Secondary battery, preparation method thereof and electronic device

Abstract

The invention discloses a secondary battery, a preparation method thereof and an electronic device. The positive pole piece comprises a positive pole current collector and a positive pole material layer arranged on at least one surface of the positive pole current collector, a base material of the positive pole current collector comprises aluminum foil or aluminum alloy foil, an oxide layer is arranged on the surface of the positive pole current collector, the resistivity of the positive pole current collector is R0 omega.cm, and 200 < = R0 < = 1500; the positive current collector comprises a first surface and a second surface which are opposite to each other, the first surface is provided with a first oxide layer, the second surface is provided with a second oxide layer, the thickness of the first oxide layer is H1 [mu] m, the thickness of the second oxide layer is H2 [mu] m, R0 = a * (H1 + H2), and 200 < = a < = 5000. The surface of the positive current collector is provided with the oxide layer, so that the safety performance of the secondary battery can be improved, and meanwhile, the secondary battery has high energy density.

Description

Secondary battery, preparation method thereof, and electronic device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery, a preparation method thereof, and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, offer advantages such as high specific energy, high operating voltage, low self-discharge, compact size, and light weight, making them widely used in consumer electronics. With the widespread adoption of lithium-ion batteries, their safety performance has become a key concern in the industry.

[0003] Currently, the safety performance of secondary batteries is usually improved by providing an undercoat layer, such as a high-resistance coating, between the positive electrode current collector and the positive electrode material layer. However, the preparation process of this method is relatively complicated and may also result in a loss of energy density of the secondary battery.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery, a method for preparing the same, and an electronic device to improve the safety performance of the secondary battery while also enabling it to have a high energy density. The specific technical solution is as follows:

[0006] A first aspect of the present application provides a secondary battery, which includes a positive electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode material layer arranged on at least one surface of the positive electrode collector, the substrate of the positive electrode collector includes aluminum foil or aluminum alloy foil, the surface of the positive electrode collector has an oxide layer, the resistivity of the positive electrode collector is R0Ω·cm, 200≤R0≤1500, preferably 300≤R0≤850; the positive electrode collector includes a first surface and a second surface relative to each other, the first surface has a first oxide layer, the second surface has a second oxide layer, the thickness of the first oxide layer is H1μm, the thickness of the second oxide layer is H2μm, R0=a×(H1+H2), 200≤a≤5000. The positive electrode current collector has an oxide layer on its surface, and the values ​​of R0 and a are regulated within the scope of this application. The above relationship is satisfied between R0 and H1+H2, and there is no need to provide an additional primer layer between the positive electrode current collector and the positive electrode material layer. This can increase the resistivity of the positive electrode current collector and reduce the risk of thermal runaway during the nailing process of the secondary battery, thereby improving the safety performance of the secondary battery while giving it a high energy density.

[0007] In one embodiment of the present application, 0.03≤H1≤3, 0.03≤H2≤3, preferably 0.05≤H1≤0.5, 0.05≤H2≤0.5. By regulating the values ​​of H1 and H2 within the above range, the positive electrode current collector can have an appropriate resistivity, reducing the risk of thermal runaway of the secondary battery while not affecting the electrical performance of the secondary battery, such as the cycle performance, and at the same time helping to improve the safety performance and energy density of the secondary battery.

[0008] In one embodiment of the present application, 0.67≤H1 / H2≤1.5. By regulating the value of H1 / H2 within the above range, the first and second oxide layers can be better utilized, the surface resistance on both sides of the positive electrode current collector can be balanced, the risk of thermal runaway of the secondary battery can be reduced, and the secondary battery can have good cycle performance while improving its safety performance.

[0009] In one embodiment of the present application, 12≤R0×(H1+H2)≤9000, preferably 30≤R0×(H1+H2)≤3000. By regulating the value of R0×(H1+H2) within the above range, the safety performance and energy density of the secondary battery are improved.

[0010] In one embodiment of the present application, the elongation E of the positive electrode current collector is in the range of 0.3% to 5%. By regulating the value of E within the above range, the positive electrode current collector has an appropriate elongation, which helps reduce the risk of oxide layer failure due to cracking of the positive electrode current collector substrate during nailing, reduces short-circuit power, and improves the safety performance of the secondary battery by improving the fire and explosion of the secondary battery.

[0011] In one embodiment of the present application, (H1+H2) / [5×(1+E)]≥0.01. By regulating the value of (H1+H2) / [5×(1+E)] within the above range, the oxide layer can better protect the positive electrode current collector substrate, thereby reducing short-circuit power, improving the short-circuit fire and explosion of the secondary battery, and improving the safety performance of the secondary battery.

[0012] In one embodiment of the present application, the thickness of the positive electrode current collector is H0 μm, 5≤H0≤30. By adjusting the value of H0 within the above range, the secondary battery can have good safety performance and high energy density.

[0013] In one embodiment of the present application, the resistivity of the positive electrode sheet is R Z Ω·cm, 250≤R Z ≤2000. By regulating R Z When the value of is within the above range, the safety performance of the secondary battery can be improved without affecting its cycle performance.

[0014] In one embodiment of the present application, the secondary battery satisfies at least one of the following characteristics: (1) the positive electrode material layer includes a conductive agent, and the mass percentage of the conductive agent is 0.5% to 3% based on the mass of the positive electrode material layer; the conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent includes at least one of conductive carbon fiber, carbon nanotube or graphite fiber, and the second conductive agent includes at least one of graphene or conductive carbon black, and the mass percentage of the first conductive agent in the conductive agent is 30% to 100%; (2) the bonding force between the positive electrode material layer and the positive electrode current collector is F1N / m, and the numerical value of F1 ranges from 3 to 30; (3) the cohesive force of the positive electrode material layer is F2N / m, and the numerical value of F2 ranges from 15 to 80. The secondary battery having the above characteristics has good cycle performance and safety performance as well as high energy density.

