Secondary battery and electronic device

Abstract

The invention belongs to the field of electrochemistry, and particularly discloses a secondary battery and an electronic device. The invention provides a secondary battery, which comprises an electrolyte and a pole piece, the pole piece comprises a current collector and an active material layer arranged on at least one side of the current collector, the current collector comprises a first polymer layer, and a second polymer layer and a conductive layer which are sequentially laminated on the surface of the first polymer layer, the second polymer layer is located between the first polymer layer and the conductive layer; the first polymer layer comprises a first polymer, and the second polymer layer comprises a second polymer; the second polymer has a porous structure. The current collector is formed by the two polymer layers and the conductive layer, so that the battery can be light and has relatively high energy density.

Description

Technical Field

[0001] This application belongs to the field of electrochemistry, and particularly relates to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries such as lithium-ion batteries have occupied the mainstream position in the market due to their advantages of high energy density, good safety, no memory effect, and long working life. The lithium-ion battery assembly includes an electrolyte, a positive electrode plate, a negative electrode plate, and current collectors provided on the positive electrode plate and the negative electrode plate. Among them, the current collector is coated with an active material layer to form a positive electrode plate or a negative electrode plate. The current collector not only serves as a carrier for the positive and negative active materials, but also serves as an electron collector and conductor for the positive and negative electrodes, collecting the current generated by the battery active materials to generate a larger output current. Therefore, an ideal current collector often needs to have comprehensive properties such as high conductivity, good stability, and good mechanical strength.

[0003] Currently, metal substrates such as aluminum foil or copper foil with relatively high conductivity are mostly used as current collectors. The metal substrates have a large density and high self-weight, resulting in a relatively high proportion of their weight in the battery and being unable to achieve lightweight; and due to their high self-weight and other reasons, they will reduce the energy density of the battery. Therefore, how to improve the energy density of the battery by lightweighting the current collector has become one of the main research directions at present. Summary of the Invention

[0004] In view of the above problems existing in the prior art, this application provides a secondary battery and an electronic device to improve the problems of large weight and low energy density of the current collector.

[0005] In a first aspect, this application provides a secondary battery, including an electrolyte and an electrode plate. The electrode plate includes a current collector and an active material layer provided on at least one side of the current collector. The current collector includes a first polymer layer, and a second polymer layer and a conductive layer sequentially stacked on the surface of the first polymer layer. The second polymer layer is located between the first polymer layer and the conductive layer; the first polymer layer includes a first polymer, and the second polymer layer includes a second polymer; the second polymer has a porous structure.

[0006] Using two polymer layers and a conductive layer to form the current collector can reduce its weight and improve the energy density of the battery compared with the traditional aluminum foil or copper foil metal substrate current collector; at the same time, the second polymer with a porous structure is not only easy to attach the conductive layer, has high electrolyte permeability and liquid absorption rate, but also can shorten the transmission path of lithium ions and improve the transmission efficiency of lithium ions. Therefore, the secondary battery of this application can achieve lightweight and relatively high energy density.

[0007] In some embodiments, the elastic modulus of the first polymer is 5 - 600 GPa. Selecting the first polymer with an elastic modulus of 5 - 600 GPa enables the current collector to have good mechanical properties, solvent resistance, thermal conductivity, chemical stability, and flame retardancy, which can further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery. Preferably, the elastic modulus of the first polymer is 5 - 230 GPa.

[0008] In some embodiments, the first polymer is selected from at least one of aramid fiber, carbon fiber, polyester fiber, polyvinyl alcohol fiber, or polyamide fiber. Selecting the above substances as the first polymer can further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0009] In some embodiments, the surface energy of the second polymer is 15 - 45 mJ / m 2 . Selecting the second polymer with a surface energy of 15 - 45 mJ / m 2 can better adsorb the conductive layer, further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery. Preferably, the surface energy of the second polymer is 22 - 45 mJ / m 2 .

[0010] In some embodiments, the second polymer is selected from at least one of polyamide, polyvinylidene fluoride - hexafluoropropylene, polytetrafluoroethylene, polypropylene, polyethylene, polyethersulfone, or polyimide. Selecting the above substances as the second polymer can further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0011] In some embodiments, the thickness of the current collector is 5 - 30 μm. Making the thickness of the current collector 5 - 30 μm can further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0012] In some embodiments, the thickness ratio of the conductive layer, the second polymer layer, and the first polymer layer is (0.05 - 2 μm):(1.5 - 5 μm):(5 - 20 μm). Making the thickness ratio of the conductive layer, the second polymer layer, and the first polymer layer satisfy the above ratio range can further reduce the density of the current collector, increase the liquid absorption rate of the current collector, and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0013] In some embodiments, the conductive layer includes conductive carbon, and the second polymer layer also includes conductive carbon. Based on the sum of the mass of conductive carbon in the second polymer and the mass of conductive carbon in the conductive layer, the mass percentage of conductive carbon in the second polymer is 5%-80%. Making the conductive layer and the second polymer layer satisfy the above settings can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0014] In some embodiments, the conductive layer includes at least one of elemental aluminum, elemental zinc, and elemental copper.

[0015] In some embodiments, when the conductive layer includes element M, the second polymer layer also includes element M, where element M is selected from at least one of Al, Zn, and Cu. Based on the sum of the mass of element M in the second polymer layer and the mass of element M in the conductive layer, the mass percentage of element M in the second polymer layer is 10%-80%. Making the conductive layer and the second polymer layer satisfy the above settings can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0016] In some embodiments, the electrolyte includes fluoroethylene carbonate. When the mass percentage content of fluoroethylene carbonate in the electrolyte is A%, and the thickness of the first polymer layer is H μm, A and H satisfy the following relationship: 1 ≤ A / H ≤ 3. Making the electrolyte and the thickness of the first polymer layer satisfy the above settings can further improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0017] In a second aspect, the present application provides an electronic device, including the secondary battery provided in the first aspect.

