Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet; the positive electrode sheet comprises 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 comprises a conductive agent; the conductive agent includes carbon black particles and carbon whiskers; and the conductive agent has an oil absorption value O1 of 300 mL / 100 g to 800 mL / 100 g. By controlling the type and oil absorption value of the conductive agent to fall within the ranges specified in the present application, the internal resistance of the secondary battery can be reduced.

Description

A secondary battery and electronic device

[0001] This application claims priority to Chinese Patent Application No. 202510382839.4, filed on March 28, 2025, entitled "A Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0003] Reducing the internal resistance of lithium-ion batteries has always been a goal of our customers. During the cycling process of lithium-ion batteries, the positive electrode impedance plays a dominant role. Selecting new conductive agents and building a good conductive network are the main directions for reducing the internal resistance of lithium-ion batteries.

[0004] In existing technologies, the internal resistance of lithium-ion batteries is generally reduced by increasing the content of conductive agents or decreasing the content of binders. However, increasing the content of conductive agents leads to a decrease in the content of positive electrode active materials, resulting in a decrease in the energy density of lithium-ion batteries; decreasing the content of binders leads to a decrease in the adhesion between the positive electrode material layer and the positive electrode current collector, as well as a decrease in the cohesive force of the positive electrode material layer itself, which can easily cause problems such as delamination and thickness expansion during the use of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that can reduce the internal resistance of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of this application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer including a conductive agent, the conductive agent including carbon black particles and whisker carbon rods, and the oil absorption value O1 of the conductive agent being 300 mL / 100 g to 800 mL / 100 g. By adjusting the conductive agent to include carbon black particles and whisker carbon rods, and the oil absorption value of the conductive agent within the scope of this application, carbon black particles are more easily coated on the surface of the positive electrode active material particles. A high oil absorption value of carbon black particles indicates that they have rich branches and good continuity, which can increase the continuity of the conductive network on the surface of the positive electrode active material particles; while whisker carbon rods can be distributed between the positive electrode active material particles, connecting different gaps, increasing the pore size, and reducing Li + Transmission tortuosity can convert closed pores into open pores, increasing the porosity of the cathode material layer and increasing Li + The transmission path can improve the continuity of the conductive network between positive electrode active material particles. Whisker carbon rods and carbon black particles together enhance the continuity of the conductive network in the positive electrode sheet, thereby increasing the Li... +Transmission path, improve Li + Transmission efficiency, reducing Li + Concentration polarization reduces the internal resistance of the secondary battery.

[0007] In one embodiment of this application, the oil absorption value O1 of the conductive agent is between 420 mL / 100 g and 700 mL / 100 g. By controlling the oil absorption value of the conductive agent within the above range, carbon black particles are more easily coated 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 improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0008] In one embodiment of this application, the oil absorption value (O2) of the carbon black particles is between 300 mL / 100 g and 900 mL / 100 g. By controlling the oil absorption value of the carbon black particles within the above range, the carbon black particles have a higher oil absorption value and a long chain structure, which improves the adsorption of electrolyte and further enhances the electrolyte retention of the positive electrode, thereby increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0009] In one embodiment of this application, the diameter D1 of the carbon whisker rod is between 20 nm and 80 nm. By controlling the diameter of the carbon whisker rod within the above range, the carbon whisker rod has a suitable diameter, reducing the possibility of the carbon whisker rods entangled with each other; and the carbon whisker rod has a suitable specific surface area, resulting in a larger effective conductive area, further improving the Li... + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0010] In one embodiment of this application, the length L of the carbon whisker rod is from 3 μm to 30 μm. By adjusting the length of the carbon whisker rod within the above range, the carbon whisker rod has a suitable length and exhibits good long-range conductivity. + It can efficiently transport along the surface of the whisker carbon rod, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery and also facilitates the dispersion of the positive electrode slurry.

[0011] In one embodiment of this application, the oil absorption value (O3) of the whisker carbon rod is between 250 mL / 100 g and 500 mL / 100 g. By adjusting 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; at the same time, the liquid retention capacity of the positive electrode sheet can be improved, which can further increase the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0012] In one embodiment of this 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 V1 of pores with a diameter of 8 μm to 15 μm is 3% to 15%, and the volume percentage V2 of pores with a 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... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0013] In one embodiment of this application, the mass percentage content W1 of the conductive agent is 0.6% to 1.5% based on the mass of the positive electrode material layer. 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 it also improves the electrolyte retention of the positive electrode sheet and increases the Li... + Transport path; whisker carbon rods can open up closed pores between positive electrode active material particles into open pores, increasing the porosity of the positive electrode material layer and further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0014] In one embodiment of this application, the positive electrode material layer further includes a positive electrode active material, and the mass percentage W2 of the positive electrode active material is 95.5% to 98.5% based on the mass of the positive electrode material layer. By adjusting the mass percentage of the positive electrode active material within the above range, the secondary battery can have a suitable energy density.

