Secondary battery, positive electrode sheet, and preparation method therefor, and electrical apparatus

Abstract

The present application relates to the technical field of batteries, and in particular, to a secondary battery, a positive electrode sheet and a preparation method therefor, and an electrical apparatus. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The positive electrode sheet comprises a positive electrode current collector, and a positive electrode coating provided on at least one surface of the positive electrode current collector. The positive electrode coating comprises an electrically conductive porous material, the electrically conductive porous material having a specific surface area of 1000m2 / g to 40002 / g. By means of incorporating the electrically conductive porous material into the positive electrode coating layer, the specific surface area of the electrically conductive porous material can be from 1000m2 / g to 40002 / g. The addition of said material can reduce the internal resistance of the battery, and improve the power of the battery.

Description

Secondary batteries, positive electrode sheets and their preparation methods, and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202411463128.1, filed on October 18, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery, a positive electrode sheet and its preparation method, and an electrical device. Background Technology

[0004] With the rapid growth of portable electronic devices, electric vehicles, and other technologies, the demand for power batteries is also constantly increasing. Among these, the electrochemical performance of batteries is receiving increasing attention.

[0005] Different applications have different battery power requirements. For example, electric vehicles and power tools require high-power batteries to provide fast response and sufficient power, but battery power drops and becomes insufficient to meet power demands in low-temperature conditions. Summary of the Invention

[0006] The main objective of this application is to provide a secondary battery, a positive electrode sheet, a method for preparing the same, and an electrical device thereof, with the aim of improving the power performance of the secondary battery.

[0007] To achieve the above objectives, this application proposes a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector and a positive electrode coating disposed on at least one surface of the positive current collector. The positive electrode coating comprises a conductive porous material with a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g.

[0008] This application incorporates a conductive porous material into the positive electrode coating. The conductive porous material has a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g, by adding this material, the internal resistance of the battery can be reduced and the battery power can be improved.

[0009] Understandably, during charging, active ions (such as lithium ions) are released from the positive electrode active material and enter the electrolyte, while the conductive porous material in the positive electrode coating adsorbs free anions (such as PF6) from the electrolyte. — Active ions (e.g., lithium ions) extracted from the positive electrode active material and active ions (e.g., lithium ions) in the electrolyte are inserted into the negative electrode material for storage.

[0010] The discharge process is the reverse of the charging process; anions (e.g., PF6) adsorbed in conductive porous materials... — The active ions (such as lithium ions) are desorbed into the electrolyte, and at the same time, some active ions (such as lithium ions) are released from the negative electrode and enter the electrolyte to achieve charge balance. Finally, the other part of the active ions (such as lithium ions) released from the negative electrode return to the positive electrode active material, so that the positive electrode active material is restored to its original state.

[0011] During the charging process described above, the conductive porous material in the positive electrode coating adsorbs free anions (e.g., PF6) from the electrolyte. — Active ions (such as lithium ions) in the electrolyte are inserted into the negative electrode material for storage. This process involves physical adsorption, which is relatively fast and helps to improve the charging speed.

[0012] During the above discharge process, anions (e.g., PF6) adsorbed in the conductive porous material — The ions desorb into the electrolyte, and at the same time, some active ions (such as lithium ions) are removed from the negative electrode and enter the electrolyte to achieve charge balance. This process involves physical desorption, which is relatively fast and helps to improve the discharge speed.

[0013] Compared to the charge-discharge process involving physical adsorption and desorption, which involves the extraction / intercalation of active ions (e.g., lithium ions) within the lattice of the positive electrode active material, the above-mentioned charge-discharge process has a faster reaction rate. In other words, the migration speed of active ions (e.g., lithium ions) is faster in the above process, which helps to improve the power performance of the battery.

[0014] Meanwhile, conductive porous materials have a large specific surface area, which can adsorb more anions, thereby increasing the charge and discharge capacity involving physical adsorption and desorption. In other words, it increases the proportion of the charge and discharge process involving physical adsorption and desorption, further improving the battery power.

[0015] In addition, the aforementioned charge and discharge processes involving physical adsorption and desorption also alleviate the problem of current polarization. It is understandable that the movement of anions between the conductive porous material and the electrolyte is part of the current flow. This part of the current can reduce the current density borne by the positive electrode active material, thereby reducing current polarization and improving the overall power of the battery.

[0016] It is understandable that the charging and discharging process involving physical adsorption and desorption is similar to the process of a capacitor storing and releasing electrical energy. This can be compared to forming a parallel connection between a lithium-ion battery and a capacitor in a circuit structure, thereby improving the overall power of the circuit by using the high-power capacitor section.

[0017] It is understandable that the aforementioned charge-discharge processes involving physical adsorption and desorption have extremely fast reaction rates, corresponding to extremely high power densities. Taking lithium-ion batteries as an example, the energy storage mechanism of conventional lithium-ion battery cathode materials such as lithium iron phosphate, layered transition metal oxides, and lithium-rich manganese-based cathode materials involves the extraction / intercalation of lithium ions within the material lattice, which is an electrochemical reaction. The reaction rate is slow, resulting in high energy density but low power density. In this application, conductive porous materials are mixed into the cathode coating. The adsorption and desorption rates of anions by conductive porous materials are greater than the extraction and intercalation rates of active ions in the cathode active material, which can reduce current polarization, lower internal resistance, and thus improve power.

[0018] Optionally, the mass percentage of the conductive porous material to the total mass of the positive electrode coating is 0.25% to 10%.

[0019] And / or, the conductive porous material includes carbon materials.

[0020] In this application, a mass percentage of conductive porous material relative to the total mass of the positive electrode coating within the aforementioned range can improve the power of the secondary battery. If the amount of conductive porous material is too low, the improvement in battery power is minimal; if the amount of conductive porous material is too high, the energy density of the secondary battery is reduced.

[0021] The conductive porous materials in this application include carbon materials.

[0022] Optionally, the volume average particle size Dv50 of the conductive porous material is from 0.1 μm to 7 μm;

[0023] And / or, the resistivity of the conductive porous material powder is from 0.05 Ωcm to 0.8 Ωcm;

[0024] And / or, the compaction density of the conductive porous material is 0.2 g / cm³. 3 Up to 0.7 g / cm 3 .

[0025] Generally, conductive porous materials have good power performance, but their energy density is lower than that of positive electrode active materials. In this application, the volume average particle size Dv50 of the conductive porous material meets the above-mentioned range, which is beneficial to maintaining the energy density of the secondary battery within a suitable range. That is, while increasing the power of the secondary battery, the energy density of the secondary battery is not significantly reduced. It is understood that if the particle size is too small, it will reduce the compaction density of the positive electrode coating, and if the particle size is too large, it will affect the uniform distribution of the positive electrode active material.

[0026] The resistivity of the conductive porous material powder in this application meets the above-mentioned range, which can reduce the internal resistance of the positive electrode coating and help improve the power of the secondary battery.

[0027] The compaction density of the conductive porous material in this application meets the above-mentioned range, which is beneficial for maintaining the energy density of the secondary battery within a suitable range. It is understood that the mixing of conductive porous material in the positive electrode coating affects the overall compaction density after mixing. If the compaction density of the conductive porous material is too low, it will lead to an excessively low compaction density of the positive electrode coating, reducing the volumetric energy density.