[0018] Advantages of the present application: The present application uses two polymer layers and a conductive layer to form a current collector. Compared with traditional aluminum foil or copper foil metal substrate current collectors, the current collector of the present application can reduce its weight and improve the battery energy density. At the same time, the second polymer with a porous structure is not only easy to attach the conductive layer, has high electrolyte permeability and liquid absorption rate, but also can shorten the lithium ion transport path, improve the lithium ion transport efficiency, and is beneficial to improving the energy density of the battery. Therefore, the secondary battery of the present application can achieve light weight and a relatively high energy density. Specific embodiments

[0019] To better illustrate the purpose, technical solutions, and advantages of the present application, the present application will be further described below through specific comparative examples and examples.

[0020] To better illustrate the purpose, technical solutions, and advantages of the present application, the technical solutions of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. And the embodiments of the present application should not be construed as a limitation of the present application.

[0021] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0022] In the description herein, unless otherwise specified, "above" and "below" include the number itself. Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various measurement methods commonly used in the art. In the description herein, a list of items connected by the terms "at least one of", "at least one item of", "at least one of", "at least one kind of" or other similar terms may mean any combination of the listed items.

[0023] To address the problems of the large weight and low current density of the current collector, the present application provides a secondary battery, including an electrolyte and a pole piece. The pole piece includes a current collector and an active material layer disposed on at least one side of the current collector. The current collector includes a first polymer layer, and a second polymer layer and a conductive layer sequentially stacked on the surface of the first polymer layer. The second polymer layer is located between the first polymer layer and the conductive layer; the first polymer layer includes a first polymer, and the second polymer layer includes a second polymer; the second polymer has a porous structure.

[0024] Using two polymer layers and a conductive layer to form the current collector can reduce its weight and increase the energy density of the battery compared to traditional current collectors made of aluminum foil or copper foil metal substrates; at the same time, the second polymer with a porous structure is not only easy to attach the conductive layer, has high electrolyte permeability, but also can shorten the transmission path of lithium ions, improve the transmission efficiency of lithium ions, and improve the kinetic performance. Therefore, the secondary battery of the present application can achieve light weight and a relatively high energy density.

[0025] In some embodiments, the elastic modulus of the first polymer is 5 - 600 GPa. Specifically, it can be 5 GPa, 50 GPa, 100 GPa, 200 GPa, 300 GPa, 400 GPa, 500 GPa, 600 GPa, or any range formed by any two of these values.

[0026] The elastic modulus of the first polymer is tested using the GB1040 - 79 plastic tensile test method.

[0027] In some embodiments, the density of the first polymer is 0.97 - 1.8 g / cm 3 , specifically, it can be 0.97 g / cm 3 、1 g / cm 3 、1.1 g / cm 3 、1.2 g / cm 3 、1.3 g / cm 3 、1.4 g / cm 3 、1.5 g / cm 3 、1.6 g / cm 3 、1.7 g / cm 3 、1.8 g / cm 3 , or any range formed by any two of these values.

[0028] In some embodiments, the tensile strength of the first polymer is 0.05 - 4.5 GPa. Specifically, it can be 0.04 GPa, 0.1 GPa, 0.5 GPa, 1 GPa, 1.5 GPa, 2 GPa, 2.5 GPa, 3 GPa, 3.5 GPa, 34 GPa, 4.5 GPa, or any range formed by any two of these values.

[0029] In some embodiments, the coefficient of thermal expansion of the first polymer is (0.5 - 180)×10 -6 K -1 , specifically, it can be 0.5×10 -6 K -1 、1×10 -6 K -1 、10×10 -6 K -1 、30×10 -6 K -1 、50×10 -6 K -1 、70×10 -6 K -1 、90×10 -6 K -1 、110×10 -6 K -1 、130×10 -6K -1 、150×10 -6 K -1 、170×10 -6 K -1 、180×10 -6 K -1 or a range formed by any two of these values.

[0030] In some embodiments, the first polymer is selected from at least one of aramid fiber, carbon fiber, polyester fiber, polyvinyl alcohol fiber or polyamide fiber.

[0031] Using the above fiber material with relatively small density and coefficient of expansion, relatively high mechanical strength and aspect ratio, and good resistance to most acids, alkalis and organic solvents as the first polymer can endow the current collector with good mechanical properties (rigidity, elasticity and strength), solvent resistance, thermal conductivity, chemical stability and flame retardancy. It can act as the base film of the second polymer, providing the main mechanical properties of the current collector, and forming a complement with the second polymer in terms of chemical stability, thermal stability and mechanical properties, meeting the requirements of the current collector as a carrier for active materials.

[0032] In some embodiments, the first polymer is also modified with amino groups. For example, the first polymer can be impregnated in an ethanol solution containing 0.5 wt% - 5 wt% of 3-aminopropyltriethoxysilane, and the amino group modification reaction is carried out at 50 °C to 70 °C for 1 - 3 h. The first polymer modified with amino groups can improve its binding strength with the second polymer.

[0033] In some embodiments, the second polymer layers are respectively disposed on two sides of the first polymer layer, and conductive layers are respectively disposed on the surfaces of the two second polymer layers.

[0034] In some embodiments, the average aspect ratio of the first polymer is 500 - 5000. Specifically, it can be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, or a range formed by any two of these values.