[0015] The second aspect of the present application provides a method for preparing the secondary battery provided in the first aspect of the present application, wherein the method for preparing the positive electrode current collector comprises the following steps: removing oil from the surface of the metal foil, washing with water, then placing the metal foil in a 10% to 20% mass fraction sulfuric acid electrolytic cell, electroplating the metal foil as the anode to form an oxide layer on the surface of the metal foil; after the electroplating is completed, the positive electrode current collector is obtained by washing and drying. The metal foil comprises aluminum foil or aluminum alloy foil, and the electroplating current density is 0.3A / dm 2 Up to 2A / dm 2 The electroplating voltage is 8V to 24V, the electroplating time is 0.3min to 10min, and the electroplating temperature is 20±10°C. The positive electrode current collector prepared by the above method has a high density of the oxide layer on the surface of the positive electrode current collector, which can make the positive electrode current collector have a high resistivity. When used in a secondary battery, it can improve the safety performance of the secondary battery while making it have a high energy density.

[0016] The third aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application or the secondary battery prepared by the preparation method provided in the second aspect of the present application. The secondary battery provided in the first aspect of the present application or the secondary battery prepared in the second aspect of the present application has good safety performance and high energy density, and thus the electronic device provided in the present application has a long service life.

[0017] Beneficial effects of this application:

[0018] The present application provides a secondary battery, a method for preparing the same, and an electronic device. The secondary battery includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The substrate of the positive electrode current collector includes aluminum foil or aluminum alloy foil. The surface of the positive electrode current collector has an oxide layer, and the resistivity of the positive electrode current collector is R0 Ω·cm, with a value of 200≤R0≤1500. The positive electrode current collector includes a first surface and a second surface facing each other, the first surface having a first oxide layer, and the second surface having a second oxide layer. The thickness of the first oxide layer is H1 μm, and the thickness of the second oxide layer is H2 μm. R0 = a×(H1+H2), with a value of 200≤a≤5000. The positive electrode current collector has an oxide layer on its surface, and the values ​​of R0 and a are regulated within the scope of the present application. The relationship between R0 and H1+H2 satisfies the above-mentioned relationship, eliminating the need for an additional primer layer between the positive electrode current collector and the positive electrode material layer. This improves the safety performance of the secondary battery while also providing a high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0020] FIG1 is a schematic structural diagram of a positive electrode current collector according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0022] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0023] Without an oxide layer on the surface of the positive electrode current collector, the short-circuit resistance of the secondary battery is too low in the event of a puncture, causing internal short-circuiting and heat generation. This can increase the risk of thermal runaway, leading to dangerous accidents such as combustion and explosion. While applying a primer layer to the surface of the positive electrode current collector can improve the safety of the secondary battery, it also reduces the energy density of the secondary battery, hindering its practical use.

[0024] In view of this, the first aspect of the present application provides a secondary battery, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the substrate of the positive electrode current collector including aluminum foil or aluminum alloy foil, the surface of the positive electrode current collector having an oxide layer, and the resistivity of the positive electrode current collector being R0 Ω·cm, 200≤R0≤1500, preferably 300≤R0≤850, for example, the value of R0 can be 200, 300, 500, 600, 700, 800, 850, 1000, 1200, 1400, 1500, or a range consisting of any two values ​​therein. As shown in FIG1 , the positive electrode current collector 10 includes a substrate 11 and a first surface 12a and a second surface 12b opposite to each other along the thickness direction of the positive electrode current collector 10 itself, the first surface 12a having a first oxide layer 13a, and the second surface 12b having a second oxide layer 13b. The thickness of the first oxide layer is H1 μm, the thickness of the second oxide layer is H2 μm, R0 = a×(H1+H2), 200≤a≤5000, for example, the value of a can be 200, 250, 500, 800, 1000, 1300, 1400, 1700, 2000, 2400, 3000, 3300, 3600, 4000, 4500, 5000 or a range consisting of any two of these values.

[0025] The inventors discovered that when the value of R0 is too small, for example, less than 200, the resistivity of the positive electrode current collector is too low, the short-circuit power of the secondary battery is too high, the risk of thermal runaway during the secondary battery nailing process increases, and the safety performance of the secondary battery cannot be improved. When the value of R0 is too large, for example, greater than 1500, the resistivity of the positive electrode current collector is too high, which will cause the internal resistance of the secondary battery to be too large, which will affect the cycle performance and energy density of the secondary battery. When the value of a is too small, for example, less than 200, the density of the oxide layer is low, the risk of thermal runaway during the secondary battery nailing process increases, and the safety performance of the secondary battery cannot be improved. At the same time, due to the large loose thickness of the oxide layer, it is not conducive to improving the energy density of the secondary battery. When the value of a is too large, for example, greater than 5000, the density of the oxide layer is too high, which will affect the cycle performance of the secondary battery. In addition, the process difficulty is too great, making it difficult to achieve production. The positive electrode current collector has an oxide layer on its surface, and the values ​​of R0 and a are regulated within the scope of this application. The above relationship is satisfied between R0 and H1+H2, and there is no need to provide an additional primer layer between the positive electrode current collector and the positive electrode material layer. This allows the positive electrode current collector to have a higher resistivity, reducing the risk of thermal runaway during the nailing process of the secondary battery, thereby improving the safety performance of the secondary battery while giving it a high energy density.

[0026] In this application, the value of a is related to the density of the oxide layer, and the density of the oxide layer can be measured by the value of a. The larger the value of a, the greater the density of the oxide layer, and the smaller the value of a, the smaller the density of the oxide layer.

[0027] In one embodiment of the present application, 0.03≤H1≤3, 0.03≤H2≤3, preferably 0.05≤H1≤0.5, 0.05≤H2≤0.5, for example, the value of H1 can be 0.03, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3 or a range consisting of any two of the values, and the value of H2 can be 0.03, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3 or a range consisting of any two of the values. By regulating the values ​​of H1 and H2 within the above range, the positive electrode current collector can have a suitable resistivity, which can reduce the risk of thermal runaway of the secondary battery without affecting the electrical properties of the secondary battery, such as the cycle performance, and is conducive to improving the safety performance and energy density of the secondary battery.

[0028] In one embodiment of the present application, 0.67≤H1 / H2≤1.5, for example, the value of H1 / H2 can be 0.67, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or a range consisting of any two of these values. By regulating the value of H1 / H2 within the above range, the role of the first oxide layer and the second oxide layer can be better exerted, so that the surface resistance on both sides of the positive electrode current collector is balanced, the risk of thermal runaway of the secondary battery is reduced, and the secondary battery can have good cycle performance while better improving its safety performance. In addition, problems such as stress deformation caused by the thickness difference between the first oxide layer and the second oxide layer can also be improved.

