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 a whisker carbon rod, and the oil absorption value O1 of the conductive agent is 300 mL / 100 g to 800 mL / 100 g. By regulating the type of the conductive agent, the oil absorption value is within the application range, and the internal resistance of the secondary battery can be reduced.

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 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. The conductive agent includes carbon black particles and whisker carbon rods. The oil absorption value O1 of the conductive agent is from 300 mL / 100 g to 800 mL / 100 g. By regulating that the conductive agent includes carbon black particles and whisker carbon rods and the oil absorption value of the conductive agent is within the scope of the present application, the carbon black particles are more likely to coat the surface of the positive electrode active material particles. The high oil absorption value of the carbon black particles indicates that its branched chains are rich and the continuity is good, which can increase the continuity of the conductive network on the surface of the positive electrode active material particles; while the whisker carbon rods can be distributed between the positive electrode active material particles, connect different voids, increase the pore size, and reduce the Li + transport tortuosity, can conduct closed pores into active pores, improve the porosity of the positive electrode material layer, and increase the Li + transport path. It can improve the continuity of the conductive network between the positive electrode active material particles. The whisker carbon rods and the carbon black particles jointly improve the continuity of the conductive network of the positive electrode tab, can increase the Li + transport path, improve the Li + transport efficiency, reduce the Li + concentration polarization, and thus reduce the internal resistance of the secondary battery.

[0006] In an embodiment of the present application, the oil absorption value O1 of the conductive agent is from 420 mL / 100 g to 700 mL / 100 g. By controlling the oil absorption value of the conductive agent within the above range, carbon black particles are more likely to coat on the surface of the positive electrode active material particles, which can further increase the continuity of the conductive network on the surface of the positive electrode active material particles and further improve the continuity of the conductive network between the positive electrode active material particles; it can further increase the Li + transmission path, further improve the Li + transmission efficiency, and further reduce the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0007] In an embodiment of the present application, the oil absorption value O2 of the carbon black particles is from 300 mL / 100 g to 900 mL / 100 g. By controlling the oil absorption value of the carbon black particles within the above range, the oil absorption value of the carbon black particles is relatively high, the carbon black particles have a long chain-like structure, and have a better adsorption effect on the electrolyte, which will further improve the liquid retention of the positive electrode sheet and further increase the Li + transmission path, further improve the Li + transmission efficiency, and further reduce the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0008] In an embodiment of the present application, the diameter D1 of the whisker carbon rod is from 20 nm to 80 nm. By controlling the diameter of the whisker carbon rod within the above range, the whisker carbon rods have a suitable diameter, and the possibility of mutual entanglement between the whisker carbon rods is small; and the whisker carbon rods have a suitable specific surface area and a large effective conductive area, which further improves the Li + transmission efficiency, and further reduces the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0009] In an embodiment of the present application, the length L of the whisker carbon rod is from 3 μm to 30 μm. By controlling the length of the whisker carbon rod within the above range, the whisker carbon rods have a suitable length, and the whisker carbon rods have a good long-range conductive effect. Li + can be efficiently transmitted along the surface of the whisker carbon rod, further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery; and it is also beneficial to the dispersion of the positive electrode paste.

[0010] In an embodiment of the present application, the oil absorption value O3 of the whisker carbon rod is from 250 mL / 100 g to 500 mL / 100 g. By controlling the oil absorption value of the whisker carbon rod within the above range, the dispersion degree of the whisker carbon rod in the positive electrode paste can be increased; at the same time, the liquid retention ability of the positive electrode sheet is improved, and it can further increase the Li + transmission path, further improve the Li+ transport efficiency and further reduce Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0011] In one embodiment of the present application, the porosity P of the positive electrode material layer is 20% to 40%; based on the total pore volume of the positive electrode material layer, the volume percentage content V1 of pores with a pore diameter of 8 μm to 15 μm is 3% to 15%, and the volume percentage content V2 of pores with a pore diameter of 0.5 μm to 5 μm is 8% to 20%. By controlling the porosity and pore size distribution of the positive electrode material layer within the above ranges, the positive electrode material layer has a high porosity and a suitable pore size distribution, which can further increase the Li + transport path and further improve the Li + transport efficiency and further reduce Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0012] In one 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 0.6% to 1.5%. By controlling the mass percentage content of the conductive agent within the above range, the conductive agent has a suitable mass percentage content. The carbon black particles have a good adsorption effect on the electrolyte, and can also improve the liquid retention of the positive electrode plate and increase the Li + transport path; the whisker carbon rod can conduct the closed pores between the positive electrode active material particles into active pores, improving the porosity of the positive electrode material layer and further increasing the Li + transport path and further improve the Li + transport efficiency and further reduce Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0013] In one embodiment of the present application, the positive electrode material layer further includes a positive electrode active material. Based on the mass of the positive electrode material layer, the mass percentage content W2 of the positive electrode active material is 95.5% to 98.5%. By controlling the mass percentage content of the positive electrode active material within the above range, the secondary battery can have a suitable energy density.

