Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive material layer arranged on at least one surface of the positive current collector, the positive material layer comprises a conductive agent, the conductive agent comprises carbon black particles and / or carbon nanotubes, and the specific surface area B0 of the conductive agent is 150 m < 2 > / g to 1500 m < 2 > / g; and the activation energy E0 of the positive pole piece is 25 kJ / mol to 65 kJ / mol. The internal resistance of the secondary battery can be reduced by regulating and controlling the type and the specific surface area of the conductive agent and the activation energy of the positive pole piece in the application range.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to a secondary battery and an electronic device. Background Art

[0002] Reducing the internal resistance of lithium-ion batteries has always been the pursuit of customers. During the cycling process of lithium-ion batteries, the positive electrode impedance dominates. Selecting a new type of conductive agent and building a good conductive network are the main directions for reducing the internal resistance of lithium-ion batteries.

[0003] In the prior art, generally, the internal resistance of lithium-ion batteries is reduced by increasing the content of the conductive agent or reducing the content of the binder. However, increasing the content of the conductive agent will lead to a decrease in the content of the positive electrode active material and a decrease in the energy density of the lithium-ion battery; reducing the content of the binder will lead to a decrease in the adhesion between the positive electrode material layer and the positive electrode current collector and a decrease in the internal cohesion of the positive electrode material layer itself, resulting in problems such as film peeling and thickness swelling during the use of the lithium-ion battery. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device that can reduce the internal resistance of the secondary battery. The specific technical solutions are as follows:

[0005] In a first aspect of the present application, a secondary battery is provided, which includes a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent. The conductive agent includes carbon black particles and / or carbon nanotubes. The specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode plate is 25 kJ / mol to 65 kJ / mol. By controlling the type, specific surface area of the conductive agent and the activation energy of the positive electrode plate within the scope of the present application, the internal resistance of the secondary battery can be reduced.

[0006] In an embodiment of the present application, the specific surface area B0 of the conductive agent is 300 m 2 / g to 800 m 2 / g. By controlling the specific surface area of the conductive agent within the above range, the conductive agent has a more suitable specific surface area, which can provide more adsorption sites for Li + and is beneficial to further reducing the activation energy of the positive electrode plate, thereby further reducing the internal resistance of the secondary battery.

[0007] In an embodiment of the present application, in the Raman spectrogram of the conductive agent, there is a first characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D , and there is a peak at 1550 cm -1To 1650 cm -1 There is a second characteristic peak with peak intensity I G within the range, and 1.0 ≤ I D / I G ≤ 1.5. By adjusting the value of I D / I G within the above range, the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial for the desolvation of Li + during the process of passing through the surface of the positive electrode active material, which is beneficial for reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0008] In an embodiment of the present application, the particle size d1 of the carbon black particles is 5 nm to 50 nm. In an embodiment of the present application, the particle size d1 of the carbon black particles is 10 nm to 40 nm. By adjusting the particle size of the carbon black particles within the above range, the carbon black particles have an appropriate particle size and an appropriate specific surface area, which can provide more adsorption sites for Li + and is beneficial for further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0009] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B1 of the carbon black particles is 100 m 2 / g to 150 m 2 / g. When the conductive agent includes carbon black particles and carbon nanotubes and the specific surface area of the carbon black particles is adjusted within the above range, the conductive agent can have an appropriate specific surface area, which can provide more adsorption sites for Li + and is beneficial for further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0010] In an embodiment of the present application, the specific surface area B1 of the carbon black particles is 700 m 2 / g to 1400 m 2 / g. By adjusting the specific surface area of the carbon black particles within the above range, the conductive agent can have a more appropriate specific surface area, which can provide more adsorption sites for Li + and is beneficial for further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0011] In an embodiment of the present application, in the Raman spectrum of the carbon black particles, there is a third characteristic peak with peak intensity I -1 within the range of 1300 cm -1 to 1400 cm D1 , and there is a peak with peak intensity I -1 within the range of 1550 cm -1 to 1650 cmG1 The fourth characteristic peak, 0.8 ≤ I D1 / I G1 ≤ 1.7. By adjusting the value of I D1 / I G1 within the above range, the number of surface defects of carbon black particles is appropriate, and the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial for Li + to be desolvated during the process of passing through the surface of the positive active material, which is beneficial to reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0012] In an embodiment of the present application, the diameter d2 of the carbon nanotubes is 3 nm to 15 nm. By adjusting the diameter of the carbon nanotubes within the above range, while making the positive electrode paste have good processing performance, it can provide a relatively large effective conductive area and can further reduce the internal resistance of the secondary battery.

[0013] In an embodiment of the present application, the specific surface area B2 of the carbon nanotubes is 200 m 2 / g to 300 m 2 / g. By adjusting the specific surface area of the carbon nanotubes within the above range, the conductive agent can have an appropriate specific surface area, which can provide more adsorption sites for Li + and is beneficial to further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0014] In an embodiment of the present application, in the Raman spectrum of the carbon nanotubes, there is a fifth characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D2 , and there is a sixth characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G2 , 0.6 ≤ I D2 / I G2 ≤ 1.3. By adjusting the value of I D2 / I G2 within the above range, the number of surface defects of the carbon nanotubes is appropriate, and the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial for Li + to be desolvated during the process of passing through the surface of the positive active material, which is beneficial to reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0015] In an embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content W1 of the conductive agent is 0.3% to 3.0%. By adjusting the mass percentage content of the conductive agent within the above range, the conductive agent has an appropriate mass percentage content, which can improve the conductivity of the positive electrode plate and reduce the internal resistance of the secondary battery.

