Current collector and battery using same

Abstract

The invention provides a current collector and a battery using the same. The current collector comprises a base material layer and N functional layers arranged on at least one surface of the base material layer, the functional layer comprises a middle layer and a metal layer which are compounded in sequence, and the middle layer is compounded with the base material layer; the thermal expansion coefficient of a material a contained in the intermediate layer at a temperature T1 is less than 0, T1 belongs to T2, T2 belongs to x, and x satisfies {x15 DEG C < = x < = 500 DEG C}; the base material layer contains a polymer material and a filler, the thermal expansion coefficient of the filler at a temperature T3 is less than 10 * 10 <-6 > / DEG C, T3 belongs to T4, T4 belongs to y, y satisfies {y15 DEG C < = y < = 500 DEG C}, and the mass ratio of the filler in the base material layer is 0.5-30%. The current collector provided by the invention is low in residual stress, the risks of interlayer defects, cracking, layering, wrinkling and falling of the current collector can be reduced, and the electrochemical performance and the safety performance of the battery applying the current collector are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a current collector and a battery using the same. Background Art

[0002] Currently, current collectors based on polymer films have received extensive attention and applications in the new energy industry. The preparation of such current collectors with polymer films as the base film usually adopts the method of physical vapor deposition (PVD) to deposit a layer of metal on the polymer film (such as polyester, polyolefin, etc.), so as to prepare a current collector with good conductivity. Compared with the traditional current collector with metal foil as the substrate, the current collector based on polymer film has the characteristics of low cost, light weight, good internal insulation, etc. These characteristics enable the current collector to reduce the cost of the battery, and improve the energy density and safety of the battery when applied in the battery.

[0003] However, during the preparation of the current collector based on polymer film, residual stress will exist between layers due to the action of thermal stress, growth stress and interface stress during the deposition process. The existence of residual stress is likely to cause failure phenomena such as cracking, delamination, wrinkling and peeling of the current collector, which will have a great impact on the electrochemical performance and safety performance of the battery based on this current collector. Summary of the Invention

[0004] In order to solve the problem that the existing current collector has failure phenomena such as cracking, delamination, wrinkling and peeling due to the residual stress between layers, and improve the electrochemical performance and safety performance of the battery using the current collector, the present invention provides a current collector and a battery using the same.

[0005] According to the first aspect of the present invention, a current collector is provided. The current collector includes a substrate layer and N functional layers provided on at least one surface of the substrate layer, where N is an integer greater than or equal to 1; the functional layer includes an intermediate layer and a metal layer which are sequentially compounded, and the intermediate layer is compounded with the substrate layer; the intermediate layer contains material a, and the thermal expansion coefficient of material a at temperature T1 is less than 0, where T1 ∈ T2, T2 ∈ x, and x satisfies {x|15°C ≤ x ≤ 500°C}; the substrate layer contains a polymer material and a filler, and the thermal expansion coefficient of the filler at temperature T3 is less than 10×10 -6 / °C, where T3 ∈ T4, T4 ∈ y, and y satisfies {y|15°C ≤ y ≤ 500°C}, and the mass percentage of the filler in the substrate layer is 0.5 - 30%.