[0028] It is understandable that conductive porous materials distributed in the positive electrode coating, together with other components, form a conductive / liquid-conducting network, which can improve coating resistance and increase the electrochemically active specific surface area of ​​the coating. For example, in one embodiment, the conductive porous material is mixed with conductive agents, binders, surfactants, and positive electrode active materials to form a conductive / liquid-conducting network. During battery charging, electrons travel from the negative electrode to the positive electrode through the external circuit and can be transferred to the conductive porous material for storage through the current collector and conductive agent in the positive electrode sheet. The storage rate is relatively fast, improving the power density of the secondary battery. During discharge, the conductive porous material in the positive electrode coating can also quickly donate electrons, improving the output power of the secondary battery. The liquid-conducting network can improve the wettability of the electrolyte in the positive electrode sheet, providing more pathways for ion transport, increasing the ion migration rate, and thus improving power.

[0029] Optionally, the mass percentage of the conductive porous material in the total mass of the positive electrode coating is 0.25% to 2.5%.

[0030] And / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black.

[0031] In this application, the percentage of the mass of the conductive porous material in the total mass of the positive electrode coating meets the above-mentioned range, which can improve the power of the secondary battery while maintaining a good energy density of the secondary battery.

[0032] In this application, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black. That is, the carbon material can be selected from any one of the above, or it can include multiple of the above.

[0033] Optionally, the positive electrode coating further includes a surfactant;

[0034] And / or, the positive electrode coating further includes a surfactant, wherein the mass percentage of the surfactant is 0.1% to 1% of the total mass of the positive electrode coating;

[0035] And / or, the positive electrode coating further includes a surfactant, the surfactant including at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid;

[0036] And / or, the positive electrode coating further includes a positive electrode active material, wherein the mass percentage of the positive electrode active material is 93% to 98% of the total mass of the positive electrode coating;

[0037] And / or, the positive electrode coating further includes a conductive agent, wherein the mass percentage of the conductive agent is 0.1% to 2% of the total mass of the positive electrode coating;

[0038] And / or, the positive electrode coating further includes a binder, wherein the mass percentage of the binder is 1% to 3% of the total mass of the positive electrode coating;

[0039] And / or, the positive electrode coating further includes a positive electrode active material, the positive electrode active material including at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide;

[0040] And / or, the positive electrode coating further includes a conductive agent, the conductive agent including at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers;

[0041] And / or, the positive electrode coating further includes an adhesive, the adhesive comprising at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0042] The positive electrode coating of this application may include surfactants, which can improve the dispersion and uniform distribution of various components in the positive electrode coating, facilitate the uniform distribution of conductive porous materials in the positive electrode coating, form a conductive / liquid-conducting network, thereby reducing the resistance of the positive electrode coating, increasing the electrochemical active specific surface area, improving the battery charge and discharge rate, and improving the battery power; at the same time, it improves the flexibility of the positive electrode coating, increases the compaction density of the coating, and thus improves the battery capacity.

[0043] In this application, the mass percentage of the surfactant in the total mass of the cathode coating meets the above-mentioned range, which is beneficial to improving the dispersion and uniform distribution of each component in the cathode coating and to the uniform distribution of conductive porous materials in the cathode coating.

[0044] The surfactants in this application include at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid, that is, they may include any one of the above or a combination of multiple of them.

[0045] In this application, the percentage of the mass of the positive electrode active material relative to the total mass of the positive electrode coating meets the above-mentioned range, which can improve the energy density of the secondary battery.

[0046] In this application, the mass percentage of the conductive agent relative to the total mass of the positive electrode coating meets the above-mentioned range, which can reduce the electrode resistance and improve the power of the secondary battery.

[0047] In this application, the mass percentage of the binder to the total mass of the positive electrode coating meets the above-mentioned range, ensuring the stability and integrity of the electrode structure during battery charging and discharging.

[0048] The positive electrode active material in this application includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide. That is, it may include any one of the above or a combination of multiple types.

[0049] The conductive agent in this application includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. That is, it may include any one of the above or a combination of multiple types.

[0050] The adhesive in this application includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. That is, it may include any one of the above or a combination of multiple types.

[0051] Optionally, the electrochemically active specific surface area of ​​the positive electrode coating is 5 m². 2 / g to 12m 2 / g;

[0052] And / or, the resistance of the positive electrode coating is 0.1Ω to 0.2Ω;

[0053] And / or, the specific surface area of ​​the positive electrode coating is 10 m². 2 / g to 200m 2 / g;

[0054] And / or, the compaction density of the positive electrode coating is 2.1 g / cm³. 3 Up to 2.65 g / cm 3 ;

[0055] And / or, the thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

[0056] In this application, the electrochemically active specific surface area of ​​the positive electrode coating meets the aforementioned range. That is, by doping with conductive porous materials, more active sites can be provided, thereby increasing the opportunities for intercalation and deintercalation reactions of active ions in the secondary battery. This helps to improve the battery's charge-discharge efficiency and power density. Secondly, a larger specific surface area helps to improve the wettability of the electrolyte in the electrode, reduce the battery's internal resistance, and thus improve the battery's charge-discharge performance.

[0057] In this application, the resistance of the positive electrode coating meets the above-mentioned range. That is, by doping with conductive porous materials, the resistance of the positive electrode coating can be reduced, which is beneficial to improving the charge and discharge rate.

[0058] In this application, the specific surface area of ​​the positive electrode coating meets the above-mentioned range. That is, doping with conductive porous materials can increase the specific surface area of ​​the coating, improve the wetting performance of the electrolyte, reduce internal resistance, and increase power.

[0059] In this application, the compaction density of the conductive porous material is within the above-mentioned range, which is beneficial to improving the energy density of the secondary battery.

[0060] In this application, the thickness of the positive electrode coating is within the above-mentioned range, which further improves the power of the secondary battery. It is understood that the thickness of the coating will affect the power of the secondary battery, and under certain conditions, reducing the thickness can increase the power.

[0061] Optionally, the volumetric energy density of the secondary battery is between 240Wh / L and 400Wh / L;

[0062] And / or, the gravimetric energy density of the secondary battery is from 120Wh / Kg to 200Wh / Kg.

[0063] In this application, after doping the positive electrode coating with conductive porous material, the volumetric energy density of the secondary battery meets the above-mentioned range.

[0064] In this application, after doping the positive electrode coating with conductive porous material, the mass energy density of the secondary battery meets the above-mentioned range.

[0065] This application also provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode coating disposed on at least one surface of the positive current collector, the positive electrode coating comprising a conductive porous material, the conductive porous material having a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g.

[0066] Optionally, the mass percentage of the conductive porous material in the total mass of the positive electrode coating is 1% to 7.5%.

[0067] And / or, the conductive porous material includes carbon materials;

[0068] And / or, the positive electrode coating may further include a surfactant.

[0069] Optionally, the volume average particle size Dv50 of the conductive porous material is from 0.1 μm to 7 μm;

[0070] And / or, the resistivity of the conductive porous material powder is from 0.05 Ωcm to 0.8 Ωcm;

[0071] And / or, the compaction density of the conductive porous material is 0.2 g / cm³. 3 Up to 0.7 g / cm 3 .

[0072] Optionally, the mass percentage of the conductive porous material to the total mass of the positive electrode coating is 2.5% to 5%.

[0073] And / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black;

[0074] And / or, the mass percentage of the surfactant in the total mass of the positive electrode coating is 0.1% to 1%;

[0075] And / or, the surfactant includes at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid.

[0076] Optionally, at least one of the following conditions must be met:

[0077] Condition A: The positive electrode coating further includes a positive electrode active material, and the mass percentage of the positive electrode active material in the total mass of the positive electrode coating is 93% to 98%.

[0078] Condition B: The positive electrode coating further includes a conductive agent, and the mass percentage of the conductive agent in the total mass of the positive electrode coating is 0.1% to 2%.

[0079] Condition C: The positive electrode coating further includes a binder, and the mass percentage of the binder to the total mass of the positive electrode coating is 1% to 3%.

