Conductive carbon black, positive pole piece, electrochemical device and electronic device

Abstract

The invention discloses conductive carbon black, a positive pole piece, an electrochemical device and an electronic device, the conductive carbon black comprises a plurality of carbon black units and pores located between the adjacent carbon black units, and the carbon black units comprise holes; the apparent density of the conductive carbon black is 0.05 g / cm < 3 > to 0.1 g / cm < 3 >, and the pore volume of the pores is 0.05 cm < 3 > / g to 0.5 cm < 3 > / g. The conductive carbon black disclosed by the embodiment of the invention has good liquid retention property, so that the liquid retention rate of the positive pole piece is improved, and the performance of the electrochemical device is further improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a conductive carbon black, a positive electrode sheet, an electrochemical device and an electronic device. Background Art

[0002] In today's energy field, lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, energy storage systems and other fields due to their advantages such as high energy density and long cycle life. With the continuous advancement of technology and the continuous growth of market demand, the requirements for lithium-ion battery performance are becoming increasingly stringent.

[0003] Conductive carbon black is a commonly used conductive additive in the positive electrode materials of lithium-ion batteries. It can build an effective conductive network between the particles of the positive electrode active material. However, the existing conductive carbon black has obvious deficiencies in liquid retention, which limits its conductivity. Summary of the invention

[0004] The embodiments of the present application provide a conductive carbon black, a positive electrode plate, an electrochemical device and an electronic device. The conductive carbon black of the present application has good liquid retention, thereby improving the liquid retention rate of the positive electrode plate and further improving the performance of the electrochemical device.

[0005] In a first aspect, the present invention provides a conductive carbon black, which comprises a plurality of carbon black units and pores between adjacent carbon black units, wherein the carbon black units comprise pores; the bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 , the pore volume is 0.05cm 3 / g~0.5cm 3 / g.

[0006] In the present application, the conductive carbon black includes a plurality of carbon black units and pores between adjacent carbon black units, the carbon black unit includes pores, and the bulk density of the conductive carbon black and the pore volume of the pores are adjusted so that the bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 , the pore volume is 0.05cm 3 / g~0.5cm 3 / g, which can make the conductive carbon black form a more efficient conductive network in the battery electrode. The carbon black unit in this application refers to a single ball that makes up the dendritic carbon black. The loose density can make the carbon black particles contact each other more closely, and the pore volume provides more channels for electron transmission, which is convenient for rapid electron migration, reduces the internal resistance of the battery, and improves the battery charging and discharging efficiency. The two can work together to accelerate the electron conduction rate of the electrode material, making the battery more stable when charging and discharging at high currents. And it provides more storage and transmission channels for the electrolyte, so that the electrolyte can better penetrate into the electrode material. As an additive to the electrode material, the pore volume of conductive carbon black can be interconnected with the pores of the electrode to form a more unobstructed electrolyte transmission network, thereby improving the wetting effect of the electrolyte on the electrode. When the loose density is too small, the contact area between the conductive carbon black is too small, which will deteriorate the conductive network; when the loose density is too large, the electrode plate is too well-preserved, which will lead to a reduction in the electrode plate gap and the anode electrolyte, which will reduce the cycle performance. When the pore volume is too large, the conductive carbon black is easy to adsorb the binder, weakening the dispersion effect of the binder in the system. The conductive carbon black is easy to agglomerate in the electrode, affecting the conductive network, thereby reducing the rate performance of the battery. In addition, if the pore volume is too large, too much electrolyte will be stored inside the conductive carbon black, and other places will lack liquid, thus affecting the cycle performance of the battery.

[0007] In some specific embodiments, the conductive carbon black has a bulk density of 0.06 g / cm 3 ~0.08g / cm 3 , and / or, the pore volume of the pores is 0.15 cm 3 / g~0.3cm 3 / g.

[0008] In the above specific implementation, the conductive carbon black can further improve the wetting effect of the electrolyte on the electrode, thereby improving the high temperature performance and cycle retention rate of the battery.

[0009] In some embodiments, the equivalent diameter of the pores is 10 nm to 45 nm.

[0010] In the above specific implementation, when the equivalent diameter of the hole is 10nm to 45nm, the electrolyte is easier to enter and exit, the liquid retention of the electrode is increased, and the electrolyte can be leached out in the later stage of the cycle to provide an ion path, which helps to form a more stable electrode-electrolyte interface on the electrode surface. In addition, the electrolyte can be fully in contact with the electrode material to form a uniform interface layer, reduce the stress and uneven electric field distribution at the interface, thereby reducing the interface resistance and improving the cycle stability and service life of the battery.

[0011] In some embodiments, the equivalent diameter of the pores is 15 nm to 30 nm.

[0012] In the above technical solution, when the equivalent diameter of the hole is 15nm to 30nm, the electrolyte can enter and exit more smoothly and efficiently. On the one hand, compared with slightly larger holes, it has better constraints on the electrolyte, which can significantly increase the amount of liquid retained by the pole piece, ensuring that there is always sufficient electrolyte to support the electrode reaction during the battery cycle. On the other hand, in the later stage of the cycle, the electrolyte can be stably leached, providing a precise and efficient path for ion migration, which greatly guarantees the continuous progress of the electrode reaction and maintains the stability of the battery performance. At the same time, it can enable the electrolyte and the electrode material to achieve more sufficient and precise contact, further improving the stability of the electrode-electrolyte interface. When the equivalent diameter of the hole is too small, the capillary effect is large, which is not conducive to the later electrolyte seepage. When the equivalent diameter of the hole is too large, it is not conducive to the uniform distribution of the electrolyte on the surface of the conductive carbon black, thereby affecting the ion transmission path.

[0013] In some embodiments, the equivalent diameter of the pore is A (nm), and the pore volume of the pore is B (cm 3 / g), conductive carbon black satisfies: 100≤A / B≤300.

[0014] In the above specific embodiment, the conductive carbon black satisfies: 100≤A / B≤300, which enables the equivalent diameter of the pores and the pore volume to cooperate with each other, ensuring that the ions have a large enough channel to pass smoothly, and providing sufficient pore volume to store and buffer the ions. In lithium-ion batteries, lithium ions can be quickly and stably transferred between the electrode and the electrolyte during the charge and discharge process, improving the battery's cycle performance and rate performance. At the same time, it helps to optimize the distribution of reaction sites on the electrode surface. Increasing the specific surface area of ​​the electrode-electrolyte interface makes the electrode reaction more complete and accelerates the electrode reaction kinetics, thereby improving the overall performance of the battery, and improving the battery's charge and discharge speed and energy conversion efficiency.

[0015] In some specific embodiments, the conductive carbon black satisfies: 100≤A / B≤200.

[0016] In the above specific embodiment, the conductive carbon black satisfies: 100≤A / B≤200, which helps to optimize the structure of the electrode material, so that the electrode can accommodate more active substances, while ensuring good conductivity and ion transport performance, thereby improving the energy density of the battery and increasing the battery life or working time.

[0017] In some specific embodiments, the conductive carbon black satisfies at least one of the following: (1) the oil absorption value of the conductive carbon black is 300mL / 100g to 450mL / 100g; (2) the ID / IG of the conductive carbon black is 0.8 to 1.3; (3) the thermal conductivity of the conductive carbon black is 0.1W / (m·K) to 0.5W / (m·K); (4) the conductive carbon black includes the plurality of carbon black units stacked to form a dendritic structure.

[0018] In the above specific embodiment, when the oil absorption value of the conductive carbon black is 300mL / 100g to 450mL / 100g, the electrolyte is adsorbed on the surface and pores of the conductive carbon black, making the contact between the conductive carbon black closer and the transmission of electrons between particles easier, thereby reducing the overall resistivity of the material and improving the conductivity efficiency. It is helpful to improve the rate performance and cycle stability of the battery, reduce the internal resistance of the battery, and increase the energy density and power density of the battery. If the oil absorption value of the conductive carbon black is too high, it will make it difficult to disperse the conductive carbon black, and then it will be easy to agglomerate in the electrode, deteriorate the conductive network, and reduce the rate performance and cycle performance.