[0006] In the present invention, a functional layer is compounded on the surface of a substrate layer. The functional layer includes an intermediate layer and a metal layer compounded in sequence, and the intermediate layer is directly compounded with the substrate layer, forming a structure in which the substrate layer, the intermediate layer, and the metal layer are compounded in sequence. First, since the intermediate layer contains a material with a coefficient of thermal expansion less than 0, space is reserved for the thermal expansion during the compounding process of the metal layer and the intermediate layer, avoiding residual stress generated by growth stresses in different directions between the intermediate layer and the metal layer, and the interface between the metal layer and the intermediate layer remains intact, which is beneficial to reducing the risk of failure phenomena such as interlayer defects, cracking, delamination, wrinkling, and peeling of the current collector. Second, the direct compounding of the intermediate layer and the substrate layer can eliminate the need for a primer. The intermediate layer serves as a primer for the connection between the substrate layer and the metal layer, which can improve the bonding strength between the substrate layer and the metal layer, making the bonding between layers more compact, and thus improving the mechanical strength of the current collector. Third, adding a filler with a low coefficient of thermal expansion to the polymer material to modify the substrate layer can reduce the coefficient of thermal expansion of the substrate layer, which is beneficial to reducing the difference in the coefficients of thermal expansion between the substrate layer and the intermediate layer, reducing the thermal stress between the substrate layer and the intermediate layer, reducing interfacial interlayer defects and interfacial stress, and being beneficial to improving the bonding strength between the substrate layer and the intermediate layer, making the bonding between layers more compact. Fourth, by controlling the content of the filler in the substrate layer within the range of 0.5 - 30%, the mechanical strength of the current collector can be improved, giving the current collector a high elongation rate, which is beneficial to reducing the risk of interlayer cracking and peeling of the current collector. Fifth, the intermediate layer and the metal layer (N > 1) can be stacked in multiple layers on the substrate layer in sequence. The multi-layer structure reduces the thickness of each layer in the current collector, thereby reducing residual stress, and at the same time, greatly inhibits grain growth, reduces the non-uniformity of grain size, and improves stability, thus solving the problem of excessive difference in the electrochemical performance and mechanical performance of the current collector after placement. Considering the above factors, the residual stress of the current collector provided by the present invention can be reduced, achieving a stress-relieving effect, and significantly improving the electrochemical performance and safety performance of the battery using this current collector.

[0007] It should be noted that: First, the material a contained in the intermediate layer only needs to satisfy that the coefficient of thermal expansion is less than 0 within a certain range of the limited temperature range of 15 - 500°C, and it is not required that the coefficient of thermal expansion within the temperature range of 15 - 500°C is less than 0; Second, the filler contained in the substrate layer also only needs to have a coefficient of thermal expansion less than 10×10 -6 / °C within a certain range of the limited temperature range of 15 - 500°C, and it is not required that the coefficient of thermal expansion within the temperature range of 15 - 500°C is less than 10×10 -6 / °C; Thirdly, the value of the thermal expansion coefficient defined above at a certain temperature does not mean that the temperature needs to reach this value during the actual application of the current collector. Only when the material a contained in the intermediate layer of the current collector and the filler contained in the base material layer can play corresponding roles. In fact, it means that when thermal stress concentration occurs during the preparation process of the current collector, resulting in the appearance of residual stress, the temperature will rise even up to several hundred degrees Celsius at this time. The intermediate layer of the current collector provided by the present invention uses the material a with the above characteristics, and the base material layer uses the filler with the above characteristics, which can prevent the occurrence of thermal stress concentration during the preparation process of the current collector, thereby achieving the technical effect of reducing the residual stress of the current collector.

[0008] Preferably, the polymer material includes at least one of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), ethylene propylene rubber (EPR), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS), polyimide (PI).

[0009] Preferably, the filler includes at least one of a metal material and a non-metal material; the metal material includes at least one of tin, tungsten, molybdenum, chromium, yttrium, gray cast iron, and invar steel; the non-metal material includes at least one of graphite, silicon, calcium carbonate, quartz glass, titanium carbide, silicon carbide, silicon nitride, aluminum oxide, beryllium oxide, cordierite, mullite, zircon, and lead titanate-based compounds.

[0010] Preferably, the material a includes at least one of an open-frame structure compound, a magnetic compound, and a ferroelectric compound.

[0011] Preferably, the open-frame structure compound includes at least one of ZrW2O8 and ZrW2O8-based doped compounds.