[0016] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes. Based on the mass of the positive electrode material layer, the mass percentage content W11 of the carbon black particles is 0.2% to 1.5%, and the mass percentage content W12 of the carbon nanotubes is 0 to 1.5%. When the conductive agent includes carbon black particles and carbon nanotubes, and the mass percentage contents of the carbon black particles and the carbon nanotubes are adjusted within the above range, the carbon black particles and the carbon nanotubes are used in combination, and the carbon black particles and the carbon nanotubes have appropriate mass percentage contents, which can make the conductive agent have an appropriate mass percentage content, improve the conductivity of the positive electrode plate, and reduce the internal resistance of the secondary battery.

[0017] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has a lower internal resistance.

[0018] Advantages of the present application:

[0019] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent, the conductive agent includes carbon black particles and / or carbon nanotubes, and the specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode plate is 25 kJ / mol to 65 kJ / mol. By adjusting the type, specific surface area of the conductive agent, and the activation energy of the positive electrode plate within the scope of the present application, the internal resistance of the secondary battery can be reduced.

[0020] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Detailed implementation manners

[0021] The technical solutions in the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0022] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries.

[0023] 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 current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent, and the conductive agent includes carbon black particles and / or carbon nanotubes (CNTs). The specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode plate is 25 kJ / mol to 65 kJ / mol. Exemplarily, the value of B0 can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500 or a range composed of any two of the above numerical values; the value of E0 can be 25, 27, 29, 30, 31, 33, 35, 37, 39, 40, 41, 43, 45, 47, 49, 50, 51, 53, 55, 57, 59, 60, 61, 63, 65 or a range composed of any two of the above numerical values. In the present application, the carbon black particles include at least one of Super P, acetylene black, or Ketjen black; the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or can be provided on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0024] In an embodiment of the present application, the secondary battery includes a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent, and the conductive agent includes carbon black particles. The specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode plate is 25 kJ / mol to 65 kJ / mol.

[0025] In an embodiment of the present application, the secondary battery includes a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent, and the conductive agent includes carbon black particles and carbon nanotubes. The specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode sheet is 25 kJ / mol to 65 kJ / mol.

[0026] The inventors' research found that when the conductive agent in the positive electrode material layer includes carbon black particles and / or carbon nanotubes, and the specific surface area of the conductive agent is too large, for example, greater than 1500 m 2 / g, it will cause the carbon black particles to be difficult to disperse and agglomerate together, affecting the conductive network of the positive electrode material layer; when the specific surface area of the conductive agent is too small, for example, less than 150 m 2 / g, it will cause the effective conductive area of the carbon black particles to decrease and increase the internal resistance of the secondary battery. When the specific surface area of the conductive agent is within the scope of this application, the conductive agent has a suitable specific surface area, which can provide more adsorption sites for Li + and the positive electrode sheet has a lower activation energy, thereby reducing the internal resistance of the secondary battery.

[0027] In an embodiment of the present application, the specific surface area B0 of the conductive agent is 300 m 2 / g to 800 m 2 / g. Exemplarily, the value of B0 can be 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800 or a range composed of any two of the above values. By adjusting the specific surface area of the conductive agent within the above range, the conductive agent has a more suitable specific surface area, which can provide more adsorption sites for Li + and is beneficial to further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0028] In an embodiment of the present application, in the Raman spectrum of the conductive agent, there is a first characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D , and there is a second characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G , and 1.0 ≤ I D / I G ≤ 1.5. Exemplarily, the value of I D / I G can be 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or a range composed of any two of the above values. The value of I D / I G can characterize the surface defects of the conductive agent. The larger the value of I D / I G , the more surface defects the conductive agent has, and the easier it is for the conductive agent to adsorb Li +, the more beneficial it is for Li + to be desolvated during the process of passing through the surface of the positive electrode active material, and the more beneficial it is to reduce the activation energy. However, excessive surface defects of the conductive agent will affect the conductivity of the conductive agent. By regulating the I D / I G value within the above range, the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial for Li + to be desolvated during the process of passing through the surface of the positive electrode active material, which is beneficial to reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0029] In an embodiment of the present application, the particle size d1 of the carbon black particles is 5 nm to 50 nm. Exemplarily, the value of d1 can be 5, 7, 10, 15, 17, 20, 25, 27, 30, 35, 37, 40, 45, 47, 50 or the range composed of any two of the above values. In an embodiment of the present application, the particle size d1 of the carbon black particles is 10 nm to 40 nm. By regulating the particle size of the carbon black particles within the above range, the carbon black particles have an appropriate particle size and an appropriate specific surface area, and can provide more adsorption sites for Li + to further reduce the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0030] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B1 of the carbon black particles is 100 m 2 / g to 150 m 2 / g. Exemplarily, the value of B1 can be 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150 or the range composed of any two of the above values. When the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area of the carbon black particles is regulated within the above range, the conductive agent can have an appropriate specific surface area and can provide more adsorption sites for Li + to further reduce the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0031] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B1 of the carbon black particles is 150 m 2 / g to 1500 m 2 / g. Exemplarily, the value of B1 can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500 or a range composed of any two of the above numerical values. In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B1 of the carbon black particles is 700 m 2 / g to 1400 m 2 / g. When the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area of the carbon black particles is regulated within the above range, the conductive agent can have a suitable specific surface area, which can provide more adsorption sites for Li + and is beneficial to further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0032] In an embodiment of the present application, the conductive agent includes carbon black particles, and the specific surface area B1 of the carbon black particles is 150 m 2 / g to 1500 m 2 / g. Exemplarily, the value of B1 can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500 or a range composed of any two of the above numerical values. When the conductive agent includes carbon black particles, and the specific surface area of the carbon black particles is regulated within the above range, the conductive agent can have a suitable specific surface area, which can provide more adsorption sites for Li + and is beneficial to reducing the activation energy of the positive electrode sheet, thereby reducing the internal resistance of the secondary battery.