[0019] When the ID / IG of conductive carbon black is 0.8-1.3, there are appropriate defects and disordered structures in the conductive carbon black. These defects can serve as electron capture and release sites, which helps the transmission of electrons between carbon black particles and makes it easier for electrons to jump in the carbon black network, thereby improving the overall conductivity of the material and reducing resistivity. When ID / IG is too small, the surface defects of conductive carbon black are few and it is easy to agglomerate; when ID / IG is too large, the conductive carbon black has poor conductivity.

[0020] When the thermal conductivity of conductive carbon black is 0.1W / (m·K)~0.5W / (m·K), it can help build a heat conduction network inside the battery, so that the heat can be evenly distributed and dissipated in time, avoiding local overheating that leads to decreased battery performance, capacity decay and increased side reactions, thereby improving the decline of battery performance, reducing polarization during charging and discharging, and improving rate performance.

[0021] When the conductive carbon black includes the plurality of carbon black units stacked to form a dendritic structure, the dendritic structure can effectively increase the contact points and contact area between the conductive carbon black and the surrounding materials. The numerous branches are intertwined with each other, and a denser, more complex and more efficient conductive network can be constructed in the matrix material. Electrons can be quickly transmitted along these dendritic structures, so that the conductivity of the material is significantly improved. At the same time, the good combination between the dendritic structure and the matrix can form a stronger interface layer inside the material. This interface layer can effectively transfer stress, coordinate the deformation between the matrix and the carbon black, and improve the overall mechanical properties of the material. At the same time, it also helps to enhance the stability of the material under different environmental conditions and reduce performance degradation caused by problems such as interface debonding.

[0022] In some specific embodiments, the conductive carbon black satisfies at least one of the following: (1) the oil absorption value of the conductive carbon black is 350 mL / 100 g to 400 L / 100 g; (2) the ID / IG of the conductive carbon black is 1.0 to 1.2; (3) the thermal conductivity of the conductive carbon black is 0.2 W / (m·K) to 0.5 W / (m·K).

[0023] In the above specific implementation, the oil absorption value of the conductive carbon black is 350mL / 100g to 400L / 100g, which can ensure good dispersion of the carbon black and stability of the conductive network, making the conductive performance of the material more stable under different environmental conditions. The conductive performance will not fluctuate significantly due to external factors, thereby improving the reliability and safety of the material.

[0024] When the ID / IG of conductive carbon black is 1.0-1.2, the conductive carbon black structure is more stable, so that the resistance performance of the material is also relatively stable. Under different environmental conditions and during use, the resistance of the material will not fluctuate greatly, and it can provide stable conductive performance for electronic equipment, etc.

[0025] When the thermal conductivity of conductive carbon black is 0.2W / (m·K) to 0.4W / (m·K), the temperature distribution inside the material can be more uniform, which allows the heat conduction of various parts of the battery to be more balanced during the charge and discharge process, avoiding local overheating, and helping to improve the overall performance and safety of the battery.

[0026] In a second aspect, the present application provides a positive electrode sheet, which includes a binder, a positive electrode active material and the conductive carbon black of the first aspect. The positive electrode sheet has good liquid retention performance and a conductive network, which can further improve the electrochemical performance of the electrochemical device.

[0027] In some specific embodiments, the positive electrode sheet satisfies at least one of the following: (1) the equivalent diameter of the hole is A (nm), the Dv50 of the positive electrode active material is E (μm), and the positive electrode sheet satisfies: 0.5≤A / E≤8; (2) the bulk density of the conductive carbon black is F (g / cm 3 ), the tap density of the positive electrode active material is G (g / cm 3 ), the compaction density of the positive electrode is H (g / cm 3 ), the positive electrode sheet satisfies: 3.5≤HF×G≤4.0; (3) the liquid retention rate of the positive electrode sheet is 10% to 26%.

[0028] In the above specific embodiment, the positive electrode sheet satisfies: 0.5≤A / E≤8, and a more efficient electron transmission channel can be constructed. The conductive carbon black pores provide a fast transmission path for electrons, and the adaptation with the positive electrode active material Dv50 improves the contact effect between the positive electrode active material and the carbon black, making the transfer of electrons between the active material and the conductive carbon black smoother, reducing the charge transfer resistance, and thus improving the charge and discharge efficiency. It further helps the diffusion of ions in the electrode material, making the transmission channel of ions inside the electrode smoother, shortening the ion diffusion path, accelerating the insertion and extraction speed of ions during the charge and discharge process, and further improving the charge and discharge efficiency of the battery. When A / E is too large, the uniformity of the electrolyte coating around the active material will be reduced, affecting the cycle stability and rate performance of the battery; when A / E is too small, the continuity of the electrolyte coating around the active material is poor, thereby affecting the rate performance and cycle stability of the battery. In addition, the reduction of the active material Dv50 is also conducive to the improvement of the rate performance, but it will reduce the cycle stability of the battery at 45°C.

[0029] When the positive electrode plate meets the condition of 3.5≤HF×G≤4.0, a conductive network can be effectively constructed to ensure that the active material can fully play its role, thereby improving the energy density of the battery. At the same time, it is beneficial for the electrolyte to fully infiltrate the plate, providing more transmission channels for lithium ions; shortening the diffusion distance of lithium ions inside the active material and between particles, allowing lithium ions to quickly migrate between the electrode and the electrolyte, improving the battery's rate performance and cycle stability.

[0030] When the liquid retention rate of the positive electrode sheet is 10% to 26%, the interface between the positive electrode sheet and the electrolyte forms good infiltration, reducing the interface resistance. This helps to improve the kinetics of the electrode reaction, making the transfer of electrons and ions at the interface easier, reducing the polarization phenomenon of the battery during the charge and discharge process, and improving the charge and discharge efficiency and energy output efficiency of the battery.

[0031] In some specific embodiments, the positive electrode sheet satisfies: 1≤A / E≤2, and / or, the positive electrode sheet satisfies: 3.6≤HF×G≤3.8. When the positive electrode sheet satisfies: 1≤A / E≤2, and / or, the positive electrode sheet satisfies: 3.6≤HF×G≤3.8, the charge and discharge efficiency of the battery can be further improved.

[0032] In a third aspect, the present application provides an electrochemical device, which comprises the positive electrode sheet, the negative electrode sheet and the separator according to the second aspect, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrochemical device has good low temperature performance and high temperature performance.

[0033] In some embodiments, the isolation membrane includes an organic coating, the organic coating includes hollow microspheres, and the hollow microspheres have a shell layer.

[0034] In the above specific embodiments, the hollow microspheres can increase the uniformity of the thickness and porosity of the separator, so that the separator has a better effect of isolating the ions and electrons between the positive and negative electrodes, effectively preventing the short circuit between the positive and negative electrodes inside the battery, and improving the safety and stability of the battery. In addition, the shell of the hollow microspheres can play a certain role in screening and guiding the transmission of ions, allowing beneficial ions such as lithium ions to pass through, while blocking other impurity ions that may cause side reactions, which helps to improve the charge and discharge efficiency and cycle performance of the battery.

[0035] In some specific embodiments, the electrochemical device satisfies at least one of the following: (1) the thickness of the shell layer is 0.07 μm to 0.3 μm; (2) the isolation membrane may further include a base membrane, the particle size of the hollow microspheres is J (μm), the porosity of the base membrane is K (%), and the electrochemical device satisfies: 0.01≤J / K≤0.03.

[0036] In the above specific embodiment, when the thickness of the shell layer is 0.07 μm to 0.3 μm, it helps to regulate the interfacial interaction between the hollow microspheres and surrounding materials (such as electrolyte, electrodes, etc.), making the ion exchange and electron transfer at the interface smoother, reducing the interface resistance, and improving the overall performance of the battery.