[0015] In one embodiment of this 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 0.5 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, thereby improving the liquid retention capacity of the positive electrode sheet and further increasing the Li + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery and also improves its high-temperature performance.

[0016] In one embodiment of this application, based on the mass of the positive electrode material layer, the mass percentage content of carbon black particles W11 is 0.2% to 0.6%, and the mass percentage content of carbon whisker rods W12 is 0.1% to 0.5%. By controlling the mass percentage content of carbon black particles and carbon whisker rods within the above ranges, the carbon black particles and carbon whisker rods have suitable mass percentages. The carbon black particles have a good adsorption effect on the electrolyte, which also improves the electrolyte retention of the positive electrode sheet and increases the Li... + Transport path; whisker carbon rods can open up closed pores between positive electrode active material particles into open pores, increasing the porosity of the positive electrode material layer and further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0017] In one embodiment of this application, the conductive agent further includes carbon nanotubes, the oil absorption value (O4) of which is between 350 mL / 100 g and 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, it can enhance the liquid retention capacity of the positive electrode sheet, which can further increase the Li... + Transmission path, further improving Li+ transmission efficiency, and further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0018] In one embodiment of this application, the diameter D2 of the carbon nanotubes is between 3 nm and 20 nm. By controlling the diameter of the carbon nanotubes within the above range, the carbon nanotubes are more uniformly dispersed in the cathode slurry, which is beneficial to improving the processing performance of the cathode slurry; at the same time, the carbon nanotubes have a suitable specific surface area and a high effective conductive area, which further reduces the internal resistance of the secondary battery.

[0019] In one embodiment of this application, the mass percentage of carbon nanotubes, W13, is 0 to 0.7% based on the mass of the cathode material layer. By controlling the mass percentage of carbon nanotubes within the above range, the carbon nanotubes have a suitable mass percentage, which can construct a good conductive network and further reduce the internal resistance of the secondary battery; at the same time, the cathode material layer has a high content of cathode active material, and the secondary battery has a high energy density.

[0020] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has a low internal resistance.

[0021] The beneficial effects of this application are:

[0022] This application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a conductive agent, which includes carbon black particles and carbon whisker rods. The oil absorption value (O1) of the conductive agent is between 300 mL / 100 g and 800 mL / 100 g. By adjusting the type and oil absorption value of the conductive agent within the scope of this application, the internal resistance of the secondary battery can be reduced.

[0023] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0024] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0025] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0026] The first aspect of this application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising a conductive agent, the conductive agent comprising carbon black particles and whisker carbon rods, the oil absorption value O1 of the conductive agent being 300mL / 100g to 800mL / 100g. For example, O1 can be 300mL / 100g, 350mL / 100g, 370mL / 100g, 400mL / 100g, 420mL / 100g, 450mL / 100g, 470mL / 100g, 500mL / 100g, 550mL / 100g, 570mL / 100g, 600mL / 100g, 650mL / 100g, 670mL / 100g, 700mL / 100g, 750mL / 100g, 770mL / 100g, 800mL / 100g, or a range consisting of any two of the above values. In this application, the carbon black particles include at least one of Super P, acetylene black, or Ketjen black. The aforementioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or 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 part of the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0027] The inventors discovered that when the conductive agent in the positive electrode material layer includes carbon black particles and whisker carbon rods, the high oil absorption value of the carbon black particles, with their long chain structure, provides excellent adsorption for the electrolyte, thus improving the electrolyte retention of the positive electrode and increasing the Li content. + Transport path; whisker carbon rods are mainly distributed between the positive electrode active material particles, connecting different gaps, increasing pore size, and reducing Li + The transmission tortuosity can convert closed pores into open pores, increasing the porosity of the cathode material layer and increasing the Li content. + Transmission path. Li + Capable of efficient transport along the surface of the conductive agent, long, straight whisker carbon rods are Li +The transfer provides a shortcut. When the oil absorption value of the conductive agent is too high, 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 failing to effectively reduce the internal resistance of the secondary battery; when the oil absorption value of the conductive agent is too low, for example, less than 300 mL / 100 g, it will cause the liquid retention capacity of the positive electrode to decrease, affecting lithium-ion transfer and failing to effectively reduce the internal resistance of the secondary battery. By controlling 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, carbon black particles are more easily coated on the surface of the positive electrode active material particles. A high oil absorption value of carbon black particles indicates that its branches are rich and continuous, which can increase the continuity of the conductive network on the surface of the positive electrode active material particles; while whisker carbon rods can be distributed between the positive electrode active material particles, connecting different gaps, increasing the pore size, and reducing Li-ion transfer. + The transmission tortuosity can convert closed pores into open pores, increasing the porosity of the cathode material layer and increasing the Li content. + The transmission path can improve the continuity of the conductive network between positive electrode active material particles. Whisker carbon rods and carbon black particles together enhance the continuity of the conductive network in the positive electrode sheet, thereby increasing the Li... + Transmission path, improve Li + Transmission efficiency, reducing Li + Concentration polarization reduces the internal resistance of the secondary battery.