[0014] In one embodiment of the present application, the particle size Dv50 of the positive electrode active material is 5 μm to 20 μm, the oil absorption value of the positive electrode material layer is O5 mL / 100g, and 100×W2 / Dv50 + W1×O1 ≤ O5 ≤ 100×W2 / Dv50 + 2×W1×O1. By controlling the particle size Dv50 of the positive electrode active material and the oil absorption value of the positive electrode material layer to meet the above characteristics, the positive electrode active material has a suitable particle size, which is beneficial to improving the oil absorption value of the positive electrode material layer, can improve the liquid retention ability of the positive electrode plate, and can further increase the Li + transport path and further improve the Li+ transport efficiency and further reduce Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery; and it can also improve the high-temperature performance 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 W11 of carbon black particles is 0.2% to 0.6%, and the mass percentage content W12 of whisker carbon rods is 0.1% to 0.5%. By controlling the mass percentage content of carbon black particles and whisker carbon rods within the above ranges, the carbon black particles and whisker carbon rods have appropriate mass percentage contents. The carbon black particles have a good adsorption effect on the electrolyte, which can also improve the liquid retention of the positive electrode sheet and increase Li + transport paths; the whisker carbon rods can conduct the closed pores between the positive electrode active material particles into active pores, improving the porosity of the positive electrode material layer and further increasing Li + transport paths and further improving the Li + transport efficiency and further reducing Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0016] In an embodiment of the present application, the conductive agent further includes carbon nanotubes, and the oil absorption value O4 of the carbon nanotubes is 350 mL / 100 g to 500 mL / 100 g. By controlling the oil absorption value of the carbon nanotubes within the above range, the dispersion degree of the carbon nanotubes in the positive electrode slurry can be increased, which is beneficial to improving the processing performance of the positive electrode slurry; at the same time, the liquid retention ability of the positive electrode sheet is improved, which can further increase Li + transport paths, further improving the Li+ transport efficiency and further reducing Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0017] In an embodiment of the present application, the diameter D2 of the carbon nanotubes is 3 nm to 20 nm. By controlling the diameter of the carbon nanotubes within the above range, the carbon nanotubes are more evenly dispersed in the positive electrode slurry, which is beneficial to improving the processing performance of the positive electrode slurry; at the same time, the carbon nanotubes have an appropriate specific surface area, and the carbon nanotubes have a higher effective conductive area, further reducing the internal resistance of the secondary battery.

[0018] In an embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content W13 of the carbon nanotubes is 0 to 0.7%. By controlling the mass percentage content of the carbon nanotubes within the above range, the carbon nanotubes have an appropriate mass percentage content, which can construct a good conductive network and further reduce the internal resistance of the secondary battery; at the same time, the content of the positive electrode active material in the positive electrode material layer is relatively high, and the secondary battery has a relatively high energy density.

[0019] 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.

[0020] Advantages of the present application:

[0021] 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 whisker carbon rods, and the oil absorption value O1 of the conductive agent is 300 mL / 100 g to 800 mL / 100 g. By regulating the type and oil absorption value of the conductive agent within the scope of the present application, the internal resistance of the secondary battery can be reduced.

[0022] 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

[0023] Next, the technical solutions in the present application will be described clearly and completely 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 of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope protected by the present application.

[0024] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is used 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.

[0025] A first aspect of the present application provides 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. The conductive agent includes carbon black particles and whisker carbon rods. The oil absorption value O1 of the conductive agent is from 300 mL / 100 g to 800 mL / 100 g. Exemplarily, O1 can be 300 mL / 100 g, 350 mL / 100 g, 370 mL / 100 g, 400 mL / 100 g, 420 mL / 100 g, 450 mL / 100 g, 470 mL / 100 g, 500 mL / 100 g, 550 mL / 100 g, 570 mL / 100 g, 600 mL / 100 g, 650 mL / 100 g, 670 mL / 100 g, 700 mL / 100 g, 750 mL / 100 g, 770 mL / 100 g, 800 mL / 100 g, or a range composed of any two of the above values. In the present application, the carbon black particles include at least one of Super P, acetylene black, or Ketjen black. The above-mentioned "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. The present application has no special limitation as long as the purpose of the present application can be achieved.

[0026] The inventors have found through research that when the conductive agent in the positive electrode material layer includes carbon black particles and whisker carbon rods, the carbon black particles with a high oil absorption value have a long chain-like structure, have a good adsorption effect on the electrolyte, and can also improve the liquid retention of the positive electrode tab, increasing the Li + transport path; the whisker carbon rods are mainly distributed between the positive electrode active material particles, connecting different voids, increasing the pore size, and reducing the Li + transport tortuosity, can conduct closed pores into active pores, improve the porosity of the positive electrode material layer, and increase the Li + transport path. Li + can be efficiently transported along the surface of the conductive agent. The long and straight whisker carbon rods provide a Li +Transportation provides a shortcut. When the oil absorption value of the conductive agent is too large, for example, greater than 800 mL / 100 g, it will cause the conductive agent to be difficult to disperse evenly, affecting the construction of the conductive network and unable to effectively reduce the internal resistance of the secondary battery; when the oil absorption value of the conductive agent is too small, for example, less than 300 mL / 100 g, it will cause the liquid retention capacity of the positive electrode sheet to decrease, affecting the lithium ion transportation and unable to effectively reduce the internal resistance of the secondary battery. By regulating the conductive agent including carbon black particles and whisker carbon rods, and the oil absorption value of the conductive agent within the scope of this application, the carbon black particles are more likely to be coated on the surface of the positive active material particles. The high oil absorption value of the carbon black particles represents that its branches are rich and the continuity is good, which can increase the continuity of the conductive network on the surface of the positive active material particles; while the whisker carbon rods can be distributed between the positive active material particles, connecting different voids, increasing the pore size, and reducing the Li + transportation tortuosity, can turn the closed pores into active pores, improve the porosity of the positive material layer, and increase the Li + transportation path, which can improve the continuity of the conductive network between the positive active material particles. The whisker carbon rods and the carbon black particles jointly improve the continuity of the conductive network of the positive electrode sheet, which can increase the Li + transportation path, improve the Li + transportation efficiency, and reduce the Li + concentration polarization, thereby reducing the internal resistance of the secondary battery.