[0037] When the electrochemical device satisfies: 0.01≤J / K≤0.03, it can provide a smooth transmission channel for lithium ions, etc., improve the ion conduction efficiency, and thus improve the battery's charge and discharge performance and energy density.

[0038] In a fourth aspect, the present application provides an electronic device, which includes the electrochemical device of the third aspect. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0040] As used in this application, the terms "including," "containing," and "comprising" are used in their open, non-limiting sense.

[0041] In addition, sometimes amounts, ratios and other numerical values ​​are presented in range format herein. It should be understood that such range format is for convenience and brevity, and should be flexibly understood to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or sub-ranges encompassed within the range, as if each numerical value and sub-range were explicitly specified.

[0042] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0043] In today's energy field, lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, energy storage systems and other fields due to their advantages such as high energy density and long cycle life. With the continuous advancement of technology and the continuous growth of market demand, the requirements for lithium-ion battery performance are becoming increasingly stringent.

[0044] In the cathode material system of lithium-ion batteries, conductive carbon black occupies an indispensable position. As a commonly used and important conductive additive, it plays an extremely critical role. Its working principle is that conductive carbon black can build an effective conductive network between the particles of the cathode active material. When the battery is in the process of charging and discharging, electrons can be quickly and smoothly transmitted between the active material particles through this conductive network, thereby significantly improving the battery's charging and discharging efficiency and overall performance. However, the existing conductive carbon black has exposed obvious shortcomings in terms of liquid retention. During the use of the battery, the electrolyte is crucial to maintaining the ion transmission inside the battery, and the conductive carbon black has insufficient liquid retention, so it cannot adsorb and retain the electrolyte well, resulting in uneven distribution of the electrolyte and drying up of the electrolyte in some areas. This not only seriously affects the transmission efficiency of ions inside the battery, but also further limits the conductivity of the conductive carbon black itself, and ultimately affects the overall performance of the lithium-ion battery.

[0045] Based on the above problems, the present application provides a conductive carbon black, a positive electrode plate, an electrochemical device and an electronic device. The conductive carbon black of the present application has good liquid retention, thereby improving the liquid retention rate of the positive electrode plate and further improving the performance of the electrochemical device.

[0046] The following is a detailed description of the implementation of the present application.

[0047] Conductive carbon black

[0048] The embodiment of the present application provides a conductive carbon black, which comprises a plurality of carbon black units and pores between adjacent carbon black units, wherein the carbon black units comprise pores; the bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 , the pore volume is 0.05cm 3 / g~0.5cm 3 / g.

[0049] For example, the bulk density of conductive carbon black can be 0.05 g / cm 3 , 0.055g / cm 3 , 0.06g / cm 3 , 0.065g / cm 3 , 0.07g / cm 3 , 0.075g / cm 3 , 0.08g / cm 3 , 0.085g / cm 3 , 0.09g / cm 3 , 0.095g / cm 3 , 0.1g / cm 3 , or a range consisting of any of the above values.

[0050] The pore volume can be 0.05cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g, 0.3cm 3 / g, 0.35cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, or any range consisting of the above values.

[0051] Optionally, the bulk density of the conductive carbon black may be 0.055 g / cm 3 ~0.1g / cm 3 , 0.06g / cm 3 ~0.1g / cm 3 , 0.06g / cm 3 ~0.095g / cm 3 , 0.06g / cm 3 ~0.09g / cm 3 , 0.06g / cm 3 ~0.085g / cm 3 , 0.06g / cm 3~0.08g / cm 3 .

[0052] Optionally, the pore volume of the hole is 0.1cm 3 / g~0.5cm 3 / g,0.1cm 3 / g~0.45cm 3 / g,0.1cm 3 / g~0.4cm 3 / g,0.1cm 3 / g~0.35cm 3 / g,0.1cm 3 / g~0.3cm 3 / g, 0.15cm 3 / g~0.5cm 3 / g,0.15cm 3 / g~0.45cm 3 / g,0.15cm 3 / g~0.4cm 3 / g, 0.15cm 3 / g~0.35cm 3 / g, 0.15cm 3 / g~0.3cm 3 / g.

[0053] According to the present application, the conductive carbon black comprises a plurality of carbon black units and pores between adjacent carbon black units, the carbon black units comprise pores, and by regulating the bulk density of the conductive carbon black and the pore volume of the pores, the bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 , the pore volume is 0.05cm 3 / g~0.5cm 3 / g, which can make the conductive carbon black form a more efficient conductive network in the battery electrode. The loose density can make the carbon black particles contact each other more closely, and the pore volume provides more channels for electron transmission, which is convenient for rapid electron migration, reduces the internal resistance of the battery, and improves the battery charging and discharging efficiency. The two can work together to accelerate the electron conduction rate of the electrode material, making the battery more stable when charging and discharging at high currents. And it provides more storage and transmission channels for the electrolyte, so that the electrolyte can better penetrate into the electrode material. As an additive to the electrode material, the pore volume of conductive carbon black can be interconnected with the pores of the electrode to form a more unobstructed electrolyte transmission network, thereby improving the wetting effect of the electrolyte on the electrode. When the loose density is too small, the contact area between the conductive carbon black is too small, which will deteriorate the conductive network; when the loose density is too large, the electrode liquid is too good, which will lead to a reduction in the electrode gap and the anode electrolyte, which will reduce the cycle performance. When the pore volume is too large, the conductive carbon black is easy to adsorb the binder, weakening the dispersion effect of the binder in the system. The conductive carbon black is easy to agglomerate in the electrode, affecting the conductive network, thereby reducing the rate performance of the battery. In addition, if the pore volume is too large, too much electrolyte will be stored inside the conductive carbon black, and other places will lack liquid, thus affecting the cycle performance of the battery.

[0054] It should be noted that the bulk density of conductive carbon black and the pore volume of the pores can be detected using methods and instruments known in the art. For example, the electrochemical device can be disassembled to obtain the positive electrode plate and then further disassembled to obtain the conductive carbon black. The mass and volume of the conductive carbon black are measured according to the method in GB / T 5162-2006 "Determination of the bulk density of metal powders", and then the bulk density of the conductive carbon black is calculated according to the formula. Using a specific surface area and pore size analyzer, based on the Brunauer-Emmett-Teller (BET) theory, by measuring the adsorption amount of gas under different relative pressures, the specific surface area of ​​the sample can be calculated using the BET equation. The measurement principle of pore volume is related to it. When the relative pressure is close to 1, the gas undergoes capillary condensation in the mesopores and macropores, and the pore volume can be calculated based on the amount of condensed gas.

[0055] In some embodiments, the equivalent diameter of the hole is 10 nm to 45 nm. For example, the equivalent diameter of the hole can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or any range thereof.

[0056] Optionally, the equivalent diameter of the hole can be 15nm~45nm, 15nm~42nm, 15nm~40nm, 15nm~38nm, 15nm~35nm, 15nm~32nm, 15nm~30nm.

[0057] According to the above embodiment, when the equivalent diameter of the hole is 10nm to 45nm, the electrolyte is easier to enter and exit, the liquid retention of the electrode is improved, and the electrolyte can be leached out in the later stage of the cycle to provide an ion path, which helps to form a more stable electrode-electrolyte interface on the electrode surface. In addition, the electrolyte can be fully in contact with the electrode material to form a uniform interface layer, reduce the stress and uneven electric field distribution at the interface, thereby reducing the interface resistance and improving the cycle stability and service life of the battery.

[0058] It should be noted that the equivalent diameter of a hole refers to the diameter of an ideal circular hole with the same volume or specific surface area as the hole. For example, if the volume of an irregularly shaped hole is equal to the volume of an ideal circular hole with a diameter of d, then d can be regarded as the equivalent volume diameter of the irregular hole. The equivalent diameter of the hole can be detected using methods and instruments known in the art. For example, the electrochemical device can be disassembled to obtain the positive electrode plate, which can then be further disassembled to obtain conductive carbon black. The surface of the conductive carbon black can be imaged using a microscope such as SEM or TEM. Professional image processing software, such as ImageJ, is used to import the collected image into the software, and the software's measurement tools are used to measure the size of the hole in the two-dimensional image, such as area, circumference and other parameters, and then the equivalent diameter of the hole is calculated according to the formula.