[0080] Condition D: The positive electrode coating further includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide;

[0081] Condition E: The positive electrode coating further includes a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] Condition F: The positive electrode coating further includes a binder, which includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0083] Condition G: The electrochemically active specific surface area of ​​the positive electrode coating is 5 m². 2 / g to 12m 2 / g;

[0084] Condition H: The resistance of the positive electrode coating is 0.1Ω to 0.2Ω;

[0085] Condition I: The specific surface area of ​​the positive electrode coating is 10 m². 2 / g to 200m 2 / g;

[0086] Condition J: The compaction density of the positive electrode coating is 2.1 g / cm³. 3 Up to 2.65 g / cm 3 ;

[0087] Condition K: The thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

[0088] This application also provides a method for preparing a positive electrode sheet, comprising:

[0089] The positive electrode active material, conductive agent, binder, conductive porous material and solvent are mixed and stirred to obtain a positive electrode slurry;

[0090] The positive electrode slurry is coated onto the current collector to obtain the positive electrode sheet. The specific surface area of ​​the conductive porous material is 1000 m². 2 / g to 4000m 2 / g.

[0091] That is, by preparing the basic raw materials for the positive electrode slurry and mixing conductive porous materials into the raw materials, the positive electrode slurry can be obtained. By coating the slurry onto the current collector, a positive electrode coating incorporating conductive porous materials can be obtained.

[0092] Optionally, the step of mixing the positive electrode active material, conductive agent, binder, conductive porous material and solvent, and stirring to obtain the positive electrode slurry includes:

[0093] A surfactant, a conductive agent, a conductive porous material, and a binder are added to a solvent and stirred to obtain a mixture.

[0094] Add the positive electrode active material and solvent to the mixture, stir, and obtain the positive electrode slurry.

[0095] It is understandable that surfactants can be added to the positive electrode slurry to improve the dispersibility and uniformity of the components. It is also understandable that the materials can be added and stirred in the above mixing steps according to their sequential order, or not in the above order.

[0096] Optionally, based on 100 parts by weight, the positive electrode active material comprises 90 to 100 parts, the conductive agent comprises 0 to 3 parts, the binder comprises 0 to 3 parts, the surfactant comprises 0 to 3 parts, and the conductive porous material comprises 0 to 7 parts.

[0097] During the preparation of the slurry, the materials are mixed according to the above proportion range and a coating is prepared. The comprehensive properties of the coating, such as conductivity, specific surface area, and compaction density, are improved.

[0098] This application also provides an electrical device, which includes a secondary battery as described above.

[0099] This application incorporates a conductive porous material into the positive electrode coating. The conductive porous material has a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g, by adding this material, the internal resistance of the battery can be reduced and the battery power improved. It is understood that during charging, active ions (such as lithium ions) are released from the positive electrode active material into the electrolyte, while the conductive porous material in the positive electrode coating adsorbs free anions (such as PF6) in the electrolyte. — Active ions (e.g., lithium ions) released from the positive electrode active material and active ions (e.g., lithium ions) in the electrolyte are inserted into the negative electrode material for storage. The discharge process is the reverse of the charging process; anions (e.g., PF6) adsorbed in the conductive porous material... — The positive electrode absorbs desorbed ions into the electrolyte. Simultaneously, some active ions (e.g., lithium ions) are released from the negative electrode and enter the electrolyte to achieve charge balance. Finally, the remaining active ions (e.g., lithium ions) released from the negative electrode return to the positive electrode active material, restoring it to its original state. During this charging process, the conductive porous material in the positive electrode coating adsorbs free anions (e.g., PF6) from the electrolyte. — In this process, active ions (such as lithium ions) in the electrolyte are inserted into the negative electrode material for storage. This process involves physical adsorption, which is relatively fast and helps to improve the charging speed. During the discharge process described above, anions (such as PF6) adsorbed in the conductive porous material... —During the desorption process, some active ions (e.g., lithium ions) are released from the negative electrode and enter the electrolyte to achieve charge balance. This process involves physical desorption, which is relatively fast and helps to improve the discharge rate. Compared with the charge-discharge process involving physical adsorption and desorption, which involves the extraction / intercalation of active ions (e.g., lithium ions) within the crystal lattice of the positive electrode active material, the above-mentioned charge-discharge process with physical adsorption and desorption has a faster reaction rate. In other words, the migration speed of active ions (e.g., lithium ions) is faster in the above process, which helps to improve the power performance of the battery. At the same time, conductive porous materials have a large specific surface area, which can adsorb more anions, thereby increasing the capacity of the charge-discharge process involving physical adsorption and desorption. That is, the proportion of the charge-discharge process involving physical adsorption and desorption in the entire process is increased, further improving the power of the battery. In addition, the aforementioned charge and discharge processes involving physical adsorption and desorption also alleviate the problem of current polarization. It is understandable that the movement of anions between the conductive porous material and the electrolyte is part of the current flow. This part of the current can reduce the current density borne by the positive electrode active material, thereby reducing current polarization and improving the overall power of the battery. Attached Figure Description

[0100] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0101] Figure 1 is a scanning electron microscope image of the ion-polished cross-sectional morphology of the positive electrode coating of Example 1 of this application;

[0102] Figure 2 is a magnified view of a portion of Figure 1;

[0103] Figure 3 is a schematic diagram of the principle structure of the secondary battery of this application;

[0104] Figure 4 is a schematic diagram of the structure of a single battery cell according to an embodiment of this application;

[0105] Figure 5 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 4;

[0106] Figure 6 is a schematic diagram of a battery module according to an embodiment of this application;

[0107] Figure 7 is a schematic diagram of a battery pack according to an embodiment of this application;

[0108] Figure 8 is an exploded view of the battery pack of one embodiment of this application shown in Figure 7;

[0109] Figure 9 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0110] Explanation of icon numbers:

[0111] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0112] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0113] The secondary battery, positive electrode sheet, preparation method thereof, and electrical device of this application are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0114] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0115] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0116] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0117] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0118] With the rapid growth of portable electronic devices, electric vehicles, and other technologies, the demand for power batteries is also constantly increasing. Different applications have different power requirements for batteries. For example, electric vehicles and power tools require high-power batteries to provide fast response and sufficient power, but battery power drops significantly in low-temperature conditions, making it difficult to meet power demands.

[0119] Understandably, a lower State of Charge (SOC) results in higher cell impedance and correspondingly lower power. Insufficient power can lead to insufficient cell voltage during high-current discharge, causing it to drop below the operating voltage of the device. To prevent this, the Battery Management System (BMS) limits the minimum usable SOC. Below this SOC, the unused capacity is wasted. For example, lithium-ion batteries used in PHEVs (Plug-in Hybrid Electric Vehicles) exhibit different power characteristics at different temperatures and SOCs. At low temperatures, the chemical reaction rate slows down, reducing the battery's charging and discharging power. A low SOC cannot provide sufficient power to meet the PHEV's power requirements, resulting in wasted battery capacity. In other words, due to insufficient power at low SOC, the battery management system may set a lower limit, stopping the battery from discharging before reaching this limit to prevent insufficient energy supply when high power output is needed. This results in some battery capacity remaining unused, reducing the battery's actual efficiency.

[0120] Understandably, a low State of Charge (SOC) power output cannot provide electrical energy at a sufficient rate, which may limit device performance or cause the device to malfunction. This phenomenon in batteries is manifested by factors such as slower migration rates of active ions in the electrodes and electrolyte, and slower migration rates of electrons from the materials to the current collector, leading to a decrease in power output.

[0121] To improve battery power, this application proposes a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector and a positive electrode coating disposed on at least one surface of the positive current collector. The positive electrode coating comprises a conductive porous material with a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g.

