rate of the corresponding battery after 100 cycles to decrease.

[0172] From Example 1, Example 6-8, Example 24-25, it can be seen that increasing the thickness of the active layer, the tensile strength of the prepared composite current collector first increases and then remains basically unchanged, and the capacity retention rate of the corresponding battery after 100 cycles first increases and then remains basically unchanged. This is due to the trend that the structure of the composite current collector first strengthens and then remains basically unchanged caused by the increase of the thickness of the active layer.

[0173] From Example 3, Example 9-12, it can be seen that compared with graphene, the carbon nanomaterial in the active layer adopts a mixture of graphene and carbon nanotubes, a mixture of graphene and carbon nanofibers, a mixture of multi-layer graphene-nanodiamond and carbon nanotubes, and a mixture of multi-layer graphene-nanodiamond and carbon nanofibers. The performance of the prepared composite current collector is better, which is because the above-mentioned combined material can form a spatial network structure better, promote the improvement of the mechanical properties and the electrical conductivity of the active layer, and then bring the improvement of the battery cycle performance.

[0174] From Example 3 and Example 13, it can be seen that compared with polyvinylidene fluoride, the fluorine-containing material carbon nanomaterial in the active layer adopts poly(vinylidene fluoride-co-hexafluoropropylene) to prepare the composite current collector. The performance is better, which is because poly(vinylidene fluoride-co-hexafluoropropylene) can form a strengthened spatial network structure with carbon nanomaterials, and can provide more F-containing sites, promote the formation of fluorine-containing compounds in the negative electrode SEI film, thereby generating a more stable SEI film, and improving the cycle performance of the battery.

[0175] From Example 3, Example 14-15, it can be seen that replacing the polymer film with a PP film or a PPS film can still achieve good results.

[0176] From Example 1, Example 16-17, Example 26-27, it can be seen that increasing the hot pressing temperature, the tensile strength of the prepared composite current collector increases, which is because as the hot pressing temperature increases, the density of the active layer increases, and the adhesion between the active layer and the polymer support layer increases, both of which promote the increase of the tensile strength of the prepared composite current collector; increasing the hot pressing temperature, the capacity retention rate of the battery assembled by the prepared composite current collector after 100 cycles first increases and then decreases, which is because as the hot pressing temperature increases, the mechanical properties and the electrical conductivity of the prepared composite current collector increase, resulting in the increase of the capacity retention rate of the battery after 100 cycles. However, if the hot pressing temperature is too high, the porosity of the active layer of the prepared composite current collector is too low, which is not conducive to the deposition of lithium ions, resulting in the decrease of the capacity retention rate of the battery after 100 cycles.

[0177] As can be seen from Example 1, Examples 18-19, Examples 28-29, the tensile strength of the prepared composite current collector increases with the increase of the hot-pressing pressure, because the density of the active layer and the adhesion between the active layer and the polymer support layer are improved with the increase of the hot-pressing pressure, which promotes the increase of the tensile strength of the prepared composite current collector. The capacity retention rate of the battery assembled by the prepared composite current collector after 100 cycles increases first and then decreases with the increase of the hot-pressing pressure, because the mechanical properties and the electrical conductivity of the prepared composite current collector are improved with the increase of the hot-pressing pressure, which leads to the increase of the capacity retention rate of the battery after 100 cycles, but the porosity of the active layer of the prepared composite current collector is too low when the hot-pressing pressure is too high, which is not conducive to the deposition of lithium ions, leading to the decrease of the capacity retention rate of the battery after 100 cycles.

[0178] As can be seen from Example 1, Examples 20-21, Examples 30-31, the tensile strength of the prepared composite current collector increases with the increase of the hot-pressing time, because the density of the active layer and the adhesion between the active layer and the polymer support layer are improved with the increase of the hot-pressing time, which promotes the increase of the tensile strength of the prepared composite current collector. The capacity retention rate of the battery assembled by the prepared composite current collector after 100 cycles increases first and then decreases with the increase of the hot-pressing time, because the mechanical properties and the electrical conductivity of the prepared composite current collector are improved with the increase of the hot-pressing time, which leads to the increase of the capacity retention rate of the battery after 100 cycles, but the porosity of the active layer of the prepared composite current collector is too low when the hot-pressing time is too long, which is not conducive to the deposition of lithium ions, leading to the decrease of the capacity retention rate of the battery after 100 cycles.