[0028] In one embodiment of this application, the oil absorption value O1 of the conductive agent is from 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 consisting of any two of the above values. By controlling the oil absorption value of the conductive agent within the above range, carbon black particles are more easily coated 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 improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0029] In one embodiment of this application, the oil absorption value (O2) of the carbon black particles is from 300 mL / 100g to 900 mL / 100g. Exemplarily, O2 can be 300 mL / 100g, 350 mL / 100g, 370 mL / 100g, 400 mL / 100g, 420 mL / 100g, 450 mL / 100g, 470 mL / 100g, 500 mL / 100g, 550 mL / 100g, 570 mL / 100g, 600 mL / 100g, 650 mL / 100g, 670 mL / 100g, 700 mL / 100g, 750 mL / 100g, 770 mL / 100g, 800 mL / 100g, 850 mL / 100g, 900 mL / 100g, or a range consisting of any two of the above values. By adjusting the oil absorption value of the carbon black particles within the aforementioned range, a higher oil absorption value and a long chain structure in the carbon black particles result in better adsorption of the electrolyte, further improving the electrolyte retention of the positive electrode and increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0030] In one embodiment of this application, the diameter D1 of the carbon whisker rod is between 20 nm and 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 consisting of any two of the above values. By controlling the diameter of the carbon whisker rod within the above range, the carbon whisker rod has a suitable diameter, reducing the likelihood of the carbon whisker rods entangled; and the carbon whisker rod has a suitable specific surface area, resulting in a larger effective conductive area, further improving the Li-N' conductivity. + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0031] In one embodiment of this application, the length L of the carbon whisker 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 of any two of the above values. By adjusting the length of the carbon whisker rod within the above range, the carbon whisker rod has a suitable length and exhibits good long-range conductivity. + It can efficiently transport along the surface of the whisker carbon rod, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery and also facilitates the dispersion of the positive electrode slurry.

[0032] In one embodiment of this application, the oil absorption value (O3) of the whisker carbon rod is between 250 mL / 100 g and 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 consisting 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; simultaneously, the liquid retention capacity of the positive electrode sheet can be improved, further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0033] In one embodiment of this application, the porosity P of the positive electrode material layer is 20% to 40%; exemplaryly, the value of P can be 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, or a range of any two of the above values; based on the total pore volume of the positive electrode material layer, the volume percentage V1 of pores with a diameter of 8 μm to 15 μm is 3% to 15%, and the volume percentage V2 of pores with a diameter of 0.5 μm to 5 μm is 8% to 20%. For example, the value of V1 can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting 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 consisting of any two of the above values. 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 higher porosity and a suitable pore size distribution, which can further increase the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0034] In one embodiment of this application, the mass percentage content W1 of the conductive agent is 0.6% to 1.5% based on the mass of the positive electrode material layer. 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 consisting of any two of the above values. 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 the electrolyte retention of the positive electrode sheet is improved, increasing the Li... + Transport path; whisker carbon rods can open up closed pores between positive electrode active material particles into open pores, increasing the porosity of the positive electrode material layer and further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0035] In one embodiment of this application, the positive electrode material layer further includes a positive electrode active material, and the mass percentage W2 of the positive electrode active material is 95.5% to 98.5% based on the mass of the positive electrode material layer. 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 consisting of any two of the above values. By controlling the mass percentage of the positive electrode active material within the above range, the secondary battery can have a suitable energy density.

[0036] In one embodiment of this 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 0.5 mL / 100g, and 100×W2 / Dv50+W1×O1≤O5≤100×W2 / Dv50+2×W1×O1. Exemplarily, 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 of any two of the above 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 a suitable particle size, which is beneficial to improving the oil absorption value of the positive electrode material layer, thereby improving the liquid retention capacity of the positive electrode sheet and further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery and also improves its high-temperature performance.

[0037] In this application, Dv50 refers to the particle size that reaches 50% of the volumetric accumulation in the particle size distribution of the material based on volume.

[0038] In one embodiment of this application, based on the mass of the cathode material layer, the mass percentage of carbon black particles W11 is 0.2% to 0.6%, and the mass percentage of whisker carbon rods W12 is 0.1% to 0.5%. For example, 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 consisting of any two of the above 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 consisting of any two of the above values. By adjusting the mass percentage of carbon black particles and carbon whiskers within the above range, carbon black particles and carbon whiskers achieve suitable mass percentages. Carbon black particles exhibit good adsorption properties for the electrolyte, improving electrolyte retention in the positive electrode and increasing Li... + Transport path; whisker carbon rods can open up closed pores between positive electrode active material particles into open pores, increasing the porosity of the positive electrode material layer and further increasing the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li + Concentration polarization further reduces the internal resistance of the secondary battery.

[0039] In one embodiment of this application, the conductive agent further includes carbon nanotubes, the oil absorption value (O4) of which is between 350 mL / 100 g and 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 consisting of any two of the above values. The aforementioned carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes. By controlling the oil absorption value of the carbon nanotubes within the above range, the dispersion degree of 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, it enhances the liquid retention capacity of the positive electrode sheet, which can further increase the Li... + Transmission path, further improving Li + Transmission efficiency, further reducing Li +Concentration polarization further reduces the internal resistance of the secondary battery.