[0122] This application incorporates a conductive porous material into the positive electrode coating. The conductive porous material has a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g, by adding this material, the internal resistance of the battery can be reduced and the battery power can be improved.

[0123] Understandably, during charging, active ions (such as lithium ions) are released from the positive electrode active material and enter the electrolyte, while the conductive porous material in the positive electrode coating adsorbs free anions (such as PF6) from the electrolyte. — Active ions (e.g., lithium ions) extracted from the positive electrode active material and active ions (e.g., lithium ions) in the electrolyte are inserted into the negative electrode material for storage.

[0124] The discharge process is the reverse of the charging process; anions (e.g., PF6) adsorbed in conductive porous materials... — The active ions (such as lithium ions) are desorbed into the electrolyte, and at the same time, some active ions (such as lithium ions) are released from the negative electrode and enter the electrolyte to achieve charge balance. Finally, the other part of the active ions (such as lithium ions) released from the negative electrode return to the positive electrode active material, so that the positive electrode active material is restored to its original state.

[0125] During the charging process described above, the conductive porous material in the positive electrode coating adsorbs free anions (e.g., PF6) from the electrolyte. — Active ions (such as lithium ions) in the electrolyte are inserted into the negative electrode material for storage. This process involves physical adsorption, which is relatively fast and helps to improve the charging speed.

[0126] During the above discharge process, anions (e.g., PF6) adsorbed in the conductive porous material —The ions desorb into the electrolyte, and at the same time, some active ions (such as lithium ions) are removed from the negative electrode and enter the electrolyte to achieve charge balance. This process involves physical desorption, which is relatively fast and helps to improve the discharge speed.

[0127] Compared to the charge-discharge process involving physical adsorption and desorption, which involves the extraction / intercalation of active ions (e.g., lithium ions) within the lattice of the positive electrode active material, the above-mentioned charge-discharge process has a faster reaction rate. In other words, the migration speed of active ions (e.g., lithium ions) is faster in the above process, which helps to improve the power performance of the battery.

[0128] Meanwhile, conductive porous materials have a large specific surface area, which can adsorb more anions, thereby increasing the charge and discharge capacity involving physical adsorption and desorption. In other words, it increases the proportion of the charge and discharge process involving physical adsorption and desorption, further improving the battery power.

[0129] In addition, the aforementioned charge and discharge processes involving physical adsorption and desorption also alleviate the problem of current polarization. It is understandable that the movement of anions between the conductive porous material and the electrolyte is part of the current flow. This part of the current can reduce the current density borne by the positive electrode active material, thereby reducing current polarization and improving the overall power of the battery.

[0130] It is understandable that the charging and discharging process involving physical adsorption and desorption is similar to the process of a capacitor storing and releasing electrical energy. This can be compared to forming a parallel connection between a lithium-ion battery and a capacitor in a circuit structure, thereby improving the overall power of the circuit by using the high-power capacitor section.

[0131] It is understandable that the aforementioned charge-discharge processes involving physical adsorption and desorption have extremely fast reaction rates, corresponding to extremely high power densities. Taking lithium-ion batteries as an example, the energy storage mechanism of conventional lithium-ion battery cathode materials such as lithium iron phosphate, layered transition metal oxides, and lithium-rich manganese-based cathode materials involves the extraction / intercalation of lithium ions within the material lattice, which is an electrochemical reaction. The reaction rate is slow, resulting in high energy density but low power density. In this application, conductive porous materials are mixed into the cathode coating. The adsorption and desorption rates of anions by conductive porous materials are greater than the extraction and intercalation rates of active ions in the cathode active material, which can reduce current polarization, lower internal resistance, and thus improve power.

[0132] As shown in Figure 3, this is a schematic diagram of the principle structure of the secondary battery of this application. Taking a lithium-ion battery as an example, the energy storage mechanism of conventional lithium-ion battery cathode materials such as lithium iron phosphate, layered transition metal oxides, and lithium-rich manganese-based cathode materials is the extraction / intercalation of lithium ions within the material lattice, which is an electrochemical reaction. The reaction rate is slow, the energy density is high, but the power density is low. In this application, conductive porous materials are mixed into the cathode coating. The specific surface area of ​​the conductive porous materials is 1000 m². 2 / g to 4000m 2 / g, the adsorption and desorption rates of conductive porous materials for anions are greater than the extraction and insertion rates of lithium ions in cathode materials. The charging and discharging processes involving physical adsorption and desorption are similar to the process of a capacitor storing and releasing electrical energy. This can be compared to forming a parallel connection between a lithium-ion battery and a capacitor in a circuit structure, thereby improving the overall power of the circuit by using a high-power capacitor.

[0133] It's also understandable that conductive porous materials can operate over a wider temperature range compared to positive electrode active materials, increasing their applicability under different environmental conditions. This helps improve the power output of secondary batteries at low temperatures. Simultaneously, activated carbon exhibits good cycle stability, which can improve the cycle life of secondary batteries.

[0134] In one embodiment, the mass percentage of the conductive porous material to the total mass of the positive electrode coating is 0.25% to 10%; and / or, the conductive porous material includes carbon material.

[0135] Carbon materials refer to a class of materials that are mainly composed of carbon elements.

[0136] In this application, the percentage of the mass of the conductive porous material relative to the total mass of the positive electrode coating within the above-mentioned range can improve the power of the secondary battery.

[0137] The conductive porous materials in this application include carbon materials.

[0138] The values ​​in the range of 0.25% to 10% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 0.25%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 7.5%, 10%, etc., as well as the range values ​​between any two of the above point values.

[0139] In one embodiment, the volume average particle size Dv50 of the conductive porous material is from 0.1 μm to 7 μm; and / or, the powder resistivity of the conductive porous material is from 0.05 Ωcm to 0.8 Ωcm; and / or, the compacted density of the conductive porous material is 0.2 g / cm³. 3 Up to 0.7 g / cm 3 .

[0140] Specific surface area, also known as BET (Brunauer-Emmett-Teller) specific surface area, is an important parameter in materials science for characterizing the surface properties of solid materials. It refers to the total surface area per unit mass of material, usually expressed in square meters per gram (m² / g). Specific surface area can be measured using the N₂ adsorption method, as detailed in GB / T19587-2004. Alternatively, an ASPA2010 physical adsorption analyzer can be used, and the specific surface area can be determined according to the instrument's operating manual.

[0141] Volume average particle size (Dv50) is the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. Physically, it means that 50% of the particles are larger than Dv50, and 50% are smaller. Dv50 can be measured using methods known in the art. For example, it can be characterized using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000, as described in GB / T 19077-2016.

[0142] Compacted density is the mass per unit volume of a material under pressure. It is commonly used to measure the density of powders, granular materials, and loose materials. The formula for calculating compacted density is: Compacted density = Surface density / Material thickness. Surface density refers to the mass per unit area, usually expressed in grams per square centimeter (g / cm²).

[0143] Powder resistivity is an important physical parameter describing the electrical conductivity of powder materials, reflecting the strength of the material's ability to conduct current. The test method and procedure for powder resistivity are as follows: refer to Appendix G of GB / T30835-2014. For example, use four equally spaced probes fixed to the sample with their tips in a straight line. A constant current source provides an appropriate current I to the two outer probes, and then measure the voltage V between the two middle probes to calculate the sample resistivity.

[0144] Understandably, specific surface area is one of the differences between conductive porous materials and ordinary conductive agents. Taking conductive carbon as an example, conductive carbon is made through carbonization and sintering, and its specific surface area is 60m². 2 Approximately / g; Taking activated carbon as an example, conductive porous materials undergo an additional activation process after carbonization. This activation process creates pores, increasing the carbon material's micropores and specific surface area to over 1000m². 2 / g.

