Composite current collector and preparation method therefor, and electrode sheet and secondary battery

Abstract

A composite current collector and a preparation method therefor, and an electrode sheet and a secondary battery. The composite current collector comprises: a base film; a transition layer, which is arranged on at least one side surface of the base film, wherein the transition layer is made of any one of metal niobium, metal tantalum, a niobium alloy, a tantalum alloy, a niobium-based compound and a tantalum-based compound, or a combination of at least two thereof; and an electrically conductive layer, which is arranged on the side surface of the transition layer that is away from the base film. A transition layer having good compactness, stability and corrosion resistance is provided between the base film and the electrically conductive layer, which can improve the adhesive force between the base film and the conductive layer, reduce the formation of holes in the electrically conductive layer, and resist the erosion of an electrolyte and a high-temperature environment, thereby improving the charging and discharging cycle performance of a battery based on the composite current collector; moreover, the provision of the transition layer avoids the thermal runaway of the battery generated by the formation of a closed loop due to the conduction of a positive-electrode current collector and a negative-electrode current collector, thereby improving the safety performance of the battery.

Description

Composite current collector and preparation method thereof, electrode sheet and secondary battery Technical Field

[0001] The present application relates to the field of battery technology, for example, a composite current collector and a preparation method thereof, an electrode sheet and a secondary battery. 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] The current composite current collectors have the following main problems: ① The adhesion between the polymer base film and the metal layer in the composite current collector is low, which is easy to separate during the battery charge and discharge cycle, resulting in poor battery cycle performance; ② The composite current collector mainly relies on the insulation and flame retardant properties of the intermediate layer, namely the polymer film layer, to improve the safety of the battery. However, although this improves the battery safety performance, the improvement is limited.

[0004] Therefore, in order to further improve the charge-discharge cycle and safety performance of composite current collector-based batteries, it is necessary to develop a new composite current collector to promote the application and promotion of composite current collectors in secondary 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] The present application provides a composite current collector and its preparation method, electrode sheet and secondary battery. The present application adds a transition layer with good compactness, stability and corrosion resistance between the base film and the conductive layer. On the one hand, it can effectively bridge the base film and the conductive layer, improve the adhesion between the two, reduce the formation of holes in the conductive layer, resist the erosion of the electrolyte and high temperature environment, and transform its structure from amorphous to crystalline through the electrochemical cycle of Li+, maintaining its cubic framework and its nanostructure throughout the lithiation / delithiation process, thereby having excellent reversible capacity and cycle stability. The improvement of adhesion, reduction of hole defects and improvement of corrosion resistance jointly improve the charge and discharge cycle performance of the battery prepared based on the composite current collector. On the other hand, the provision of the transition layer avoids the formation of a closed loop by the conduction of the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0008] In a first aspect, the present application provides a composite current collector, comprising:

[0009] basement membrane;

[0010] A transition layer provided on at least one side of the base film, wherein the material of the transition layer is any one of metallic niobium, metallic tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound, or a combination of at least two thereof;

[0011] The conductive layer is arranged on the surface of the transition layer on a side relatively far away from the base film.

[0012] The present application adds a transition layer with good density, stability and corrosion resistance between the base film and the conductive layer, which can effectively bridge the base film and the conductive layer and improve the adhesion between the two. The transition layer has dielectric properties, which can reduce the formation of holes in the process of preparing the conductive layer. The transition layer can also resist the erosion of the electrolyte and high temperature environment. Through the electrochemical cycle of Li+, its structure is transformed from amorphous to crystalline, and its cubic framework and nanostructure are maintained during the entire lithiation / delithiation process, thereby having excellent reversible capacity and cycle stability, and the improvement of adhesion. , the reduction of hole defects and the improvement of corrosion resistance jointly improve the charge and discharge cycle performance of the battery prepared based on the composite current collector; on the other hand, in the needle penetration test of battery safety detection, the steel needle applies a force in the Z direction to the composite current collector, causing microcracks in the transition layer, which quickly spreads and causes large-scale fractures. Due to the strong adhesion between the transition layer and the conductive layer, the conductive layer will undergo similar fractures along with the transition layer, thereby separating the conductive 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.