[0027] In an embodiment of the present application, the oil absorption value O1 of the conductive agent is 420 mL / 100 g to 700 mL / 100 g. Exemplarily, O1 can be 420 mL / 100 g, 450 mL / 100 g, 470 mL / 100 g, 500 mL / 100 g, 550 mL / 100 g, 570 mL / 100 g, 600 mL / 100 g, 650 mL / 100 g, 670 mL / 100 g, 700 mL / 100 g or a range composed of any two of the above values. By regulating the oil absorption value of the conductive agent within the above range, the carbon black particles are more likely to be coated on the surface of the positive active material particles, which can further increase the continuity of the conductive network on the surface of the positive active material particles and further improve the continuity of the conductive network between the positive active material particles; it can further increase the Li + transportation path, further improve the Li + transportation efficiency, and further reduce the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0028] In an embodiment of the present application, the oil absorption value O2 of the carbon black particles is from 300 mL / 100 g to 900 mL / 100 g. Exemplarily, O2 can be 300 mL / 100 g, 350 mL / 100 g, 370 mL / 100 g, 400 mL / 100 g, 420 mL / 100 g, 450 mL / 100 g, 470 mL / 100 g, 500 mL / 100 g, 550 mL / 100 g, 570 mL / 100 g, 600 mL / 100 g, 650 mL / 100 g, 670 mL / 100 g, 700 mL / 100 g, 750 mL / 100 g, 770 mL / 100 g, 800 mL / 100 g, 850 mL / 100 g, 900 mL / 100 g or a range composed of any two of the above values. By controlling the oil absorption value of the carbon black particles within the above range, the carbon black particles have a high oil absorption value, the carbon black particles have a long chain-like structure, have a better adsorption effect on the electrolyte, and will further improve the liquid retention of the positive electrode sheet, and further increase the Li + transport path, and further improve the Li + transport efficiency, and further reduce the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0029] In an embodiment of the present application, the diameter D1 of the whisker carbon rod is from 20 nm to 80 nm. Exemplarily, the value of D1 can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 or a range composed of any two of the above values. By controlling the diameter of the whisker carbon rod within the above range, the whisker carbon rods have a suitable diameter, and the possibility of mutual entanglement between the whisker carbon rods is small; and the whisker carbon rods have a suitable specific surface area and a large effective conductive area, further improving the Li + transport efficiency, and further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0030] In an embodiment of the present application, the length L of the whisker carbon rod is from 3 μm to 30 μm. Exemplarily, the value of L can be 3, 5, 7, 9, 10, 13, 15, 17, 19, 20, 23, 25, 27, 29, 30 or a range composed of any two of the above values. By controlling the length of the whisker carbon rod within the above range, the whisker carbon rods have a suitable length, the whisker carbon rods have a good long-range conductive effect, and Li + can be efficiently transported along the surface of the whisker carbon rod, further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery; and it is also beneficial to the dispersion of the positive electrode slurry.

[0031] In an embodiment of the present application, the oil absorption value O3 of the whisker carbon rod is from 250 mL / 100 g to 500 mL / 100 g. Exemplarily, O3 can be 250 mL / 100 g, 270 mL / 100 g, 300 mL / 100 g, 350 mL / 100 g, 370 mL / 100 g, 400 mL / 100 g, 420 mL / 100 g, 450 mL / 100 g, 470 mL / 100 g, 500 mL / 100 g or a range composed of any two of the above values. By controlling the oil absorption value of the whisker carbon rod within the above range, the dispersion degree of the whisker carbon rod in the positive electrode slurry can be increased; meanwhile, the liquid retention capacity of the positive electrode sheet can be improved, and the Li + transmission path can be further increased, and the Li + transmission efficiency can be further improved, and the Li + concentration polarization can be further reduced, thereby further reducing the internal resistance of the secondary battery.

[0032] In an embodiment of the present application, the porosity P of the positive electrode material layer is from 20% to 40%; Exemplarily, the value of P can be 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40% or a range composed of any two of the above values; Based on the total pore volume of the positive electrode material layer, the volume percentage content V1 of pores with a pore diameter of 8 μm to 15 μm is from 3% to 15%, and the volume percentage content V2 of pores with a pore diameter of 0.5 μm to 5 μm is from 8% to 20%. Exemplarily, the value of V1 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 values; The value of V2 can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range composed of any two of the above values. By controlling the porosity and pore size distribution of the positive electrode material layer within the above range, the positive electrode material layer has a high porosity, and the positive electrode material layer has a suitable pore size distribution, which can further increase the Li + transmission path, further improve the Li + transmission efficiency, further reduce the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0033] 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 0.6% to 1.5%. Exemplarily, the value of W1 can be 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 numerical values. By adjusting the mass percentage content of the conductive agent within the above range, the conductive agent has an appropriate mass percentage content, the carbon black particles have a good adsorption effect on the electrolyte, and it will also improve the liquid retention of the positive electrode sheet, increasing the Li + transmission path; the whisker carbon rod can conduct the closed pores between the positive electrode active material particles into active pores, improving the porosity of the positive electrode material layer and further increasing the Li + transmission path, further improving the Li + transmission efficiency and further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0034] In an embodiment of the present application, the positive electrode material layer further includes a positive electrode active material. Based on the mass of the positive electrode material layer, the mass percentage content W2 of the positive electrode active material is 95.5% to 98.5%. Exemplarily, the value of W2 can be 95.5%, 96.0%, 96.1%, 96.3%, 96.5%, 96.7%, 96.9%, 97.0%, 97.1%, 97.3%, 97.5%, 97.7%, 97.9%, 98.0%, 98.1%, 98.3%, 98.5% or a range composed of any two of the above numerical values. By adjusting the mass percentage content of the positive electrode active material within the above range, the secondary battery can have an appropriate energy density.

[0035] In an embodiment of the present application, the particle size Dv50 of the positive electrode active material is 5 μm to 20 μm, the oil absorption value of the positive electrode material layer is O5 mL / 100g, and 100×W2 / Dv50 + W1×O1 ≤ O5 ≤ 100×W2 / Dv50 + 2×W1×O1. Exemplarily, the value of the particle size Dv50 of the positive electrode active material can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range composed of any two of the above numerical values. By adjusting the particle size Dv50 of the positive electrode active material and the oil absorption value of the positive electrode material layer to meet the above characteristics, the positive electrode active material has an appropriate particle size, which is beneficial to improving the oil absorption value of the positive electrode material layer, can improve the liquid retention ability of the positive electrode sheet, and can further increase the Li + transmission path, further improving the Li + transmission efficiency and further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery; and it can also improve the high-temperature performance of the secondary battery.

[0036] In this application, Dv50 refers to the particle size at which the cumulative volume reaches 50% when measured from the smaller particle size in the particle size distribution based on the volume of the material.