[0029] In one embodiment of the present application, 12≤R0×(H1+H2)≤9000, preferably 30≤R0×(H1+H2)≤3000. For example, the value of R0×(H1+H2) can be 12, 30, 100, 300, 500, 600, 800, 1000, 2000, 3000, 5000, 7000, 9000, or a range consisting of any two values ​​thereof. By regulating the value of R0×(H1+H2) within the above range, the safety performance and energy density of the secondary battery can be improved while the secondary battery has good charge and discharge performance and cycle performance.

[0030] In one embodiment of the present application, the elongation E of the positive electrode current collector ranges from 0.3% to 5%. For example, the value of E can be 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. By regulating the value of E within the above range, the positive electrode current collector has a suitable elongation, which is conducive to the protective effect of the oxide layer on the substrate of the positive electrode current collector, and can reduce the risk of oxide layer failure due to cracking of the substrate of the positive electrode current collector during nailing, reduce short-circuit power, and thus improve the safety performance of the secondary battery.

[0031] Typically, the elongation of the positive electrode current collector is changed by selecting different types and compositions of materials. This application does not have any particular restrictions on this, and those skilled in the art can select and adjust according to actual needs, as long as the purpose of this application can be achieved.

[0032] In one embodiment of the present application, (H1+H2) / [5×(1+E)]≥0.01, for example, the value of (H1+H2) / [5×(1+E)] can be 0.01, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1, 1.1, 1.2, 1.3, 1.5, 2, or a range consisting of any two of these values. In some embodiments, 0.01≤(H1+H2) / [5×(1+E)]≤1.2. By regulating the value of (H1+H2) / [5×(1+E)] within the above range, the thickness of the oxide layer and the elongation of the positive electrode current collector are matched, so that the oxide layer can better play a protective role on the positive electrode current collector substrate, and reduce the risk of oxide layer failure due to cracking of the positive electrode current collector substrate during the nailing process, thereby reducing the short-circuit power, so that the secondary battery has high energy density and good cycle performance while improving the safety performance of the secondary battery.

[0033] In one embodiment of the present application, the thickness of the positive electrode current collector is H0 μm, 5 ≤ H0 ≤ 30, for example, the value of H0 can be 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or a range consisting of any two of these values. By regulating the value of H0 within the above range, the oxide layer on the surface of the positive electrode current collector can better protect the positive electrode current collector substrate, which can enable the secondary battery to have good cycle performance while further improving its safety performance.

[0034] In one embodiment of the present application, the resistivity of the positive electrode sheet is R Z Ω·cm, 250≤R Z ≤2000. For example, R ZThe value of can be 250, 350, 500, 750, 1000, 1250, 1500, 1750, 2000 or a range consisting of any two values ​​therein. Z The value of within the above range indicates that the positive electrode sheet has a suitable resistivity, which can reduce the risk of thermal runaway of the secondary battery due to nail penetration, improve the safety performance of the secondary battery, and will not affect its cycle performance.

[0035] In one embodiment of the present application, the positive electrode material layer includes a conductive agent, and the mass percentage of the conductive agent is 0.5% to 3% based on the mass of the positive electrode material layer, for example, the mass percentage of the conductive agent can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, or a range consisting of any two values ​​therein. The conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent includes at least one of conductive carbon fiber, carbon nanotube or graphite fiber, and the second conductive agent includes at least one of graphene or conductive carbon black, and the mass percentage of the first conductive agent to the conductive agent is 30% to 100%, for example, the mass percentage of the first conductive agent to the conductive agent is 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range consisting of any two values ​​therein. The conductive agent includes a first conductive agent and a second conductive agent. By regulating the mass percentage of the conductive agent and the mass percentage of the first conductive agent in the conductive agent within the above range, the first conductive agent can form a connection between the positive electrode active material particles, which helps to improve the cohesion of the positive electrode material layer and helps to reduce the risk of short circuit of the positive electrode material layer during the nailing process. In addition, the first conductive agent can form a connection between the positive electrode active material particles and also help to form a conductive network in the positive electrode material layer, which helps to transport ions in the positive electrode material layer, thereby improving the cycle performance of the secondary battery. In addition, the content of the conductive agent can be controlled within a lower range, and the relative content of the positive electrode active material can be increased, so that the secondary battery can have a higher energy density.

[0036] In one embodiment of the present application, the bonding force between the positive electrode material layer and the positive electrode current collector is F1 N / m, where the value of F1 ranges from 3 to 30. For example, the value of F1 can be 3, 5, 10, 13, 15, 18, 20, 23, 25, 28, 30, or a range consisting of any two of these values. The inventors have discovered that the presence of an oxide layer on the surface of the positive electrode current collector not only gives the positive electrode current collector a higher resistivity, but also increases the surface roughness of the positive electrode current collector, thereby increasing the bonding force between the positive electrode material layer and the positive electrode current collector, which is beneficial for improving the safety and cycle performance of the secondary battery.

[0037] In one embodiment of the present application, the cohesive force of the positive electrode material layer is F2 N / m, and the value of F2 ranges from 15 to 80. For example, the value of F2 can be 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or a range consisting of any two of these values. This indicates that the cohesive force of the positive electrode material layer is high, which is beneficial to improving the safety and cycle performance of the secondary battery.

[0038] The second aspect of the present application provides a method for preparing the secondary battery provided in the first aspect of the present application, wherein the method for preparing the positive electrode current collector comprises the following steps: removing oil from the surface of the metal foil, washing with water, then placing the metal foil in a 10% to 20% mass fraction sulfuric acid electrolytic cell, electroplating the metal foil as the anode to form an oxide layer on the surface of the metal foil; after the electroplating is completed, the positive electrode current collector is obtained by washing and drying. The metal foil comprises aluminum foil or aluminum alloy foil, and the electroplating current density is 0.3A / dm 2 Up to 2A / dm 2 The electroplating voltage is 8V to 24V, the electroplating time is 0.3min to 10min, and the electroplating temperature is 20±10℃. For example, the electroplating current density can be 0.3A / dm 2 , 0.5A / dm 2 , 0.8A / dm 2 , 1A / dm 2 , 1.2A / dm 2 , 1.5A / dm 2 , 1.7A / dm 2 , 2A / dm 2 or a range consisting of any two values ​​thereof, the electroplating voltage may be 8V, 10V, 12V, 14V, 15V, 16V, 18V, 20V, 22V, 24V or a range consisting of any two values ​​thereof, the electroplating time may be 0.3min, 0.5min, 1min, 2min, 3min, 5min, 7min, 8min, 10min or a range consisting of any two values ​​thereof, and the electroplating temperature may be 10°C, 13°C, 15°C, 18°C, 20°C, 23°C, 25°C, 28°C, 30°C or a range consisting of any two values ​​thereof. The positive electrode current collector prepared by the above method has a high density of the oxide layer on the surface of the positive electrode current collector, which can make the positive electrode current collector have a high resistivity. When used in a secondary battery, it can improve the safety performance of the secondary battery while making it have a high energy density.