[0033] In an embodiment of the present application, the conductive agent includes carbon black particles, and the specific surface area B1 of the carbon black particles is 700 m 2 / g to 1400 m 2 / g. Exemplarily, the value of B1 can be 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400 or a range composed of any two of the above numerical values. When the conductive agent includes carbon black particles, and the specific surface area of the carbon black particles is regulated within the above range, the conductive agent can have a more suitable specific surface area, which can provide more adsorption sites for Li +Providing more adsorption sites is beneficial to further reduce the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0034] In an embodiment of the present application, in the Raman spectrogram of the carbon black particles, there is a third characteristic peak with a peak intensity of I within the range of 1300 cm -1 to 1400 cm -1 ; there is a fourth characteristic peak with a peak intensity of I within the range of 1550 cm D1 to 1650 cm -1 ; 0.8 ≤ I -1 / I G1 ≤ 1.7. Exemplarily, the value of I D1 / I G1 can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or a range composed of any two of the above numerical values. The value of I D1 / I G1 can characterize the surface defects of the carbon black particles. The larger the value of I D1 / I G1 , the more surface defects the carbon black particles have, and the easier it is for the carbon black particles to adsorb Li D1 / I G1 , which is more beneficial for the desolvation of Li + during the process of passing through the surface of the positive active material, and is more beneficial for reducing the activation energy. However, too many surface defects of the carbon black particles will affect the conductivity of the carbon black particles. By controlling the value of I + / I D1 / I G1 within the above range, the number of surface defects of the carbon black particles is appropriate, and the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial for the desolvation of Li + during the process of passing through the surface of the positive active material, and is beneficial for reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0035] In an embodiment of the present application, the diameter d2 of the carbon nanotubes is 3 nm to 15 nm. Exemplarily, the value of d2 can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range composed of any two of the above numerical values. By controlling the diameter of the carbon nanotubes within the above range, while the positive electrode paste has good processing performance, it can provide a relatively large effective conductive area and can further reduce the internal resistance of the secondary battery.

[0036] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B2 of the carbon nanotubes is 200 m 2 / g to 300 m 2 / g. Exemplarily, the value of B2 can be 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300 or a range composed of any two of the above numerical values. When the conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area of the carbon nanotubes is regulated within the above range, the conductive agent can have a suitable specific surface area, which can provide more adsorption sites for Li + to provide more adsorption sites, which is beneficial to further reducing the activation energy of the positive electrode sheet, thereby further reducing the internal resistance of the secondary battery.

[0037] In an embodiment of the present application, in the Raman spectrum of the carbon nanotubes, there is a fifth characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D2 , and there is a sixth characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G2 , 0.6 ≤ I D2 / I G2 ≤ 1.3. Exemplarily, the value of I D2 / I G2 can be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 or a range composed of any two of the above numerical values. The value of I D2 / I G2 can characterize the surface defects of the carbon nanotubes. The larger the value of I D2 / I G2 , the more surface defects the carbon nanotubes have, and the easier it is for the carbon nanotubes to adsorb Li + , which is more beneficial to the desolvation of Li + during the process of passing through the surface of the positive electrode active material, and is more beneficial to reducing the activation energy. However, too many surface defects of the carbon nanotubes will affect the conductivity of the carbon nanotubes. By regulating the value of I D2 / I G2 within the above range, the number of surface defects of the carbon nanotubes is appropriate, and the number of surface defects of the conductive agent is appropriate. On the one hand, it is beneficial to the desolvation of Li + during the process of passing through the surface of the positive electrode active material, which is beneficial to reducing the activation energy; on the other hand, the conductive agent also has high conductivity, which can further reduce the internal resistance of the secondary battery.

[0038] In an embodiment of the present application, the conductive agent includes carbon black particles. Based on the mass of the positive electrode material layer, the mass percentage content W1 of the conductive agent is 0.3% to 3.0%. Exemplarily, the value of W1 can be 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.0% or a range composed of any two of the above values. When the conductive agent includes carbon black particles and the mass percentage content of the conductive agent is adjusted within the above range, the conductive agent has an appropriate mass percentage content, which can improve the conductivity of the positive electrode sheet and reduce the internal resistance of the secondary battery.

[0039] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes. Based on the mass of the positive electrode material layer, the mass percentage content W1 of the conductive agent is 0.3% to 3.0%. Exemplarily, the value of W1 can be 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.0% or a range composed of any two of the above values. When the conductive agent includes carbon black particles and carbon nanotubes and the mass percentage content of the conductive agent is adjusted within the above range, the conductive agent has an appropriate mass percentage content, which can improve the conductivity of the positive electrode sheet and reduce the internal resistance of the secondary battery.

[0040] In an embodiment of the present application, the conductive agent includes carbon black particles and carbon nanotubes. Based on the mass of the positive electrode material layer, the mass percentage content W11 of the carbon black particles is 0.2% to 1.5%, and the mass percentage content W12 of the carbon nanotubes is 0 to 1.5%. Exemplarily, the value of W11 can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range composed of any two of the above values; the value of W12 can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range composed of any two of the above values. When the conductive agent includes carbon black particles and carbon nanotubes and the mass percentage contents of the carbon black particles and the carbon nanotubes are adjusted within the above range, the carbon black particles and the carbon nanotubes are used in combination, and the carbon black particles and the carbon nanotubes have appropriate mass percentage contents, which can enable the conductive agent to have an appropriate mass percentage content, improve the conductivity of the positive electrode sheet, and reduce the internal resistance of the secondary battery.

[0041] In an embodiment of the present application, for a secondary battery with a capacity of 3000 mAh to 4000 mAh, the 1s DC resistance (DCR) at 25°C and 20% state of charge (SOC) is 30 mΩ to 60 mΩ, and the internal resistance growth rate R1 after 800 cycles at 25°C is 10% to 60%. The 1s DC resistance of the secondary battery and the internal resistance growth rate after 800 cycles are within the above ranges, indicating that the secondary battery has a low internal resistance.