[0037] In one embodiment of this application, based on the mass of the positive electrode material layer, the mass percentage content W11 of carbon black particles is 0.2% to 0.6%, and the mass percentage content W12 of whisker carbon rods is 0.1% to 0.5%. Exemplarily, the value of W11 can be 0.2%, 0.23%, 0.25%, 0.27%, 0.3%, 0.33%, 0.35%, 0.37%, 0.4%, 0.43%, 0.45%, 0.47%, 0.5%, 0.53%, 0.55%, 0.57%, 0.6% or a range composed of any two of the above numerical values; the value of W12 can be 0.1%, 0.13%, 0.15%, 0.17%, 0.2%, 0.23%, 0.25%, 0.27%, 0.3%, 0.33%, 0.35%, 0.37%, 0.4%, 0.43%, 0.45%, 0.47%, 0.5% or a range composed of any two of the above numerical values. By adjusting the mass percentage content of carbon black particles and whisker carbon rods within the above range, the carbon black particles and whisker carbon rods have appropriate mass percentage contents. The carbon black particles have a good adsorption effect on the electrolyte, which can also improve the liquid retention of the positive electrode sheet and increase the Li + transmission path; the whisker carbon rods can conduct the closed pores between the positive electrode active material particles into active pores, improving the porosity of the positive electrode material layer and further increasing the Li + transmission path, further improving the Li + transmission efficiency, and further reducing the Li + concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0038] In one embodiment of this application, the conductive agent further includes carbon nanotubes, and the oil absorption value O4 of the carbon nanotubes is 350 mL / 100 g to 500 mL / 100 g. Exemplarily, O4 can be 350 mL / 100 g, 370 mL / 100 g, 400 mL / 100 g, 420 mL / 100 g, 450 mL / 100 g, 470 mL / 100 g, 500 mL / 100 g or a range composed of any two of the above numerical values. The above carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes. By adjusting the oil absorption value of the carbon nanotubes within the above range, the dispersion degree of the carbon nanotubes in the positive electrode slurry can be increased, which is beneficial to improving the processing performance of the positive electrode slurry; at the same time, the liquid retention ability of the positive electrode sheet is improved, which can further increase the Li + transmission path, further improving the Li + transmission efficiency, and further reducing the Li +Concentration polarization, thereby further reducing the internal resistance of the secondary battery.

[0039] In one embodiment of the present application, the diameter D2 of the carbon nanotubes is 3 nm to 20 nm. Exemplarily, the value of D2 can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range composed of any two of the above numerical values. By controlling the diameter of the carbon nanotubes within the above range, the carbon nanotubes are more uniformly dispersed in the positive electrode paste, which is beneficial to improving the processing performance of the positive electrode paste; at the same time, the carbon nanotubes have a suitable specific surface area, and the carbon nanotubes have a higher effective conductive area, further reducing the internal resistance of the secondary battery.

[0040] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content W13 of the carbon nanotubes is 0 to 0.7%. Exemplarily, the value of W13 can be 0, 0.1%, 0.13%, 0.15%, 0.17%, 0.2%, 0.23%, 0.25%, 0.27%, 0.3%, 0.33%, 0.35%, 0.37%, 0.4%, 0.43%, 0.45%, 0.47%, 0.5%, 0.53%, 0.55%, 0.57%, 0.6%, 0.63%, 0.65%, 0.67%, 0.7% or a range composed of any two of the above numerical values. By controlling the mass percentage content of the carbon nanotubes within the above range, the carbon nanotubes have a suitable mass percentage content, can construct a good conductive network, and further reduce the internal resistance of the secondary battery; at the same time, the content of the positive electrode active material in the positive electrode material layer is relatively high, and the secondary battery has a relatively high energy density.

[0041] In one embodiment of the present application, when the secondary battery has a capacity of 3000 mAh to 4000 mAh, the 1s DC resistance (DCR) at 25°C and 20% state of charge (SOC) is 50 mΩ to 100 mΩ, and the internal resistance growth rate R1 after 500 cycles at 45°C is 30% to 80%. The DC resistance of the secondary battery and the internal resistance growth rate after 500 cycles are within the above range, indicating that the secondary battery has a relatively low internal resistance.

[0042] The present application does not particularly limit the preparation method of the carbon black particles, as long as the purpose of the present application can be achieved. For example, the preparation method of the carbon black particles may include the following steps: selecting acetylene or tar as the raw material; performing a high-temperature cracking reaction on the raw material, the temperature of the high-temperature cracking reaction is 1000°C to 1500°C, and the time of the high-temperature cracking 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 has no particular limitation on the preparation method of the whisker carbon rod, as long as the object of the present application can be achieved. For example, the preparation method of the whisker carbon rod may include the following steps: mixing a catalyst and a carbon source and then injecting them into a high-temperature furnace at 1000°C to 1500°C for catalytic synthesis, the catalytic synthesis time being 3 s to 30 s, and then performing high-temperature graphitization at 2500°C to 3000°C, the high-temperature graphitization time being 1 h to 5 h, to obtain the whisker carbon rod. The present application has no particular limitation on the catalyst, as long as the object of the present application can be achieved. For example, the catalyst can be ferrocene. The present application has no particular limitation on the carbon source, as long as the object of the present application can be achieved. For example, the carbon source can be natural gas.

[0044] The present application has no particular limitation on the preparation method of the carbon nanotube, as long as the object of the present application can be achieved. For example, the preparation method of the carbon nanotube may include the following steps: selecting a cobalt-based or iron-based catalyst, depositing the cobalt-based or iron-based catalyst on a silicon-based substrate and placing it in a reaction furnace; introducing an inert protective gas into the reaction furnace and heating the reaction furnace to 600°C to 900°C; introducing a reaction gas into the reaction furnace for 30 min to 120 min, and the carbon formed by the cracking of the reaction gas in the reaction furnace is deposited on the cobalt-based or iron-based catalyst to form a carbon nanotube bundle with a cluster structure; and obtaining single-dispersed carbon nanotubes through high-speed sanding and dispersion. The present application has no particular limitation on the rotation speed of the above high-speed sanding and dispersion, as long as the object of the present application can be achieved. For example, the rotation speed is 1700 r / min to 2300 r / min. The above inert protective gas can be argon or nitrogen. The present application has no particular limitation on the cobalt-based catalyst, as long as the object of the present application can be achieved. For example, the cobalt-based catalyst can be nano-metal cobalt, nano-cobalt oxide or nano-cobalt iron composite catalyst. The present application has no particular limitation on the iron-based catalyst, as long as the object of the present application can be achieved. For example, the iron-based catalyst can be nano-metal iron, nano-iron oxide or nano-iron nickel composite catalyst. The present application has no particular limitation on the reaction gas, as long as the object of the present application can be achieved. For example, the reaction gas can be methane, ethylene or acetylene.