[0013] As an optional technical solution of the present application, the material of the base film is a polymer, and the polymer includes any one or a combination of at least two 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).

[0014] In one embodiment, the base film has a thickness of 1-10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm or 9 μm.

[0015] In this application, considering the application requirements of the composite current collector and the difficulty and cost of the preparation process, the thickness of the base film is limited to 1-10 μm, which can meet the above requirements at the same time.

[0016] As an optional technical solution of the present application, the niobium alloy includes any one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy or lithium niobate alloy, or a combination of at least two thereof.

[0017] In one embodiment, the tantalum alloy includes any one of a tantalum-niobium alloy, a tantalum-tungsten alloy, a tantalum-tungsten-hafnium alloy, or a cobalt-tantalum-zirconium alloy, or a combination of at least two thereof.

[0018] In one embodiment, the niobium-based compound and the tantalum-based compound independently include any one or a combination of at least two of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides, or tellurides.

[0019] In one embodiment, the oxide is any one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide or tantalum pentoxide, or a combination of at least two thereof.

[0020] In one embodiment, the nitride is niobium nitride and / or tantalum nitride.

[0021] In one embodiment, the carbide is niobium carbide and / or tantalum carbide.

[0022] In one embodiment, the sulfide is niobium disulfide and / or tantalum disulfide.

[0023] In one embodiment, the fluoride is niobium pentafluoride and / or tantalum pentafluoride.

[0024] In one embodiment, the silicide is niobium disilicide and / or tantalum disilicide.

[0025] In one embodiment, the phosphide is niobium phosphide and / or tantalum phosphide.

[0026] In one embodiment, the selenide is niobium diselenide and / or tantalum diselenide.

[0027] In one embodiment, the telluride is niobium ditelluride and / or tantalum ditelluride.

[0028] In one embodiment, the material of the transition layer is any one of metallic niobium, metallic tantalum, niobium pentoxide, tantalum pentoxide, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, lithium niobate alloy, tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy, cobalt-tantalum-zirconium alloy, niobium nitride, tantalum nitride, niobium carbide or tantalum carbide, or a combination of at least two thereof.

[0029] In one embodiment, transition layers are provided on both surfaces of the base film.

[0030] In one embodiment, the thickness of the transition layer on one side is greater than or equal to 5 nm, for example, it can be 5 nm, 10 nm, 30 nm, 50 nm, 70 nm, 90 nm, 120 nm, 150 nm or 200 nm, etc., and can be optionally 10-100 nm.

[0031] In the present application, if the thickness of the single-sided transition layer is too small, the improvement in battery safety performance will not be obvious; if the thickness of the single-sided transition layer is too large, the cycle and safety performance of the battery will not be further improved.

[0032] As an optional technical solution of the present application, the material of the conductive layer is metal, and the metal includes any one of elemental aluminum, elemental copper, elemental gold, elemental silver, elemental nickel, elemental zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, nickel alloy or zinc alloy, or a combination of at least two of them.

[0033] In one embodiment, the thickness of the conductive layer on one side is 500-2000 nm, for example, 500 nm, 1000 nm, 1500 nm or 2000 nm, etc., and can be optionally 800-1200 nm.

[0034] In this application, if the thickness of the single-sided conductive layer is too small, the conductivity is poor, and if the thickness of the single-sided conductive layer is too large, it is not conducive to improving the energy density of the battery. A thickness of 800-1200nm can improve both conductivity and energy density.

[0035] As an optional technical solution of the present application, a protective layer is provided on the surface of the conductive layer on a side relatively far away from the base film.

[0036] In the present application, the protective layer is provided to prevent the conductive layer from being chemically corroded or physically damaged.

[0037] In one embodiment, the material of the protective layer includes any one of metallic nickel, metallic chromium, nickel-chromium alloy, nickel alloy, copper alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene or graphene oxide, or a combination of at least two thereof.

[0038] It should be noted that the materials of the protective layers on both sides of the current collector may be the same or different.