[0035] In some embodiments, the specific surface area of the first polymer is 0.1 - 5.0 m 2 / g. Specifically, it can be 0.1 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, or a range formed by any two of these values.

[0036] In some embodiments, the molecular weight of the first polymer is 1,000 - 5,000,000 g / mol. Specifically, it can be 1,000 g / mol, 5,000 g / mol, 10,000 g / mol, 500,000 g / mol, 1,000,000 g / mol, 2,000,000 g / mol, 3,000,000 g / mol, 4,000,000 g / mol, 5,000,000 g / mol, or a range composed of any two of these values.

[0037] In some embodiments, the porosity of the first polymer is 20% - 95%. Specifically, it can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or a range composed of any two of these values.

[0038] In some embodiments, the average pore diameter of the first polymer is 150 - 250 nm. Specifically, it can be 150 nm, 170 nm, 190 nm, 210 nm, 230 nm, 250 nm, or a range composed of any two of these values.

[0039] In some embodiments, the pore diameter of the second polymer is larger than that of the first polymer. The larger pore diameter of the second polymer than that of the first polymer enables the depth of penetration of the conductive substance to only reach the second polymer, preventing the conductive substance in the second polymer from further penetrating into the first polymer and causing a short circuit.

[0040] In some embodiments, the surface energy of the second polymer is 15 - 45 mJ / m 2 , specifically, it can be 15 mJ / m 2 , 20 mJ / m 2 , 25 mJ / m 2 , 30 mJ / m 2 , 35 mJ / m 2 , 40 mJ / m 2 , 45 mJ / m 2 , or a range composed of any two of these values. Thus, the second polymer has high surface properties and is more likely to deposit and adhere to the conductive substance, making it easier for the conductive layer to bind to the second polymer and form a current collector with a stable structure. The surface energy can be measured by conventional methods, such as the contact angle method for the surface energy of the second polymer.

[0041] In some embodiments, the first polymer layer is further sequentially treated with acetone and oxygen plasma; in some embodiments, the time of the oxygen plasma pretreatment is 1-10 min, and the power of the oxygen plasma pretreatment is 20-150 W. After the plasma treatment, the surface energy and the degree of surface roughening can be increased, and the bonding strength between the first polymer and the second polymer can be improved.

[0042] In some embodiments, the density of the second polymer is 0.91-2.6 g / cm 3 , specifically, it can be 0.91 g / cm 3 , 1 g / cm 3 , 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 , 2 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , or the range formed by any two of these values.

[0043] In some embodiments, the tensile strength of the second polymer is 20-150 MPa, specifically, it can be 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, 120 MPa, 140 MPa, 150 MPa, or the range formed by any two of these values.

[0044] In some embodiments, the elastic modulus of the second polymer is 0.5-4 GPa, specifically, it can be 0.5 GPa, 1 GPa, 2 GPa, 3 GPa, 4 GPa, or the range formed by any two of these values. The elastic modulus of the second polymer is tested by the GB1040-79 plastic tensile test method.

[0045] In some embodiments, the coefficient of thermal expansion of the second polymer is (20-180)×10 -6 K -1 , specifically, it can be 20×10 -6 K -1 , 30×10 -6 K -1 , 50×10 -6 K -1 , 70×10 -6 K -1 , 90×10 -6 K -1 , 110×10 -6 K -1, 130×10 -6 K -1 , 150×10 -6 K -1 , 170×10 -6 K -1 , 180×10 -6 K -1 , or a range formed by any two of these values.

[0046] In some embodiments, the molecular weight of the second polymer is 10,000 - 2,000,000 g / mol. Specifically, it can be 10,000 g / mol, 500,000 g / mol, 1,000,000 g / mol, 1,500,000 g / mol, 2,000,000 g / mol, or a range formed by any two of these values.

[0047] In some embodiments, the pore size of the second polymer is 0.01 - 10 μm. Specifically, it can be 0.01 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range formed by any two of these values.

[0048] In some embodiments, the porosity of the second polymer is 20% - 95%. Specifically, it can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or a range formed by any two of these values.

[0049] In some embodiments, the second polymer is selected from at least one of polyamide (PA), polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP), polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), polyethersulfone (PES), or polyimide (PI).

[0050] The above - mentioned second polymer has a porous structure with a uniform pore size distribution, is lightweight, and has good mechanical strength, corrosion resistance, stability, and flame retardancy. It can better adsorb the conductive layer, has high electrolyte permeability, can also shorten the lithium - ion transmission path, improve the lithium - ion transmission efficiency, improve the kinetic performance, and further increase the energy density of the battery.

[0051] The second polymer can be a commercially available porous polymer membrane or can be formed by polymerizing the corresponding polymer monomers to form a porous - structured second polymer.

[0052] The preparation method of the second polymer layer can be attached to the first polymer layer in a conventional manner. For example, it can include coating a solution containing the second polymer on the surface of the first polymer layer, followed by phase separation induction, standing, and annealing in sequence to obtain the second polymer layer. In some embodiments, the mass percentage content of the polymer in the solution containing the second polymer is 5%-15%. In some embodiments, the solution containing the second polymer includes at least one solvent selected from hexafluoroisopropanol (HFIP), N,N-dimethylformamide (DMF), NMP, or water. In some embodiments, the second polymer solution includes HFIP and water, and the volume ratio of HFIP to water is (0.5-2):(3-5). In some embodiments, the coating method includes at least one of spraying, spin coating, or roll coating. In some embodiments, the spraying distance is 10-20 cm, the spraying rate is 10-20 m / s, and the spraying pressure is 0.2-0.4 MPa. In some embodiments, the solution for phase separation induction includes a mixed solution of water and ethanol, the volume of water and ethanol is 1:0.5-2, and in the phase separation induction, the immersion time in the solution for phase separation induction is 5-15 min. In some embodiments, the standing time is 12-48 h, the annealing temperature is 60-85 °C, and the annealing time is 1-3 h.