[0045] The present application has no particular limitation on the method for regulating the oil absorption value of the carbon black particles, as long as the object of the present application can be achieved. For example, the oil absorption value of the carbon black particles can be regulated by regulating the high-temperature cracking reaction time. For example, during the high-temperature cracking reaction, the diameter of the reaction furnace tube can be reduced near the discharge port compared to the reaction part, so that the carbon black particles collide and link together to form longer carbon black chains, thereby increasing the oil absorption value of the carbon black particles. For example, commercially available carbon black particles with different oil absorption values can be selected, and the oil absorption value of the carbon black particles can be tested by combining the test method of "testing the oil absorption value of carbon black particles" in the present application, and carbon black particles with the required oil absorption value can be selected.

[0046] The present application has no particular limitation on the method for regulating the oil absorption value of the whisker carbon rod, as long as the object of the present application can be achieved. For example, the oil absorption value of the whisker carbon rod can be regulated by regulating the length or diameter of the whisker carbon rod. For example, commercially available whisker carbon rods with different oil absorption values can be selected, and the oil absorption value of the whisker carbon rod can be tested in combination with the test method of "testing the oil absorption value of the whisker carbon rod" in the present application, and the whisker carbon rod with the required oil absorption value can be selected.

[0047] The present application has no particular limitation on the method for regulating the oil absorption value of the conductive agent, as long as the object of the present application can be achieved. For example, the oil absorption value of the conductive agent can be regulated by regulating the oil absorption values of the carbon black particles and the whisker carbon rod respectively, and the regulation methods of the oil absorption values of the carbon black particles and the whisker carbon rod are as described above.

[0048] The present application has no particular limitation on the method for regulating the diameter of the whisker carbon rod, as long as the object of the present application can be achieved. For example, the diameter of the whisker carbon rod can be regulated by regulating the size of the catalyst.

[0049] The present application has no particular limitation on the method for regulating the length of the whisker carbon rod, as long as the object of the present application can be achieved. For example, the length of the whisker carbon rod can be regulated by regulating the temperature of the catalytic synthesis.

[0050] The present application has no particular limitation on the method for regulating the porosity of the positive electrode material layer, as long as the object of the present application can be achieved. For example, the porosity of the positive electrode material layer can be regulated by regulating the mass percentage contents of the carbon black particles and the whisker carbon rod.

[0051] The present application has no particular limitation on the method for regulating the volume percentage content of pores with a pore diameter of 8 μm to 15 μm and the volume percentage content of pores with a pore diameter of 0.5 μm to 5 μm, as long as the object of the present application can be achieved. For example, the addition of the whisker carbon rod will affect the volume percentage content of pores with a pore diameter of 8 μm to 15 μm. The whisker carbon rod connects small pores in series, which can increase the pore diameter size and may reduce the volume percentage content of pores with a pore diameter of 0.5 μm to 5 μm. The addition of the carbon black particles will affect the volume percentage content of pores with a pore diameter of 0.5 μm to 5 μm. The carbon black particles with a high oil absorption value have a long chain-like structure, and it is easy to form small-pore-diameter pores between the carbon black particles, increasing the porosity of the positive electrode material layer and increasing the volume percentage content of pores with a pore diameter of 0.5 μm to 5 μm.

[0052] The present application has no particular limitation on the method for 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 for regulating the mass percentage of the positive electrode active material, as long as the object of the present application can be achieved. For example, the mass percentage of the positive electrode active material can be regulated by regulating the mass of the added positive electrode active material.

[0054] The present application has no particular limitation on the method for regulating the particle size Dv50 of the positive electrode active material, as long as the object of the present application can be achieved. For example, the particle size Dv50 of the positive electrode active material can be regulated by grinding the positive electrode active material. For example, the particle size Dv50 of the positive electrode active material can be regulated by regulating the grinding time. Exemplarily, when other conditions remain unchanged, by prolonging the grinding time, the particle size Dv50 of the positive electrode active material decreases; by shortening the grinding time, the particle size Dv50 of the positive electrode active material increases.

[0055] The present application has no particular limitation on the method for regulating the mass percentages of carbon black particles and whisker carbon rods, as long as the object of the present application can be achieved. For example, the mass percentage of carbon black particles can be regulated by regulating the mass of the added carbon black particles; the mass percentage of whisker carbon rods can be regulated by regulating the mass of the added whisker carbon rods.

[0056] The present application has no particular limitation on the method for regulating the oil absorption value of carbon nanotubes, as long as the object of the present application can be achieved. For example, the oil absorption value of carbon nanotubes can be regulated by regulating the length or diameter of the carbon nanotubes. For example, commercially available carbon nanotubes with different oil absorption values can be selected, and the oil absorption value of the carbon nanotubes can be tested in combination with the test method of "testing the oil absorption value of carbon nanotubes" in the present application, and carbon nanotubes with the required oil absorption value can be selected.

[0057] The present application has no particular limitation on the method for regulating the diameter of carbon nanotubes, as long as the object of the present application can be achieved. For example, the diameter of carbon nanotubes can be regulated by regulating the size of cobalt-based or iron-based catalysts.

[0058] The present application has no particular limitation on the method for regulating the mass percentage of carbon nanotubes, as long as the object of the present application can be achieved. For example, the mass percentage of carbon nanotubes can be regulated by regulating the mass of the added carbon nanotubes.

[0059] 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.

[0060] The present application places no particular limitation on the cathode active material, as long as the object of the present application can be achieved. For example, the cathode active material may 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-mentioned lithium nickel cobalt manganate may 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 / 3 O2 (NCM111). The cathode material layer of the present application further includes a cathode binder. The present application places no particular limitation on the cathode binder, as long as the object of the present application can be achieved. For example, the cathode 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, nitrile rubber, 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 places no particular limitation on the mass percentage content of the cathode binder in the cathode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, based on the mass of the cathode material layer, the mass percentage content W3 of the cathode binder is 0.8% to 3.0%.