[0039] In one embodiment, the thickness of the protective layer on one side is 10-100 nm, for example, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, etc., and can be optionally 20-80 nm.

[0040] It should be noted that the thickness of the protective layers on both sides of the current collector may be the same or different.

[0041] In one embodiment, the thickness of the protective layer on one side is less than one tenth of the thickness of the conductive layer on one side.

[0042] In the present application, if the thickness of the protective layer is too small, it is difficult to prevent the conductive layer from being chemically corroded or physically damaged. If the thickness of the protective layer is too large, there will be no further improvement and the overall thickness of the film will increase.

[0043] In a second aspect, the present application provides a method for preparing the composite current collector as described in the first aspect, the preparation method comprising the following steps:

[0044] A transition layer is prepared on at least one surface of the base film, and then a conductive layer is prepared on the surface of the transition layer on a side relatively far away from the base film to obtain the composite current collector.

[0045] It should be noted that the present application does not limit the preparation method of the base film. For example, a melt-extrusion-biaxial stretching method can be used.

[0046] As an optional technical solution of the present application, the method for preparing the transition layer includes magnetron sputtering.

[0047] In one embodiment, the method for preparing the conductive layer comprises any one of evaporation, magnetron sputtering, chemical plating, electroplating or CVD, or a combination of at least two thereof.

[0048] In one embodiment, after depositing the conductive layer, a protective layer is formed on the surface of the conductive layer that is relatively far away from the base film.

[0049] In one embodiment, the protective layer is prepared by any one of physical vapor deposition, chemical vapor deposition, in-situ forming or coating, or a combination of at least two thereof.

[0050] As an optional technical solution of the present application, the preparation method comprises the following steps:

[0051] (1) preparing a polymer base film with a thickness of 1-10 μm;

[0052] (2) Depositing a transition layer with a thickness of 10-100 nm on both sides of the polymer base film to obtain a composite film with a transition layer on the surface. The specific process conditions are: power density of 4-7 W / cm 2 (For example, it can be 4W / cm 2 , 5W / cm 2 , 6W / cm 2 or 7W / cm 2 The flow rate of argon gas is 50-60 mL / min (for example, 50 mL / min, 52 mL / min, 54 mL / min, 56 mL / min, 58 mL / min or 60 mL / min), the vacuum degree of the coating is 0.08-0.1 Pa (for example, 0.08 Pa, 0.09 Pa or 0.1 Pa), the coating time is 1-20 s (1 s, 5 s, 10 s, 15 s or 20 s), and the cooling temperature of the main roller during the coating process is 0-20°C (0°C, 5°C, 10°C, 15°C or 20°C).

[0053] (3) depositing a conductive layer with a thickness of 500-2000 nm on each side of the composite film to obtain a composite film containing a transition layer and a conductive layer;

[0054] (4) Preparing a protective layer on the conductive layer: placing the composite film containing the transition layer and the conductive layer in a raw material solution of the protective layer for immersion treatment, and then washing and drying to obtain the composite current collector.

[0055] In a third aspect, the present application provides an electrode sheet, comprising the composite current collector as described in the first aspect.

[0056] In a fourth aspect, the present application provides a secondary battery, comprising the electrode sheet as described in the third aspect.

[0057] 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 space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0058] Compared with the related art, this application has the following beneficial effects:

[0059] The present application adds a transition layer with good density, stability and corrosion resistance between the base film and the conductive layer, which can effectively bridge the base film and the conductive layer and improve the adhesion between the two. The transition layer has dielectric properties, which can reduce the formation of holes in the process of preparing the conductive layer. The transition layer can also resist the corrosion of the electrolyte and high temperature environment. Through the electrochemical cycle of Li+, its structure is transformed from amorphous to crystalline, and its cubic framework and nanostructure are maintained during the entire lithiation / delithiation process, thereby having excellent reversible capacity and cycle stability, improved adhesion, reduced hole defects and The improvement in corrosion resistance has jointly improved the charge and discharge cycle performance of the battery prepared based on the composite current collector; on the other hand, in the needle penetration test of battery safety testing, the steel needle applies a force in the Z direction to the composite current collector, causing microcracks in the transition layer, which quickly spreads and causes large-scale fractures. Due to the strong adhesion between the transition layer and the conductive layer, the conductive layer will undergo similar fractures along with the transition layer, thereby separating the conductive 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 and promoting the promotion and application of the composite current collector.