[0042] The present application does not particularly limit the preparation method of carbon black particles, as long as the purpose of the present application can be achieved. For example, the preparation method of carbon black particles may include the following steps: selecting acetylene or tar as the raw material; performing a high-temperature pyrolysis reaction on the raw material, where the temperature of the high-temperature pyrolysis reaction is 1000°C to 1500°C and the time of the high-temperature pyrolysis reaction is 0.1 s to 3 s to obtain carbon black particles; blowing out, cooling, and collecting the above carbon black particles from the furnace tube to obtain the required carbon black particles.

[0043] The present application does not particularly limit the method for regulating the specific surface area of carbon black particles, as long as the purpose of the present application can be achieved. For example, the specific surface area of carbon black particles can be regulated by controlling the high-temperature pyrolysis reaction time of the carbon black particles. For example, commercially available carbon black particles with different specific surface areas can be selected, and the specific surface area of the carbon black particles can be measured in combination with the "measurement method for the specific surface area of carbon black particles" in the present application, and carbon black particles with the required specific surface area can be selected.

[0044] The present application does not particularly limit the method for regulating the specific surface area of carbon nanotubes, as long as the purpose of the present application can be achieved. For example, the specific surface area of carbon nanotubes can be regulated by controlling the diameter of the carbon nanotubes. For example, commercially available carbon nanotubes with different specific surface areas can be selected, and the specific surface area of the carbon nanotubes can be measured in combination with the "measurement method for the specific surface area of carbon nanotubes" in the present application, and carbon nanotubes with the required specific surface area can be selected.

[0045] The present application does not particularly limit the method for regulating the specific surface area of the conductive agent, as long as the purpose of the present application can be achieved. For example, when the conductive agent includes carbon black particles, the specific surface area of the conductive agent can be regulated by controlling the specific surface area of the carbon black particles, and the regulation method of the specific surface area of the carbon black particles is as described above. When the conductive agent includes carbon black particles and carbon nanotubes, the specific surface area of the conductive agent can be regulated by controlling the specific surface area of each of the carbon black particles and carbon nanotubes, and the regulation methods of the specific surface areas of the carbon black particles and carbon nanotubes are as described above.

[0046] The present application does not particularly limit the method for regulating the I D1 / I G1 value of carbon black particles, as long as the purpose of the present application can be achieved. For example, the I of carbon black particles can be regulated by controlling the high-temperature pyrolysis reaction time.D1 / I G1 value

[0047] This application has no particular limitation on the method of regulating the I D2 / I G2 value of carbon nanotubes, as long as the purpose of this application can be achieved. For example, the I D2 / I G2 value of carbon nanotubes can be regulated by regulating the synthesis temperature of carbon nanotubes.

[0048] This application has no particular limitation on the method of regulating the I D / I G value of the conductive agent, as long as the purpose of this application can be achieved. For example, when the conductive agent includes carbon black particles, the I D1 / I G1 value of carbon black particles can be regulated by regulating the high-temperature pyrolysis reaction time, thereby regulating the I D / I G value of the conductive agent. When the conductive agent includes carbon black particles and carbon nanotubes, the I D1 / I G1 value of carbon black particles and the I D2 / I G2 value of carbon nanotubes can be used to regulate the I D / I G value of the conductive agent. The regulation methods of the I D1 / I G1 value of carbon black particles and the I D2 / I G2 value of carbon nanotubes are as described above.

[0049] This application has no particular limitation on the method of regulating the activation energy of the positive electrode sheet, as long as the purpose of this application can be achieved. For example, when the conductive agent includes carbon black particles, the activation energy of the positive electrode sheet can be regulated by regulating the specific surface area of carbon black particles. When the conductive agent includes carbon black particles and carbon nanotubes, the activation energy of the positive electrode sheet can be regulated by regulating the respective contents of carbon black particles and carbon nanotubes.

[0050] This application has no particular limitation on the method of regulating the particle size of carbon black particles, as long as the purpose of this application can be achieved. For example, the particle size of carbon black particles can be regulated by regulating the high-temperature pyrolysis reaction time. For example, commercially available carbon black particles with different particle sizes can be selected.

[0051] This application has no particular limitation on the method of regulating the diameter of carbon nanotubes, as long as the purpose of this application can be achieved. For example, the diameter of carbon nanotubes can be regulated by regulating the synthesis temperature of carbon nanotubes. For example, commercially available carbon nanotubes with different diameters can be selected.

[0052] The present application has no particular limitation on the method of regulating the mass percentage content of the conductive agent, as long as the object of the present application can be achieved. For example, the mass percentage content of the conductive agent can be regulated by regulating the mass of the added conductive agent.

[0053] The present application has no particular limitation on the method of regulating the mass percentage content of carbon black particles and the mass percentage content of carbon nanotubes, as long as the object of the present application can be achieved. For example, the mass percentage content of carbon black particles can be regulated by regulating the mass of the added carbon black particles; the mass percentage content of carbon nanotubes can be regulated by regulating the mass of the added carbon nanotubes.

[0054] The present application has no particular limitation on the positive electrode current collector, as long as the object of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector), etc.

[0055] In the present application, the positive electrode material layer further includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material, as long as the object of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium-rich manganese-based material or lithium titanate. The above lithium nickel cobalt manganate can include LiNi 0.95 Co 0.03 Mn 0.02 O2 (Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2 (Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3At least one of O2 (NCM111). The positive electrode material layer of the present application further includes a positive electrode binder. The present application has no particular limitation on the positive electrode binder, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride - hexafluoropropylene, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyamide, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, styrene - butadiene rubber (SBR), polypropylene, polyethylene, polyetherimide, copolymer of alkene derivatives or carboxymethyl cellulose salt. The above - mentioned carboxymethyl cellulose salt may include, but is not limited to, at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application has no particular limitation on the mass percentage content of the positive electrode active material and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs 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 content W2 of the positive electrode active material is 94% to 99.2%, and the mass percentage content W3 of the positive electrode binder is 0.5% to 3.0%.