[0059] In some embodiments, the equivalent diameter of the pore is A (nm), and the pore volume of the pore is B (cm 3 / g), the conductive carbon black satisfies: 100≤A / B≤300. For example, A / B can be 100, 120, 150, 180, 200, 220, 250, 280, 300, or any range thereof.

[0060] Optional, 100≤A / B≤290, 100≤A / B≤280, 100≤A / B≤270, 100≤A / B≤260, 100≤A / B≤250, 100≤A / B≤240, 100≤A / B≤230, 100≤A / B≤220, 100≤A / B≤210, 100≤A / B≤200.

[0061] According to the above embodiment, the conductive carbon black satisfies: 100≤A / B≤300, which enables the equivalent diameter of the pores and the pore volume to cooperate with each other, ensuring that the ions have a large enough channel to pass smoothly, and providing sufficient pore volume to store and buffer the ions. In lithium-ion batteries, lithium ions can be quickly and stably transferred between the electrode and the electrolyte during the charge and discharge process, improving the battery's cycle performance and rate performance. At the same time, it helps to optimize the distribution of reaction sites on the electrode surface. Increasing the specific surface area of ​​the electrode-electrolyte interface makes the electrode reaction more complete and accelerates the electrode reaction kinetics, thereby improving the overall performance of the battery, and improving the battery's charge and discharge speed and energy conversion efficiency.

[0062] In some embodiments, the conductive carbon black satisfies at least one of the following: (1) the oil absorption value of the conductive carbon black is 300 mL / 100 g to 450 mL / 100 g; (2) the ID / IG of the conductive carbon black is 0.8 to 1.3; (3) the thermal conductivity of the conductive carbon black is 0.1 W / (m·K) to 0.5 W / (m·K); (4) the conductive carbon black includes a plurality of carbon black units stacked to form a dendritic structure.

[0063] For example, the oil absorption value of the conductive carbon black can be 300mL / 100g, 310mL / 100g, 320mL / 100g, 330mL / 100g, 340mL / 100g, 350mL / 100g, 360mL / 100g, 370mL / 100g, 380mL / 100g, 390mL / 100g, 400mL / 100g, 410mL / 100g, 420mL / 100g, 430mL / 100g, 440mL / 100g, 450mL / 100g, or a range consisting of any of the above values.

[0064] The ID / IG of the conductive carbon black may be 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or a range consisting of any of the above values.

[0065] The thermal conductivity of conductive carbon black can be 0.1W / (m·K), 0.15W / (m·K), 0.2W / (m·K), 0.25W / (m·K), 0.3W / (m·K), 0.35W / (m·K), 0.4W / (m·K), 0.45W / (m·K), 0.5W / (m·K), or a range consisting of any of the above values.

[0066] Optionally, the oil absorption value of the conductive carbon black can be 310mL / 100g~450mL / 100g, 320mL / 100g~450mL / 100g, 330mL / 100g~450mL / 100g, 340mL / 100g~450mL / 100g, 350mL / 100g~450mL / 100g, 350mL / 100g~440mL / 100g, 350mL / 100g~430mL / 100g, 350mL / 100g~420mL / 100g, 350mL / 100g~410mL / 100g, 350mL / 100g~400mL / 100g.

[0067] Optionally, the ID / IG of the conductive carbon black may be 0.85-1.3, 0.9-1.3, 0.95-1.3, 1.0-1.3, 1.0-1.25, or 1.0-1.2.

[0068] Optionally, the thermal conductivity of the conductive carbon black may be 0.11W / (m·K) to 0.5W / (m·K), 0.12W / (m·K) to 0.5W / (m·K), 0.13W / (m·K) to 0.5W / (m·K), 0.14W / (m·K) to 0.5W / (m·K), 0.15W / (m·K) to 0.5W / (m·K), 0.16W / (m·K) to 0.5W / (m·K), 0.17W / (m·K) to 0.5W / (m·K), 0.18W / (m·K) to 0.5W / (m·K), 0.19W / (m·K) to 0.5W / (m·K) , 0.2W / (m·K)~0.5W / (m·K).

[0069] According to the above embodiment, the oil absorption value of the conductive carbon black is 300mL / 100g~450mL / 100g. The electrolyte is adsorbed on the surface and pores of the conductive carbon black, making the contact between the conductive carbon black closer and the transmission of electrons between particles easier, thereby reducing the overall resistivity of the material and improving the conductivity efficiency. It is helpful to improve the rate performance and cycle stability of the battery, reduce the internal resistance of the battery, and increase the energy density and power density of the battery. If the oil absorption value of the conductive carbon black is too high, it will make it difficult to disperse the conductive carbon black, and then it will be easy to agglomerate in the electrode, deteriorate the conductive network, and reduce the rate performance and cycle performance.

[0070] When the ID / IG of conductive carbon black is 0.8-1.3, there are appropriate defects and disordered structures in the conductive carbon black. These defects can serve as electron capture and release sites, which helps the transmission of electrons between carbon black particles and makes it easier for electrons to jump in the carbon black network, thereby improving the overall conductivity of the material and reducing resistivity. When ID / IG is too small, the surface defects of conductive carbon black are few and it is easy to agglomerate; when ID / IG is too large, the conductive carbon black has poor conductivity.

[0071] When the thermal conductivity of conductive carbon black is 0.1W / (m·K)~0.5W / (m·K), it can help build a heat conduction network inside the battery, so that the heat can be evenly distributed and dissipated in time, avoiding local overheating that leads to decreased battery performance, capacity decay and increased side reactions, thereby improving the decline of battery performance, reducing polarization during charging and discharging, and improving rate performance.

[0072] When the conductive carbon black includes the plurality of carbon black units stacked to form a dendritic structure, the dendritic structure can effectively increase the contact points and contact area between the conductive carbon black and the surrounding materials. The numerous branches are intertwined with each other, and a denser, more complex and more efficient conductive network can be constructed in the matrix material. Electrons can be quickly transmitted along these dendritic structures, so that the conductivity of the material is significantly improved. At the same time, the good combination between the dendritic structure and the matrix can form a stronger interface layer inside the material. This interface layer can effectively transfer stress, coordinate the deformation between the matrix and the carbon black, and improve the overall mechanical properties of the material. At the same time, it also helps to enhance the stability of the material under different environmental conditions and reduce performance degradation caused by problems such as interface debonding.

[0073] It should be noted that the oil absorption value, ID / IG, thermal conductivity and dendritic structure of conductive carbon black can be detected using methods and instruments known in the art. For example, the electrochemical device can be disassembled to obtain the positive electrode plate and then further disassembled to obtain the conductive carbon black, and then the DBP purified by vacuum distillation is slowly dripped into the carbon black sample using an acid burette, and the DBP is continuously ground to fill the carbon black pores and adsorb on the surface until a uniform paste without free-flowing liquid and capable of maintaining its shape is formed, and the oil absorption value of the conductive carbon black is calculated based on the consumed DBP volume and the mass of the conductive carbon black in combination with the formula. The Raman spectrum of the conductive carbon black is measured using a Raman spectrometer, and the Raman spectrum data is analyzed using software. The peak fitting function of the software is used to fit the D peak and the G peak to determine their accurate peak position and peak intensity, and further calculate the ID / IG. Using the heat flow meter method, the conductive carbon black is first made into a round or square piece of a specific specification, then the heat flow meter device is checked and calibrated, and then the sample is installed, the heating source power is set to form a temperature difference, and after the temperature stabilizes, the relevant data is recorded and the thermal conductivity of the conductive carbon black is calculated. The dendritic structure of the conductive carbon black can be observed through the microscopic images taken by TEM.