[0039] The present application has no special restrictions on the material of the cathode used in the electroplating process, as long as the purpose of the present application can be achieved. For example, the material of the cathode can include but is not limited to stainless steel. The present application has no special restrictions on the method of surface degreasing and cleaning, as long as the purpose of the present application can be achieved. For example, it can be achieved by plasma cleaning and degreasing agent cleaning. The present application has no special restrictions on the parameters of plasma cleaning. For example, the plasma emitter power can be set to 20 kilowatts (kW) × 8 groups, and the conveying speed of the positive electrode current collector can be 60m / min. The present application has no special restrictions on the type of degreasing agent, as long as the purpose of the present application can be achieved. For example, degreasing agents include but are not limited to dodecyl alcohol polyoxyethylene ether and sodium dodecylbenzene sulfonate. The present application has no special restrictions on the drying temperature, as long as the purpose of the present application can be achieved. For example, the drying temperature can be 70°C to 90°C.

[0040] Generally, the values ​​of a, H1, and H2 can be changed by changing the mass fraction of sulfuric acid, the current density, voltage, and time of electroplating. For example, while keeping other parameters unchanged, increasing the electroplating current density increases a, H1, and H2, while decreasing the electroplating current density decreases a, H1, and H2. Increasing the electroplating voltage increases a, H1, and H2, while decreasing the electroplating voltage decreases a, H1, and H2. Prolonging the electroplating time increases a, H1, and H2, while shortening the electroplating time decreases a, H1, and H2. Increasing the mass fraction of sulfuric acid increases a, H1, and H2, while decreasing the mass fraction of sulfuric acid decreases a, H1, and H2. While keeping the electroplating voltage unchanged, increasing the electroplating current density and shortening the electroplating time can increase a while keeping H1 and H2 constant. Reducing the electroplating current density and extending the electroplating time can decrease a while keeping H1 and H2 constant. When the electroplating current density remains unchanged, increasing the electroplating voltage and shortening the electroplating time can control H1 and H2 unchanged and increase a. Reducing the electroplating voltage and extending the electroplating time can control H1 and H2 unchanged and reduce a.

[0041] In the present application, the value of R0 can be changed by changing the values ​​of a, H1 and H2. Those skilled in the art can make adjustments according to actual needs, as long as the purpose of this application can be achieved. In the present application, the coverage of the oxide layer on the surface of the positive electrode current collector can be 90% to 100%. The above-mentioned oxide layer has a high coverage of the positive electrode current collector, which can better play the protective role of the oxide layer on the surface of the positive electrode current collector, so that the positive electrode current collector has a higher resistivity, reducing the risk of thermal runaway during the nailing process of the secondary battery, thereby helping to improve the safety performance of the secondary battery while making it have a high energy density. In addition, the oxide layer of the present application is prepared by the above method, and it is easy to obtain an oxide layer with a high coverage rate, which has the advantages of simple process and easy implementation.

[0042] In the present application, the positive electrode material layer includes a positive electrode active material. There is no particular restriction on the type of positive electrode active material in this application, as long as the purpose of this application can be achieved. The positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, or lithium iron manganese phosphate. There is no particular restriction on the type of NCM in this application, as long as the purpose of this application can be achieved. For example, it may include at least one of NCM811, NCM622, NCM523, or NCM111. The above-mentioned positive electrode active materials may be doped. In some embodiments, the elements used for doping may include at least one of K, Na, Ca, Mg, B, Al, Co, Si, V, Ga, Sn, or Zr. There is no particular restriction on the thickness of the positive electrode material layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector surface, or it can be a partial area of ​​the positive electrode current collector surface. This application has no special restrictions, as long as the purpose of this application can be achieved. The positive electrode material layer of this application may also contain a positive electrode binder. This application has no special restrictions on the positive electrode binder, as long as the purpose of this application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon at least one. The present application has no particular restrictions on the mass percentage of the positive electrode active material and the positive electrode binder, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material can be 94.5% to 98.5%, and the mass percentage of the positive electrode binder can be 1% to 2.5%.

[0043] The secondary battery of the present application also includes a negative electrode sheet. The present application has no particular restrictions on the negative electrode sheet, as long as the purpose of the present application can be achieved. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, carbon-based current collector or composite current collector (such as carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector), etc. In the present application, the negative electrode material layer includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, as long as the purpose of the present application can be achieved. The negative electrode active material includes a material that reversibly embeds / de-embeds lithium ions. In some embodiments, the material that reversibly embeds / de-embeds lithium ions includes at least one of lithium metal, lithium alloy, carbon material or silicon-based material. In some embodiments, the lithium alloy may include at least one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg, or Li-Mg-Si. The carbon material includes at least one of crystalline carbon or amorphous carbon. The silicon-based material includes silicon, silicon oxide (SiO k , 0<k≤2), at least one of silicon-carbon compounds or silicon alloys. The negative electrode material layer of the present application may also include a negative electrode conductive agent, a negative electrode binder and a negative electrode dispersant. The present application has no particular restrictions on the negative electrode conductive agent and the negative electrode binder, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), graphite, carbon fiber, carbon nanowire, graphene, metal materials or conductive polymers, and the above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but are not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The negative electrode binder may be the same as the above-mentioned positive electrode binder. The negative electrode dispersant may include sodium carboxymethyl cellulose.