[0012] Preferably, the magnetic compound includes at least one of Invar alloy and Mn3AX with an inverse perovskite structure. Among them, the Invar alloy is selected from at least one of 4J32 super-Invar alloy and 4J36 alloy. In Mn3AX with an inverse perovskite structure, A is selected from one of Cu, Zn, Sn, Ni, Al, Ga, Ge, and X is selected from one of N, C.

[0013] Preferably, the ferroelectric compound includes at least one of PbTiO3 and PbTiO3-based doped compounds.

[0014] By adopting a specific intermediate layer material, it is beneficial to further improve the stress removal effect of the current collector, and further improve the electrochemical performance and safety performance of the battery using the current collector.

[0015] Preferably, the metal layer contains at least one of aluminum, copper, gold, silver, nickel, zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, nickel alloy, and zinc alloy.

[0016] Preferably, the current collector further includes a protective layer, and the protective layer is compounded with the surface of the functional layer away from the substrate layer; the protective layer contains at least one of nickel, chromium, nickel-chromium alloy, nickel-based alloy, copper-based alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nanotube, carbon nanofiber, graphene, and graphene oxide.

[0017] By compounding a protective layer containing specific materials on the surface of the functional layer away from the substrate layer (i.e., the surface of the metal layer on the outermost side of the current collector), it can not only effectively prevent the metal layer from being chemically corroded or physically damaged, ensure that the current collector functions better, but also extend the service life of the current collector.

[0018] Preferably, the current collector further includes a protective layer, and the protective layer is compounded with the surface of the functional layer away from the substrate layer, and the protective layer contains material a.

[0019] In addition to additionally providing a protective layer on the surface of the functional layer, an additional intermediate layer can also be provided on the side of the functional layer away from the substrate layer as a protective layer, which can also protect the outermost metal layer. It can ensure that there is an intermediate layer on both sides of each metal layer, and then the stress-relieving effect can be achieved, so that the electrochemical performance and safety performance of the battery using the current collector are significantly improved.

[0020] Preferably, the thickness of the substrate layer is 1-10 μm.

[0021] Preferably, the substrate layer is prepared by the melt-extrusion-biaxial stretching method.

[0022] Preparing the substrate layer by the melt-extrusion-biaxial stretching method and controlling the thickness of the substrate layer between 1-10 μm can not only meet the actual application requirements of the current collector but also take into account the difficulty of the preparation process and the level of cost.

[0023] Preferably, the thickness of the intermediate layer is 5-200 nm.

[0024] Preferably, the intermediate layer is one or more layers, and the total thickness of the intermediate layer is less than 30% of the thickness of the metal layer.

[0025] Preferably, the thickness of the metal layer is 50-1200 nm.

[0026] Controlling the thickness of the metal layer between 50 and 1200 nm can not only improve the conductivity of the metal layer and the current collector, but also contribute to increasing the energy density of the battery using this current collector. If the thickness of the metal layer is too thin, the conductivity of the metal layer and the current collector will be poor; if the thickness of the metal layer is too thick, the current collector will be too heavy, which is not conducive to increasing the energy density of the battery using this current collector.

[0027] Preferably, the metal layer is prepared by one or more of vacuum evaporation, magnetron sputtering, electroless plating, electroplating, chemical vapor deposition (CVD).

[0028] Preferably, the metal layer is prepared by electroplating or magnetron sputtering.

[0029] Preferably, the conditions for preparing the metal layer by electroplating are as follows: the anode is a metal with a purity of ≥99.9%, the cathode is a titanium plate; the current intensity is 20000 - 50000 A, and the current density is 5000 - 10000 A / m 2 ; the copper ion concentration is 65 - 100 g / L, and the acid concentration of the electrolyte is 90 - 110 g / L.

[0030] Preferably, the conditions for preparing the metal layer by magnetron sputtering are as follows: the target is copper with a purity of ≥99.9%, the target power supply is a DC power supply, the power is 8 - 15 kW, the vacuum degree of the vacuum chamber is ≤0.1 Pa, the gas source is argon, the argon flow rate is 20 - 500 mL / min, and the coating time for each time is 0.1 - 120 s.