[0145] Generally, conductive porous materials have good power performance, but their energy density is lower than that of positive electrode active materials. In this application, the volume average particle size Dv50 of the conductive porous material meets the above-mentioned range, which is beneficial to maintaining the energy density of the secondary battery within a suitable range. That is, while increasing the power of the secondary battery, the energy density of the secondary battery is not significantly reduced. It is understood that if the particle size is too small, it will reduce the compaction density of the positive electrode coating, and if the particle size is too large, it will affect the uniform distribution of the positive electrode active material.

[0146] Understandably, the volume average particle size Dv50 is the second difference between conductive porous materials and ordinary conductive agents. Ordinary conductive agents typically have small particle sizes (nm level) to achieve good conductivity, while the conductive porous materials in this scheme are at the micrometer level. For example, activated carbon is usually sourced from biomass materials such as coconut shells, which are carbonized, activated, and then pulverized, resulting in a larger particle size. This characteristic is significantly different from conductive carbon (nm level). In the process of distinguishing between conductive agents and conductive porous materials, the two can be differentiated by morphology or by analyzing the specific surface area of ​​the electrode.

[0147] The resistivity of the conductive porous material powder in this application meets the above-mentioned range, which can reduce the internal resistance of the positive electrode coating and help improve the power of the secondary battery.

[0148] The compaction density of the conductive porous material in this application meets the above-mentioned range, which is beneficial for maintaining the energy density of the secondary battery within a suitable range. It is understood that the mixing of conductive porous material in the positive electrode coating affects the overall compaction density after mixing. If the compaction density of the conductive porous material is too low, it will lead to an excessively low compaction density of the positive electrode coating, reducing the volumetric energy density.

[0149] It is understandable that conductive porous materials distributed in the positive electrode coating, together with other components, form a conductive / liquid-conducting network, which can improve coating resistance and increase the electrochemically active specific surface area of ​​the coating. For example, in one embodiment, the conductive porous material is mixed with a conductive agent, a binder, and a positive electrode active material to form a conductive / liquid-conducting network. During battery charging, electrons travel from the negative electrode to the positive electrode through the external circuit and can be transferred to the conductive porous material for storage through the current collector and conductive agent in the positive electrode sheet. This storage rate is relatively fast, improving the power of the secondary battery. During discharge, the conductive porous material can also quickly donate electrons in the positive electrode coating, improving the output power of the secondary battery. The liquid-conducting network can improve the wettability of the electrolyte in the positive electrode sheet, providing more pathways for ion transport, increasing the ion migration rate, and thus improving power.

[0150] The above 1000m 2 / g to 4000m 2In / g, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 1000m. 2 / g, 1500m 2 / g、2000m 2 / g、2500m 2 / g、3000m 2 / g、3500m 2 / g、4000m 2 / g, etc., and the range of values ​​between any two of the above point values.

[0151] The values ​​in the range of 0.1μm to 7μm include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.1μm, 1μm, 3μm, 4μm, 5μm, 6μm, 7μm, etc., as well as the range values ​​between any two of the above point values.

[0152] The values ​​in the range of 0.05Ωcm to 0.8Ωcm include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.05Ωcm, 0.1Ωcm, 0.5Ωcm, 0.6Ωcm, 0.8Ωcm, etc., as well as the range values ​​between any two of the above point values.

[0153] The above 0.2 g / cm 3 Up to 0.7 g / cm 3 In this context, the values ​​include the minimum and maximum values ​​within the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 0.2 g / cm³. 3 0.4g / cm 3 0.5g / cm 3 0.6g / cm 3 0.7g / cm 3 And so on, as well as the range of values ​​between any two of the above point values.

[0154] In one embodiment, the mass percentage of the conductive porous material to the total mass of the positive electrode coating is 0.25% to 5%; and / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black.

[0155] Activated carbon is a porous carbon material with a very large specific surface area and a well-developed microporous structure. It is usually made from carbon-rich raw materials such as wood, coal, and coconut shells through high-temperature carbonization and activation treatment. Its specific surface area is typically >1000 m². 2 / g.

[0156] Ordered mesoporous carbon is a type of mesoporous carbon material with a regular pore structure and a pore size between 2 and 50 nanometers.

[0157] Disordered mesoporous carbon is a porous carbon material with an irregular pore structure, typically with pore sizes ranging from 2 to 50 nanometers. Compared to ordered mesoporous carbon, disordered mesoporous carbon lacks long-range order in its pore structure.

[0158] Carbon nanotubes are one-dimensional nanomaterials composed of carbon atoms. They have a unique tubular structure, and the walls of carbon nanotubes are formed by hexagonal carbon atoms bonded together through sp^2 hybridization.

[0159] Graphene is a two-dimensional material formed by a single layer of carbon atoms in sp^2 hybridization, with these carbon atoms arranged in a hexagonal honeycomb lattice.

[0160] Porous carbon black is a type of carbon material formed from the incomplete combustion of fuels such as coal, petroleum, and biomass. Its main component is elemental carbon, with trace amounts of oxygen, hydrogen, and sulfur. Porous carbon black is a carbon material with varying pore sizes, ranging from ultrafine nanopores (molecular size) to micron-sized pores suitable for microbial activity.

[0161] In this application, the percentage of the mass of the conductive porous material in the total mass of the positive electrode coating meets the above-mentioned range, which can improve the power of the secondary battery while maintaining a good energy density of the secondary battery.

[0162] In this application, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black. That is, the carbon material can be selected from any one of the above, or it can include multiple of the above.

[0163] The values ​​in the range of 2.5% to 5% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 2.5%, 3%, 3.5%, 5%, etc., as well as the range values ​​between any two of the above point values.

[0164] In one embodiment, the positive electrode coating further includes a surfactant; and / or, the positive electrode coating further includes a surfactant, wherein the mass percentage of the surfactant is 0.1% to 1% of the total mass of the positive electrode coating; and / or, the positive electrode coating further includes a surfactant, wherein the surfactant includes at least one selected from polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid; and / or, the positive electrode coating further includes a positive electrode active material, wherein the mass percentage of the positive electrode active material is 93% to 98% of the total mass of the positive electrode coating; and / or, the positive electrode coating further includes a conductive agent, wherein the mass percentage of the conductive agent is 0.1% to 2% of the total mass of the positive electrode coating; and / or The positive electrode coating further includes a binder, the mass percentage of which is 1% to 3% of the total mass of the positive electrode coating; and / or, the positive electrode coating further includes a positive electrode active material, the positive electrode active material including at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide; and / or, the positive electrode coating further includes a conductive agent, the conductive agent including at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or, the positive electrode coating further includes a binder, the binder including at least one of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0165] Positive electrode active materials provide active ions and are used in secondary batteries to provide the energy storage capacity of the secondary battery. For example, during charging, active ions are released from the positive electrode active material, pass through the electrolyte, and then insert into the negative electrode material; during discharging, active ions are released from the negative electrode material, pass through the electrolyte, and then insert into the positive electrode active material.

[0166] Conductive agents are used to ensure that the electrodes have good charge and discharge performance. They play a role in collecting micro-currents between active materials and between active materials and current collectors, thereby reducing the contact resistance of the electrodes and accelerating the movement rate of electrons.

[0167] Adhesives are materials with adhesive properties used to bond different substances together.

[0168] Surfactants are a class of compounds with special amphiphilic structures that are used to improve the dispersibility of components in a mixture and make the components more uniformly distributed.