[0060] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further described below through specific implementation methods. 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 of the present application.

[0062] Example 1

[0063] This embodiment provides a composite current collector, comprising:

[0064] A base film, wherein the base film is a PP film with a thickness of 6 μm;

[0065] The transition layers provided on both sides of the base film include a first transition layer and a second transition layer, wherein the first transition layer and the second transition layer are both metal niobium layers with a thickness of 50 nm;

[0066] The conductive layers provided on both sides of the transition layer relatively away from the base film include a first conductive layer and a second conductive layer, wherein the first conductive layer and the second conductive layer are both single copper layers with a thickness of 900 nm;

[0067] The protective layers arranged on both sides of the conductive layer relatively away from the base film include a first protective layer and a second protective layer, and both the first protective layer and the second protective layer are made of chromium oxide with a thickness of 20 nm.

[0068] This embodiment also provides a method for preparing the composite current collector, which comprises the following steps:

[0069] (1) A 6 μm thick PP film was prepared by melt-extrusion-biaxial stretching method;

[0070] (2) The PP film was placed in a magnetron sputtering machine, and a 50 nm thick layer of metal niobium was deposited on both sides of the PP film to obtain a composite film with a metal niobium layer on both surfaces. The specific process conditions were as follows: a niobium target (purity: 99.99%) was used as the target material, the power was 10.8 kW, the flow rate of argon was 60 mL / min, the vacuum degree of the coating was 0.1 Pa, the coating time was 5 s, and the cooling temperature of the main roller during the coating process was 0°C;

[0071] (3) placing the composite film containing the metal niobium layer on both sides of the surface in a magnetron sputtering machine, and depositing a layer of single copper layer with a thickness of 900 nm on both sides of the composite film, thereby obtaining a composite film containing the metal niobium layer and the single copper layer on both sides of the surface. The specific process conditions are: a copper target (purity: 99.99%) as the target material, a power of 12 kW, an argon flow rate of 70 mL / min, a coating vacuum of 0.1 Pa, a coating time of 100 s, and a cooling temperature of -5°C for the main roller during the coating process;

[0072] (4) Preparing a protective layer on the conductive layer: The composite film containing a metal niobium layer and a single copper layer on both surfaces is immersed in a 0.5 g / L chromic anhydride aqueous solution (25° C.) for 20 seconds, and then washed with a pure water tank. After washing, the composite current collector is dried in an oven at 60° C. to obtain the composite current collector.

[0073] Example 2

[0074] The difference between this embodiment and Example 1 is that the transition layer is a lithium niobate alloy layer, and the specific process conditions are: a lithium niobate target (purity: 99.99%) is used as the target material, the power density is 11.7KW, the flow rate of argon gas is 50mL / min, the vacuum degree of the coating is 0.1Pa, the coating time is 5s, and the temperature of the main roller during the coating process is 0°C.

[0075] The rest of the preparation methods and parameters remained the same as in Example 1.

[0076] Example 3

[0077] The difference between this embodiment and Example 1 is that the transition layer is a niobium pentoxide layer, and the specific process conditions are: a niobium pentoxide target (purity: 99.99%) is used as the target material, the power density is 18.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0078] The rest of the preparation methods and parameters remained the same as in Example 1.

[0079] Example 4

[0080] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium nitride layer, and the specific process conditions are: a niobium nitride target (purity: 99.99%) is used as the target material, the power is 11.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0081] The rest of the preparation methods and parameters remained the same as in Example 1.

[0082] Example 5

[0083] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium carbide layer, and the specific process conditions are: a niobium carbide target (purity: 99.99%) is used as the target material, the power is 11.6 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0084] The rest of the preparation methods and parameters remained the same as in Example 1.