[0031] Preferably, the thickness of the protective layer is 10 - 100 nm.

[0032] Preferably, the protective layer is prepared by one or more of physical vapor deposition, chemical vapor deposition, in-situ forming, coating.

[0033] According to the second aspect of the present invention, a battery is provided, which includes the above current collector.

[0034] Applying the current collector provided by the present invention to a battery can improve the electrochemical performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of the current collector provided in Example 1.

[0036] Figure 2 It is a schematic structural diagram of the current collector provided in Example 11. DETAILED DESCRIPTION OF THE INVENTION

[0037] The technical features in the technical solutions provided by the present invention will be further clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0038] Example 1

[0039] A current collector has a structure as Figure 1 shown. The current collector includes a substrate layer 1 and a layer of functional layer 2 and a protective layer 3 sequentially provided on two surfaces of the substrate layer. In the direction away from the substrate layer 1, the functional layer 2 includes an intermediate layer 4 and a metal layer 5 which are sequentially compounded. Among them, the thickness of the substrate layer 1 is 4.5 μm, the thickness of the intermediate layer is 100 nm, the thickness of the metal layer is 900 nm, and the thickness of the protective layer is 20 nm;

[0040] The current collector provided in this embodiment is prepared through the following steps:

[0041] S1. Alumina ceramic particles and polyethylene terephthalate (PET) are mixed evenly according to a mass ratio of 5:95, and then a base film with a thickness of 4.5 μm is prepared by the melt-extrusion-biaxial stretching method, and this base film is used as the substrate layer 1;

[0042] S2. The prepared base film is placed in a magnetron sputtering machine, and ZrW 1.9 Nb 0.1 O8 is used as the target, and a 100-nm intermediate layer 4 is deposited on each of the two surfaces of the base film to obtain a PET composite film with the intermediate layer 4 on the surface;

[0043] Among them, ZrW 1.9 Nb 0.1 O8 is prepared through the following steps: ZrO2, WO3, and Nb2O5 are mixed according to a molar ratio of 1:1.9:0.05 and ball-milled for 12 hours. Then, the ball-milled mixture is pre-sintered at 950 °C for 10 hours, and finally sintered at 1150 °C under argon protection for 36 hours to obtain ZrW 1.9 Nb 0.1 O8. Among them, WO3 should be in an excess of 2% and sealed to prevent volatilization;

[0044] S3. Place the prepared PET composite film in a magnetron sputtering machine, and deposit a metal layer 5 with a thickness of 900 nm on each of the two surfaces of the PET composite film with an intermediate layer on the surface, to obtain a PET composite film with an intermediate layer 4 and a metal layer 5 on the surface. The preparation conditions are as follows: Use copper with a purity of 99.99% as the target, the power is 12.0 kW, the argon flow rate is 70 mL / min, the coating vacuum is 0.1 Pa, the coating time is 100 s, and the cooling temperature of the main roller during the coating process is -5°C;

[0045] S4. Place the prepared PET composite film with an intermediate layer 4 and a metal layer 5 on the surface in an aqueous solution of chromic anhydride (chromium trioxide) with a concentration of 0.5 g / L (25°C) and soak it for 20 s. After the treatment is completed, wash it through a pure water tank. After the washing is completed, place it in an oven at 60°C for drying to form a protective layer 3 with a thickness of 20 nm, and obtain the current collector of this example.

[0046] Example 2

[0047] This example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, the mass ratio of alumina ceramic particles to PET is 0.5:99.5. Except for the above differences, the materials, formula ratios, and preparation operations used in this example are strictly the same as those in Example 1.

[0048] Example 3

[0049] This example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, the mass ratio of alumina ceramic particles to PET is 30:70. Except for the above differences, the materials, formula ratios, and preparation operations used in this example are strictly the same as those in Example 1.