[0169] The positive electrode coating of this application may include surfactants, which can improve the dispersion and uniform distribution of various components in the positive electrode coating, facilitate the uniform distribution of conductive porous materials in the positive electrode coating, form a conductive / liquid-conducting network, thereby reducing the resistance of the positive electrode coating, increasing the electrochemical active specific surface area, improving the battery charge and discharge rate, and improving the battery power; at the same time, it improves the flexibility of the positive electrode coating, increases the compaction density of the coating, and thus improves the battery capacity.

[0170] In this application, the mass percentage of the surfactant in the total mass of the cathode coating meets the above-mentioned range, which is beneficial to improving the dispersion and uniform distribution of each component in the cathode coating and to the uniform distribution of conductive porous materials in the cathode coating.

[0171] The surfactants in this application include at least one of the following: polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid. That is, they may include any one of the above or a combination of multiple of them.

[0172] In this application, the percentage of the mass of the positive electrode active material relative to the total mass of the positive electrode coating meets the above-mentioned range, which can improve the energy density of the secondary battery.

[0173] In this application, the mass percentage of the conductive agent relative to the total mass of the positive electrode coating meets the above-mentioned range, which can reduce the electrode resistance and improve the power of the secondary battery.

[0174] In this application, the mass percentage of the binder to the total mass of the positive electrode coating meets the above-mentioned range, ensuring the stability and integrity of the electrode structure during battery charging and discharging.

[0175] The positive electrode active material in this application includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide. That is, it may include any one of the above or a combination of multiple types.

[0176] The conductive agent in this application includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. That is, it may include any one of the above or a combination of multiple types.

[0177] The adhesive in this application includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. That is, it may include any one of the above or a combination of multiple types.

[0178] In one embodiment, the electrochemically active specific surface area of ​​the positive electrode coating is 5 m². 2 / g to 12m 2 / g; and / or, the resistivity of the positive electrode coating is 0.1Ω to 0.2Ω; and / or, the specific surface area of ​​the positive electrode coating is 10m². 2 / g to 200m 2 / g; and / or, the compaction density of the positive electrode coating is 2.1 g / cm³. 3 Up to 2.65 g / cm 3 ; and / or, the thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

[0179] Electrochemically active specific surface area refers to the effective surface area that actually participates in the electrochemical reaction. The testing method is as follows: First, the sample electrodes are assembled into a coin cell. When a certain potential is applied to the porous electrode coated with active material, electrons are transferred through the current collector to the surface of the electroactive sites of the active material. At these electroactive sites, redox couples in the electrolyte undergo redox reactions. For systems where electrochemical behavior is diffusion-controlled, the peak current is proportional to the square root of the scan rate and is also related to the electrochemically active specific surface area of ​​the working electrode surface. This area can be calculated using the Randles-Sevick equation, and is thus the electrochemical specific surface area.

[0180] The resistance of the positive electrode coating is an important physical parameter describing the conductivity of the coating. It reflects the strength of the coating's ability to conduct current. The coating resistance is tested by using the two-probe method. Two probes are placed in contact with the front and back sides of the electrode film (coating), a known current I is applied, and the voltage V between the two ends is measured. Ohm's law R = V / I is used to obtain the film (coating) resistance.

[0181] The specific surface area of ​​the positive electrode coating refers to the total area of ​​a unit mass of material, usually expressed in square meters per gram (m2 / g). The specific surface area can be determined by the N2 adsorption method.

[0182] The compaction density of the positive electrode coating is calculated as: Compaction density = Areal density / (Thickness of the electrode after compaction - Thickness of the current collector), unit: g / cm³. 3 Test method for compaction density (PD): Take an area of ​​1540.25 mm². 2 The basic unit is a circular positive electrode sheet of a certain size. The total weight of the positive electrode sheet coated with positive active material on both sides is M, the weight of the positive current collector is B, the thickness of the positive current collector is T, and the thickness of the copper foil / aluminum foil is μ. Then PD=(MB) / (T-μ) / 1540.25*1000.

[0183] The thickness of the positive electrode coating was measured using a micrometer.

[0184] In this application, the electrochemically active specific surface area of ​​the positive electrode coating meets the aforementioned range. That is, by doping with conductive porous materials, more active sites can be provided, thereby increasing the opportunities for intercalation and deintercalation reactions of active ions in the secondary battery. This helps to improve the battery's charge-discharge efficiency and power density. Secondly, a larger specific surface area helps to improve the wettability of the electrolyte in the electrode, reduce the battery's internal resistance, and thus improve the battery's charge-discharge performance.

[0185] In this application, the resistance of the positive electrode coating meets the above-mentioned range. That is, by doping with conductive porous materials, the resistance of the positive electrode coating can be reduced, which is beneficial to improving the charge and discharge rate.

[0186] In this application, the specific surface area of ​​the positive electrode coating meets the above-mentioned range. That is, doping with conductive porous materials can increase the specific surface area of ​​the coating, improve the wetting performance of the electrolyte, reduce internal resistance, and increase power.

[0187] In this application, the compaction density of the conductive porous material is within the above-mentioned range, which is beneficial to improving the energy density of the secondary battery.

[0188] In this application, the thickness of the positive electrode coating is within the above-mentioned range, which further improves the power of the secondary battery. It is understood that the thickness of the coating will affect the power of the secondary battery, and under certain conditions, reducing the thickness can increase the power.

[0189] The above 5m 2 / g to 12m 2 In / g, the values ​​include the minimum and maximum values ​​within the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 5m. 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g, etc., and the range of values ​​between any two of the above point values.

[0190] The values ​​in the range of 0.1Ω to 0.2Ω include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 0.1Ω, 0.15Ω, 0.2Ω, etc., and the range values ​​between any two of the above point values.

[0191] The above 10m 2 / g to 200m 2In / g, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 10m. 2 / g、30m 2 / g, 50m 2 / g、80m 2 / g, 100m 2 / g, 120m 2 / g, 150m 2 / g、180m 2 / g、200m 2 / g, etc., and the range of values ​​between any two of the above point values.

[0192] The above 2.1 g / cm 3 Up to 2.65 g / cm 3 In this context, the values ​​include the minimum and maximum values ​​within the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 2.1 g / cm³. 3 2.3g / cm 3 2.5g / cm 3 2.6g / cm 3 2.65g / cm 3 And so on, as well as the range of values ​​between any two of the above point values.

[0193] The values ​​in the range of 0.13mm to 0.24mm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.13mm, 0.16mm, 0.18mm, 0.2mm, 0.23mm, 0.24mm, etc., as well as the range values ​​between any two of the above point values.

[0194] In one embodiment, the volumetric energy density of the secondary battery is from 240 Wh / L to 400 Wh / L; and / or, the gravimetric energy density of the secondary battery is from 120 Wh / Kg to 200 Wh / Kg.

[0195] Volumetric energy density refers to the amount of energy a battery can store within a given volume. The test method is as follows: measure the physical dimensions of the battery cell to calculate the volume V, discharge the battery cell to the minimum voltage under constant current, record the total amount of electricity Q released during the discharge process, convert the amount of electricity into energy E, and use the formula E = Q * V, where V is the average voltage during the discharge process (unit: volts V), and the volumetric energy density = E / V (volume).

[0196] Mass energy density refers to the amount of energy a battery can store at a given mass. The test method is as follows: using E, which is measured in the volumetric energy density test as above, the mass M in the cell is measured, and the mass energy density is calculated using the formula: mass energy density = E / M.

[0197] In this application, after doping the positive electrode coating with conductive porous material, the volumetric energy density of the secondary battery meets the above-mentioned range.

[0198] In this application, after doping the positive electrode coating with conductive porous material, the mass energy density of the secondary battery meets the above-mentioned range.