[0056] The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 16 μm. The present application has no particular limitation on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single - sided positive electrode material layer is 25 μm to 250 μm.

[0057] Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The present application has no particular limitation on the composition of the conductive layer, and it can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application has no particular limitation on the conductive agent and the binder in the conductive layer, and they can be at least one of the above - mentioned conductive agent and the above - mentioned positive electrode binder. The present application has no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0058] In the present application, the secondary battery further includes a negative electrode plate. The negative electrode plate 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 above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its own thickness direction, or can be provided on both surfaces of the negative electrode current collector along its own thickness direction. 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. There is no special limitation in the present application as long as the purpose of the present application can be achieved. There is no special limitation on the negative electrode current collector in the present application as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector, etc.

[0059] The negative electrode material layer of the present application includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium, etc. The negative electrode material layer of the present application further includes a negative electrode binder and a negative electrode conductive agent. There is no special limitation on the negative electrode binder and the negative electrode conductive agent in the negative electrode material layer of the present application as long as the purpose of the present application can be achieved. For example, the negative electrode binder can be at least one of the above-mentioned positive electrode binders, and the negative electrode conductive agent can be at least one of the above-mentioned conductive agents. There is no special limitation on the mass ratio of the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent in the negative electrode material layer in the present application, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0060] There is no special limitation on the thickness of the negative electrode current collector in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm. There is no special limitation on the thickness of the negative electrode material layer in the present application 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 30 μm to 250 μm.

[0061] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. There is no particular limitation on the composition of the conductive layer in the present application, and it may be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. There is no particular limitation on the conductive agent and the binder in the conductive layer in the present application, and they may be at least one of the above-mentioned negative electrode conductive agents and the above-mentioned negative electrode binders. There is no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0062] In the present application, the secondary battery further includes an electrolyte. The electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. There is no particular limitation on the non-aqueous solvent in the present application, as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include but are 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 (EMC). The above cyclic carbonate compounds may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above 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 trifluoromethyl ethylene carbonate. The above 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, decanolide, valerolactone, or caprolactone. The above ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include but are 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. There is no particular limitation on the mass percentage content of the lithium salt and the non-aqueous solvent in the present application, as long as the object of the present application can be achieved.

[0063] In the present application, the secondary battery further includes a separator. The separator is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass through freely, and does not affect the progress of the electrochemical charge and discharge process. There is no particular limitation on the separator in the present application, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0064] In the present application, the separator may include a base film and a surface treatment layer. The base film may be a non-woven fabric or a composite film having a porous structure, and the material of the base film may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the base film, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a separator binder. There is no particular limitation on the above-mentioned inorganic particles in the present application. For example, it may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. There is no particular limitation on the above-mentioned separator binder in the present application. For example, it may be at least one of the aforementioned positive electrode binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0065] The secondary battery of the present application further includes a packaging bag for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the art in the secondary battery. There is no limitation on the above-mentioned other components in the present application. There is no particular limitation on the packaging bag in the present application, and it may be a packaging bag well-known in the art, as long as it can achieve the purpose of the present application.

[0066] There is no particular limitation on the type of the secondary battery in the present application, and it may include any device that undergoes an electrochemical reaction. In the present application, the secondary battery may include, but is not limited to: lithium metal secondary battery, lithium ion secondary battery (lithium ion battery), lithium polymer secondary battery or lithium ion polymer secondary battery, etc.

[0067] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and the present application has no special limitations. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound structure electrode assembly, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or, stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging. Among them, the packaging bag is a known packaging bag in the art, and the present application does not limit it.

[0068] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has a lower internal resistance.

[0069] The present application does not particularly limit the type of the electronic device, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0070] Examples

[0071] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0072] Testing methods and equipment:

[0073] Conductive agent sampling method:

[0074] (1) Disassemble the lithium-ion battery to obtain the positive electrode sheet; (2) Immerse the above positive electrode sheet in the solvent N-methylpyrrolidone (NMP) to remove the film, dissolve the film layer of the positive electrode material in the solvent, and use a disperser to disperse evenly to obtain a slurry; (3) Take the above slurry and use centrifugation to separate the positive electrode binder in the slurry to obtain a slurry containing the positive electrode active material and the conductive agent; (4) Digest the positive electrode active material (lithium cobaltate or lithium nickel cobalt manganate) in the above slurry containing the positive electrode active material and the conductive agent with hydrochloric acid. The lithium iron phosphate-based positive electrode active material is digested with hydrochloric acid-hydrogen peroxide, and then dried to obtain the conductive agent. The conductive agent in the following specific surface area test of the conductive agent and the Raman spectrum test of the conductive agent is sampled by the above method.

[0075] Specific surface area test of the conductive agent:

[0076] According to the national standard "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), use a specific surface area analyzer (model TristarⅡ3020M) to test the specific surface area of the above conductive agent by gas adsorption method.

[0077] Raman spectrum test of the conductive agent:

[0078] Use a laser confocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instruments Division) to test the Raman spectrum of the above conductive agent. The peak intensity of the conductive agent at 1350 cm -1 is I D , and the peak intensity at 1580 cm -1 is I G . The value of I D / I G of the conductive agent is obtained by the following method: Place the above conductive agent powder on the Raman test sample stage, test the Raman spectrum of the conductive agent powder to obtain the value of I D / I G , test 12 times, and take the average value as the value of I D / I G of the conductive agent.