[0074] Positive electrode

[0075] The embodiment of the present application provides a positive electrode sheet, which includes a binder, a positive electrode active material and the above-mentioned conductive carbon black. The positive electrode sheet has good liquid retention performance and a conductive network, which can further improve the electrochemical performance of the electrochemical device.

[0076] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) the equivalent diameter of the hole is A (nm), the Dv50 of the positive electrode active material is E (μm), and the positive electrode sheet satisfies: 0.5≤A / E≤8; (2) the bulk density of the conductive carbon black is F (g / cm 3 ), the tap density of the positive electrode active material is G (g / cm 3 ), the compaction density of the positive electrode is H (g / cm 3 ), the positive electrode sheet satisfies: 3.5≤HF×G≤4.0; (3) the liquid retention rate of the positive electrode sheet is 10% to 26%.

[0077] For example, A / E can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range consisting of any of the above values.

[0078] HF×G may be 3.5, 3.55, 3.6, 3.65, 3.7, 3.75, 3.8, 3.85, 3.9, 3.95, 4.0, or a range consisting of any of the above values.

[0079] The liquid retention rate of the positive electrode sheet is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, or a range consisting of any of the above values.

[0080] Optional, 1≤A / E≤8, 1≤A / E≤7, 1≤A / E≤6, 1≤A / E≤5, 1≤A / E≤4, 1≤A / E≤3, 1≤A / E≤2.

[0081] Optionally, 3.55≤HF×G≤4.0, 3.6≤HF×G≤4.0, 3.6≤HF×G≤3.95, 3.6≤HF×G≤3.9, 3.6≤HF×G≤3.85, 3.6≤HF×G≤3.8.

[0082] According to the embodiment of the present application, the positive electrode sheet satisfies: 0.5≤A / E≤8, and a more efficient electron transmission channel can be constructed. The conductive carbon black pores provide a fast transmission path for electrons, and the adaptation with the positive electrode active material Dv50 improves the contact effect between the positive electrode active material and the carbon black, making the transfer of electrons between the active material and the conductive carbon black smoother, reducing the charge transfer resistance, and thus improving the charge and discharge efficiency. It further helps the diffusion of ions in the electrode material, making the transmission channel of ions inside the electrode smoother, shortening the ion diffusion path, accelerating the insertion and extraction speed of ions during the charge and discharge process, and further improving the charge and discharge efficiency of the battery. When A / E is too large, the uniformity of the electrolyte coating around the active material will be reduced, affecting the cycle stability and rate performance of the battery; when A / E is too small, the continuity of the electrolyte coating around the active material is poor, thereby affecting the rate performance and cycle stability of the battery. In addition, the reduction of the active material Dv50 is also conducive to the improvement of the rate performance, but it will reduce the cycle stability of the battery at 45°C.

[0083] When the positive electrode plate meets the condition of 3.5≤HF×G≤4.0, a conductive network can be effectively constructed to ensure that the active material can fully play its role, thereby improving the energy density of the battery. At the same time, it is beneficial for the electrolyte to fully infiltrate the plate, providing more transmission channels for lithium ions; shortening the diffusion distance of lithium ions inside the active material and between particles, allowing lithium ions to quickly migrate between the electrode and the electrolyte, improving the battery's rate performance and cycle stability.

[0084] When the liquid retention rate of the positive electrode sheet is 10% to 26%, the interface between the positive electrode sheet and the electrolyte forms good infiltration, reducing the interface resistance. This helps to improve the kinetics of the electrode reaction, making the transfer of electrons and ions at the interface easier, reducing the polarization phenomenon of the battery during the charge and discharge process, and improving the charge and discharge efficiency and energy output efficiency of the battery.

[0085] It should be noted that A / E, HF×G and the liquid retention rate of the positive electrode plate can all be detected using methods and instruments known in the art. For example, the electrochemical device can be disassembled to obtain the positive electrode plate, which can then be further disassembled to obtain the conductive carbon black and the positive electrode active material, and the Dv50 of the positive electrode active material can be measured using a laser particle size analyzer to further obtain A / E. The loose density of the conductive carbon black, the tap density of the positive electrode active material and the compacted density of the positive electrode plate are measured respectively to obtain HF×G. The dried electrode plate is immersed in a sufficient amount of electrolyte of the same type, and the excess electrolyte is taken out after soaking, and the surface electrolyte is gently absorbed with a quantitative filter paper, and then the mass of the electrode plate at this time is weighed. Then weigh the mass of the electrolyte after the electrode plate is soaked, and then the electrode plate with the surface electrolyte absorbed is placed in the electrode plate to obtain the mass of the residual electrolyte in the electrode plate and the liquid retention rate of the positive electrode plate.

[0086] Electrochemical Devices

[0087] The embodiment of the present application provides an electrochemical device, which includes the above-mentioned positive electrode sheet, negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrochemical device has good low temperature performance and high temperature performance.

[0088] In some embodiments, the isolation film includes an organic coating, the organic coating includes hollow microspheres, and the hollow microspheres have a shell layer.

[0089] According to the above embodiment, the hollow microspheres can increase the uniformity of the thickness and porosity of the separator, so that the separator has a better effect of isolating the ions and electrons between the positive and negative electrodes, effectively preventing the short circuit between the positive and negative electrodes inside the battery, and improving the safety and stability of the battery. In addition, the shell of the hollow microspheres can play a certain role in screening and guiding the transmission of ions, allowing beneficial ions such as lithium ions to pass through, while blocking other impurity ions that may cause side reactions, which helps to improve the charge and discharge efficiency and cycle performance of the battery.

[0090] In some embodiments, the electrochemical device satisfies at least one of the following: (1) the thickness of the shell layer is 0.07 μm to 0.3 μm; (2) the isolation membrane may also include a base membrane, the particle size of the hollow microspheres is J (μm), the porosity of the base membrane is K (%), and the electrochemical device satisfies: 0.01≤J / K≤0.03.

[0091] For example, the thickness of the shell layer may be 0.07 μm, 0.1 μm, 0.12 μm, 0.15 μm, 0.18 μm, 0.2 μm, 0.22 μm, 0.25 μm, 0.28 μm, 0.3 μm, or a range consisting of any of the above values.

[0092] J / K may be 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, 0.03, or a range consisting of any of the above values.

[0093] According to the above embodiment, when the thickness of the shell layer is 0.07 μm to 0.3 μm, it is helpful to regulate the interface interaction between the hollow microspheres and the surrounding materials (such as electrolyte, electrode, etc.), making the ion exchange and electron transfer at the interface smoother, reducing the interface resistance and improving the overall performance of the battery.

[0094] When the electrochemical device satisfies: 0.01≤J / K≤0.03, it can provide a smooth transmission channel for lithium ions, etc., improve the ion conduction efficiency, and thus improve the battery's charge and discharge performance and energy density.

[0095] It should be noted that the isolation membrane can be obtained by disassembling the electrochemical device, and then further disassembled to obtain the base membrane and hollow microspheres. The X-CT method is used to perform multi-angle X-ray scanning on the hollow microspheres, and the three-dimensional structure of the sample is reconstructed using computer tomography technology. For hollow microspheres, the internal structure information can be intuitively obtained to obtain the thickness and particle size of the shell of the hollow microspheres. The gas adsorption method is used to perform vacuum degassing at a certain temperature to remove impurities and gases adsorbed on the surface. Then the base membrane is placed in the sample tube of the gas adsorption instrument, the instrument is cooled to about liquid nitrogen temperature (77K), nitrogen at different pressures is introduced, and the adsorption amount of nitrogen is measured. Through the analysis of the adsorption isotherm, the specific surface area of ​​the sample is calculated using methods such as the BET equation, and the porosity is calculated in combination with the relevant model.