[0061] The present application places no particular limitation on the thickness of the cathode current collector, as long as the object of the present application can be achieved. For example, the thickness of the cathode current collector is 6 μm to 16 μm. The present application places no particular limitation on the thickness of the cathode material layer, as long as the object of the present application can be achieved. For example, the thickness of the single-sided cathode material layer is 25 μm to 250 μm.

[0062] Optionally, the positive electrode sheet may further include a conductive layer located between the positive current collector and the positive electrode material layer. There is no particular limitation on the composition of the conductive layer in this 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 this application, and they may be at least one of the above-mentioned conductive agents and the above-mentioned positive electrode binder. There is no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer in this application, and those skilled in the art can select according to actual needs as long as the object of this application can be achieved.

[0063] In this application, the secondary battery further includes a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative electrode material layer provided on at least one surface of the negative current collector. The above-mentioned "negative electrode material layer provided on at least one surface of the negative current collector" means that the negative electrode material layer may be provided on one surface of the negative current collector along its own thickness direction, or may be provided on two surfaces of the negative current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the negative current collector or a partial area of the negative current collector, and there is no particular limitation in this application as long as the object of this application can be achieved. There is no particular limitation on the negative current collector in this application as long as the object of this application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector, etc.

[0064] The negative electrode material layer of this application includes a negative electrode active material. There is no particular limitation on the negative electrode active material in this application as long as the object of this application can be achieved. For example, the negative electrode active material may 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 this application further includes a negative electrode binder and a negative electrode conductive agent. There is no particular limitation on the negative electrode binder and the negative electrode conductive agent in the negative electrode material layer in this application as long as the object of this application can be achieved. For example, the negative electrode binder may be at least one of the above-mentioned positive electrode binders, and the negative electrode conductive agent may be at least one of the above-mentioned conductive agents. There is no particular 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 this application, and those skilled in the art can select according to actual needs as long as the object of this application can be achieved.

[0065] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm. The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the object 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.

[0066] Optionally, the negative electrode sheet may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular limitation on the composition of the conductive layer, and it may 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 it may be at least one of the above-mentioned negative electrode conductive agents and the above-mentioned negative electrode binders. The present application has no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0067] 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-mentioned 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-mentioned 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-mentioned 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-mentioned fluorinated carbonate compounds may include but are not limited to at least one of fluorinated ethylene 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-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, decanolide, valerolactone, or caprolactone. The above-mentioned 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-mentioned 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.

[0068] In the present application, the secondary battery further includes a separator. The separator is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass 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) such as polyethylene (PE) and polypropylene (PP), polyesters (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.

[0069] 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, 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).

[0070] The secondary battery of the present application further includes a packaging bag for accommodating the positive electrode plate, the separator, the negative electrode plate 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. It may be a packaging bag well-known in the art as long as it can achieve the purpose of the present application.

[0071] 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.

[0072] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and there is no particular limitation 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 sequence, and winding, folding, etc. as required to obtain a wound structure electrode assembly, placing the electrode assembly in a packaging bag, injecting 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 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 in 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. may be placed in the packaging bag as required to prevent the pressure inside the secondary battery from rising and overcharging / discharging. Among them, the packaging bag is a packaging bag known in the art, and the present application does not limit it.

[0073] 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.

[0074] The present application does not particularly limit the type of the electronic device, and it may 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 earphone, a video recorder, a liquid crystal 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, 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.

[0075] Examples

[0076] 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.

[0077] Testing methods and equipment:

[0078] Oil absorption value test of carbon black particles:

[0079] The oil absorption value of carbon black particles was tested by the paraffin oil + torque method: An oil absorption meter of model DABS-H was selected, and the oil absorption value of carbon black particles was tested with reference to the national standard "Carbon black - Part 2: Determination of oil absorption value" (GB / T 3780.2—2007). The sample carbon black particles were added into the mixing tank of the oil absorption meter, and paraffin oil was added to the sample at a rate of 4 mL / min with a burette. As the oil absorption value of the sample increased, the mixture changed from a free-flowing state to a semi-plastic aggregate, and the viscosity of the mixture continuously increased. This viscosity was transmitted to the torque sensing system of the oil absorption meter. When the viscosity of the mixture reached a predetermined torque value, the oil absorption meter and the burette were automatically closed simultaneously. The volume of the added oil was directly read from the reading burette, and the volume of oil absorbed per unit mass of the sample was the oil absorption value of the sample.

[0080] Testing the oil absorption value of the conductive agent:

[0081] (1) Disassemble the lithium-ion battery to obtain the positive electrode plate; (2) Immerse the above positive electrode plate 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 the gradient centrifugation method to separate the positive electrode binder in the slurry to obtain a slurry containing the positive electrode active material and the conductive agent; (4) Use a 2 mol / L hydrochloric acid solution to treat 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 at 60 °C for 2 hours. For the lithium iron phosphate-based positive electrode active material, use hydrochloric acid-hydrogen peroxide for digestion, and then dry to obtain the conductive agent; (5) Use the paraffin oil + torque method described above to test the oil absorption value of the conductive agent.

[0082] Testing the oil absorption value of the whisker carbon rod:

[0083] Use the paraffin oil + torque method described above to test the oil absorption value of the whisker carbon rod.

[0084] Testing the oil absorption value of carbon nanotubes:

[0085] Use the paraffin oil + torque method described above to test the oil absorption value of carbon nanotubes.

[0086] Testing the oil absorption value of the positive electrode material layer:

[0087] (1) The lithium-ion battery is discharged at a constant current of 0.5C to 3.0V, then disassembled to obtain the positive electrode plate. Then the positive electrode plate is soaked in dimethyl carbonate (DMC) at room temperature for 30 min, dried in air; then soaked in NMP at room temperature for 20 min. The positive current collector aluminum foil is peeled off from the positive electrode material layer, and the positive electrode material layer is dried at 80°C and then kept at 800°C in a nitrogen atmosphere for 30 min to decompose the positive electrode binder and obtain a powder; (2) The oil absorption value of the powder obtained in step (1) is measured by the paraffin oil + torque method described above, which is the oil absorption value of the positive electrode material layer.