[0085] Example 6

[0086] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium disulfide layer, and the specific process conditions are: a niobium disulfide target (purity: 99.99%) is used as the target material, the power is 12.3 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0087] The rest of the preparation methods and parameters remained the same as in Example 1.

[0088] Example 7

[0089] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium pentafluoride layer, and the specific process conditions are: a niobium pentafluoride target (purity: 99.99%) is used as the target material, the power is 14.4 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0090] The rest of the preparation methods and parameters remained the same as in Example 1.

[0091] Example 8

[0092] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium disilicide layer, and the specific process conditions are: a niobium disilicide target (purity: 99.99%) is used as the target material, the power is 11.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0093] The rest of the preparation methods and parameters remained the same as in Example 1.

[0094] Example 9

[0095] The difference between this embodiment and Example 1 is that the transition layer is a niobium phosphide layer, and the specific process conditions are: a niobium phosphide target (purity: 99.99%) is used as the target material, the power is 12.1 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0096] The rest of the preparation methods and parameters remained the same as in Example 1.

[0097] Example 10

[0098] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium diselenide layer, and the specific process conditions are: a niobium diselenide target (purity: 99.99%) is used as the target material, the power is 18.8 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0099] The rest of the preparation methods and parameters remained the same as in Example 1.

[0100] Example 11

[0101] The difference between this embodiment and embodiment 1 is that the transition layer is a metal tantalum layer. The specific process conditions are: tantalum target (purity: 99.99%) is used as the target material, and the power density is 15.5W / cm 2 , the flow rate of argon gas is 50 mL / min, the vacuum degree of coating is 0.08 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 10 °C.

[0102] The rest of the preparation methods and parameters remained the same as in Example 1.

[0103] Example 12

[0104] The difference between this embodiment and Example 1 is that the transition layer is a tantalum-niobium alloy layer, and the specific process conditions are: a tantalum-niobium target (purity: 99.99%) is used as the target material, the power is 12.3 kW, the flow rate of argon gas is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 10°C.

[0105] The rest of the preparation methods and parameters remained the same as in Example 1.

[0106] Example 13

[0107] The difference between this embodiment and Example 1 is that the transition layer is a tantalum pentoxide layer, and the specific process conditions are: a tantalum pentoxide target (purity: 99.99%) is used as the target material, the power is 19.5KW, the flow rate of argon gas is 50mL / min, the vacuum degree of the coating is 0.1Pa, the coating time is 5s, and the temperature of the main roller during the coating process is 10°C.

[0108] The rest of the preparation methods and parameters remained the same as in Example 1.

[0109] Example 14

[0110] The difference between this embodiment and embodiment 1 is that the material of the transition layer is a mixture of niobium pentoxide and tantalum pentoxide. The specific process conditions are: a mixture of niobium pentoxide and tantalum pentoxide (mass ratio of 1:1) (purity: 99.99%) is used as the target material, the power is 19.3 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0111] The rest of the preparation methods and parameters remained the same as in Example 1.

[0112] Example 15

[0113] The difference between this embodiment and embodiment 1 is that the material of the transition layer is a mixture of niobium pentoxide and lithium niobate alloy, and the specific process conditions are: using a mixture of niobium pentoxide and lithium niobate alloy (mass ratio of 1:1) (purity: 99.99%) as the target material, the power is 15.3KW, the argon flow rate is 50mL / min, the vacuum degree of the coating is 0.1Pa, the coating time is 5s, and the temperature of the main roller during the coating process is 20°C.

[0114] The rest of the preparation methods and parameters remained the same as in Example 1.

[0115] Example 16

[0116] The difference between this embodiment and embodiment 1 is that the material of the transition layer is a mixture of niobium carbide and niobium nitride. The specific process conditions are: using a mixture of niobium carbide and niobium nitride (mass ratio of 1:1) (purity: 99.99%) as the target material, the power is 12.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0117] The rest of the preparation methods and parameters remained the same as in Example 1.