[0096] In some embodiments, the electrochemical device further comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet and the negative electrode sheet are separated by a separator disposed therebetween. In some embodiments, the positive electrode sheet comprises a positive current collector and a positive electrode active material layer disposed on the positive current collector, the positive electrode active material layer may include a positive electrode active material, the negative electrode sheet comprises a negative current collector and a negative electrode active material layer disposed on the negative current collector, the negative electrode active material layer may include a negative electrode active material.

[0097] In some embodiments, the negative electrode plate may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may be disposed on one side or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a partial area of ​​the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that these are exemplary only and other suitable thicknesses may be used.

[0098] In some embodiments, as described above, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material includes at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon-oxygen compound, a silicon-carbon compound, or a silicon alloy.

[0099] In some embodiments, the negative electrode active material layer may also include a negative electrode conductor and / or a negative electrode binder. The negative electrode conductor may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the negative electrode binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, polyvinyl pyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are only exemplary, and the negative electrode active material layer may be made of any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductor, and the negative electrode binder in the negative electrode active material layer may be (80-99): (0.5-10): (0.5-10), and it should be understood that this is only exemplary and not intended to limit the present application.

[0100] In some embodiments, the positive electrode plate includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer may be located on one side or both sides of the positive current collector. In some embodiments, the positive current collector may be made of aluminum foil, and of course, other positive current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive current collector may be 1 μm to 200 μm. In some embodiments, the positive active material layer may be coated only on a partial area of ​​the positive current collector. In some embodiments, the thickness of the positive active material layer may be 10 μm to 500 μm. It should be understood that these are exemplary only, and other suitable thicknesses may be used.

[0101] In some embodiments, as described above, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the positive electrode active material may be doped and / or coated.

[0102] In some embodiments, the surface of the positive electrode material includes lithium phosphate and / or lithium niobate, the mass ratio of the two is 1:5 to 1:1, and the thickness of the covering layer is 1 μm to 2 μm.

[0103] In some embodiments, the positive electrode active material layer also includes a positive electrode binder and a positive electrode conductor. In some embodiments, the positive electrode binder may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. In some embodiments, the positive electrode conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes or carbon fibers.

[0104] In the present application, the electrochemical device includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalate borate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 5% to 23%, for example, the concentration of the lithium salt in the electrolyte can be 5%, 8%, 12%, 16%, 20%, 23% or a range consisting of any two of the above values. The present application has no particular restrictions on non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, non-aqueous solvents may include but are 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 (MEC). The above-mentioned cyclic carbonate may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is 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, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is 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, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.The present application has no particular limitation on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0105] In some embodiments, the isolation film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the safety of the battery through the shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 3μm to 480μm.

[0106] In some embodiments, the isolation membrane has a porous layer, and the binder of the porous layer is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece. The diaphragm can also include a high melting point crystalline polymer or a high temperature resistant amorphous polymer, and the high temperature resistant resin includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene, polyvinylidene fluoride and cycloolefin copolymers. The high melting point crystalline polymer includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene or polyvinylidene fluoride, and the high temperature resistant amorphous polymer includes cycloolefin copolymers. Based on the mass of the polyolefin porous substrate, the mass percentage Z of the high temperature resistant resin is 2% to 10%. For example, the mass percentage Z of the high temperature resistant resin is 2%, 3%, 5%, 7%, 8%, 10% or a range consisting of any two of these values. When the above-mentioned type of high temperature resistant resin is added to the polyolefin porous substrate and the mass percentage of the high temperature resistant resin is controlled within the above range, it is beneficial to increase the melting point of the diaphragm, improve the strength and high temperature performance of the electrochemical device.

[0107] In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto.

[0108] In some embodiments of the present application, taking lithium-ion batteries as an example, the positive electrode sheet, the isolation membrane, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, and then placed in a shell such as an aluminum-plastic film for packaging, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0109] Preparation method of conductive carbon black

[0110] The raw materials are placed in a reactor to undergo a cracking reaction at a high temperature of 1000°C to 1500°C to generate carbon black particles, which are blown out of the furnace tube, cooled and collected. The present application does not particularly limit the types of the above raw materials, as long as the purpose of the present application can be achieved. For example, the raw materials may include but are not limited to acetylene or tar.

[0111] Electronic Devices

[0112] The present application embodiment also provides an electronic device including the above-mentioned electrochemical device. The electronic device of the present application embodiment is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0113] Test Section

[0114] The test method is as follows:

[0115] 1. Liquid retention rate of positive electrode:

[0116] a. Fully discharge the battery cell to 3.0V, disassemble it to get the positive electrode sheet, soak the positive electrode sheet in DMC at (25±3)℃ for 30min, and then take it out and air it for 3h.

[0117] b. Take the part of the positive electrode plate with coating on both sides A and B in a, weigh it and record it as M1. Soak it completely in the electrolyte at (85±3)℃ for 2h. Then take out the plate and dry it in an environment of (25±3)℃ and humidity of 1% to 10% for 10min, weigh it as M2, and the liquid retention rate of the positive electrode plate is (M2-M1) / M1.

[0118] 2. Cycle capacity retention rate:

[0119] Take the lithium ion battery in the embodiment or comparative example and perform the following tests at -10±2°C, 45±2°C or 60±2°C:

[0120] (1) After standing for 2 hours, discharge at a constant current of 0.5C to 3.0V and then stand for 5 minutes.

[0121] (2) Charge to 4.5V at 1.0C constant current, and charge at 4.5V at constant voltage until the current is less than or equal to 0.05C; let it stand for 5 minutes; then discharge to 3.0V at 0.5C constant current, and record the discharge capacity at this time as C1; let it stand for 5 minutes; repeat the above steps for 49 times; then perform the 50th cycle, charge to 4.5V at 1.0C constant current, and charge at 4.5V at constant voltage until the current is less than or equal to 0.05C; let it stand for 5 minutes; then discharge to 3.0V at 0.2C constant current.

[0122] (3) Then, after the above step (2) is cycled 10 times, the battery is charged to 4.5 V at a constant current of 1.0 C, and then charged to a current of less than or equal to 0.05 C at a constant voltage of 4.5 V; the battery is allowed to stand for 5 min; the battery is then discharged to 3.0 V at a constant current of 0.5 C, and the capacity of the lithium-ion battery at the 501st cycle is recorded as C501; the capacity retention rate of the lithium-ion battery after 500 cycles at 45° C. is C501 / C1.

[0123] 3. Discharge rate:

[0124] Take the lithium ion battery in the embodiment or comparative example and perform the following test at 25±2°C:

[0125] (1) After standing for 2 hours, discharge at a constant current of 0.5C to 3.0V and then stand for 5 minutes.

[0126] (2) Charge to 4.5V at 1.0C constant current, charge at 4.5V at constant voltage until the current is less than or equal to 0.05C; let stand for 5 minutes; then discharge to 3.0V at 0.2C constant current, record the discharge capacity at this time as C0; let stand for 5 minutes; then charge to 4.5V at 1.0C constant current, charge at 4.5V at constant voltage until the current is less than or equal to 0.05C; let stand for 5 minutes; then discharge to 3.0V at 2C constant current, record the discharge capacity at this time as C1, then the 2C discharge rate is C1 / C0, and the test methods for 3C discharge rate and 4C discharge rate are similar.

[0127] 4. Bulk density of conductive carbon black:

[0128] a. Take 5g to 7g of conductive carbon material and dry it in an oven at 105±2℃ for 1 hour, and cool it to (25±3)℃ in a dryer.

[0129] b. Place the dried carbon powder in a into a vibrator, the model of which may be VTD-100, and record its weight as M (g). Set the vibration frequency of the vibrator to 250 times / min. After vibrating 3 times, record its volume as V (cm3). The bulk density of the first carbon material (g / cm3) = M / V.

[0130] 5. Pore volume & equivalent diameter of conductive carbon black:

[0131] a. Weigh 0.2 g of conductive carbon black and record the mass (m).