[0088] Measurement of the diameter of the whisker carbon rod, the length of the whisker carbon rod, and the diameter of the carbon nanotube:

[0089] (1) Disassemble the lithium-ion battery to obtain the positive electrode plate; (2) Soak 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), and measure the diameters and lengths of a total of no less than 20 whisker carbon rods and the diameters of a total of no less than 30 carbon nanotubes in 10 regions, and take the average value as the diameter of the whisker carbon rod, the length of the whisker carbon rod, and the diameter of the carbon nanotube.

[0090] Measurement of the porosity and pore size distribution of the positive electrode material layer:

[0091] (1) The lithium-ion battery is discharged at a constant current of 0.5C to 3.0V, then disassembled to obtain the positive electrode plate. Then the positive electrode plate is soaked in dimethyl carbonate (DMC) at room temperature for 30 min, dried in air; (2) Cut the positive electrode plate obtained in step (1) into a sample of 30 cm × 2 cm, dry it at 120°C for 2 h, then degas it in a degassing chamber for 12 h, and then use a mercury intrusion porosimeter to measure the porosity and pore size distribution of the positive electrode material layer. Among them, the model of the mercury intrusion porosimeter is MicroActive AutoPore V 9605, and the pressure is set to 33000 psia.

[0092] Measurement of particle size Dv50:

[0093] Use a Malvern particle size analyzer (model MasterSizer 2000) to measure the particle size of the positive electrode active material. Add 0.02 g of positive electrode active material particles to a 50 mL clean beaker, add 20 mL of dispersant ethanol, and ultrasonicate in a 120 W ultrasonic cleaner for 30 min to completely disperse the positive electrode active material particles in ethanol to obtain a sample dispersion. Use the Malvern particle size analyzer to test the above sample dispersion to obtain the particle size Dv50 of the positive electrode active material particles.

[0094] 1s DC Resistance (DCR) Test:

[0095] Take the lithium-ion batteries in the examples or comparative examples and conduct the following tests at 25 ± 2 °C: (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 °C and 20% SOC is (V0 - V1) / 1.0C1.

[0096] Internal Resistance Growth Rate Test after 500 Cycles at 45 °C:

[0097] Take the lithium-ion batteries in the examples or comparative examples and conduct the following tests at 45 ± 2 °C:

[0098] (1) Let it stand for 2 h, discharge it at a constant current of 0.7C to 3.0V, and let it stand for 5 min;

[0099] (2) 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 0.05C; Let it stand for 5 min; Then discharge it 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 sine current of 1000Hz and record it as IMP1; Let it stand for 5 min; Repeat the above steps 49 times, and the internal resistances of the lithium-ion battery are recorded as IMP1, IMP2,..., IMP49 in turn; Then conduct the 50th cycle, in the 50th cycle, 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 0.05C; Let it stand for 5 min; Then discharge it 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;

[0100] (3) Then repeat the above step (2) 10 times, and 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 0.05C; Let it stand for 5 min; Then discharge it at a constant current of 0.5C to 3.0V, and record the internal resistance of the lithium-ion battery at the 501st cycle as IMP501; Then the internal resistance growth rate R1 (%) of the lithium-ion battery after 500 cycles at 45 °C = IMP501 / IMP1 - 100%.

[0101] Example 1-1

[0102] <Preparation of the positive electrode plate>

[0103] After mixing lithium cobalt oxide (LiCoO2) as the positive active material, acetylene black particles as the conductive agent, carbon whisker carbon rods as the conductive agent, carbon nanotubes as the conductive agent, and polyvinylidene fluoride (PVDF) as the positive electrode binder in a weight ratio of 97.5:0.4:0.2:0.4:1.5, N-methylpyrrolidone (NMP) is added as a solvent and stirred and mixed 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 carbon nanotubes are multi-walled carbon nanotubes; the particle size Dv50 of the positive active material is 15 μm. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and dried at 120°C for 1 h to obtain a positive electrode plate 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 plate with a positive electrode material layer coated on both sides. Dry it under vacuum conditions at 120°C for 1 h, and then obtain a positive electrode plate 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 。

[0104] <Preparation of the negative electrode plate>

[0105] After mixing artificial graphite as the negative active material, sodium carboxymethyl cellulose (CMC-Na) as the negative electrode binder, and styrene-butadiene rubber (SBR) as the negative electrode binder in a weight ratio of 95:2:3, 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 plate 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 plate with a negative electrode material layer coated on both sides. Dry it under vacuum conditions at 120°C for 1 h, and then obtain a negative electrode plate with a specification of 78 mm × 875 mm after cold pressing, slicing, and slitting. Among them, the compaction density during the cold pressing process is 1.75 g / cm 3 。

[0106] <Preparation of the electrolyte>

[0107] In an argon atmosphere glove box with a water content of 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 base 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 base solvent.

[0108] <Preparation of the separator>

[0109] Use a polyethylene (PE) film with a thickness of 15 μm.

[0110] <Preparation of Lithium-Ion Batteries>

[0111] Stack the above-prepared positive electrode sheet, separator, negative electrode sheet, and separator 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, inject the electrolyte after drying, and obtain a lithium-ion battery through vacuum packaging, standing, formation, degassing, and trimming processes.

[0112] Examples 1-2 to Examples 1-7

[0113] Except that the oil absorption value of the carbon black particles is adjusted by adjusting the high-temperature cracking reaction time as shown in Table 1, the rest is the same as Example 1-1.

[0114] Examples 1-8 to Examples 1-24

[0115] Except that the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-3.

[0116] Examples 2-1 to Examples 2-15

[0117] Except that the relevant preparation parameters are adjusted according to Table 2, the rest is the same as Example 1-3.