[0079] Raman spectrum test of carbon black particles:

[0080] Use a laser confocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instruments Division) to test the Raman spectrum of carbon black particles. The peak intensity of carbon black particles at 1350 cm -1 is I D1 , and the peak intensity at 1580 cm -1 is I G1 . The value of I D1 / I G1The value is obtained as follows: Place the above carbon black particles on the Raman test sample stage, test the Raman spectrum of the carbon black particles, and obtain the I D1 / I G1 value. Test 12 times and take the average value as the I D1 / I G1 value of the carbon black particles.

[0081] Raman spectrum test of carbon nanotubes:

[0082] Use a laser confocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instruments Division) to test the Raman spectrum of carbon nanotubes. The peak intensity of the carbon nanotubes at 1350 cm -1 is I D2 , and the peak intensity at 1580 cm -1 is I G2 . The I D2 / I G2 value of the carbon nanotubes is obtained as follows: Place the above carbon nanotubes on the Raman test sample stage, test the Raman spectrum of the carbon nanotubes, and obtain the I D2 / I G2 value. Test 12 times and take the average value as the I D2 / I G2 value of the carbon nanotubes.

[0083] Activation energy test of the positive electrode plate:

[0084] (1) Take a lithium-ion battery and add a post-reference electrode to make a three-electrode battery;

[0085] (2) Take the above three-electrode battery, set the temperature T to (273±2) K, (283±2) K, (298±2) K, (308±2) K, and use electrochemical impedance spectroscopy (EIS) to scan to obtain Rct at the corresponding temperature;

[0086] (3) Calculate the activation energy of the positive electrode plate according to the Arrhenius equation k = Aexp(-Ea / RT): Establish a scatter plot with lnRct as the ordinate and 1000 / T as the abscissa, substitute the corresponding temperature T and Rct in step (2), obtain 4 points, fit the linear equation of the above 4 points, and multiply the slope of the linear equation by the gas constant R (8.314 J·mol -1 ·K -1 ) to obtain the activation energy E0 of the positive electrode plate.

[0087] Particle size test of carbon black particles and diameter test of carbon nanotubes:

[0088] (1) Disassemble the lithium-ion battery to obtain the positive electrode plate; (2) Immerse the above positive electrode plate in dimethyl carbonate (DMC) at room temperature for 60 min, take it out, and dry it at room temperature; (3) Take the positive electrode plate obtained in step (2), and obtain the cross-section of the positive electrode material layer on the positive electrode plate by brittle fracture with liquid nitrogen; (4) Observe the above cross-section through a scanning electron microscope (SEM, model Thermo Fisher FEI-Apreo S), and measure the particle sizes of no less than 50 carbon black particles and the diameters of no less than 30 carbon nanotubes in 10 regions, and take the average value as the particle size of the carbon black particles and the diameter of the carbon nanotubes.

[0089] Specific surface area test of carbon black particles:

[0090] According to the national standard "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), use a specific surface area analyzer (model TristarⅡ3020M) to test the specific surface area of carbon black particles by gas adsorption method.

[0091] Specific surface area test of carbon nanotubes:

[0092] According to the national standard "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), use a specific surface area analyzer (model TristarⅡ3020M) to test the specific surface area of carbon nanotubes by gas adsorption method.

[0093] 1s DC resistance (DCR) test:

[0094] Take the lithium-ion battery in the example or comparative example and conduct the following tests at 25±2℃: (1) Let it stand for 2 h; (2) Then charge it at a constant current of 1.0C to 4.50V, and charge it at a constant voltage of 4.50V until the current is less than or equal to 0.025C; let it stand for 2 h; (3) Then discharge it at a constant current of 0.2C to 3.0V, and take the discharge capacity of this step as C1, and let it stand for 5 h; (4) Then charge it at a constant current of 1.0C1 to 4.50V, and charge it at a constant voltage of 4.50V until the current is less than or equal to 0.025C1; let it stand for 10 min; (5) Then discharge it at a constant current of 0.1C1 until the capacity is 0.2C1, let it stand for 15 min, record the voltage at this time as V0, and then discharge it at a constant current of 1.0C1 for 1 s, record the voltage at this time as V1, then the 1s DCR at 25℃ and 20% SOC is (V0 - V1) / 1.0C1.

[0095] Internal resistance growth rate test after 800 cycles at 25℃:

[0096] Take the lithium-ion battery in the example or comparative example and conduct the following tests at 25±2℃:

[0097] (1) Stand still for 2 h, discharge at a constant current of 0.7C to 3.0V, and stand still for 5 min;

[0098] (2) Charge at a constant current of 1.0C to 4.50V, and then charge at a constant voltage of 4.50V until the current is less than or equal to 0.05C; stand still for 5 min; then discharge at a constant current of 0.5C to 3.0V, and test the internal resistance of the lithium-ion battery at this time with a sinusoidal current of 1000 Hz and record it as IMP1; stand still for 5 min; cycle 49 times according to the above steps, and the internal resistances of the lithium-ion battery are recorded as IMP1, IMP2, ……, IMP49 in turn; then perform the 50th cycle. In the 50th cycle, charge at a constant current of 1.0C to 4.50V, and then charge at a constant voltage of 4.50V until the current is less than or equal to 0.05C; stand still for 5 min; then discharge at a constant current of 0.2C to 3.0V, and record the internal resistance of the lithium-ion battery at this time as IMP50;

[0099] (3) Then cycle the above step (2) 16 times, and then charge at a constant current of 1.0C to 4.50V, and then charge at a constant voltage of 4.50V until the current is less than or equal to 0.05C; stand still for 5 min; then discharge at a constant current of 0.5C to 3.0V, and record the internal resistance of the lithium-ion battery in the 801st cycle as IMP801; then the internal resistance growth rate R1(%) of the lithium-ion battery after 800 cycles at 25℃ = IMP801 / IMP1 - 100%.