[0040] In one embodiment of this application, the diameter D2 of the carbon nanotubes is from 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 consisting of any two of the above values. By controlling the diameter of the carbon nanotubes within the above range, the carbon nanotubes are more uniformly 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 a suitable specific surface area and a high effective conductive area, further reducing the internal resistance of the secondary battery.

[0041] In one embodiment of this application, the mass percentage of carbon nanotubes, W13, is 0 to 0.7% based on the mass of the cathode material layer. 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 consisting of any two of the above values. By controlling the mass percentage of carbon nanotubes within the above range, a suitable mass percentage of carbon nanotubes can be achieved, enabling the construction of a good conductive network and further reducing the internal resistance of the secondary battery. At the same time, the positive electrode material layer has a high content of positive electrode active material, resulting in a high energy density for the secondary battery.

[0042] In one embodiment of this application, the secondary battery, with a capacity of 3000mAh to 4000mAh, has a 1s DC resistance (DCR) of 50mΩ to 100mΩ at 25°C and 20% state of charge (SOC), and an internal resistance growth rate R1 of 30% to 80% after 500 cycles at 45°C. The fact that the DC resistance and the internal resistance growth rate after 500 cycles are within the above range indicates that the secondary battery has a low internal resistance.

[0043] This application does not impose any particular limitation on the preparation method of carbon black particles, as long as it can achieve the purpose of this application. For example, the preparation method of carbon black particles may include the following steps: selecting acetylene or tar as raw materials; subjecting the raw materials to a high-temperature pyrolysis reaction at a temperature of 1000°C to 1500°C and a reaction time of 0.1s to 3s to obtain carbon black particles; blowing the carbon black particles out of the furnace tube, cooling and collecting them to obtain the desired carbon black particles.

[0044] This application does not impose any particular limitation on the preparation method of whisker carbon rods, as long as it achieves the purpose of this application. For example, the preparation method of whisker carbon rods may include the following steps: mixing a catalyst and a carbon source and injecting them into a high-temperature furnace at 1000°C to 1500°C for catalytic synthesis for 3 to 30 seconds, followed by high-temperature graphitization at 2500°C to 3000°C for 1 to 5 hours to obtain whisker carbon rods. This application does not impose any particular limitation on the catalyst, as long as it achieves the purpose of this application. For example, the catalyst can be ferrocene. This application does not impose any particular limitation on the carbon source, as long as it achieves the purpose of this application. For example, the carbon source can be natural gas.

[0045] This application does not impose any particular limitation on the preparation method of carbon nanotubes, as long as it achieves the purpose of this application. For example, the preparation method of carbon nanotubes may include the following steps: selecting a cobalt-based or iron-based catalyst, depositing the cobalt-based or iron-based catalyst on a silicon substrate and placing it in a reactor; introducing an inert protective gas into the reactor and heating the reactor to 600°C to 900°C; introducing a reaction gas into the reactor for 30 min to 120 min, and depositing the carbon formed by the cracking of the reaction gas in the reactor onto the cobalt-based or iron-based catalyst to form a cluster of carbon nanotubes; and dispersing the nanotubes by high-speed sand milling to obtain individually dispersed carbon nanotubes. This application does not impose any particular limitation on the rotation speed of the high-speed sand milling dispersion, as long as it achieves the purpose of this application. For example, the rotation speed is 1700 r / min to 2300 r / min. The inert protective gas can be argon or nitrogen. This application does not impose any particular limitation on the cobalt-based catalyst, as long as it achieves the purpose of this application. For example, the cobalt-based catalyst can be nano-metallic cobalt, nano-cobalt oxide, or a nano-cobalt-iron composite catalyst. This application does not impose any particular restrictions on iron-based catalysts, as long as they can achieve the objectives of this application. For example, the iron-based catalyst can be nano-metallic iron, nano-iron oxide, or a nano-iron-nickel composite catalyst. This application also does not impose any particular restrictions on the reaction gas, as long as it can achieve the objectives of this application. For example, the reaction gas can be methane, ethylene, or acetylene.

[0046] This application does not impose any particular restrictions on the method of controlling the oil absorption value of carbon black particles, as long as the purpose of this application can be achieved. For example, the oil absorption value of carbon black particles can be controlled by adjusting the high-temperature pyrolysis reaction time. For example, during the high-temperature pyrolysis reaction, the diameter of the reactor tube can be reduced near the discharge port compared to the reaction port, causing the carbon black particles to collide and link together, forming longer carbon black chains and 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 using the "Oil Absorption Value Test of Carbon Black Particles" method in this application, and carbon black particles with the desired oil absorption value can be selected.