[0050] Example 4

[0051] This example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, an equal amount of metallic tin is used to replace the alumina ceramic particles. Except for the above differences, the materials, formula ratios, and preparation operations used in this example are strictly the same as those in Example 1.

[0052] Example 5

[0053] This example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S2 of the current collector, 4J32 invar alloy is used as the target. Except for the above differences, the materials, formula ratios, and preparation operations used in this example are strictly the same as those in Example 1.

[0054] Example 6

[0055] This embodiment provides a current collector. Compared with Embodiment 1, the difference in composition is that in the preparation step S2 of the current collector, Mn3ZnN is used as the target material. Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0056] Embodiment 7

[0057] This embodiment provides a current collector. Compared with Embodiment 1, the difference in composition is that in the preparation step S2 of the current collector, Mn3Cu 0.85 Ge 0.15 N is used as the target material;

[0058] Among them, Mn3Cu 0.85 Ge 0.15 N is prepared through the following steps: Weigh the Mn source material, Cu source material, and Ge source material according to the molar ratio of Mn:Cu:Ge = 3:0.85:0.15, mix them evenly, then melt them 3 times under argon protection, then nitridize them in an ammonia atmosphere at 650 °C for 15 hours (control the ammonia flow rate at 30 mL / min), and finally keep them at 750 °C for 15 hours to obtain Mn3Cu 0.85 Ge 0.15 N.

[0059] Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0060] Embodiment 8

[0061] This embodiment provides a current collector. Compared with Embodiment 1, the difference in composition is that in the preparation step S2 of the current collector, Pb 0.9 Bi 0.1 TiO3 is used as the target material;

[0062] Among them, Pb 0.9 Bi 0.1 TiO3 is prepared through the following steps: Weigh the Pb source material, Bi source material, and Ti source material according to the molar ratio of Pb:Bi:Ti = 0.9:0.1:1, mix them evenly, pre-burn them at 550 °C for 4 hours, then sinter them at 950 °C for 2 hours using the double crucible method, and add PbZrO3 buffer powder to prevent volatilization. Finally, anneal them in an oxygen atmosphere at 600 °C for 8 hours to obtain Pb 0.9 Bi 0.1 TiO3.

[0063] Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0064] Embodiment 9

[0065] This embodiment provides a current collector. Compared with Embodiment 1, the difference in composition is that the thickness of the intermediate layer is 5 nm. Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0066] Embodiment 10

[0067] This embodiment provides a current collector. Compared with Embodiment 1, the difference in composition is that the thickness of the intermediate layer is 200 nm. Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0068] Embodiment 11

[0069] A current collector, compared with Embodiment 1, the difference in composition is that the structure of the current collector provided in this embodiment is as Figure 2 shown. The current collector includes a substrate layer 1 and two functional layers 2 and a protective layer 3 sequentially provided on the two surfaces of the substrate layer. In the direction away from the substrate layer 1, each functional layer 2 includes an intermediate layer 4 and a metal layer 5 sequentially laminated. Among them, the thickness of the substrate layer 1 is 4.5 μm, the thickness of each intermediate layer is 100 nm, the thickness of each metal layer is 450 nm, and the thickness of the protective layer is 20 nm. Except for the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly the same as those in Embodiment 1.

[0070] Embodiment 12

[0071] A current collector, compared with Embodiment 11, the difference in composition is that the protective layer is replaced by an intermediate layer, and the material of the intermediate layer is ZrW 1.9 Nb 0.1 O8.

[0072] Comparative Example 1

[0073] This comparative example provides a current collector. Compared with Embodiment 1, the difference in composition is that the current collector provided in this comparative example does not contain an intermediate layer. Except for the above differences, the materials, formulation ratios, and preparation operations used in this comparative example are strictly the same as those in Embodiment 1.