[0132] b. Place the sample in a sample container and dry it in an oven at 105±2℃ for 2 hours to remove surface moisture and adsorbed gas. After drying, cool the sample to room temperature.

[0133] c. Transfer the dried sample to the sample tube of the surface area and porosity analyzer (model: ASAP 2460 Version 3.01), ensuring that the sample is evenly distributed. The sample tube is sealed and connected to the test system of the analyzer.

[0134] d. Evacuate the sample tube and degas it, usually at around 100°C for 1-2 hours, to further remove adsorbed gas and moisture on the sample surface.

[0135] e. Cool the sample tube to liquid nitrogen temperature (about -196°C), introduce a certain pressure of nitrogen into the sample tube, and measure the adsorption amount of nitrogen under different pressures.

[0136] f. Usually, multi-point measurements are performed under different relative pressures (p / p0), where (p) is the pressure of nitrogen, (p0) is the saturated vapor pressure of nitrogen, and the p / p0 selection range is 0.05 to 0.30, such as 0.05, 0.10, 0.20, and 0.30.

[0137] g. After the measurement, in the report output by the instrument, select the pore volume & equivalent diameter of the conductive carbon black under the BJH algorithm (Barrett, Joyner, and Halenda Algorithm).

[0138] 6. Oil absorption value of conductive carbon black: tested by paraffin oil + torque method.

[0139] Use the DABS-H oil absorption meter. Add carbon powder into the mixing tank of the oil absorption meter, and use a constant dripper to add paraffin oil to the sample at a rate of 4ml / min. As the oil absorption value of the sample increases, the mixture changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continues to increase. The viscosity is transmitted to the torque sensing system of the oil absorption meter. When the viscosity of the mixture reaches the predetermined torque value, the oil absorption meter and the burette are automatically closed at the same time. Read the volume of the added oil directly from the reading burette, and select the volume of oil absorbed per unit mass of the sample at 70% of the predetermined torque as the oil absorption value of the sample.

[0140] 7. ID / IG of conductive carbon black:

[0141] The Raman spectrum of carbon black particles was tested using a laser microscope confocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instrument Division). The peak intensity of carbon black particles at 1350cm-1 is ID1, and the peak intensity at 1580cm-1 is IG1. The ID1 / IG1 value of carbon black particles is obtained by the following method: the carbon black particles are placed on the Raman test sample table, the Raman spectrum of the carbon black particles is tested, and the ID1 / IG1 value is obtained. The test is repeated 12 times, and the average value is the ID / IG value of the carbon black particles.

[0142] 8. Thermal conductivity of conductive carbon black: Use Hot Disk TPS2500S tester and heat flow method for testing.

[0143] a. Place the sample between the hot plate (heat source) and the temperature sensor. Make sure the sample surface is flat and the thickness is uniform. The conductive carbon black can be compacted into a block in the form of powder.

[0144] b. Test parameters: test time: 20s, heating power: 3W, sample thickness: (2±0.5)mm, temperature range: (25±3)℃.

[0145] c. After the test is completed, the thermal conductivity of the conductive carbon black can be directly read in the instrument. Measure three times and take the average value as the final result.

[0146] Example

[0147] The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0148] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

[0149] Example 1-1

[0150] The natural gas is placed in a reaction furnace to undergo a cracking reaction at a high temperature of 1000°C to 1500°C to generate carbon black particles, which are blown out of the furnace tube, cold pressed for 5 minutes to cool to 20°C and collected. The parameters of the conductive carbon black are shown in Table 1.

[0151] Positive electrode: lithium cobalt oxide, conductive graphite and polyvinylidene fluoride are mixed in a weight ratio of 88:6:6 and added into N-methylpyrrolidone, and stirred into a uniform slurry. The slurry is stirred, coated, dried, rolled and spot welded to obtain the positive electrode of the battery.

[0152] Electrolyte: In a glove box filled with argon, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a mass ratio of 3:4:3, propyl propionate accounting for 20% of the total mass of the electrolyte was added, a certain amount of lithium hexafluorophosphate was added so that the mass of the lithium hexafluorophosphate based on the total mass of the electrolyte was 8.5% of the mass percentage of the electrolyte, and a certain amount of fluoroethylene carbonate was added so that the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte was 2.5%.

[0153] Isolation membrane: The first filler particles, the second microsphere filler, and the polyacrylic acid binder are fully dispersed in deionized water at a solid content mass ratio of 91:5:4 to obtain a porous coating slurry; the porous coating slurry is evenly coated on both surfaces of a polyethylene porous substrate with a thickness of 5μm, and then dried in an oven to obtain a diaphragm. The thickness of the porous coating is 2μm, and the thickness of the diaphragm is 9μm. The first filler particles are boehmite with an average particle size of 1μm. The second microsphere particles include a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the second microsphere particle cavity, the first shell layer is polystyrene, and the second shell layer is a copolymer of n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particles is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles is 0.75:1.

[0154] Negative electrode: artificial graphite, a negative electrode active material, conductive carbon black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed at a weight ratio of 97:1:1:1, deionized water was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 80wt%. The negative electrode slurry was evenly coated on one side of the negative electrode current collector copper foil, and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer with a thickness of 90μm on one side, and the above steps were repeated on the other side of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides, and then after cold pressing, cutting, and slitting, a negative electrode sheet with a specification of 476mm×93.5mm was obtained, and the surface resistance of the negative electrode sheet was tested to be 0.002mΩ / cm 2 .

[0155] Preparation of lithium-ion batteries: stack the positive electrode sheet lithium iron phosphate, the isolation membrane, and the negative electrode sheet silicon carbon negative electrode in order, so that the isolation membrane is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and wind them to obtain an electrode assembly. After welding the pole ears, place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80°C, inject the above-mentioned electrolyte, and undergo vacuum packaging, standing, formation, shaping, capacity testing and other processes to obtain a lithium-ion battery.

[0156] Examples 1-2 to 1-20, Comparative Examples 1-1 to 1-6

[0157] The preparation of the lithium-ion battery is substantially the same as that of Example 1-1, the only difference being the bulk density of the conductive carbon black, the pore volume, the equivalent diameter of the pores, A / B and the oil absorption value of the conductive carbon black. The specific parameters are shown in Table 1.

[0158] The positive electrode was subjected to a liquid retention rate test, and the lithium-ion battery was subjected to a 45°C cycle capacity retention rate test and a 2C discharge rate test. The results are shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162] According to Table 1, compared with the comparative example, the liquid retention rate of the positive electrode sheet in each embodiment is controlled within the scope of the present application, and the 45°C cycle capacity retention rate and 2C discharge rate of the lithium-ion battery are significantly improved. When the conductive carbon black of the present application is used, and the bulk density and pore volume of the conductive carbon black meet the scope of the present application, the two work together, and the lithium-ion battery has good cycle performance and charge and discharge performance.

[0163] According to Examples 1-1 to 1-13 and Comparative Examples 1-1 to 1-6, the bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 , the pore volume is 0.05cm 3 / g~0.5cm 3 / g, the cycle performance and charge and discharge performance of lithium-ion batteries are better.

[0164] On this basis, according to Examples 1-3 to 1-6, and Examples 1-9 to 1-11, the bulk density of the conductive carbon black is 0.06 g / cm 3 ~0.08g / cm 3 , and / or, the pore volume of the pores is 0.15 cm 3 / g~0.3cm3 / g, lithium-ion batteries have better cycle performance and charge and discharge performance.

[0165] According to Examples 1-1 to 1-7, when the oil absorption value of the conductive carbon black is 300 mL / 100 g to 450 mL / 100 g, the lithium-ion battery has good cycle performance and charge-discharge performance.

[0166] On this basis, according to Examples 1-3 to 1-5, it can be seen that when the oil absorption value of the conductive carbon black is 350 mL / 100 g to 400 mL / 100 g, the lithium-ion battery has better cycle performance and charge and discharge performance.