[0179] As can be seen from Example 1 and Comparative Example 2, if the material in the active layer only contains carbon nanomaterial, the prepared active layer has poor structural stability, and cannot form a surface with a lower Fermi level and an SEI film, leading to poor cycle charge-discharge performance of the battery prepared therefrom.

[0180] As can be seen from Example 1 and Comparative Example 3, if the material in the active layer only contains fluorine-containing polymer material, the prepared active layer has poor electrical conductivity, leading to high internal resistance of the battery prepared therefrom during the cycle charge-discharge process, thereby causing poor cycle performance.

[0181] The applicant declares that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A composite current collector, characterized by, The composite current collector comprises a polymer support layer and a carbon-based composite active layer arranged on at least one side surface of the polymer support layer; The material in the carbon-based composite active layer comprises carbon nanomaterial and fluoropolymer material; The mass ratio of the carbon nanomaterial and the fluoropolymer material is 1:(0.1-10); The carbon nanomaterial comprises any one of a combination of graphene and carbon nanotube, a combination of graphene and carbon nanofiber, a combination of multi-layer graphene-nanodiamond composite material and carbon nanotube, or a combination of multi-layer graphene-nanodiamond composite material and carbon nanofiber; The thickness of the polymer support layer is 3-10 μm; and the material of the polymer support layer comprises polyethylene terephthalate; The composite current collector is prepared by the following method comprising the following steps: (1) preparing a coating solution of the carbon-based composite active layer; (2) coating the coating solution on at least one side surface of the polymer support layer, drying, and then hot pressing to obtain the composite current collector; In step (2), the hot pressing is performed at a temperature of 50-120 ℃, a pressure of 0.1-1 MPa, and for a time of 5-60 s.

2. The composite current collector of claim 1, wherein The fluoropolymer material comprises any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, poly(vinylidene fluoride-co-hexafluoropropylene), or ethylene-tetrafluoroethylene copolymer.

3. The composite current collector of claim 1, wherein The mass ratio of the carbon nanomaterial and the fluoropolymer material is 1:(1-8).

4. The composite current collector of claim 1, wherein The thickness of the carbon-based composite active layer on one side is ≥1 μm.

5. A method of making a composite current collector as claimed in any one of claims 1 to 4, characterised in that, The preparation method comprises the following steps: (1) preparing a coating solution of the carbon-based composite active layer; (2) coating the coating solution on at least one side surface of the polymer support layer, drying, and then hot pressing to obtain the composite current collector; In step (2), the hot pressing is performed at a temperature of 50-120 ℃, a pressure of 0.1-1 MPa, and for a time of 5-60 s.

6. The production method according to claim 5, wherein The preparation method of the coating solution in step (1) comprises: The carbon nanomaterial, the fluoropolymer material, and an organic solvent are mixed to obtain the coating solution; The solid content of the coating solution is 5-30%; The mixing is performed at a temperature of 40-90 ℃.

7. The preparation method according to claim 5, characterized in that The coating method in step (2) comprises a coating method. The drying temperature in step (2) is 50-100 ℃.

8. The preparation method according to claim 5, characterized in that The preparation method comprises the following steps: (1) adding the carbon nanomaterial to an organic solvent, uniformly dispersing by ultrasonic at a power of 200-1000 W, then adding the fluoropolymer material, and mixing by heating to 40-90 ℃ to obtain a coating solution; (2) coating the coating solution on at least one side surface of the polymer support layer by using a slot extrusion coating or doctor blade coating device, then drying in an oven at 50-100 ℃, and then hot rolling the dried sample in a hot roller pressing device at a temperature of 50-120 ℃, a pressure of 0.2-1.0 MPa, and for a time of 5-60 s to obtain the composite current collector.

9. Use of the composite current collector according to any one of claims 1-4 in a negative electrode-free lithium metal battery.

Images