[0118] Example 17

[0119] The difference between this embodiment and embodiment 1 is that the material of the transition layer is a mixture of niobium carbide, niobium nitride and niobium pentoxide. The specific process conditions are: using a mixture of niobium carbide, niobium nitride and niobium pentoxide (mass ratio of 1:1:1) (purity: 99.99%) as the target material, the power is 12.5 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0120] The rest of the preparation methods and parameters remained the same as in Example 1.

[0121] Example 18

[0122] The difference between this embodiment and embodiment 3 is that the thickness of the single-sided transition layer is 100 nm, that is, the specific process conditions for adjusting the transition layer are: the coating time is 10 s, and the temperature of the main roller during the coating process is 20°C.

[0123] The rest of the preparation methods and parameters remained the same as in Example 3.

[0124] Example 19

[0125] The difference between this embodiment and Example 1 is that the thickness of the single-sided transition layer is 5 nm, that is, the specific process conditions for adjusting the transition layer are: power is 7.8 KW, argon flow rate is 50 mL / min, coating time is 1 s, and the temperature of the main roller during the coating process is 0°C.

[0126] The rest of the preparation methods and parameters remained the same as in Example 1.

[0127] Example 20

[0128] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided transition layer is 2 nm, that is, the specific process conditions for adjusting the transition layer are: power density is 2.1 W / cm 2 , the flow rate of argon gas is 50 mL / min, the coating time is 1 s, and the temperature of the main roller during the coating process is 0 °C.

[0129] The rest of the preparation methods and parameters remained the same as in Example 1.

[0130] Example 21

[0131] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided conductive layer is 500 nm, that is, the specific process parameters of the conductive layer are adjusted as follows: the coating time is 45 s.

[0132] The rest of the preparation methods and parameters remained the same as in Example 1.

[0133] Example 22

[0134] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided conductive layer is 1200 nm, that is, the specific process parameters of the conductive layer are adjusted as follows: the coating time is 120 s.

[0135] The rest of the preparation methods and parameters remained the same as in Example 1.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 1 is that no transition layer is provided, that is, step (2) is not performed.

[0138] The rest of the preparation methods and parameters remained the same as in Example 1.

[0139] Comparative Example 2

[0140] The difference between this comparative example and Example 1 is that the transition layer is a nickel-chromium alloy layer, that is, the specific process conditions of step (2) are adjusted to: a nickel-chromium target (purity: 99.99%) is used as the target material, and the power density is 2W / cm 2 , the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time is 10 s, and the temperature of the main roller during the coating process is 20 °C.

[0141] The rest of the preparation methods and parameters remained the same as in Example 1.

[0142] Performance Testing

[0143] The adhesive force of the composite current collectors prepared in the above examples and comparative examples and the safety performance and cycle performance of the batteries assembled therefrom were tested. The specific testing methods are as follows:

[0144] (1) Adhesion test

[0145] The prepared flat composite current collector sample was cut into a specimen with a width of 24 mm and a length of 300 mm. One end of the cut specimen was folded with the adhesive surface to form a folded layer about 12 mm long. The other end of the specimen was attached to one end of a steel plate and rolled twice with an adhesive tape roller at a speed of 600 mm / min. The specimen was placed in an electronic peel tester with a test speed of 300 mm / min and a specimen width of 24 mm. The equipment automatically recorded the force value during the peeling process and reported the peel strength of the specimen accordingly.

[0146] (2) Safety performance test

[0147] ①Battery assembly:

[0148] For the positive electrode, the positive electrode current collector is made of aluminum foil (thickness is 13μm), and the positive electrode material is LiNi 0.6 Mn 0.2 Co 0.2 O2(NCM622);

[0149] For the negative electrode: the negative electrode current collector adopts the composite current collector prepared in the above embodiment and comparative example, and the negative electrode material adopts artificial graphite;

[0150] For the diaphragm, alumina ceramic-coated polyethylene diaphragm (thickness 25 μm) was used;

[0151] For the electrolyte, 1 mol·L -1 LiPF6 carbonate solution, the solvent is a mixture of propylene carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1;

[0152] The above materials are used to assemble a lithium-ion battery.