[0047] This application does not impose any particular limitation on the method of adjusting the oil absorption value of the whisker carbon rod, as long as the purpose of this application can be achieved. For example, the oil absorption value of the whisker carbon rod can be adjusted by controlling 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 using the test method of "oil absorption value test of whisker carbon rod" in this application, and a whisker carbon rod with the desired oil absorption value can be selected.

[0048] This application does not impose any particular limitation on the method of controlling the oil absorption value of the conductive agent, as long as the purpose of this application can be achieved. For example, the oil absorption value of the conductive agent can be controlled by adjusting the oil absorption values ​​of the carbon black particles and the whisker carbon rods, and the methods for controlling the oil absorption values ​​of the carbon black particles and the whisker carbon rods are as described above.

[0049] This application does not impose any particular restrictions on the method of controlling the diameter of the carbon whisker rods, as long as the purpose of this application can be achieved. For example, the diameter of the carbon whisker rods can be controlled by adjusting the size of the catalyst.

[0050] This application does not impose any particular restrictions on the method of controlling the length of the whisker carbon rods, as long as the purpose of this application can be achieved. For example, the length of the whisker carbon rods can be controlled by adjusting the temperature of the catalytic synthesis.

[0051] This application does not impose any particular restrictions on the method of controlling the porosity of the cathode material layer, as long as the purpose of this application can be achieved. For example, the porosity of the cathode material layer can be controlled by adjusting the mass percentage of carbon black particles and whisker carbon rods.

[0052] This application does not impose any particular restrictions on the method of controlling the volume percentage of pores with a diameter of 8μm to 15μm and the volume percentage of pores with a diameter of 0.5μm to 5μm, as long as the purpose of this application can be achieved. For example, the addition of carbon whiskers will affect the volume percentage of pores with a diameter of 8μm to 15μm. Carbon whiskers connect small pores in series, which can increase the pore size and may reduce the volume percentage of pores with a diameter of 0.5μm to 5μm. The addition of carbon black particles will affect the volume percentage of pores with a diameter of 0.5μm to 5μm. Carbon black particles with high oil absorption value have a long chain structure, and small pores are easily formed between carbon black particles, increasing the porosity of the cathode material layer and increasing the volume percentage of pores with a diameter of 0.5μm to 5μm.

[0053] This application does not impose any particular limitation on the method of controlling the mass percentage content of the conductive agent, as long as the purpose of this application can be achieved. For example, the mass percentage content of the conductive agent can be controlled by adjusting the mass of the added conductive agent.

[0054] This application does not impose any particular restrictions on the method of controlling the mass percentage content of the positive electrode active material, as long as the purpose of this application can be achieved. For example, the mass percentage content of the positive electrode active material can be controlled by adjusting the mass of the added positive electrode active material.

[0055] This application does not impose any particular limitation on the method of controlling the particle size Dv50 of the positive electrode active material, as long as the purpose of this application can be achieved. For example, the particle size Dv50 of the positive electrode active material can be controlled by grinding it. For example, the particle size Dv50 of the positive electrode active material can be controlled by adjusting the grinding time. Exemplarily, when other conditions remain unchanged, extending the grinding time reduces the particle size Dv50 of the positive electrode active material; shortening the grinding time increases the particle size Dv50 of the positive electrode active material.

[0056] This application does not impose any particular restrictions on the method of controlling the mass percentage content of carbon black particles and carbon whiskers, as long as the purpose of this application can be achieved. For example, the mass percentage content of carbon black particles can be controlled by controlling the mass of the added carbon black particles; the mass percentage content of carbon whiskers can be controlled by controlling the mass of the added carbon whiskers.

[0057] This application does not impose any particular restrictions on the method of controlling the oil absorption value of carbon nanotubes, as long as the purpose of this application can be achieved. For example, the oil absorption value of carbon nanotubes can be controlled by adjusting 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 using the test method of "oil absorption value test of carbon nanotubes" in this application, and then the carbon nanotube with the desired oil absorption value can be selected.

[0058] This application does not impose any particular restrictions on the method of controlling 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 controlled by adjusting the size of cobalt-based or iron-based catalysts.

[0059] This application does not impose any particular restrictions on the method of controlling the mass percentage content of carbon nanotubes, as long as the purpose of this application can be achieved. For example, the mass percentage content of carbon nanotubes can be controlled by adjusting the mass of the added carbon nanotubes.

[0060] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0061] This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, at least one of lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium-rich manganese-based materials, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide 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 At least one of O2 (NCM111). The positive electrode material layer of this application also includes a positive electrode binder. This application does not have any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyamide, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber (SBR), polypropylene, polyethylene, polyetherimide, nitrile rubber, copolymers of propylene derivatives, or carboxymethyl cellulose salts. The above-mentioned carboxymethyl cellulose salts may include, but are not limited to, at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or lithium carboxymethyl cellulose. This application does not have any particular limitation on the mass percentage content of the positive electrode binder in the positive electrode material layer, and those skilled in the art can choose according to actual needs, as long as it can achieve the purpose of this application. For example, based on the mass of the positive electrode material layer, the mass percentage content W3 of the positive electrode binder is 0.8% to 3.0%.