[0044] The present application has no special restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 20μm. In the present application, there is no special restriction on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30μm to 130μm. In the present application, the negative electrode material layer can be arranged on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0045] The secondary battery of the present application also includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt and the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium nitrate (LiNO3) or lithium difluorophosphate (LiPO2F2). The non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound. The above-mentioned chain carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include but are not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0046] In the present application, the secondary battery also includes a diaphragm, which is arranged between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include any one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0047] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0048] The secondary battery of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In one embodiment of the present application, the secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium metal secondary battery (lithium metal battery), a sodium ion secondary battery (sodium ion battery), a sodium metal secondary battery (sodium metal battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0049] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0050] The third aspect of the present application provides an electronic device, which includes the secondary battery provided in the first aspect of the present application or the secondary battery prepared by the preparation method provided in the second aspect of the present application. The secondary battery provided in the first aspect of the present application or the secondary battery prepared in the second aspect of the present application has good safety performance and high energy density, so the electronic device provided in the present application has a long service life. The electronic device of the present application is not particularly limited and can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to: a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0051] Example

[0052] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0053] Test methods and equipment:

[0054] Sampling method of positive electrode sheet and positive electrode current collector:

[0055] In an environment of 25±3°C, the lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to remove the positive electrode sheet. The residual electrolyte on the surface of the positive electrode sheet was wiped off with dust-free paper to obtain the positive electrode sheet. The above-mentioned positive electrode sheet sample was immersed in the solvent N-methylpyrrolidone (NMP) to separate the positive electrode material layer and the positive electrode current collector. The positive electrode material layer was washed away to obtain a positive electrode current collector with an oxide layer on the surface. The NMP on the surface of the positive electrode current collector was adsorbed with dust-free paper and dried on a flat workbench at room temperature to obtain the positive electrode current collector.

[0056] In the following tests, such as resistivity test, thickness test, elongation test, adhesion test, and cohesion test, the positive electrode sheet or positive electrode current collector taken out according to the above steps is tested.

[0057] Resistivity test:

[0058] The resistivity of the positive electrode current collector was tested using a resistance tester (instrument model BER1200). The adjacent test points were spaced 2.5 mm apart. The resistivity of 15 different points was calculated and the average value was used to obtain the resistivity of the positive electrode current collector. The test parameters were: the pressure head area was 153.94 mm 2 , the pressure is 2 tons (t), and the pressurizing time is 50s.

[0059] Thickness test:

[0060] The positive electrode sheet sample was cut along the thickness direction of the positive electrode sheet by plasma to obtain the cross section of the positive electrode sheet. The cross section of the positive electrode sheet was observed by scanning electron microscopy. The adjacent test points were separated by 2.5 mm. The thickness of the first oxide layer, the thickness of the second oxide layer and the thickness of the positive electrode current collector were measured at 15 test points, and the average value was calculated to obtain the thickness H1 of the first oxide layer, the thickness H2 of the second oxide layer and the thickness H0 of the positive electrode current collector.

[0061] Elongation test:

[0062] The positive electrode current collector was made into a 15 mm × 60 mm spline and stretched along the length direction of the spline at a speed of 5 mm / min under a 500 mm gauge using a high-speed rail tensile tester. The length of the spline when it broke was L mm, and the elongation (%) = (L-60) / 60×100%. Five samples were tested and the average value was calculated to obtain the elongation E of the positive electrode current collector.

[0063] Adhesion test:

[0064] The adhesion between the positive electrode material layer and the positive electrode current collector was measured using a 90° peel test. The positive electrode sheet was cut into 15mm×100mm strips, and the positive electrode material layer on one surface of the double-sided positive electrode current collector was scraped off to obtain a test specimen for the adhesion test between the positive electrode material layer and the positive electrode current collector. A 15mm×50mm double-sided tape (NITTO.NO5000NS) was attached to a steel plate, and then the test specimen was attached to the double-sided tape with the side coated with the positive electrode material layer facing down. A 15mm×70mm paper tape was connected to one end of the test specimen via the double-sided tape. A small stick with a mass of 2kg was manually pushed and rolled on the test specimen 8 times to obtain a test sample. The test was performed using a tensile testing machine. The test sample was fixed to the test bench. The paper tape was folded 90° and secured with a clamp. When the tension between the clamps reached 0.5 N, the tensile testing machine began to pull the paper tape at a speed of 50 mm / min until the positive electrode material layer and the positive electrode current collector separated. The test was terminated and the test data was saved. The average tension measured in the plateau was recorded as the bonding force F1 between the positive electrode material layer and the positive electrode current collector, in N / m.

[0065] Cohesion test:

[0066] The cohesion of the positive electrode material layer was measured using a 90° peel test. The positive electrode sheet was cut into 15mm×50mm strips, and the positive electrode material layer on one surface of the double-sided coated positive electrode current collector was scraped off to obtain a test specimen for the cohesion test of the positive electrode material layer. A 15mm×50mm double-sided tape (NITTO.NO5000NS) was attached to a steel plate, and then the test specimen was attached to the double-sided tape with the side coated with the positive electrode material layer facing up. A 15mm×100mm double-sided tape was attached to the surface of the positive electrode material layer, with one end of the double-sided tape aligned with one end of the positive electrode sheet, leaving a 50mm blank end at the other end. A small stick with a mass of 2kg was manually pushed and rolled on the test specimen 8 times to obtain a test sample. The test was performed using a tensile testing machine. Secure the test sample to the test bench, fold the double-sided tape 90°, and secure the blank end of the tape with a clamp. When the clamp tension reaches 0.5N, begin pulling the paper tape at a speed of 50mm / min until the positive electrode material layer and the positive electrode current collector separate. The test is terminated and the test data is saved. The average tensile force measured in the plateau is recorded as the cohesive force F2 of the positive electrode material layer, in N / m.

[0067] Safety performance test:

[0068] The safety performance of lithium-ion batteries is evaluated by the nail penetration pass rate. The higher the nail penetration pass rate, the better the safety performance of the lithium-ion battery, and the lower the nail penetration pass rate, the worse the safety performance of the lithium-ion battery. The lithium-ion batteries of each embodiment or comparative example are charged to 4.5V at a constant current of 0.5 times (C), and then charged to a cut-off current of 0.025C at a constant voltage of 4.5V to fully charge the lithium-ion battery. Photos are taken to record the appearance of the lithium-ion battery before the nail penetration test. The lithium-ion battery is subjected to a nail penetration test in an environment of 25±3℃. The diameter of the steel nail is 4mm, the penetration speed is 30mm / s, and the nail penetration position is located at the geometric center of the lithium-ion battery. The test is stopped after 3.5 minutes or when the surface temperature of the electrode assembly drops to 50℃. 20 lithium-ion batteries are grouped together to observe the status of the lithium-ion battery during the test. If the lithium-ion battery does not burn or explode after the nail penetration is completed, it is determined to have passed the test. Nail penetration pass rate = N / 20×100%, where N is the number of lithium-ion batteries that passed the test.