[0100] Example 1-1

[0101] <Preparation of the positive electrode sheet>

[0102] Mix the positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent acetylene black particles, the conductive agent multi-walled carbon nanotubes, and the positive electrode binder polyvinylidene fluoride (PVDF) according to a weight ratio of 97.6:0.3:0.6:1.5, then add N-methylpyrrolidone (NMP) as a solvent, stir and mix evenly to obtain a positive electrode slurry, where the solid content of the positive electrode slurry is 70 wt%; the acetylene black particles are acetylene black, and the multi-walled carbon nanotubes are multi-walled carbon nanotubes. Coat the positive electrode slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and dry it at 120℃ for 1 h to obtain a positive electrode sheet with a positive electrode material layer with a thickness of 100 μm coated on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a positive electrode material layer coated on both sides. Dry it under vacuum conditions at 120℃ for 1 h, and then obtain a positive electrode sheet with a specification of 74 mm × 867 mm after cold pressing, slicing, and slitting. Among them, the compaction density during the cold pressing process is 4.2 g / cm 3 。

[0103] <Preparation of the negative electrode sheet>

[0104] The artificial graphite as the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) as the negative electrode binder, and styrene-butadiene rubber (SBR) as the negative electrode binder are mixed in a weight ratio of 95:2:3, and then deionized water is added as a solvent and stirred and mixed evenly to obtain a negative electrode slurry, where the solid content of the negative electrode slurry is 75 wt%; the negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm and dried at 120 °C to obtain a negative electrode sheet with a negative electrode material layer with a thickness of 120 μm coated on one side. Repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. Dry in a vacuum condition at 120 °C for 1 h, and then obtain a negative electrode sheet with a specification of 78 mm × 875 mm after cold pressing, slicing, and slitting. Among them, the compaction density in the cold pressing process is 1.75 g / cm 3 。

[0105] <Preparation of electrolyte>

[0106] In a glove box with an argon atmosphere where the water content is less than 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a weight ratio of 1:1:1 to obtain a basic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage content of the lithium salt is 12.5%, and the balance is the basic solvent.

[0107] <Preparation of separator>

[0108] A polyethylene (PE) film with a thickness of 15 μm is used.

[0109] <Preparation of lithium-ion battery>

[0110] Stack the positive electrode sheet, separator, negative electrode sheet, and separator prepared above in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and wind to obtain an electrode assembly. After welding the electrode tabs, place the electrode assembly in an aluminum-plastic film packaging bag, dry it, inject the electrolyte, and obtain a lithium-ion battery after vacuum packaging, standing, forming, degassing, and trimming processes.

[0111] Examples 1-2 to Examples 1-6

[0112] Except that by adjusting the high-temperature cracking reaction time of the carbon black particles, the particle size and specific surface area of the carbon black particles are as shown in Table 1, the rest are the same as Example 1-1.

[0113] Examples 1-7 to Examples 1-11

[0114] Except that by adjusting the high-temperature cracking reaction time of the carbon black particles, the I D1 / I G1Except that the values are as shown in Table 1, the rest is the same as in Examples 1-3.

[0115] Examples 1-12 to Examples 1-15

[0116] Except that by adjusting the carbon nanotube synthesis temperature, the diameter and specific surface area of the carbon nanotubes are as shown in Table 1, the rest is the same as in Examples 1-3.

[0117] Examples 1-16 to Examples 1-18

[0118] Except that by adjusting the carbon nanotube synthesis temperature, the I D2 / I G2 value is as shown in Table 1, the rest is the same as in Examples 1-3.

[0119] Examples 2-1 to Examples 2-11

[0120] Except that the relevant preparation parameters are adjusted according to Table 2, the rest is the same as in Examples 1-3.

[0121] Comparative Examples 1-1 to Comparative Examples 1-4

[0122] Except that the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Examples 1-3.

[0123] Comparative Example 1-5

[0124] Except that in the <Preparation of the positive electrode sheet>, the positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent graphene, and the positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.6:0.9:1.5, and then NMP is added as a solvent and stirred and mixed evenly to obtain the positive electrode slurry, the rest is the same as in Examples 1-3.

[0125] Comparative Example 2-1

[0126] Except that the relevant preparation parameters are adjusted according to Table 2, the rest is the same as in Examples 1-3.

[0127] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 2.

[0128] Table 1

[0129]

[0130]

[0131] Note: (1) In Table 1, " / " indicates no relevant preparation parameters.

[0132] Table 2

[0133]

[0134] Note: (1) In Table 2, taking Examples 1-3 as an example, the type of the positive electrode active material is "LCO", which means the positive electrode active material is lithium cobalt oxide (LiCoO₂), and the same applies to other examples.

[0135] It can be seen from Examples 1-1 to 1-18, Examples 2-1 to 2-11, Comparative Examples 1-1 to 1-5, and Comparative Example 2-1 that when the type, specific surface area of the conductive agent, and activation energy of the positive electrode sheet are within the scope of this application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced. In Comparative Examples 1-1 to 1-2 and Comparative Example 2-1, the specific surface area of the conductive agent and the activation energy of the positive electrode sheet are not within the scope of this application. In Comparative Examples 1-3 to 1-4, the activation energy of the positive electrode sheet is not within the scope of this application. In Comparative Example 1-5, the type of the conductive agent is not within the scope of this application. The prepared lithium-ion battery has a higher 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery is higher. In Comparative Example 1-2, the specific surface area of the conductive agent is too large, making it difficult to process the positive electrode slurry, and the conductive agent agglomerates, resulting in a higher 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 800 cycles at 25°C of the lithium-ion battery, and the internal resistance of the lithium-ion battery is larger.