[0074] Comparative Example 2

[0075] This comparative example provides a current collector. Compared with Embodiment 9, the difference in composition is that in the preparation step S2 of the current collector, nickel-chromium alloy is used to replace ZrW 1.9 Nb 0.1 O8 as the target material. Except for the above differences, the materials, formulation ratios, and preparation operations used in this comparative example are strictly the same as those in Embodiment 1.

[0076] Comparative Example 3

[0077] This comparative example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, the base material layer does not contain alumina ceramic particles. Except for the above difference, the materials, formula ratios, and preparation operations used in this comparative example are strictly the same as those in Example 1.

[0078] Comparative Example 4

[0079] This comparative example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, the mass ratio of alumina ceramic particles to PET is 0.1:99.9. Except for the above difference, the materials, formula ratios, and preparation operations used in this comparative example are strictly the same as those in Example 1.

[0080] Comparative Example 5

[0081] This comparative example provides a current collector. Compared with Example 1, the difference in composition is that in the preparation step S1 of the current collector, the mass ratio of alumina ceramic particles to PET is 35:65. Except for the above difference, the materials, formula ratios, and preparation operations used in this comparative example are strictly the same as those in Example 1.

[0082] Test Example

[0083] 1. Test Subjects

[0084] In this test example, the composite current collectors prepared in Examples 1 to 12 and Comparative Examples 1 to 5 were used as test subjects for relevant performance tests.

[0085] 2. Test Contents

[0086] (1) Test of Initial Resistance and Sheet Resistance after 24 Hours of Placement

[0087] The prepared current collector samples were placed on the sample stage, and the initial sheet resistance and the sheet resistance after 24 hours of placement of the current collector were tested using a four-probe sheet resistance meter.

[0088] (2) Tensile Strength Test

[0089] The tensile strength of the prepared current collector was tested in accordance with Standard GB / T 1040.3 - 2006.

[0090] (3) Safety Performance Test

[0091] Apply the current collector to a lithium-ion battery, and then test the safety performance of the lithium-ion battery according to the following steps: Verify the safety performance of the lithium-ion battery by means of a nail penetration test. Specifically, place the lithium-ion battery in a nail penetration test device for testing. Among them, the diameter of the nail is 3 mm, the nail penetration speed is 10 mm / s, the sampling interval is 100 ms, and the sampling time is 15 min.

[0092] Take 100 lithium-ion batteries as test samples. If the battery does not explode, catch fire, or emit smoke, it indicates that the safety performance of the lithium-ion battery is qualified. Finally, record the number of lithium-ion batteries with qualified safety performance, and express the safety performance of the lithium-ion battery with the current collector applied by the qualification rate. The calculation formula for the qualification rate is as follows: Qualification rate (%) = Number of lithium-ion batteries with qualified safety performance / Total number of test samples × 100%.

[0093] The lithium-ion batteries used for testing are prepared according to the following steps:

[0094] ① Preparation of the positive electrode sheet: Use LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622) as the positive electrode active material, use carbon black as the conductive agent, and form a positive electrode active material layer on the surface of the positive electrode current collector aluminum foil (thickness: 13 μm), thereby obtaining the positive electrode sheet;

[0095] ② Preparation of the negative electrode sheet: Use the current collectors prepared in Examples 1 to 12 and Comparative Examples 1 to 3 as the negative electrode current collector, use artificial graphite as the negative electrode active material, use carbon black as the conductive agent, and form a negative electrode active material layer on the surface of the negative electrode current collector, thereby obtaining the negative electrode sheet;

[0096] ③ Selection of the separator: Use an alumina ceramic-coated polyethylene separator (thickness: 25 μm) as the separator for assembling the lithium-ion battery;

[0097] ④ Preparation of the electrolyte: Mix propylene carbonate, ethylene carbonate, and ethyl methyl carbonate evenly according to a mass ratio of 1:1:1 to obtain a carbonate solvent. Add LiPF6 to the above carbonate solvent to prepare a carbonate solution containing 1 mol / L LiPF6, and use this carbonate solution as the electrolyte of the lithium-ion battery;

[0098] ⑤ Assembly of the lithium-ion battery: Stack the positive electrode sheet, separator, and negative electrode sheet prepared above in sequence to prepare a bare battery cell. Then place the bare battery cell in the outer packaging case of the lithium-ion battery, inject the electrolyte after drying, and obtain the lithium-ion battery through processes such as vacuum packaging, standing, formation, and shaping.