[0062] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be 6 μm to 16 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be 25 μm to 250 μm.

[0063] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and it can be at least one of the aforementioned conductive agents and positive electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0064] 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 disposed on at least one surface of the negative current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its own thickness direction, or on two surfaces of the negative current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative current collector or a part of the negative current collector; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative current collector, as long as the purpose of this application is achieved, for example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors, etc.

[0065] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 The negative electrode material layer of this application includes at least one of Li-Al alloy or metallic lithium. The negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. This application does not impose any particular limitation on the negative electrode binder and negative electrode conductive agent in the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the negative electrode binder can be at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent can be at least one of the aforementioned conductive agents. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application can be achieved.

[0066] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 12 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer can be from 30 μm to 250 μm.

[0067] 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. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned negative electrode conductive agents and negative electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0068] In this application, the secondary battery also includes an electrolyte. The electrolyte includes lithium salts and non-aqueous solvents. The lithium salts 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. This application does not have any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application, for example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain 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 methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned 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. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the mass percentage of lithium salt and non-aqueous solvents, as long as the purpose of this application is achieved.

[0069] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the negative electrode, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0070] In this application, the diaphragm may include a base membrane and a surface treatment layer. The base membrane may be a nonwoven fabric or composite membrane with a porous structure, and the material of the base membrane may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the base membrane. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, 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. This application does not impose any particular limitation on the adhesive used for the diaphragm described above; for example, it may be at least one of the aforementioned positive electrode adhesives. The polymer layer contains a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0071] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0072] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0073] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound 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, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked 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, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0074] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has a low internal resistance.

[0075] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0076] Example

[0077] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0078] Test methods and equipment:

[0079] Oil absorption value test of carbon black particles:

[0080] The oil absorption value of carbon black particles was tested using the paraffin oil + torque method: A DABS-H model oil absorption meter was selected, and the oil absorption value of carbon black particles was tested according to the national standard "Carbon Black Part 2: Determination of Oil Absorption Value" (GB / T 3780.2—2007). The carbon black sample was added to the mixing tank of the oil absorption meter, and paraffin oil was added to the sample at a rate of 4 mL / min using a titrator. As the oil absorption value of the sample increased, the mixture changed from a free-flowing state to a semi-plastic agglomerate, 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 titrator automatically shut off simultaneously. The volume of oil added was read directly from the burette; the volume of oil absorbed per unit mass of sample is the oil absorption value of the sample.

[0081] Oil absorption value test of conductive agent:

[0082] (1) Disassemble the lithium-ion battery to obtain the positive electrode sheet; (2) Take the above positive electrode sheet and immerse it in the solvent N-methylpyrrolidone (NMP) to remove the film, so that the positive electrode material film layer is dissolved in the solvent, and disperse it evenly with a disperser to obtain a slurry; (3) Take the above slurry and separate the positive electrode binder in the slurry by gradient centrifugation to obtain a slurry containing positive electrode active material and conductive agent; (4) Treat the above slurry containing positive electrode active material and conductive agent with 2 mol / L hydrochloric acid solution at 60°C for 2 hours to digest the positive electrode active material (lithium cobalt oxide or lithium nickel cobalt manganese oxide), and the positive electrode active material of lithium iron phosphate is digested with hydrochloric acid-hydrogen peroxide, and then dried to obtain the conductive agent; (5) Test the oil absorption value of the conductive agent by the paraffin oil + torque method described above.

[0083] Oil absorption value test of whisker carbon rods:

[0084] The oil absorption value of the whisker carbon rod was tested using the paraffin oil + torque method described above.

[0085] Oil absorption value test of carbon nanotubes:

[0086] The oil absorption value of carbon nanotubes was tested using the paraffin oil + torque method described above.

[0087] Oil absorption value test of positive electrode material layer:

[0088] (1) Discharge the lithium-ion battery to 3.0V at a constant current of 0.5C, then disassemble it to obtain the positive electrode sheet, then soak the positive electrode sheet in dimethyl carbonate (DMC) at room temperature for 30 minutes and air dry it; then soak it in NMP at room temperature for 20 minutes, take out the positive electrode sheet and peel the positive current collector aluminum foil off the positive electrode material layer, dry the positive electrode material layer at 80°C, and then keep it in a nitrogen atmosphere at 800°C for 30 minutes to decompose the positive electrode binder and obtain powder; (2) Use the paraffin oil + torque method described above to test the oil absorption value of the powder obtained in step (1), which is the oil absorption value of the positive electrode material layer.

[0089] Testing of the diameter and length of carbon whisker rods, and the diameter of carbon nanotubes:

[0090] (1) Disassemble the lithium-ion battery to obtain the positive electrode sheet; (2) Immerse the positive electrode sheet in dimethyl carbonate (DMC) at room temperature for 60 minutes, take it out and air dry at room temperature; (3) Take the positive electrode sheet obtained in step (2) and obtain the cross-section of the positive electrode material layer on the positive electrode sheet by liquid nitrogen brittle fracture; (4) Observe the cross-section by scanning electron microscope (SEM), test the diameter and length of no less than 20 whisker carbon rods and the diameter of no less than 30 carbon nanotubes in 10 regions, and take the average value as the diameter of whisker carbon rods, the length of whisker carbon rods, and the diameter of carbon nanotubes.