[0069] Cyclic performance test:

[0070] The capacity retention rate is used to evaluate the cycling performance of lithium-ion batteries. The higher the capacity retention rate, the better the cycling performance of the lithium-ion battery, and the lower the capacity retention rate, the worse the cycling performance of the lithium-ion battery. The lithium-ion batteries of each embodiment or comparative example were left at rest in an environment of 25±3°C for 2 hours, discharged at 0.7C to 3V, and left at rest for 5 minutes. The first cycle process is: charge at 1.5C to a cutoff voltage of 4.5V, charge at 4.5V to 0.05C; let it rest for 5 minutes; discharge at 0.7C to a set voltage of 3.0V, and let it rest for 5 minutes. This is the first charge and discharge cycle process, and the first discharge capacity of the lithium-ion battery is recorded as C1. The charge and discharge cycle is then repeated according to the above first cycle process, and the discharge capacity of the lithium-ion battery is recorded after each cycle. At the 50th, 100th, 150th, 200th, 250th, and so on to the 800th cycle, the charge and discharge process is carried out according to the following second cycle process. The second cycle process is: charge at 0.5C to 4.5V, charge at 4.5V to 0.05C; let it rest for 5 minutes; discharge at 0.7C to a set voltage of 3V. Finally, the first cycle process is repeated for the 801st cycle, and the discharge capacity of the lithium-ion battery is recorded as C2. Capacity retention rate = C2 / C1×100%.

[0071] Energy density test:

[0072] The lithium-ion batteries of each embodiment or comparative example were discharged at a current of 0.5C to a set voltage of 3V and allowed to stand for 30 minutes; then fully charged at a current of 0.2C to 4.5V, charged at 4.5V to a current of 0.025C, and allowed to stand for 30 minutes; then fully discharged at a current of 0.2C to 3V. The discharge energy at this step was recorded as the actual energy E of the lithium-ion battery. The volume of the lithium-ion battery at this time was V. The energy density of the lithium-ion battery, ED, is calculated as E / V, in units of Wh / L.

[0073] Example 1-1

[0074] <Preparation of Positive Electrode Current Collector>

[0075] The aluminum foil was cleaned by plasma corona (plasma emitter 20kW×8 groups, aluminum foil conveying speed 60m / min) for surface degreasing. Then, it was placed in a 15% mass fraction sulfuric acid electrolytic cell with aluminum foil as anode and 316 stainless steel foil as cathode. The electroplating was carried out at 20°C with a current density of 0.8A / dm -2 The electroplating voltage U was 15V, and the electroplating time t was 2 minutes. After the electroplating was completed, the positive electrode current collector was washed with deionized water in a cleaning tank and dried in an 80°C oven to obtain a positive electrode current collector. The positive electrode current collector had an oxide layer on its surface, and the oxide layer was composed of Al2O3.

[0076] <Preparation of positive electrode sheet>

[0077] The positive electrode active material, lithium cobalt oxide (LiCoO2), the first conductive agent, carbon nanotubes (CNTs), the second conductive agent, conductive carbon black (Super P), and the positive electrode binder, polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 97.2:0.7:0.5:1.6. N-methylpyrrolidone (NMP) was added as a solvent and stirred under vacuum to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on the first surface of the prepared positive electrode current collector with a thickness of 12 μm and dried at 90°C to obtain a positive electrode sheet coated on one side with a positive electrode material layer. The above steps were then repeated on the second surface of the positive electrode current collector to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. After drying at 90°C, the sheet was cold pressed, cut into pieces, and the tabs were welded to obtain a positive electrode sheet measuring 74 mm x 867 mm for future use. The thickness of the single-sided positive electrode material layer after cold pressing is 45μm, and the compaction density of the positive electrode sheet is 4.15g / cm 3 .

[0078] <Preparation of negative electrode sheet>

[0079] The negative electrode active material artificial graphite, the negative electrode binder styrene-butadiene rubber (SBR), and the negative electrode dispersant sodium carboxymethyl cellulose (CMC-Na) were mixed in a mass ratio of 97.4:1.2:1.4, deionized water was added as a solvent, and the mixture was stirred in a vacuum to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was evenly coated on one surface of a 6μm thick negative electrode current collector copper foil and dried at 90°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The above steps were then repeated on the other surface of the negative electrode current collector to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. After drying at 90°C, the mixture was cold pressed, cut into pieces, and the tabs were welded to obtain a negative electrode sheet with a size of 78mm×875mm for use. After cold pressing, the thickness of the negative electrode material layer on one side was 57μm, and the compaction density of the negative electrode sheet was 1.7g / cm 3 .

[0080] <Preparation of Electrolyte>

[0081] In an argon atmosphere glove box with a water content of less than 10 ppm, in a dry argon atmosphere glove box, non-aqueous solvents ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and ethyl propionate (EP) are mixed in a mass ratio of EC:PC:DEC:EP=3:1:3:3, and then lithium salt LiPF6 is added to the non-aqueous solvent, dissolved and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of the lithium salt is 12.5%, and the balance is the non-aqueous solvent.

[0082] <Diaphragm>

[0083] A porous polyethylene film with a thickness of 7 μm (supplied by Celgard) was used as the separator.

[0084] <Preparation of lithium-ion batteries>

[0085] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order so that the separator is located between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an aluminum-plastic film packaging bag, and moisture is removed at 80°C, and the above-prepared electrolyte is injected. After vacuum packaging, standing, formation (temperature 75°C, 1C constant current charging for 35 minutes, 0.7C constant current charging to 4.5V, then 4.5V constant voltage charging to 0.1C, then 0.5C discharge to 3V, and finally 1C charging for 30 minutes), and shaping processes, a lithium-ion battery is obtained.

[0086] Example 1-2 to Example 1-7

[0087] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0088] Examples 1-8

[0089] Except for using the positive electrode current collector prepared in the following <Preparation of Positive Electrode Current Collector>, the rest is the same as Example 1-1.