[0053] In addition, the second polymer layer can be laminated on the first polymer layer by methods such as melt coating, electrospinning, and hot pressing to form the second polymer layer.

[0054] In some embodiments, the thickness of the current collector is 5-30 μm. Specifically, it can be 7 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, or the range composed of any two of these values. Making the thickness of the current collector 5-30 μm can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0055] In some embodiments, the thickness of the conductive layer is 0.05-3 μm. Specifically, it can be 0.005 μm, 0.1 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or the range composed of any two of these values.

[0056] In some embodiments, the thickness H of the first polymer layer is 3-21 μm. Specifically, it can be 3 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21 μm, or the range composed of any two of these values.

[0057] In some embodiments, the thickness of the second polymer layer is 1-6 μm. Specifically, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or a range composed of any two of these values.

[0058] In some embodiments, the thickness ratio of the conductive layer, the second polymer layer, and the first polymer layer is (0.05-2 μm):(1.5-5 μm):(5-20 μm). Specifically, it can be 0.05:1.5:5, 0.05:2.5:5, 0.05:5:5, 1:1.5:5, 1:2.5:5, 1:5:5, 2:1.5:5, 2:2.5:5, 0.05:1.5:7.5, 0.05:2.5:10, 0.05:5:15, 1:1.5:17.5, 1:2.5:20, or a range composed of any two of these values. Making the thickness ratio of the conductive layer, the second polymer layer, and the first polymer layer satisfy the above ratio range can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0059] In some embodiments, the conductive layer includes at least one of a metal and its oxide, an alloy, and a carbon material.

[0060] In some embodiments, when the conductive layer includes conductive carbon, the second polymer layer also includes conductive carbon. Based on the sum of the mass of conductive carbon in the second polymer and the mass of conductive carbon in the conductive layer, the mass percentage of conductive carbon in the second polymer is 5%-80%. Specifically, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, or a range composed of any two of these values. Making the conductive layer and the second polymer layer satisfy the above settings can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0061] When the conductive layer contains a conductive carbon material, the conductive carbon material will penetrate into the pores of the second polymer layer. The distribution of the deposited carbon material mainly depends on the thickness, pore size, and deposition conditions of the second polymer layer. If the content of the deposited conductive carbon material is too low, the conductivity may not meet the requirements for conduction. When the content of the conductive carbon material is too high and the penetration of the conductive carbon into the second polymer layer is excessive, it may affect the mechanical properties of the second polymer layer, such as a decrease in toughness, and may even affect the stability of the overall structure. When the mass percentage of conductive carbon in the second polymer layer is in the range of 5%-80%, the current collector can have good enough conductivity and will not significantly reduce the mechanical properties of the second polymer layer, enabling the current collector to maintain good stability.

[0062] In some embodiments, the carbon material is a conductive carbon material, specifically including at least one of carbon nanotubes or graphene.

[0063] In some embodiments, the conductive layer includes at least one of elemental aluminum, elemental zinc, and elemental copper.

[0064] In some embodiments, when the conductive layer includes element M, the second polymer layer also includes element M, and element M is selected from at least one of Al, Zn, and Cu. Based on the sum of the mass of element M in the second polymer layer and the mass of element M in the conductive layer, the mass percentage of element M in the second polymer layer is 10%-80%. Specifically, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or the range composed of any two of these values. Making the conductive layer and the second polymer layer satisfy the above settings can further reduce the density of the current collector, improve the liquid absorption rate of the current collector and the lithium ion transport efficiency, and improve the energy density of the secondary battery.

[0065] When preparing the conductive layer by depositing metal, the metal element will penetrate into the porous structure of the second polymer layer. The diffusion distance and content of the metal element are related to the pore size, porosity, pore structure, surface chemical properties of the selected second polymer layer, and the deposition rate of the metal in the conductive layer, and are also related to the deposition conditions. For example, for electroplating deposition, the deposition of the conductive layer is related to the current density, electroplating time, electrolyte concentration, reducing agent concentration, temperature, deposition temperature, vacuum degree, deposition time, etc. By adjusting these parameters, a complete surface deposition of the conductive layer can be achieved, and the mass percentage of element M in the second polymer layer can be controlled to be 10%-80%, which can make the overall current collector have high conductivity, good mechanical properties, and low weight. Element M can be tested by common methods in the prior art, such as including ICP testing method, etc.

[0066] The conductive layer can be deposited on the second polymer layer by conventional methods, such as at least one of physical vapor deposition method, chemical vapor deposition method, or chemical electroplating method. In some embodiments, the physical vapor deposition method includes at least one of vacuum evaporation method, atomic layer deposition method, or magnetron sputtering method. In some embodiments, the power of the magnetron sputtering is 50W-100KW, and the substrate transmission rate of the magnetron sputtering is 0.1-0.5μm / s. When the deposited conductive layer is metallic aluminum, the temperature of the substrate is controlled to be less than 80°C, so that Al forms a film at low temperature, which can make the aluminum denser and have a strong bonding force with the second polymer layer. In some embodiments, in the atomic deposition method, the deposition temperature is 80°C-120°C, and the thickness of a single deposition is 0.09nm-0.15nm.