[0118] Comparative Examples 1-1 to Comparative Examples 1-2

[0119] Except that the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0120] Comparative Example 1-3

[0121] Except that in the <Preparation of Positive Electrode Sheet>, the positive active material lithium cobaltate (LiCoO2), conductive agent carbon black particles, conductive agent carbon nanotubes, and positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.7:0.4:0.4:1.5, and then NMP is added as a solvent and stirred and mixed evenly to obtain a positive electrode paste, the rest is the same as Example 1-3.

[0122] Comparative Example 1-4

[0123] Except that in the <Preparation of Positive Electrode Sheet>, the positive active material lithium cobaltate (LiCoO2), conductive agent carbon black particles, conductive agent graphene, conductive agent carbon nanotubes, and positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:0.4:0.2:0.4:1.5, and then NMP is added as a solvent and stirred and mixed evenly to obtain a positive electrode paste, the rest is the same as Example 1-3.

[0124] Comparative Example 2-1

[0125] Except for adjusting the relevant preparation parameters according to Table 2, the rest are the same as those in Examples 1-3.

[0126] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 2.

[0127] Table 1

[0128]

[0129]

[0130] Note: In Table 1, " / " indicates no relevant preparation parameters.

[0131]

[0132]

[0133] It can be seen from Examples 1-1 to 1-24, Examples 2-1 to 2-15, Comparative Examples 1-1 to 1-4, and Comparative Example 2-1 that when the type and oil absorption value of the conductive agent 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 500 cycles at 45°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 oil absorption value of the conductive agent is not within the scope of this application, and the prepared lithium-ion battery has a higher 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of the lithium-ion battery is higher. In Comparative Examples 1-3 to 1-4, the type of the conductive agent is not within the scope of this application, and the prepared lithium-ion battery has a higher 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of the lithium-ion battery is higher.

[0134] The oil absorption value of carbon black particles usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-7 that by controlling the oil absorption value 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 500 cycles at 45°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0135] The diameter and length of the whisker carbon rods usually affect the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, Examples 1-8 to Examples 1-19 that by adjusting the diameter and length of the whisker carbon rods within the scope of this application, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced. In Examples 1-3, Examples 1-13 to Examples 1-19, the increase in the length of the whisker carbon rods will increase the oil absorption value of the whisker carbon rods. However, the length of the whisker carbon rods in Example 1-18 is too long, and it is easy to agglomerate and not easy to open in the positive electrode sheet, which will affect the oil absorption value of the whisker carbon rods.

[0136] The diameter of the carbon nanotubes usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-1, Examples 1-20 to Examples 1-24 that by adjusting the diameter of the carbon nanotubes within the scope of this application, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0137] The mass percentage content of each substance in the positive electrode material layer usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, Examples 2-1 to Examples 2-8 that by adjusting the mass percentage content of each substance in the positive electrode material layer within the scope of this application, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0138] The particle size Dv50 of the positive electrode active material usually affects the internal resistance of lithium-ion batteries. It can be seen from Examples 1-3, Examples 2-9 to Examples 2-11 that by adjusting the particle size Dv50 of the positive electrode active material within the scope of this application, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0139] It can be seen from Examples 2-12 to Examples 2-13 that within the scope of this application for the type of positive electrode binder, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0140] It can be seen from Examples 2-14 to Examples 2-15 that within the scope of this application for the type of positive electrode active material, the prepared lithium-ion batteries have a lower 1sDCR at 25°C and 20% SOC and an internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0141] It should be noted that in this document, 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 term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method or article comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method or article.

[0142] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other, and the differences between each embodiment and other embodiments are emphasized.

[0143] 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 within the scope of protection of the present application.

Claims

1. A secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a conductive agent, the conductive agent comprising carbon black particles and whisker carbon rods, and the oil absorption value O1 of the conductive agent is 300mL / 100g to 800mL / 100g.

2. The secondary battery according to claim 1, wherein The conductive agent has an oil absorption value O1 of 420 mL / 100 g to 700 mL / 100 g.

3. The secondary battery according to claim 1, wherein The oil absorption value O2 of the carbon black particles is 300 mL / 100 g to 900 mL / 100 g.

4. The secondary battery according to claim 1, wherein The diameter D1 of the whisker carbon rod is 20 nm to 80 nm.

5. The secondary battery according to claim 1, wherein The length L of the whisker carbon rod is 3 μm to 30 μm.

6. The secondary battery according to claim 1, wherein The oil absorption value O3 of the whisker carbon rod is 250 mL / 100 g to 500 mL / 100 g.

7. The secondary battery according to claim 1, wherein The porosity P of the positive electrode material layer is 20% to 40%; based on the total pore volume of the positive electrode material layer, the volume percentage V1 of pores with a pore diameter of 8μm to 15μm is 3% to 15%, and the volume percentage V2 of pores with a pore diameter of 0.5μm to 5μm is 8% to 20%.

8. The secondary battery according to claim 1, wherein Based on the mass of the positive electrode material layer, the mass percentage W1 of the conductive agent is 0.6% to 1.5%.

9. The secondary battery according to claim 8, wherein The positive electrode material layer further includes a positive electrode active material. Based on the mass of the positive electrode material layer, the mass percentage W2 of the positive electrode active material is 95.5% to 98.5%.

10. The secondary battery according to claim 9, wherein The particle size Dv50 of the positive electrode active material is 5 μm to 20 μm, the oil absorption value of the positive electrode material layer is O5 mL / 100 g, and 100×W2 / Dv50+W1×O1≤O5≤100×W2 / Dv50+2×W1×O1.

11. The secondary battery according to claim 1, wherein Based on the mass of the positive electrode material layer, the mass percentage W11 of the carbon black particles is 0.2% to 0.6%, and the mass percentage W12 of the whisker carbon rods is 0.1% to 0.5%.

12. The secondary battery according to claim 1, wherein The conductive agent further includes carbon nanotubes, and the oil absorption value O4 of the carbon nanotubes is 350 mL / 100 g to 500 mL / 100 g.

13. The secondary battery according to claim 12, which satisfies at least one of the following characteristics: (1) The diameter D2 of the carbon nanotube is 3 nm to 20 nm; (2) Based on the mass of the positive electrode material layer, the mass percentage W13 of the carbon nanotubes is 0 to 0.7%. 14 . An electronic device comprising the secondary battery according to claim 1 .

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