[0090] <Preparation of Positive Electrode Current Collector>

[0091] Aluminum foil was cleaned and degreased by passing it through a plasma corona (20kW plasma emitters, 8 sets, aluminum foil feed speed 60m / min). Opposite surfaces along the thickness of the foil were designated as side A and side B. Insulating adhesive (made of polypropylene) was applied to side B. The foil was then placed in a 15% sulfuric acid electrolytic cell, with the aluminum foil as the anode and 316 stainless steel foil as the cathode. The first electroplating step was performed, forming an oxide layer on side A. After electroplating, the insulating adhesive on side B was removed. The positive electrode current collector was rinsed in a cleaning cell with deionized water and then dried in an 80°C oven. Insulating adhesive was applied to side A to protect the oxide layer. The foil was then placed in a 15% sulfuric acid electrolytic cell, with the aluminum foil as the anode and 316 stainless steel foil as the cathode. A second electroplating step was performed, forming an oxide layer on side B. After electroplating, the insulating adhesive on side B was removed. The positive electrode current collector was rinsed in a cleaning cell with deionized water and then dried in an 80°C oven. The parameters of the first and second electroplating processes: current density I, electroplating voltage U, and electroplating time t are shown in Table 1. The thicknesses H1 and H2 of the oxide layers on the two surfaces of the positive electrode current collector are shown in Table 1.

[0092] Example 1-9 to Example 1-11

[0093] Except for adjusting the time of the first electroplating and the time of the second electroplating according to Table 1, the rest is the same as Example 1-8.

[0094] Example 1-12 to Example 1-15

[0095] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0096] Example 2-1 to Example 2-6

[0097] Except that the mass percentages of the conductive agent and the positive electrode binder are adjusted according to Table 2 and the mass percentages of the positive electrode active material are changed accordingly, the rest is the same as Example 1-1.

[0098] Comparative Example 1

[0099] Except for using the positive electrode current collector prepared in the following <Preparation of Positive Electrode Current Collector>, the rest is the same as Example 1-1.

[0100] <Preparation of Positive Electrode Current Collector>

[0101] At room temperature, the aluminum foil was treated in ammonia water for 2 hours with a concentration of 1 mol / L. The aluminum foil was then taken out and heat treated at 400°C for 7 hours. After cooling to room temperature, the positive electrode current collector was obtained. Aluminum oxide layer.

[0102] Comparative Examples 2 to 4

[0103] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0104] Comparative Example 5

[0105] Except for the positive electrode sheet prepared by the following <Preparation of Positive Electrode Sheet>, the rest is the same as Comparative Example 1-1.

[0106] <Preparation of positive electrode sheet>

[0107] The base coating materials carbon nanotubes and polyvinylidene fluoride are mixed in a mass ratio of 40:60, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred evenly to form a base coating slurry with a solid content of 75wt%. The positive electrode active material lithium cobalt oxide (LiCoO2), the first conductive agent carbon nanotubes (CNT), the second conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.2:0.7:0.5:1.6, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred evenly in a vacuum to form a positive electrode slurry with a solid content of 75wt%.

[0108] First, apply the primer slurry on one surface of the positive electrode collector and dry it at 90°C to obtain a positive electrode sheet with a primer coating on one side. Then, evenly apply the positive electrode slurry on the first surface of a positive electrode collector with a thickness of 12μm (the same preparation method as that of Comparative Example 1-1) and dry it at 90°C to obtain a positive electrode sheet with a primer coating and a positive electrode material layer on one side. Then, repeat the above steps on the second surface of the positive electrode collector to obtain a positive electrode sheet with a primer coating and a positive electrode material layer on both sides. After drying at 90°C, cold press the sheet, cut the sheet, and weld the tabs to obtain a positive electrode sheet with a specification of 74mm×867mm for standby use. After cold pressing, the thickness of the single-sided primer coating is 6μm, the thickness of the single-sided positive electrode material layer is 45μm, and the compaction density of the positive electrode sheet is 4.15g / cm 3 .

[0109] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0110] Referring to Table 1, it can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 5 that the lithium-ion battery includes the positive electrode current collector of the present application and regulates the values ​​of R0 and a within the scope of the present application, and it is not necessary to additionally set a primer layer between the positive electrode current collector and the positive electrode material layer, so that the resistivity of the positive electrode sheet (R z ) is higher, the lithium-ion battery has a higher capacity retention rate and energy density while having a higher nail penetration rate, thereby making the lithium-ion battery have good cycle performance and high energy density while improving its safety performance. The positive electrode current collector of Comparative Example 1 has an oxide layer on its surface, and its preparation method is different from that of the present application, and the value of R0 is not within the scope of the present application. In Comparative Examples 2 to 4, at least one of the values ​​of R0 and a is not within the scope of the present application. The positive electrode current collector of Comparative Example 5 is additionally provided with a primer layer on the basis of Comparative Example 1. The lithium-ion batteries of the above comparative examples cannot simultaneously achieve a high nail penetration rate, capacity retention rate, and energy density, indicating that it is difficult to give a comprehensive balance between the safety performance, cycle performance, and energy density of lithium-ion batteries.

[0111] The value of R0 usually affects the safety performance, cycle performance and energy density of lithium-ion batteries. It can be seen from Examples 1-1 to 1-7 and Comparative Examples 2 to 3 that when R0 is too small, such as Comparative Example 2, although the lithium-ion battery has a higher capacity retention rate and energy density, its nail penetration rate is low. When R0 is too large, such as Comparative Example 3, although the lithium-ion battery has a higher nail penetration rate, its capacity retention rate and energy density are low. This shows that the safety performance, cycle performance and energy density of lithium-ion batteries are difficult to take into account. Thus, by regulating the value of R0 within the scope of this application, the lithium-ion battery can have a higher capacity retention rate and energy density while having a higher nail penetration rate, thereby illustrating that the lithium-ion battery has good cycle performance and a higher energy density while having good safety performance.