[0067] In some embodiments, in order to improve the adhesion of the conductive layer, before depositing the conductive layer, the composite film layer of the first polymer layer and the second polymer layer is also subjected to oxygen plasma treatment.

[0068] In some embodiments, trimethylaluminum (TMA) and H2O are used as precursors, and an aluminum oxide conductive layer is deposited by atomic layer deposition. To enhance the conductivity of the aluminum oxide conductive layer, conductive phases of AlOxNγ or AlOxCγ can be formed by nitrogen doping (such as by NH3 plasma treatment) or carbon doping (using C2H4 co-deposition).

[0069] In some embodiments, the electrolyte includes fluoroethylene carbonate. When the mass percentage content of fluoroethylene carbonate in the electrolyte is A%, and the thickness of the first polymer layer is H μm, A and H satisfy the following relationship: 0.45 ≤ A / H ≤ 3. Specifically, the value of A / H can be 0.45, 0.5, 1, 1.5, 2, 2.5, 3, or the range composed of any two of these values.

[0070] In some embodiments, the electrolyte includes fluoroethylene carbonate. When the mass percentage content of fluoroethylene carbonate in the electrolyte is A%, and the thickness of the first polymer layer is H μm, A and H satisfy the following relationship: 1 ≤ A / H ≤ 3.

[0071] Fluoroethylene carbonate (FEC) can improve the distribution of the electrolyte in the porous polymer structure, ensure the uniform penetration of the electrolyte into the pores, thereby improving the battery performance and the utilization rate of the electrolyte. In addition, an increase in the FEC content is beneficial to reducing the resistance of the ion transport path and improving the permeability of the electrolyte in the porous polymer. When H is small, a low content of FEC is required to reduce the impedance of the thick SEI film and improve the rate performance; for a medium-thickness base film, an appropriate amount of FEC is needed to balance the wettability and interface stability; for a thick base film, a high content of FEC is required to enhance the electrolyte penetration and SEI repair ability and extend the cycle life. Therefore, when the range of A / H is selected, the comprehensive performance of the battery is better.

[0072] In some embodiments, A is 4% - 10%. Specifically, it can be 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or the range composed of any two of these values.

[0073] In some embodiments, the electrode sheet includes a positive electrode sheet and a negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet includes the current collector.

[0074] In some embodiments, the positive electrode sheet includes the current collector and a positive electrode active material layer provided on at least one side of the current collector.

[0075] In some embodiments, the positive electrode sheet further includes a binder and a conductive agent.

[0076] In some embodiments, the binder includes at least one of styrene-butadiene rubber (SBR), aqueous acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA). It is not limited to the above types, and the binder can be selected according to actual needs.

[0077] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium manganate, lithium manganese iron phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, or lithium manganese silicate.

[0078] In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode active material is 50%-99%.

[0079] In some embodiments, in the positive electrode sheet, based on the total mass of the positive electrode active material layer, the mass percentage of the binder is less than or equal to 5%.

[0080] In some embodiments, the conductive agent includes at least one of graphite, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, or carbon nanofibers, but is not limited to the above several, and the conductive agent can be selected according to actual needs.

[0081] In some embodiments, in the positive electrode sheet, based on the total mass of the positive electrode active material layer, the mass percentage of the conductive agent is 1% to 3%.

[0082] The positive electrode sheet can be prepared by a conventional preparation method in the art. For example, the preparation method of the positive electrode sheet includes the following steps: mixing a solvent, a conductive agent, a binder, and a positive electrode material to obtain a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and drying and cold pressing to obtain a positive electrode sheet.

[0083] In some embodiments, the solvent may include N-methylpyrrolidone (NMP), but is not limited thereto.

[0084] In some embodiments, the negative electrode sheet includes the current collector and a negative electrode active material layer provided on at least one side of the current collector.

[0085] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon material, silicon-oxygen material, Li alloy, and metallic lithium, but is not limited thereto.

[0086] In some embodiments, based on the total mass of the negative electrode active material layer, the mass percentage of the negative electrode active material is 50%-99%.

[0087] In some embodiments, the secondary battery further includes a separator located between the positive electrode sheet and the negative electrode sheet. In some embodiments, the separator includes a resin in the form of a porous sheet or non-woven fabric, and the resin includes at least one of polyolefin, aromatic polyamide, polytetrafluoroethylene, or polyethersulfone, but is not limited thereto.

[0088] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The types of the organic solvent and the lithium salt are not specifically limited in this application and can be selected according to actual needs.

[0089] In some embodiments, the organic solvent can be at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), or diethyl sulfone (ESE).

[0090] In some embodiments, the organic solvent includes FEC, PC, and EC.

[0091] In some embodiments, the organic solvent includes PC and EC, and the mass ratio of PC to EC is (2.5-3.5):1.

[0092] In some embodiments, the lithium salt may be at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), or lithium bis(oxalato)borate (LiBOB).

[0093] The secondary battery of the present application can be prepared by conventional methods in the art. For example, the preparation method may specifically include the following steps: stacking the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator between the positive electrode sheet and the negative electrode sheet, and winding to obtain an electrode assembly; placing the electrode assembly in a packaging shell, injecting an electrolyte, and sealing to obtain a secondary battery.

[0094] In a second aspect, the present application provides an electronic device including the secondary battery. The electronic device of the present application can be used in various fields such as electronic products, energy storage, power batteries, and electric vehicles, such as mobile phones, laptop computers, power tools, video recorders, backup power supplies, electric vehicles, electric motorcycles, game consoles, cameras, and drones.