[0153] ②Acupuncture pass rate:

[0154] i. Use a needle penetration test to verify the safety performance of the battery. Measure 100 samples and record the pass rate.

[0155] ii. Experimental procedures: The battery prepared above was placed in a needle puncture test apparatus, wherein the needle diameter was 3 mm, the puncture speed was 10 mm / s, the sampling interval was 100 ms, and the sampling time was 15 min. The battery was qualified if it did not explode, catch fire, or emit smoke. The needle puncture pass rate was recorded, that is, the number of samples that passed × 100%.

[0156] (3) Cyclic performance test

[0157] The test steps include: 1) discharging the battery cell at I1 (1-hour discharge current) to the discharge termination voltage at 25°C and allowing it to stand for 30 minutes; 2) charging the battery cell at a constant current of I1 to the charge termination voltage, then switching to constant voltage charging, and stopping charging when the charge termination current drops to 0.05 times of I1, and allowing it to stand for 30 minutes after charging; 3) discharging the battery cell at I1 to the discharge termination voltage; 4) cycling continuously for 1000 times according to steps 1)-3), recording the battery capacity at the first cycle and the 1000th cycle, and calculating the battery capacity retention rate, which is the battery capacity at the 1000th cycle / the battery capacity at the first cycle × 100%.

[0158] The test results are shown in Table 1.

[0159] Table 1

[0160] analyze:

[0161] As can be seen from the above table, the present application adds a transition layer between the base film and the conductive layer. On the one hand, it can effectively bridge the base film and the conductive layer, thereby improving the adhesion between the two. On the other hand, it effectively improves the charge and discharge cycle performance and safety performance of the battery based on the composite current collector, thereby promoting the promotion and application of the composite current collector.

[0162] From the data results of Examples 1-17, it can be seen that the use of transition layers of different materials affects the adhesion and conductivity of the composite current collector, thereby causing differences in the charge and discharge performance and safety performance of batteries based on the composite current collector.

[0163] It can be seen from the data results of Example 1, Example 3, Example 18 and Example 19 that an appropriate transition layer thickness is beneficial to improving the safety performance and cycle performance of the battery.

[0164] It can be seen from the data results of Example 1 and Example 20 that if the thickness of the transition layer is too small, it will be detrimental to bridging the base film and the conductive layer, and the charge and discharge cycle performance and safety performance of the battery will be greatly reduced.

[0165] It can be seen from the data results of Examples 1 and 21-22 that if the thickness of the conductive layer is too small, the conductivity is poor, and the battery cycle performance cannot be improved; if the thickness of the conductive layer is too large, it is not conducive to improving the energy density of the battery, and its cycle performance and safety performance are not significantly improved.

[0166] It can be seen from the data results of Example 1 and Comparative Example 1 that if a transition layer is not provided, the adhesion between the base film and the conductive layer will be too poor, copper removal will easily occur, and the safety performance of the battery based on this composite current collector will be extremely poor.

[0167] It can be seen from the data results of Example 1, Example 3, Example 13, Example 14, Example 17 and Comparative Example 2 that compared with using a traditional nickel-chromium alloy layer as a transition layer, a transition layer of any one of metallic niobium, metallic tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound or a combination of at least two thereof can significantly improve the battery cycle performance and safety performance.

[0168] The applicant declares that while the above-mentioned embodiments are used to illustrate the technical solutions of this application, this application is not limited to these embodiments, and does not imply that this application must rely on these embodiments in order to be implemented. Persons skilled in the art should understand that any improvements to this application, equivalent replacements for the raw materials of the products of this application, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of this application.

Claims

1. A composite current collector, wherein: The composite current collector comprises: Basement membrane; A transition layer disposed on at least one side of the base film, wherein the material of the transition layer is any one of metal niobium, metal tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound or a combination of at least two thereof; The conductive layer is arranged on the surface of the transition layer on a side relatively far from the base film.

2. The composite current collector according to claim 1, wherein: The base film is made of a polymer, and the polymer includes any one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene or polyimide, or a combination of at least two thereof.