[0112] The value of a usually affects the safety performance, cycle performance and energy density of lithium-ion batteries. From Example 1-1 to Example 1-7 and Comparative Example 4, it can be seen that when a is too small, such as Comparative Example 4, although the lithium-ion battery has a high capacity retention rate and energy density, its nail penetration rate is low, indicating that the safety performance, cycle performance and energy density of the lithium-ion battery are difficult to take into account. When a is too large, the process is difficult and it is difficult to achieve production. Thus, by regulating the value of a within the scope of this application, the lithium-ion battery can have a high capacity retention rate and energy density while having a high nail penetration rate, thereby indicating that the lithium-ion battery has good cycle performance and high energy density while having good safety performance.

[0113] The values ​​of H1, H2, and R0×(H1+H2) generally affect the safety, cycle performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 to 1-7, by adjusting the values ​​of the above parameters within the scope of this application, the lithium-ion battery can have a high capacity retention rate and energy density while also having a high nail penetration rate, thereby demonstrating that the lithium-ion battery has good cycle performance and high energy density while also having good safety performance.

[0114] The H1 / H2 ratio generally affects the safety, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-8, and 1-11, by adjusting the H1 / H2 ratio within the scope of this application, lithium-ion batteries can achieve both high capacity retention and high energy density while also achieving a high nail penetration rate. This demonstrates that lithium-ion batteries have both good cycling performance and high energy density while maintaining good safety.

[0115] The value of E generally affects the safety, cycle performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-12, and 1-13, by adjusting the value of E within the scope of this application, lithium-ion batteries can have high capacity retention and energy density while also having a high nail penetration rate, thereby demonstrating that lithium-ion batteries have good cycle performance, high energy density, and good safety performance.

[0116] The value of (H1+H2) / [5×(1+E)] generally affects the safety, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 to 1-13, by adjusting the value of (H1+H2) / [5×(1+E)] within the scope of this application, the lithium-ion battery can have a high capacity retention rate and energy density while also having a high nail penetration rate, thereby demonstrating that the lithium-ion battery has good cycling performance and high energy density while also having good safety performance.

[0117] The value of H0 generally affects the safety, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-14, and 1-15, by adjusting the value of H0 within the scope of this application, lithium-ion batteries can have high capacity retention and energy density while also having a high nail penetration rate, thereby demonstrating that lithium-ion batteries have good cycling performance, high energy density, and good safety performance.

[0118] As shown in Table 2, the composition and mass percentage of the conductive agent generally affect the safety performance, cycle performance, and energy density of the lithium-ion battery. As can be seen from Examples 1-1, 2-1, and 2-6, by selecting the type of conductive agent within the scope of this application and regulating the mass percentage of the conductive agent and the mass percentage of the first conductive agent in the conductive agent within the scope of this application, the bonding force F1 between the positive electrode material layer and the positive electrode current collector and the cohesive force F2 of the positive electrode material layer can be increased, and the lithium-ion battery has a higher capacity retention rate and energy density while having a higher nail penetration rate, thereby indicating that the lithium-ion battery has good cycle performance and high energy density while having good safety performance.

[0119] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising a positive electrode tab, the positive electrode tab including a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, the base material of the positive electrode current collector including aluminum foil or aluminum alloy foil, the surface of the positive electrode current collector having an oxide layer, and the resistivity of the positive electrode current collector being R0 Ω·cm, where 200 ≤ R0 ≤ 1500; The positive electrode current collector includes opposite first and second surfaces, the first surface having a first oxide layer and the second surface having a second oxide layer, the thickness of the first oxide layer being H1 μm and the thickness of the second oxide layer being H2 μm, with R0 = a×(H1 + H2), where 200 ≤ a ≤ 5000.

2. The secondary battery according to claim 1, wherein, 300≤R0≤850。 3. The secondary battery according to claim 1, wherein, 0.03 ≤ H1 ≤ 3, 0.03 ≤ H2 ≤ 3.

4. The secondary battery according to claim 1, wherein 0.05 ≤ H1 ≤ 0.5, 0.05 ≤ H2 ≤ 0.

5.

5. The secondary battery according to claim 1, wherein 0.67 ≤ H1 / H2 ≤ 1.

5.

6. The secondary battery according to claim 1, wherein, 12 ≤ R0×(H1 + H2) ≤ 9000.

7. The secondary battery according to claim 1, wherein 30 ≤ R0×(H1 + H2) ≤ 3000.

8. The secondary battery according to claim 1, wherein The elongation E of the positive electrode current collector ranges from 0.3% to 5%.

9. The secondary battery according to claim 8, wherein, (H1 + H2) / [5×(1 + E)] ≥ 0.

01.

10. The secondary battery according to claim 1, wherein, The thickness of the positive electrode current collector is H0 μm, where 5 ≤ H0 ≤ 30.

11. The secondary battery according to claim 1, wherein, The resistivity of the positive electrode plate is R Z Ω·cm, and 250 ≤ R Z ≤ 2000.

12. The secondary battery according to claim 1, satisfying at least one of the following features: (1) The positive electrode material layer contains a conductive agent, and based on the mass of the positive electrode material layer, the mass percentage content of the conductive agent is 0.5% to 3%; the conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent including at least one of conductive carbon fiber, carbon nanotube, or graphite fiber, and the second conductive agent including at least one of graphene or conductive carbon black, and the mass percentage content of the first conductive agent in the conductive agent is 30% to 100%; (2) The adhesion force between the positive electrode material layer and the positive electrode current collector is F1 N / m, and the value range of F1 is 3 to 30; (3) The cohesive force of the positive electrode material layer is F2 N / m, and the value range of F2 is 15 to 80.

13. A method for preparing a secondary battery according to any one of claims 1 to 12, wherein, The method for preparing the positive electrode current collector includes the following steps: Degreasing and cleaning the surface of the metal foil, followed by water washing, and then placing it in a sulfuric acid electrolytic cell with a mass fraction of 10% to 20%, and electroplating with the metal foil as the anode to form an oxide layer on the surface of the metal foil; after the electroplating is completed, it is washed and dried to obtain the positive electrode current collector; Among them, the metal foil includes aluminum foil or aluminum alloy foil, and the current density of electroplating is 0.3 A / dm 2 to 2 A / dm 2 , the voltage of electroplating is 8 V to 24 V, the time of electroplating is 0.3 min to 10 min, and the temperature of electroplating is 20 ± 10 °C.

14. An electronic device, comprising the secondary battery according to any one of claims 1 to 12 or the secondary battery prepared by the preparation method according to claim 13.

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