[0095] The technical solution of the present application will be described below with reference to specific examples and comparative examples. Unless otherwise specified, materials, reagents, equipment, etc. used can be obtained through commercial channels.

[0096] Example 1

[0097] (1) First polymer layer: A porous aramid fiber Kevlar membrane with an average pore diameter of 200 nm, a porosity of 55%, and a thickness of 10 μm is used as the first polymer. It is treated with O2 plasma with a power of 100 W for 3 minutes during the treatment process to increase the surface energy; then it is ultrasonically treated for 10 minutes in a mixed solution with a volume ratio of ethanol to deionized water of 1:1 to remove surface impurities, and dried in a vacuum oven at 60 °C for 2 hours. It is used as the first polymer layer, and this first polymer layer serves as the base film for the subsequent second polymer layer.

[0098] (2) Composite membrane: polyamide polymer (PA) was dissolved in hexafluoroisopropanol (HFIP) and the PA concentration was controlled to be 12 wt %; deionized water (water to solvent volume ratio of 1:4) was added and stirred at room temperature for 4 h until a transparent solution was obtained; the first polymer layer was kept flat and the homogeneous solution was evenly sprayed on both sides of the first polymer layer by spraying, and it was ensured that the solution completely covered the first polymer layer to control the target thickness; the first polymer layer was immersed in a mixed solution bath of water and ethanol (volume ratio of 1:1) for 10 minutes to induce phase separation, and the layer was allowed to stand in a fume hood at 25°C for 24 h, and then annealed at 80°C for 1 h to form a double-sided second polymer layer on the first polymer layer. The thickness of the second polymer layers on both sides was the same, and then O2 plasma treatment was performed. The power of the treatment process was 100 W and the treatment time was 10 minutes to enhance the surface energy and obtain a composite membrane.

[0099] (3) Conductive layer: Conductive carbon (carbon black), binder (PVDF) and solvent (NMP) are mixed evenly in a mass ratio of 40:5:55, and the viscosity is adjusted to obtain a conductive slurry; the conductive slurry is transferred to a vacuum impregnation tank, the composite membrane is immersed in the slurry, and vacuum is applied for 30 minutes; the vacuum is slowly released and the mixture is allowed to stand for 10 minutes to ensure filling; the mixture is cured and NMP is removed in an oven at 80°C for 2 hours, and then annealed in a N2 atmosphere at 250°C for 1 hour to form a conductive layer with a continuous conductive network on both sides of the composite membrane. The thickness of the conductive layers on both sides is the same, and a positive electrode current collector is obtained.

[0100] Since the second polymer layer is a porous structure, the conductive material of the conductive layer will penetrate into the second polymer layer and form a conductive layer of a certain thickness on the surface of the second polymer. The thickness of the conductive layer referred to herein is the thickness of the conductive material finally deposited on the surface of the second polymer layer. When conductive carbon is deposited as the conductive material of the conductive layer, the conductive carbon is generally first deposited on the surface of the second polymer to form a layer, and then the deposited conductive layer penetrates into the second polymer layer; when metal is deposited as the conductive material of the conductive layer, the metal is generally first filled in the pore structure of the second polymer part, and then deposited on its surface to form a layer.

[0101] (4) The positive electrode active material lithium cobalt oxide, acetylene black conductive agent, and polyvinylidene fluoride binder are mixed in a weight ratio of 96:2:2, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and then stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode collector prepared in step (3), and dried to obtain a positive electrode sheet coated with a positive electrode material layer on one side. Repeat the above steps on the other surface of the positive electrode collector aluminum foil to obtain a double-sided positive electrode active material layer on the collector. After drying, cold pressing, cutting, and welding of the pole ears, a positive electrode sheet coated with a positive electrode active material layer on both sides is obtained.

[0102] (5) In a dry argon atmosphere glove box, lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solution containing propylene carbonate (PC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC). Based on the mass of the electrolyte, the mass percentage content of LiPF6 was 12.5%, the mass percentage content of fluoroethylene carbonate (FEC) was 9%, and the balance solvent was propylene carbonate (PC) and ethylene carbonate (EC), and the ratio of the mass percentage contents of propylene carbonate (PC) and ethylene carbonate (EC) was 3:1.

[0103] (6) Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water according to a mass ratio of 96:2:2, stirred evenly, and formulated into a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was evenly coated on one surface of the negative electrode current collector copper foil, dried, and a negative electrode sheet with a negative electrode material layer coated on one side was obtained. The above steps were repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a negative electrode active material layer on both sides of the negative electrode current collector copper foil. After drying, cold pressing, cutting, and welding the tab, a negative electrode sheet with a negative electrode active material layer coated on both sides was obtained.

[0104] (7) The positive electrode sheet, the separator (polyethylene porous film), and the negative electrode sheet were stacked in sequence, with the separator placed in the middle between the positive electrode and the negative electrode to play a role in isolation, and then wound to obtain an electrode assembly; the electrode assembly was placed in an outer packaging aluminum-plastic film, injected with electrolyte, encapsulated, and a lithium-ion battery was obtained through processes such as formation, degassing, and edge trimming.

[0105] Among them, the information related to the prepared first polymer layer, second polymer layer, conductive layer, and the content of FEC in the electrolyte, etc. is shown in Tables 1 and 2.

[0106] Examples 2 - 5

[0107] Compared with Example 1, in Examples 2 - 5, the type of the first polymer layer was changed. Among them, the materials of the first polymer layer in Examples 2 - 5 were carbon fiber, polyester fiber, polyvinyl alcohol fiber, and polyamide fiber respectively, and the specific differences are shown in Tables 1 and 2, and the rest are the same.