[0136] The particle size and specific surface area of carbon black particles usually affect the internal resistance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-6 that by controlling the particle size and specific surface area of carbon black particles within the scope of this application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced. Among Examples 1-1 to 1-6, the specific surface area of the carbon black particles in Example 1-1 is relatively large, which will affect the dispersion of the carbon black particles to a certain extent, and some carbon black may agglomerate, affecting the conductive network of the positive electrode material layer, so that the 1sDCR at 25°C and 20% SOC and the internal resistance growth rate after 800 cycles at 25°C of the lithium-ion battery are relatively high.

[0137] The I of carbon black particles D1 / I G1 value usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, 1-7 to 1-11 that by controlling the I of carbon black particles D1 / I G1The values are within the scope of this application. The prepared lithium-ion battery has a low 1sDCR at 25°C and 20% SOC, and a low internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced. In Examples 1-3, 1-7 to 1-11, as the I D1 / I G1 value of the carbon black particles increases, the internal resistance growth rate after 800 cycles at 25°C first decreases and then increases. This is because as the I D1 / I G1 value of the carbon black particles increases, the surface defects of the carbon black particles increase, which is beneficial to reducing the activation energy of the positive electrode sheet and reducing the internal resistance growth rate of the lithium-ion battery after 800 cycles at 25°C. However, when the I D1 / I G1 value of the carbon black particles is relatively high, while reducing the activation energy of the positive electrode sheet, the defects of the conductive agent also increase, which can catalyze the occurrence of side reactions. Therefore, the internal resistance growth rate of the lithium-ion battery after 800 cycles at 25°C increases.

[0138] The diameter and specific surface area of carbon nanotubes usually affect the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, 1-12 to 1-15 that by adjusting the diameter and specific surface area of carbon nanotubes within the scope of this application, the prepared lithium-ion battery has a low 1sDCR at 25°C and 20% SOC, and a low internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced. In Examples 1-3, 1-12 to 1-15, the specific surface area of the carbon nanotubes in Example 1-12 is relatively large, which will increase the viscosity of the positive electrode slurry, and it is necessary to reduce the solid content of the positive electrode slurry, reduce the coating and drying efficiency, and increase the production cost.

[0139] The I D2 / I G2 value of carbon nanotubes usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, 1-16 to 1-18 that by adjusting the I D2 / I G2 value of carbon nanotubes within the scope of this application, the prepared lithium-ion battery has a low 1sDCR at 25°C and 20% SOC, and a low internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0140] The I D / I G value of the conductive agent usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-18 that by adjusting the I D / I GWhen the value is within the scope of the present application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC, and a lower internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0141] The mass percentage content of the conductive agent usually affects the internal resistance of the lithium-ion battery. It can be seen from Examples 1-3, Examples 2-1 to 2-7 that by adjusting the mass percentage content of the conductive agent within the scope of the present application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC, and a lower internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0142] It can be seen from Examples 2-8 to 2-9 that when the type of the positive electrode binder is within the scope of the present application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC, and a lower internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0143] It can be seen from Examples 2-10 to 2-11 that when the type of the positive electrode active material is within the scope of the present application, the prepared lithium-ion battery has a lower 1sDCR at 25°C and 20% SOC, and a lower internal resistance growth rate after 800 cycles at 25°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0144] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or article.

[0145] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0146] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, which includes a positive electrode tab. The positive electrode tab includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a conductive agent, and the conductive agent includes carbon black particles and / or carbon nanotubes. The specific surface area B0 of the conductive agent is 150 m 2 / g to 1500 m 2 / g; the activation energy E0 of the positive electrode tab is 25 kJ / mol to 65 kJ / mol.

2. The secondary battery according to claim 1, wherein, The specific surface area B0 of the conductive agent is 300 m 2 / g to 800 m 2 / g.

3. The secondary battery according to claim 1, wherein, In the Raman spectrogram of the conductive agent, there is a first characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D , and there is a second characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G . 1.0 ≤ I D / I G ≤ 1.

5.

4. The secondary battery according to claim 1 satisfies at least one of the following characteristics: (1) The particle size d1 of the carbon black particles is 5 nm to 50 nm; (2) The conductive agent includes carbon black particles and carbon nanotubes, and the specific surface area B1 of the carbon black particles is 100 m 2 / g to 150 m 2 / g.

5. The secondary battery according to claim 1 satisfies at least one of the following characteristics: (1) The particle size d1 of the carbon black particles is 10 nm to 40 nm; (2) The specific surface area B1 of the carbon black particles is 700 m 2 / g to 1400 m 2 / g.

6. The secondary battery according to claim 1, wherein, In the Raman spectrogram of the carbon black particles, there is a third characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D1 , and a fourth characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G1 . 0.8 ≤ I D1 / I G1 ≤ 1.

7.

7. The secondary battery according to claim 1, wherein The diameter d2 of the carbon nanotubes is 3 nm to 15 nm.

8. The secondary battery according to claim 1, wherein, The specific surface area B2 of the carbon nanotubes is 200 m 2 / g to 300 m 2 / g.

9. The secondary battery according to claim 1, wherein, In the Raman spectrum of the carbon nanotubes, there is a fifth characteristic peak with a peak intensity of I -1 in the range of 1300 cm -1 to 1400 cm D2 , and a sixth characteristic peak with a peak intensity of I -1 in the range of 1550 cm -1 to 1650 cm G2 . 0.6 ≤ I D2 / I G2 ≤ 1.

3.

10. The secondary battery according to claim 1, wherein, Based on the mass of the positive electrode material layer, the mass percentage content W1 of the conductive agent is 0.3% to 3.0%.

11. The secondary battery according to claim 1, wherein, The conductive agent includes the carbon black particles and the carbon nanotubes. Based on the mass of the positive electrode material layer, the mass percentage content W11 of the carbon black particles is 0.2% to 1.5%, and the mass percentage content W12 of the carbon nanotubes is 0 to 1.5%.

12. An electronic device, which includes the secondary battery according to any one of claims 1 to 11.

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