[0199] The values ​​in the range of 240Wh / L to 400Wh / L include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 240Wh / L, 300Wh / L, 340Wh / L, 400Wh / L, etc., and the range values ​​between any two of the above point values.

[0200] The values ​​in the range of 120Wh / Kg to 200Wh / Kg include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 120Wh / L, 150Wh / L, 180Wh / L, 200Wh / L, etc., and the range values ​​between any two of the above point values.

[0201] In one embodiment, this application also provides a positive electrode sheet, which includes a positive current collector and a positive electrode coating disposed on at least one surface of the positive current collector. The positive electrode coating includes a conductive porous material with a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g.

[0202] In one embodiment, the conductive porous material accounts for 0.25% to 10% of the total mass of the positive electrode coating; and / or, the conductive porous material includes carbon materials; and / or, the positive electrode coating also includes surfactants.

[0203] In one embodiment, the volume average particle size Dv50 of the conductive porous material is from 0.1 μm to 7 μm; and / or, the powder resistivity of the conductive porous material is from 0.05 Ωcm to 0.8 Ωcm; and / or, the compacted density of the conductive porous material is 0.2 g / cm³. 3 Up to 0.7 g / cm 3 .

[0204] In one embodiment, the conductive porous material accounts for 0.25% to 10% of the total mass of the positive electrode coating; and / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black; and / or, the surfactant accounts for 0.1% to 1% of the total mass of the positive electrode coating; and / or, the surfactant includes at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid.

[0205] In one embodiment, at least one of the following conditions is satisfied: Condition A: The positive electrode coating further includes a positive electrode active material, the mass percentage of which is 93% to 98% of the total mass of the positive electrode coating; Condition B: The positive electrode coating further includes a conductive agent, the mass percentage of which is 0.1% to 2% of the total mass of the positive electrode coating; Condition C: The positive electrode coating further includes a binder, the mass percentage of which is 1% to 3% of the total mass of the positive electrode coating; Condition D: The positive electrode coating further includes a positive electrode active material, the positive electrode active material including lithium iron phosphate, lithium manganese iron phosphate, ternary lithium... The cathode coating comprises at least one of the following: lithium cobalt oxide, lithium manganese oxide, and other materials; Condition E: The cathode coating further comprises a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; Condition F: The cathode coating further comprises a binder, which includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin; Condition G: The electrochemically active specific surface area of ​​the cathode coating is 5 m². 2 / g to 12m 2 / g; Condition H: The resistivity of the positive electrode coating is 0.1Ω to 0.2Ω; Condition I: The specific surface area of ​​the positive electrode coating is 10m². 2 / g to 200m 2 / g; Condition J: The compaction density of the positive electrode coating is 2.1 g / cm³. 3 Up to 2.65 g / cm 3 Condition K: The thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

[0206] In one embodiment, this application also provides a method for preparing a positive electrode sheet, comprising: mixing a positive active material, a conductive agent, a binder, a conductive porous material and a solvent, and stirring to obtain a positive electrode slurry; coating the positive electrode slurry onto a current collector to obtain a positive electrode sheet.

[0207] That is, by preparing the basic raw materials for the positive electrode slurry and mixing conductive porous materials into the raw materials, the positive electrode slurry can be obtained. By coating the slurry onto the current collector, a positive electrode coating incorporating conductive porous materials can be obtained.

[0208] In one embodiment, the step of mixing the positive electrode active material, conductive agent, binder, conductive porous material and solvent and stirring to obtain a positive electrode slurry includes: adding surfactant, conductive agent, conductive porous material and binder to solvent and stirring to obtain a mixture; adding positive electrode active material and solvent to the mixture and stirring to obtain a positive electrode slurry.

[0209] It is understandable that surfactants can be added to the positive electrode slurry to improve the dispersibility and uniformity of the components. It is also understandable that the materials can be added and stirred in the above mixing steps according to their sequential order, or not in the above order.

[0210] In one embodiment, based on 100 parts by weight, the positive electrode active material comprises 90 to 100 parts, the conductive agent comprises 0 to 3 parts, the binder comprises 0 to 3 parts, the surfactant comprises 0 to 3 parts, and the conductive porous material comprises 0 to 7 parts.

[0211] During the preparation of the slurry, the materials are mixed according to the above proportion range and a coating is prepared. The comprehensive properties of the coating, such as conductivity, specific surface area, and compaction density, are improved.

[0212] This application also provides an electrical device, which includes a secondary battery as described above.

[0213] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0214] In one embodiment of this application, a secondary battery is provided.

[0215] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through. The separator described above is the type used in this application.

[0216] The positive electrode includes a positive current collector and a positive coating disposed on at least one surface of the positive current collector.

[0217] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive coating is disposed on either or both of the two opposite surfaces of the positive current collector.

[0218] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0219] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0220] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0221] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0222] In some embodiments, the positive electrode coating may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0223] In some embodiments, the positive electrode coating may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0224] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0225] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0226] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0227] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0228] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0229] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0230] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0231] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0232] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0233] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0234] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0235] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0236] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0237] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0238] In some implementations, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0239] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square battery cell 5 as an example.

[0240] In some embodiments, referring to FIG5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0241] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0242] Figure 6 shows a battery module 4 as an example. Referring to Figure 6, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0243] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0244] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0245] Figures 7 and 8 show a battery pack 1 as an example. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0246] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0247] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0248] Figure 9 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0249] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0250] Example

[0251] Example 1

[0252] Preparation of the positive electrode: Lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, surfactant (polyvinylpyrrolidone), and conductive porous activated carbon (specific surface area of ​​1400 m²) are combined. 2 The powder has the following characteristics: g / g, volume average particle size Dv50 of 5.5 μm, powder resistivity of 0.5 Ωcm (at 8 MPa pressure), and compacted density of 0.6 g / cm³.3 The mixture is prepared by mixing the following components in a mass ratio of 94.7%:0.7%:1.8%:0.3%:2.5% and then adding the solvent N-methylpyrrolidone and stirring. The uniformly mixed slurry is then coated on both sides of an aluminum foil and, after cold pressing and cutting, the positive electrode sheet is obtained.

[0253] Preparation of negative electrode sheet: Artificial graphite, conductive carbon black, carboxymethyl cellulose (CMC), polystyrene rubber and binder are mixed evenly in a mass ratio of 96.2:0.4:0.9:2:0.5. Then, deionized water is added as a solvent for kneading and stirring. The evenly stirred slurry is coated on both sides of copper foil. After cold pressing and cutting, the negative electrode sheet is obtained.

[0254] Separator: A 7μm thick polyethylene membrane is used as the separator, with CCS (ceramic coating) and PCS (polymer coating) coatings on the surface.

[0255] Electrolyte: Ethyl carbonate, diethyl carbonate, and dimethyl carbonate are mixed in a volume ratio of 1:1:1. LiPF6 is dissolved in the above solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte is 1 mol / L.

[0256] Assembly: The electrodes are arranged in the order of "diaphragm-negative electrode-diaphragm-positive electrode." One end of the positive electrode, negative electrode, and two diaphragms is fixed to the discharge roller, and the other ends are stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode, negative electrode, and two diaphragms to obtain a wound bare cell. The bare cell then undergoes Mylar (polyester film) coating, casing, welding, helium testing, primary electrolyte injection, wetting, formation, secondary electrolyte injection, sealing nail welding, high-temperature aging, settling, and capacity testing to obtain the finished cell. The cell in Example 1 is a pouch cell.

[0257] Example 2, Example 3

[0258] Based on Example 1, the mass percentage of conductive porous material was adjusted to 5% and 7.5%, with a corresponding reduction in the amount of positive electrode active material.