[0167] According to Examples 1-14 to 1-20, when the equivalent diameter of the pores is 10 nm to 45 nm or 100≤A / B≤300, the lithium-ion battery has good cycle performance and charge-discharge performance.

[0168] On this basis, according to Examples 1-16 to 1-17, it can be seen that when the equivalent diameter of the pores is 15 nm to 30 nm or 100≤A / B≤200, the lithium-ion battery has better cycle performance and charge and discharge performance.

[0169] Example 2-1 to Example 2-12

[0170] The preparation of the lithium-ion battery is substantially the same as that of Example 1-1, the only difference being the ID / IG and thermal conductivity of the conductive carbon black. The specific parameters are shown in Table 2.

[0171] The lithium-ion battery was subjected to a 60°C cycle capacity retention test and a 3C discharge rate test. The results are shown in Table 2.

[0172] Table 2

[0173]

[0174] According to Table 2, the ID / IG and thermal conductivity of the conductive carbon black are controlled within the range of the present application, and the lithium-ion battery has good high-temperature cycle performance and charge-discharge performance.

[0175] According to Examples 1-4, 2-1 to 2-5, 2-10 and 2-11, when the ID / IG of the conductive carbon black is 0.8 to 1.3, the lithium-ion battery has good high-temperature cycle performance and charge-discharge performance.

[0176] On this basis, according to Examples 1-4, 2-3 and 2-4, it can be seen that when the ID / IG of the conductive carbon black is 1.0 to 1.2, the lithium-ion battery has better high-temperature cycle performance and charge and discharge performance.

[0177] According to Examples 1-4, 2-6 to 2-9 and 2-12, when the thermal conductivity of the conductive carbon black is 0.1 W / (m·K) to 0.5 W / (m·K), the lithium-ion battery has good high-temperature cycle performance and charge and discharge performance.

[0178] Example 3-1 to Example 3-26

[0179] The preparation of lithium-ion batteries is roughly the same as that of Examples 1-4, with the only differences being the equivalent diameter of the pores, Dv50, A / E, HF×G of the positive electrode active material, thickness of the shell layer, porosity of the base film, and J / K. The difference between Example 3-27 and Example 1-1 is that the diaphragm coating in Example 3-27 does not contain a microsphere structure. The specific parameters are shown in Table 3.

[0180] The lithium-ion battery was subjected to -10°C cycle capacity retention test and 4C discharge rate test. The results are shown in Table 3.

[0181] Table 3

[0182]

[0183]

[0184] According to Table 3, the A / E and HF×G of the positive electrode sheet and the thickness and J / K of the shell layer of the hollow microspheres in the electrochemical device are controlled within the range of the present application, and the lithium-ion battery has good low-temperature cycle performance and charge and discharge performance.

[0185] According to Examples 1-4, 3-1 to 3-8, 3-24 and 3-25, when the positive electrode sheet satisfies: 0.5≤A / E≤8, the lithium-ion battery has good low-temperature cycle performance and charge-discharge performance.

[0186] On this basis, according to Examples 1-4, 3-3, and 3-4, it can be seen that when the positive electrode sheet satisfies: 1≤A / E≤2, the lithium-ion battery has good high-temperature cycle performance and charge and discharge performance.

[0187] According to Examples 1-4 and 3-9 to 3-17, when the positive electrode sheet satisfies: 3.5≤HF×G≤4.0, the lithium-ion battery has good low-temperature cycle performance and charge-discharge performance.

[0188] On this basis, according to Examples 3-11 to 3-13, when the positive electrode sheet satisfies: 3.6≤HF×G≤3.8, the lithium-ion battery has better low-temperature cycle performance and charge and discharge performance.

[0189] According to Examples 1-4, 3-18 to 3-23, 3-26 and 3-27, the isolation membrane includes an organic coating, the organic coating includes hollow microspheres, the hollow microspheres have a shell layer, and when the thickness of the shell layer is 0.07 μm to 0.3 μm, the lithium-ion battery has good low-temperature cycle performance and charge and discharge performance.

[0190] It can be seen from Examples 3-1 to 3-23 that when the electrochemical device satisfies: 0.01≤J / K≤0.03, the lithium-ion battery has good low-temperature cycle performance and charge-discharge performance.

[0191] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A conductive carbon black, characterized in that: The conductive carbon black comprises a plurality of carbon black units and pores between adjacent carbon black units, wherein the carbon black units comprise holes; The bulk density of the conductive carbon black is 0.05 g / cm 3 ~0.1g / cm 3 The pore volume of the hole is 0.05cm 3 / g~0.5cm 3 / g.

2. The conductive carbon black according to claim 1, characterized in that The bulk density of the conductive carbon black is 0.06 g / cm 3 ~0.08g / cm 3 , and / or, the pore volume of the pore is 0.15cm 3 / g~0.3cm 3 / g.

3. The conductive carbon black according to claim 1, characterized in that The equivalent diameter of the hole is 10nm to 45nm.

4. The conductive carbon black according to claim 3, characterized in that The equivalent diameter of the hole is 15nm to 30nm.

5. The conductive carbon black according to claim 1, characterized in that The equivalent diameter of the pore is A (nm), and the pore volume of the pore is B (cm 3 / g), and the conductive carbon black satisfies: 100≤A / B≤300.

6. The conductive carbon black according to claim 5, characterized in that The conductive carbon black satisfies: 100≤A / B≤200.

7. The conductive carbon black according to any one of claims 1 to 6, characterized in that The conductive carbon black satisfies at least one of the following: (1) The oil absorption value of the conductive carbon black is 300 mL / 100 g to 450 mL / 100 g; (2) The ID / IG of the conductive carbon black is 0.8 to 1.3; (3) The thermal conductivity of the conductive carbon black is 0.1W / (m·K) to 0.5W / (m·K); (4) The conductive carbon black includes a plurality of carbon black units stacked to form a dendritic structure.

8. The conductive carbon black according to claim 7, characterized in that The conductive carbon black satisfies at least one of the following: (1) The oil absorption value of the conductive carbon black is 350mL / 100g to 400L / 100g; (2) The ID / IG of the conductive carbon black is 1.0 to 1.2; (3) The thermal conductivity of the conductive carbon black is 0.2 W / (m·K) to 0.5 W / (m·K).

9. A positive electrode sheet, characterized in that: The invention comprises a binder, a positive electrode active material and the conductive carbon black according to any one of claims 1 to 8.

10. The positive electrode sheet according to claim 9, characterized in that: The positive electrode plate satisfies at least one of the following: (1) The equivalent diameter of the pore is A (nm), the Dv50 of the positive electrode active material is E (μm), and the positive electrode sheet satisfies: 0.5≤A / E≤8; (2) The bulk density of the conductive carbon black is F (g / cm 3 ), the tap density of the positive electrode active material is G (g / cm 3 ), the compaction density of the positive electrode sheet is H (g / cm 3 ), the positive electrode sheet satisfies: 3.5≤HF×G≤4.0; (3) The liquid retention rate of the positive electrode sheet is 10% to 26%.

11. The positive electrode sheet according to claim 10, characterized in that: The positive electrode plate satisfies: 1≤A / E≤2, and / or, the positive electrode plate satisfies: 3.6≤HF×G≤3.

8.

12. An electrochemical device, characterized in that: It comprises the positive electrode sheet, the negative electrode sheet and the separator as claimed in any one of claims 9 to 11, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

13. The electrochemical device according to claim 12, characterized in that The isolation film includes an organic coating, the organic coating includes hollow microspheres, and the hollow microspheres have a shell layer.

14. The electrochemical device according to claim 13, characterized in that The electrochemical device satisfies at least one of the following: (1) The thickness of the shell layer is 0.07 μm to 0.3 μm; (2) The isolation membrane further includes a base membrane, the particle size of the hollow microspheres is J (μm), the porosity of the base membrane is K (%), and the electrochemical device satisfies: 0.01≤J / K≤0.

03.

15. An electronic device, characterized in that: An electrochemical device comprising any one of claims 12 to 14.

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