[0091] Porosity and pore size distribution testing of the cathode material layer:

[0092] (1) The lithium-ion battery was discharged to 3.0V at a constant current of 0.5C, and then the positive electrode was obtained by disassembly. The positive electrode was then soaked in dimethyl carbonate (DMC) at room temperature for 30 min and then dried. (2) The positive electrode obtained in step (1) was cut into 30cm×2cm samples, dried at 120℃ for 2 h, and then degassed in a degassing chamber for 12 h. The porosity and pore size distribution of the positive electrode material layer were then tested using a mercury porosimeter. The mercury porosimeter was a MicroActive AutoPore V 9605, and the pressure was set to 33000psia.

[0093] Particle size Dv50 test:

[0094] The particle size of the positive electrode active material was measured using a Malvern particle size analyzer (MasterSizer 2000). 0.02 g of positive electrode active material particles were added to a 50 mL clean beaker, along with 20 mL of ethanol as a dispersant. The mixture was ultrasonicated for 30 min in a 120 W ultrasonic cleaner to completely disperse the particles in the ethanol, obtaining a sample dispersion. The particle size Dv50 of the positive electrode active material particles was then measured using the Malvern particle size analyzer.

[0095] 1s DC Impedance (DCR) Test:

[0096] Take the lithium-ion battery from the example or comparative example and perform the following tests at 25±2℃: (1) let it stand for 2 hours; (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 hours; (3) then discharge it at a constant current of 0.2C to 3.0V, take the discharge capacity of this step as C1, and let it stand for 5 hours; (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 minutes; (5) then discharge it at a constant current of 0.1C1 to a capacity of 0.2C1, let it stand for 15 minutes, record the voltage at this time as V0, then discharge it at a constant current of 1.0C1 for 1 second, record the voltage at this time as V1, then the 1s DCR at 25℃ and 20% SOC is (V0-V1) / 1.0C1.

[0097] Internal resistance growth rate test after 500 cycles at 45℃:

[0098] The lithium-ion batteries from the examples or comparative examples were subjected to the following tests at 45±2℃:

[0099] (1) Let stand for 2 hours, discharge at a constant current of 0.7C to 3.0V, and let stand for 5 minutes;

[0100] (2) Charge the battery at a constant current of 1.0C to 4.50V, and then 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 minutes; 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 sinusoidal current of 1000Hz, and record it as IMP1; let it stand for 5 minutes; repeat the above steps for 49 cycles, and record the internal resistance of the lithium-ion battery as IMP1, IMP2, ..., IMP49 in sequence; then perform the 50th cycle, charge the battery at a constant current of 1.0C to 4.50V, and then 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 minutes; 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;

[0101] (3) Then repeat step (2) 10 times, then charge at a constant current of 1.0C to 4.50V, and charge at a constant voltage of 4.50V until the current is less than or equal to 0.05C; let stand for 5 minutes; then discharge at a constant current of 0.5C to 3.0V, and record the internal resistance of the lithium-ion battery in the 501st cycle as IMP501; then the internal resistance growth rate R1 (%) of the lithium-ion battery after 500 cycles at 45℃ is = IMP501 / IMP1-100%.

[0102] Example 1-1

[0103] <Preparation of the positive electrode>

[0104] Lithium cobalt oxide (LiCoO2), conductive carbon black particles, conductive carbon whisker rods, conductive carbon nanotubes, and polyvinylidene fluoride (PVDF) binder were mixed in a weight ratio of 97.5:0.4:0.2:0.4:1.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 70 wt%. The carbon black particles were acetylene black, and the carbon nanotubes were multi-walled carbon nanotubes. The particle size Dv50 of the positive electrode active material was 15 μm. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of a 100 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The cathode was dried under vacuum at 120℃ for 1 hour, followed by cold pressing, cutting, and slitting to obtain a positive electrode sheet with dimensions of 74mm × 867mm. The compaction density during the cold pressing process was 4.2 g / cm³. 3 .

[0105] <Preparation of Negative Electrode Sheets>

[0106] Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (CMC-Na) (negative electrode binder), and styrene-butadiene rubber (SBR) (negative electrode binder) were mixed in a weight ratio of 95:2:3. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 120 °C to obtain a negative electrode sheet with a single-sided coating of a 120 μm thick negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material layer. The sheet was dried under vacuum at 120 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 78 mm × 875 mm. The compaction density during the cold pressing process was 1.75 g / cm³. 3 .

[0107] <Preparation of Electrolyte>

[0108] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a weight ratio of 1:1:1 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the lithium salt content was 12.5% ​​by mass, with the remainder being the base solvent.

[0109] <Preparation of the diaphragm>

[0110] A polyethylene (PE) film with a thickness of 15 μm is used.