3. The composite current collector according to claim 1 or 2, wherein: The base film has a thickness of 1-10 μm.

4. The composite current collector according to any one of claims 1 to 3, wherein: The niobium alloy includes any one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy or lithium niobate alloy, or a combination of at least two thereof.

5. The composite current collector according to any one of claims 1 to 4, wherein: The tantalum alloy includes any one of tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy or cobalt-tantalum-zirconium alloy or a combination of at least two thereof; Optionally, the niobium-based compound and the tantalum-based compound independently include any one or a combination of at least two of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides or tellurides; Optionally, the material of the transition layer is any one of metal niobium, metal tantalum, niobium pentoxide, tantalum pentoxide, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, lithium niobate alloy, tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy, cobalt-tantalum-zirconium alloy, niobium nitride, tantalum nitride, niobium carbide or tantalum carbide, or a combination of at least two thereof; Optionally, transition layers are provided on both surfaces of the base film.

6. The composite current collector according to any one of claims 1 to 5, wherein: The thickness of the transition layer on one side is greater than or equal to 5 nm, and can be optionally 10-100 nm.

7. The composite current collector according to any one of claims 1 to 6, wherein: The conductive layer is made of metal, and the metal includes any one of elemental aluminum, elemental copper, elemental gold, elemental silver, elemental nickel, elemental zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, nickel alloy or zinc alloy, or a combination of at least two of them.

8. The composite current collector according to any one of claims 1 to 7, wherein: The thickness of the conductive layer on one side is 500-2000 nm, and can be optionally 800-1200 nm.

9. The composite current collector according to any one of claims 1 to 8, characterized in that: A protective layer is provided on the surface of the conductive layer on a side relatively far from the base film; Optionally, the material of the protective layer includes any one of metal nickel, metal chromium, nickel-chromium alloy, nickel alloy, copper alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene or graphene oxide, or a combination of at least two thereof; Optionally, the thickness of the protective layer on one side is 10-100 nm, and optionally 20-80 nm; Optionally, the thickness of the protective layer on one side is less than one tenth of the thickness of the conductive layer on one side.

10. A method for preparing the composite current collector according to any one of claims 1 to 9, comprising the following steps: A transition layer is prepared on at least one surface of the base film, and then a conductive layer is prepared on the surface of the transition layer on a side relatively far from the base film to obtain the composite current collector.

11. The preparation method according to claim 10, wherein: The method for preparing the transition layer includes a magnetron sputtering method; Optionally, the method for preparing the conductive layer includes any one of evaporation, magnetron sputtering, chemical plating, electroplating or CVD, or a combination of at least two thereof.

12. The preparation method according to claim 10 or 11, wherein: After the conductive layer is deposited, a protective layer is prepared on the surface of the conductive layer on a side relatively far from the base film; Optionally, the preparation method of the protective layer includes any one of physical vapor deposition, chemical vapor deposition, in-situ forming or coating, or a combination of at least two of them.

13. The preparation method according to any one of claims 10 to 12, comprising the following steps: (1) preparing a polymer base film with a thickness of 1-10 μm; (2) Depositing a transition layer with a thickness of 10-100 nm on both sides of the polymer base film to obtain a composite film with a transition layer on the surface. The specific process conditions are: power density of 4-7 W / cm 2 , the flow rate of argon gas is 50-60mL / min, the vacuum degree of coating is 0.08-0.1Pa, the coating time is 1-20s, and the cooling temperature of the main roller during coating is 0-20℃; (3) depositing a conductive layer with a thickness of 500-2000 nm on both sides of the composite film to obtain a composite film containing a transition layer and a conductive layer; (4) Preparing a protective layer on the conductive layer: placing the composite film containing the transition layer and the conductive layer in a raw material solution of the protective layer for immersion treatment, and then washing and drying to obtain the composite current collector.

14. An electrode sheet, wherein: The electrode sheet comprises the composite current collector according to any one of claims 1 to 9.

15. A secondary battery, wherein: The secondary battery includes the electrode sheet as claimed in claim 14.

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