[0099] (4) Coefficient of thermal expansion

[0100] The coefficient of thermal expansion of the material was tested by a high-precision dilatometer (push-rod type), and the test principle and specific operation steps are as follows:

[0101] a. Principle: One end of the sample is fixed, and the other end is connected to a displacement sensor (such as an LVDT, a laser interferometer, or a capacitance sensor). During the heating process, the sample expands, pushing the push-rod to generate displacement, and the temperature-displacement curve is recorded by the sensor;

[0102] b. Steps: The sample is processed into a standard size (such as Φ6×25 mm) and the surface is ensured to be flat to obtain the sample to be tested; the instrument is calibrated using a standard sample with a known CTE (such as sapphire, quartz); the temperature is increased at a constant rate (1-5 °C / min) in an inert atmosphere (such as nitrogen), and the temperature and displacement are recorded synchronously; through the formula the linear expansion coefficient of the material (i.e., the coefficient of thermal expansion) is calculated, where α represents the linear expansion coefficient of the material, with the unit of °C -1 or K -1 , ΔL represents the change in the length of the material, with the unit of m or mm, L0 represents the initial length of the material, with the unit of m or mm, and ΔT represents the change in temperature, with the unit of °C or K.

[0103] 3. Experimental results

[0104] Table 1 Test results of the relevant properties of the current collector and the lithium-ion battery

[0105]

[0106]

[0107] The test results of the relevant properties of the current collectors prepared in Examples 1-12 and Comparative Examples 1-5 and the lithium-ion batteries using them are shown in Table 1.

[0108] The current collector provided in Comparative Example 1 does not contain an intermediate layer. The intermediate layer material of the current collector provided in Comparative Example 2 is nickel-chromium alloy, and the thermal expansion coefficient of nickel-chromium alloy is greater than 0 in the entire range of 15 to 500 °C. Compared with Comparative Examples 1-2, the material used for the intermediate layer of the current collectors provided in Examples 1-12 is one of an open-frame structure compound, a magnetic compound, and a ferroelectric compound. By comparing the performance test data of the current collectors prepared in Comparative Examples 1-2 and Examples 1-12 and the lithium-ion batteries using them, it can be seen that the initial resistance and the resistance after being placed for 24 h of the current collectors prepared in Examples 1-12 are lower than those of Comparative Examples 1-2, the tensile strength is higher than that of Comparative Examples 1-2, and the safety performance of the lithium-ion batteries using the current collectors provided in Examples 1-12 is also higher than that of Comparative Examples 1-2. The reason for the above results is that: the material used for the intermediate layer of the current collectors provided in Examples 1-12 is one of an open-frame structure compound, a magnetic compound, and a ferroelectric compound, and the thermal expansion coefficient of these materials is less than 0 in a certain range within the entire range of 15 to 500 °C. First, it reserves space for the thermal expansion during the compounding process of the metal layer and the intermediate layer, avoiding the residual stress generated by the growth stress in different directions between the intermediate layer and the metal layer, and the interface between the metal layer and the intermediate layer remains intact, which is beneficial to reducing the risk of failure phenomena such as interlayer defects, cracking, delamination, wrinkling, and peeling of the current collector, thereby improving the electrochemical performance and safety performance of the current collector. Second, the intermediate layer containing the above materials is used as a primer for the connection between the substrate layer and the metal layer, which can improve the bonding force between the substrate layer and the metal layer, make the bonding between the layers more compact, and further improve the tensile strength of the current collector.