[0108] Example 6

[0109] Compared with Example 1, in Example 6, the mass percentage content of FEC in the electrolyte was changed, and at the same time, the mass percentage contents of PC and EC were adjusted adaptively, and the ratio of the mass percentage contents of PC and EC remained unchanged. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0110] Examples 7 - 11

[0111] Examples 7-11 are compared with Example 1, where the material of the second polymer layer and the content of FEC in the electrolyte are changed. Among them, the materials of the second polymer layer in Examples 7-11 are polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), and polyethersulfone (PES), respectively. While changing the FEC content, the mass percentages of PC and EC are adjusted adaptively, and the ratio of the percentages of PC and EC remains unchanged. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0112] Examples 12-13

[0113] Examples 12-13 are compared with Example 1, where the thickness of the first polymer layer and the content of FEC in the electrolyte are changed. While changing the FEC content, the mass percentages of PC and EC are adjusted adaptively, and the ratio of the percentages of PC and EC remains unchanged. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0114] Examples 14-15

[0115] Examples 14-15 are compared with Example 1, where the thickness of the first polymer layer is changed. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0116] Examples 16-17

[0117] Examples 16-17 are compared with Example 1, where the thickness of the second polymer layer is changed. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0118] Examples 18-20

[0119] Examples 18-20 are compared with Example 1, where the thickness of the conductive layer is changed. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0120] Examples 21-23

[0121] Examples 21-23 are compared with Example 1, where the material and / or thickness of the conductive layer are changed. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0122] Among them, the conductive material in Examples 21-23 is elemental Al metal, and its deposition method is as follows: using a high-purity aluminum target as the target, at an argon pressure of 0.52 Pa, a magnetron sputtering power of 100 W, and the substrate temperature controlled below 80 °C, a conductive layer of elemental Al metal is sputter-deposited on one side of the composite film, the composite film is flipped, and a conductive layer of elemental Al metal is continuously sputter-deposited on the other side to obtain a double-sided conductive layer on the composite film.

[0123] Example 24

[0124] In Example 24, compared with Example 22, the material of the conductive layer was changed. The specific differences are shown in Tables 1 and 2, and the rest are the same.

[0125] Among them, the conductive material in this example was Al2O3, and its deposition method was as follows: Using atomic layer deposition (ALD) technology, trimethylaluminum (TMA) and H2O were used as precursors, nitrogen was used as the isolation gas, and at a deposition temperature of 100 °C, the Al2O3 conductive layer was cyclically deposited on one surface of the composite film, and the thickness of a single cycle was 0.1 nm; then the other surface was flipped, and the above steps were repeated to obtain the conductive layer on both sides of the composite film.

[0126] Testing method:

[0127] (1) Positive current collector density (g / cm 3 ): Take the current collectors of the same volume size prepared above, weigh them, calculate their density, and a smaller density is more advantageous for the energy density.

[0128] (2) Absorption rate test of the current collector:

[0129] 1. After drying the current collector sample (size 5×5 cm), weigh it (m0), and the weight change rate for three consecutive weighings < 2%;

[0130] 2. Immerse it completely in the electrolyte (the electrolyte corresponding to each example), and start timing;

[0131] 3. Take out the sample every 10 seconds, quickly wipe off the surface droplets and then weigh it (m t ), and the weight change rate for three consecutive weighings < 2%;

[0132] 4. Calculate the absorption rate: Absorption rate = (m t - m0) / (A×t), where A is the sample area (cm 2 ), t is the time (s), and the unit of the absorption rate is mg / (cm 2 ·s).

[0133] (3) Diffusion coefficient measurement: By measuring the diffusion coefficient of ions in the electrolyte, the ion transport efficiency was evaluated. An electrochemical workstation was used for diffusion coefficient measurement, and the diffusion coefficient was measured by chronoamperometry (constant potential step method) or chronopotentiometry (constant current step method), and the diffusion coefficient was calculated by analyzing the current-time curve or voltage-time curve.

[0134] (4) Battery energy density:

[0135] Replace the positive current collector in Example 1 with aluminum foil of the same thickness, and keep the rest the same to form a traditional lithium-ion battery. Test and obtain the energy density of this traditional lithium-ion battery and the lithium-ion batteries of the above-mentioned various examples respectively, and calculate the improvement rate of the energy density of the lithium-ion batteries of the above-mentioned various examples based on the energy density of the traditional lithium-ion battery. When using aluminum foil as the positive current collector of the lithium-ion battery, the mass per unit area is m0; when using the positive current collector prepared in the above example as the positive current collector of the lithium-ion battery, the mass per unit area is m1; then the weight reduction ratio of the positive current collector = (m0 - m1) / m0. However, the energy density is calculated based on the weight of the entire battery. Therefore, keeping other factors unchanged, the weight reduction ratio of the entire battery is the weight reduction ratio of the positive current collector multiplied by the proportion of the positive current collector in the battery weight (denoted as C%). Then the energy density improvement rate = (m0 - m1) / m0 * C%. Select 12μm aluminum foil as a reference, m0 = 32.4×10 -4 g / cm 2 , and the proportion of the current collector weight in the battery weight is 5%, that is, C% = 5%.