[0111] <Preparation of Lithium-ion Batteries>

[0112] The positive electrode, separator, negative electrode, and separator prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0113] Examples 1-2 to Examples 1-7

[0114] Except for adjusting the high-temperature pyrolysis reaction time to achieve the oil absorption value of the carbon black particles as shown in Table 1, the rest is the same as in Example 1-1.

[0115] Examples 1-8 to Examples 1-24

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-3.

[0117] Examples 2-1 to 2-15

[0118] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-3.

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

[0120] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0121] Comparative Examples 1-3

[0122] Except for the preparation of the positive electrode sheet, in which the positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black particles, conductive 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 to mix evenly to obtain the positive electrode slurry, the rest is the same as in Examples 1-3.

[0123] Comparative Examples 1-4

[0124] Except for the preparation of the positive electrode sheet, in which the positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black particles, conductive graphene, conductive 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 to obtain a uniform positive electrode slurry, the rest is the same as in Examples 1-3.

[0125] Comparative Example 2-1

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

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

[0128] Table 1 Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0129] As 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, when the type of conductive agent and the oil absorption value are within the range of this application, the prepared lithium-ion batteries have lower 1s DCR at 25°C and 20% SOC, and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced. In Comparative Examples 1-1 to 1-2 and 2-1, the oil absorption value of the conductive agent is not within the range of this application, and the prepared lithium-ion batteries have higher 1s DCR at 25°C and 20% SOC, and higher internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries is higher. In Comparative Examples 1-3 to 1-4, the type of conductive agent is not within the range of this application, and the prepared lithium-ion batteries have higher 1s DCR at 25°C and 20% SOC, and higher internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries is higher.

[0130] The oil absorption value of carbon black particles typically affects the internal resistance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-7, by adjusting the oil absorption value of carbon black particles within the scope of this application, the prepared lithium-ion batteries exhibit lower 1s DCR at 25°C and 20% SOC, and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0131] The diameter and length of the carbon whisker rods typically affect the internal resistance of lithium-ion batteries. As seen in Examples 1-3 and 1-8 to 1-19, by controlling the diameter and length of the carbon whisker rods within the scope of this application, the prepared lithium-ion batteries exhibit lower 1s DCR at 25°C and 20% SOC, and a lower 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 and 1-13 to 1-19, increasing the length of the carbon whisker rods improves their oil absorption value. However, in Examples 1-18, the carbon whisker rods are too long, making them prone to agglomeration in the positive electrode and difficult to separate, thus affecting their oil absorption value.

[0132] The diameter of carbon nanotubes typically affects the internal resistance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-24, by controlling the diameter of carbon nanotubes within the scope of this application, the prepared lithium-ion batteries exhibit lower 1sDCR at 25°C and 20% SOC, and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0133] The mass percentage of each substance in the cathode material layer typically affects the internal resistance of a lithium-ion battery. As can be seen from Examples 1-3 and Examples 2-1 to 2-8, by controlling the mass percentage of each substance in the cathode material layer within the scope of this application, the prepared lithium-ion battery exhibits a lower 1s DCR at 25°C and 20% SOC, and a lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of the lithium-ion battery can be reduced.

[0134] The particle size Dv50 of the positive electrode active material typically affects the internal resistance of lithium-ion batteries. As can be seen from Examples 1-3, 2-9 to 2-11, by controlling the particle size Dv50 of the positive electrode active material within the scope of this application, the prepared lithium-ion batteries exhibit lower 1s DCR at 25°C and 20% SOC, and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0135] As can be seen from Examples 2-12 to 2-13, the types of positive electrode binders are within the scope of this application. The prepared lithium-ion batteries have lower 1sDCR at 25°C and 20% SOC and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0136] As can be seen from Examples 2-14 to 2-15, the types of positive electrode active materials are within the scope of this application. The prepared lithium-ion batteries have lower 1s DCR at 25°C and 20% SOC and lower internal resistance growth rate after 500 cycles at 45°C, indicating that the internal resistance of lithium-ion batteries can be reduced.

[0137] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0138] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0139] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

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

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

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

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 from 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 from 250 mL / 100g to 500 mL / 100g.

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 diameter of 8 μm to 15 μm is 3% to 15%, and the volume percentage V2 of pores with a diameter of 0.5 μm to 5 μm 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, and 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 5μm to 20μm, and the oil absorption value of the positive electrode material layer is 0.5 mL / 100g, 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 cathode material layer, the mass percentage of the carbon black particles W11 is 0.2% to 0.6%, and the mass percentage of the whisker carbon rods W12 is 0.1% to 0.5%.

12. The secondary battery according to claim 1, wherein, The conductive agent also includes carbon nanotubes, the carbon nanotubes having an oil absorption value (O4) of 350 mL / 100g to 500 mL / 100g.

13. The secondary battery according to claim 12, wherein it 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 cathode material layer, the mass percentage of the carbon nanotubes W13 is 0 to 0.7%.

14. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 13.

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