[0109] The substrate layer of the current collector provided in Comparative Example 3 does not contain a filler. The mass percentage of the filler in the substrate layer of the current collectors provided in Comparative Examples 4 and 5 is 0.1% and 35% respectively. Compared with Comparative Examples 3-5, the substrate layer of the current collector provided in Example 1 contains a filler with a thermal expansion coefficient less than 10×10 -6 / °C within a certain range in the entire range of 15 to 500 °C, and the mass percentage of the filler in the substrate layer is between 0.5% and 30%. The test results show that the tensile strength of the current collector prepared in Example 1 is higher than that of Comparative Examples 3-5, and the lithium-ion battery using the current collector provided in Example 1 has excellent safety performance.

[0110] The above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A current collector, characterized in that: The current collector includes a substrate layer and N functional layers provided on at least one surface of the substrate layer, where N is an integer greater than or equal to 1; The functional layer includes an intermediate layer and a metal layer which are sequentially compounded, and the intermediate layer is compounded with the substrate layer; The intermediate layer contains material a, and the thermal expansion coefficient of material a at temperature T1 is less than 0, where T1 ∈ T2, T2 ∈ x, and x satisfies {x|15°C ≤ x ≤ 500°C}; The substrate layer contains a polymer material and a filler, and the coefficient of thermal expansion of the filler at temperature T3 is less than 10×10 -6 / °C, where T3 ∈ T4, T4 ∈ y, and y satisfies {y|15°C ≤ y ≤ 500°C}, and the mass percentage of the filler in the substrate layer is 0.5 to 30%.

2. The current collector according to claim 1, wherein: The filler includes at least one of a metal material and a non-metal material; The metal material includes at least one of tin, tungsten, molybdenum, chromium, yttrium, gray cast iron, and invar steel; The non-metal material includes at least one of graphite, silicon, calcium carbonate, quartz glass, titanium carbide, silicon carbide, silicon nitride, aluminum oxide, beryllium oxide, cordierite, mullite, zircon, and lead titanate-based compounds; 3. The current collector according to claim 1, characterized in that: The material a includes at least one of an open-framework structure compound, a magnetic compound, and a ferroelectric compound; 4. The current collector according to claim 3, characterized in that: The open-framework structure compound includes at least one of ZrW2O8 and ZrW2O8-based doped compounds; The magnetic compound includes at least one of an Invar alloy and Mn3AX having an inverse perovskite structure. Among them, the Invar alloy is selected from at least one of 4J32 super-Invar alloy and 4J36 alloy. In the Mn3AX having an inverse perovskite structure, A is selected from one of Cu, Zn, Sn, Ni, Al, Ga, Ge, and X is selected from one of N and C; The ferroelectric compound includes at least one of PbTiO3 and PbTiO3-based doped compounds; 5. The current collector according to claim 1, wherein: The polymer material includes at least one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene, and polyimide; 6. The current collector according to claim 1, wherein: The metal layer contains at least one of aluminum, copper, gold, silver, nickel, zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, and nickel alloy; 7. The current collector according to claim 1, wherein: The current collector further includes a protective layer, and the protective layer is compounded with the surface of the functional layer away from the substrate layer; The protective layer contains at least one of nickel, chromium, nickel-chromium alloy, nickel-based alloy, copper-based 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, and graphene oxide; 8. The current collector according to claim 1, wherein: The current collector further includes a protective layer, the protective layer is compounded with the surface of the functional layer away from the substrate layer, and the protective layer contains the material a; 9. The current collector according to claim 7 or 8, characterized in that: The thickness of the substrate layer is 1 - 10 μm, and / or the thickness of the intermediate layer is 5 - 200 nm, and / or the thickness of the metal layer is 50 - 1200 nm, and / or the thickness of the protective layer is 10 - 100 nm; 10. A battery, characterized in that: The battery includes the current collector according to any one of claims 1 - 9.

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