[0136] Table 1

[0137]

[0138]

[0139] Table 2

[0140]

[0141]

[0142] Table 3

[0143]

[0144] As can be seen from Examples 1-24, the current collector of the present application is composed of two polymer layers and a conductive layer. Compared with the traditional current collector of aluminum foil or copper foil metal substrate, the current collector of the present application can reduce its weight and improve the energy density of the battery. Among them, the density of the current collector is 0.7 - 2.1 g / cm 3 , and compared with the battery with the traditional current collector, the energy density is increased by 0.9% - 5%; at the same time, the second polymer with a porous structure is not only easy to attach the conductive layer, has high electrolyte permeability, but also can shorten the transmission path of lithium ions, improve the transmission efficiency of lithium ions, and is beneficial to improving the energy density of the battery. Among them, the liquid absorption rate of the current collector reaches 0.04 - 0.25 mg / (cm 2 ·s), and the diffusion coefficient reaches (3 - 4.5)×10 -11 m 2 / s. Therefore, the secondary battery of the present application can achieve light weight and high energy density.

[0145] As can be seen from Examples 1-5, the type of the first polymer layer affects its positive current collector density, liquid absorption rate, diffusion rate, and energy density. Among them, the aramid fiber has a small density, and the liquid absorption rate, diffusion rate, and energy density are the highest.

[0146] Compared with Example 1, in Example 6, the concentration of FEC is reduced, and the liquid absorption rate of the current collector slightly increases, and the diffusion coefficient slightly increases. Compared with Example 1, in Examples 14-15, the value of H is increased, and the current collector density, liquid absorption rate, and diffusion coefficient slightly decrease. However, the energy density can be significantly improved. At the same time, by combining and analyzing Examples 1, 6, 12-13, and 14-15, it can be seen that when the ratio of A / H is 1-3, the liquid absorption rate is greater than 0.1 mg / (cm 2 ·s), the diffusion coefficient can be greater than 4×10 -11 m 2 / s, the energy density improvement rate can reach more than 3%, and the liquid absorption rate, diffusion coefficient, and energy density improvement rate are all relatively high, and its comprehensive performance is better.

[0147] Compared with Example 1, in Examples 18-20, the thickness of the conductive layer is changed, which causes a change in the content of the conductive substance in the second polymer layer. As the thickness of the conductive layer increases, the content of the conductive substance in the second polymer layer gradually decreases, the current collector density gradually increases, the diffusion coefficient slightly decreases, and the energy density slightly decreases. Therefore, it is better to select a relatively small thickness of the conductive layer for the current collector.

[0148] Compared with Example 1, in Examples 21-23, the conductive substance is changed from carbon to metal Al, which causes a change in the conductive substance and its content in the second polymer layer. At the same time, compared with conductive carbon, using a metal single substance as the conductive layer, the current collector density increases, and the diffusion coefficient and energy density slightly decrease; and as the thickness of the conductive layer increases, the content of the conductive substance in the second polymer layer decreases, the current collector density increases, and the liquid absorption rate, diffusion coefficient, and energy density decrease. Therefore, it is better to select conductive carbon as the conductive layer for the performance of the current collector.

[0149] Compared with Example 22, in Example 24, the conductive substance of the conductive layer is changed from Al metal single substance to Al2O3. As a metal conductive layer, Al is usually dense and has a low porosity, while Al2O3 may have different structures, which affect the surface energy and pore structure. Therefore, the electrolyte penetration rate is slightly higher, and the diffusion coefficient is slightly lower due to the insulation of Al2O3, resulting in a decrease in the diffusion coefficient. Therefore, compared with metal oxides, it is better to select a metal single substance as the conductive layer for the comprehensive performance of the current collector.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising an electrolyte and a pole piece, wherein the pole piece comprises a current collector and an active material layer disposed on at least one side of the current collector, characterized in that: The current collector includes a first polymer layer, and a second polymer layer and a conductive layer stacked in sequence on the surface of the first polymer layer, wherein the second polymer layer is located between the first polymer layer and the conductive layer; the first polymer layer includes a first polymer, and the second polymer layer includes a second polymer; and the second polymer has a porous structure.

2. The secondary battery according to claim 1, wherein: Include at least one of the following: The elastic modulus of the first polymer is 5-600 GPa; The surface energy of the second polymer is 15-45 mJ / m 2 .

3. The secondary battery according to claim 1, wherein: Include at least one of the following: The second polymer is selected from at least one of polyamide, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polypropylene, polyethylene, polyether sulfone or polyimide; The first polymer is selected from at least one of aramid fiber, carbon fiber, polyester fiber, polyvinyl alcohol fiber or polyamide fiber.

4. The secondary battery according to claim 1, wherein: The thickness of the current collector is 5-30 μm.

5. The secondary battery according to claim 1, wherein: The thickness ratio of the conductive layer, the second polymer layer and the first polymer layer is (0.05-2 μm):(1.5-5 μm):(5-20 μm).

6. The secondary battery according to claim 1, wherein: When the conductive layer includes conductive carbon, the second polymer layer also includes conductive carbon, and based on the sum of the mass of the conductive carbon in the second polymer and the mass of the conductive carbon in the conductive layer, the mass proportion of the conductive carbon in the second polymer is 5%-80%.

7. The secondary battery according to claim 1, wherein: The conductive layer includes at least one of aluminum, zinc and copper.

8. The secondary battery according to claim 1, wherein: When the conductive layer includes the M element, the second polymer layer also includes the M element, and the M element is selected from at least one of Al, Zn, and Cu. Based on the sum of the mass of the M element in the second polymer layer and the mass of the M element in the conductive layer, the mass proportion of the M element in the second polymer layer is 10%-80%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The electrolyte includes fluoroethylene carbonate. When the mass percentage of fluoroethylene carbonate in the electrolyte is A%, the thickness of the first polymer layer is H μm, and A and H satisfy the following relationship: 1≤A / H≤3.

10. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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