[0259] Example 4

[0260] Based on Example 1, the conductive porous material was replaced with carbon nanotubes (specific surface area of ​​1000 m²). 2 The powder has the following characteristics: g / g, volume average particle size Dv50 of 0.1 μm, powder resistivity of 0.05 Ωcm, and compacted density of 0.2 g / cm³. 3 The mass percentage of conductive porous material was adjusted to 2.5%.

[0261] Examples 5 and 6

[0262] Based on Example 1, a conductive porous material with a specific surface area of ​​1000 m² was added to the positive electrode coating. 2 / g、4000m 2 / g.

[0263] Examples 7 and 8

[0264] Based on Example 1, the volume average particle size Dv50 of the conductive porous material was adjusted to 7 μm, and the mass percentage was adjusted to 0.25% and 10%.

[0265] Example 9

[0266] Based on Example 1, the amount of conductive porous material was adjusted to 1%, and the battery cell was adjusted to a hard-shell battery cell.

[0267] Comparative Example 1

[0268] Based on Example 1, the positive electrode coating does not contain conductive porous material, and the amount of positive electrode active material is increased accordingly.

[0269] Comparative Example 2

[0270] Based on Example 1, a conductive porous material with a specific surface area of ​​900 m² was added to the positive electrode coating. 2 / g.

[0271] Comparative Example 3

[0272] Based on Example 1, the conductive porous material was adjusted to be carbon nanotubes, with a specific surface area of ​​90 m². 2 / g.

[0273] Comparative Example 4

[0274] Based on Example 9, the amount of conductive porous material was adjusted to 0.

[0275] Ion Polishing Cross-Sectional Morphology Analysis: Ion beam interface polishing is a technique that uses a high-energy ion beam to physically and chemically treat the surface of a material. This method can effectively remove damaged layers, contaminants, and oxide layers from the material surface, thereby obtaining a smooth and clean interface. The operation steps are as follows: the electrode sample is adhered to a baffle plate. Under vacuum conditions and the influence of an electric field, a high-energy argon ion beam bombards the sample, and the electrode above the baffle plate is bombarded, ultimately resulting in a smooth interface. The accelerating voltage is 2-5 kV, the beam spot diameter is 50-200 mm, and the polishing time is 0.5-1 h. These steps expose the cross-sectional structure of the electrode.

[0276] Scanning electron microscopy (SEM): It uses a high-energy electron beam to bombard the sample surface, generating various physical signals to obtain information about the sample's morphology and composition. The high-energy electron beam scans the sample surface; when the electron beam interacts with the sample surface, it excites atoms on the sample surface to emit secondary electrons. These secondary electrons are received by a detector, and the intensity and distribution of the electron signals generate a morphological image of the sample surface. Simultaneously, elements in the sample are excited and emit characteristic X-rays; by measuring the energy of these X-rays, the types and contents of elements in the sample can be determined. The operating procedure is as follows: the sample (cross-sectional structure of the electrode) is attached to the sample stage, placed in the electron microscope chamber, a vacuum is drawn, the electron beam is turned on, and appropriate parameters are set for characterization. Parameters for observing the morphology: accelerating voltage 5-20kV, aperture 30-120μm, working distance 8-20mm. Figures 1 and 2 show SEM images of the cross-sectional structure of the positive electrode in Example 1. The black particles in the figures, with a size in the micrometer range, are activated carbon, which is uniformly distributed in the positive electrode coating. It is understandable that activated carbon has better conductivity than lithium iron phosphate, the positive electrode active material, and therefore appears darker in scanning electron microscope images; the difference between it and conductive carbon black is the particle size, with conductive carbon particles in the nm range and activated carbon particles around 5 μm.

[0277] Elemental analysis of conductive porous materials in electrode cross-section structures: Energy-dispersive spectroscopy (EDS) analysis parameters: accelerating voltage 5-20 kV, aperture 10-100 μm, working distance 15 mm. EDS is a testing mode in scanning electron microscopy that uses an electron beam to excite characteristic X-rays in a material to analyze its elements and types. The specific steps are: adjust the working distance to 15 mm, voltage 5-20 kV, turn on the EDS probe, select the area to be acquired, and collect the acquisition signal.

[0278] Performance testing:

[0279] HPPC Pulse Power Test: The battery cell is stabilized at the set temperature of 25℃ in a constant temperature chamber and charged and discharged to the test SOC, which are 90%, 50%, 20%, 10%, and 5% SOC respectively; at the corresponding SOC, it is discharged at a rate of 10C for 10s, and the change voltage ΔU is recorded. The DC internal resistance DCR is calculated by the formula R=ΔU / I, where R is the DC internal resistance and I is the discharge current.

[0280] The battery cell was stabilized at the set temperature of -20℃ in a constant temperature chamber and charged and discharged to the test SOC, which were 50% and 10% SOC respectively. At the corresponding SOC, it was discharged at a rate of 0.4C for 10s, and the change voltage ΔU was recorded. The DC internal resistance DCR was calculated.

[0281] Cycle performance testing: A three-plate steel equivalent clamp is used outside the cell, with a preload of 3000N; the ambient temperature is set at 60℃, and the charge / discharge voltage is 2.8-3.8V, cycling within the 3%-100% SOC range; the cycle charge / discharge rate is 1C / 1C; one charge / discharge cycle is recorded as 1 cycle. Capacity retention is tested at different cycle counts. For example, the capacity retention (wt%) after 200 cycles = [discharge capacity of the 200th cycle / discharge capacity of the 1st cycle] × 100wt%.

[0282] Table 1 lists the resistance and electrochemical specific surface area parameters of the cathode coatings in Examples 1 to 3 and Comparative Example 1.

[0283] As can be seen from Table 1, with the addition of activated carbon to the positive electrode coating, the resistance of the positive electrode coating decreases and the electrochemical activity specific surface area of ​​the positive electrode coating is improved.

[0284] Table 2 List of DC Internal Resistance (DCR) Parameters

[0285] Soft-pack battery cell, test temperature: 25℃, pulse test condition DC 10s, charge / discharge rate 10C

[0286] As shown in Table 2, at room temperature, compared to Comparative Example 1, Examples 1 to 8 of the soft-pack battery cell improved the DC internal resistance (DCR) of the cell by incorporating conductive porous materials into the positive electrode coating, thereby improving power. Under the same conditions, Comparative Example 2, compared to Example 5, had a specific surface area of ​​less than 1000 m². 2 / g of activated carbon did not improve the DC internal resistance at low SOC as well as in Example 5.

[0287] Table 3. List of DC Internal Resistance (DCR) Parameters

[0288] Soft-pack battery cell, test temperature: -20℃, pulse test conditions: DC 10s, charge / discharge rate: 0.4C

[0289] As shown in Table 3, at low temperatures, compared to Comparative Example 1, Examples 1 to 8 of the soft-pack battery cell improved the DC internal resistance (DCR) of the cell by incorporating conductive porous materials into the positive electrode coating, thereby improving power. Under the same conditions, Comparative Example 2, compared to Example 5, had a specific surface area of ​​less than 1000 m². 2 / g of activated carbon did not improve the DC internal resistance at low SOC as well as in Example 5.

[0290] Table 4. List of DC Internal Resistance (DCR) Parameters

[0291] Hard-cased battery cell, test temperature: -20℃, pulse test conditions: DC 10s, charge / discharge rate: 0.5C

[0292] As can be seen from Table 4, under low temperature and DC (direct current) conditions, the hard-shell cell, compared with Example 9 and Comparative Example 2, improved the DC internal resistance (DCR) of the cell by mixing conductive porous material (with the same specific surface area as Example 1) into the positive electrode coating, thereby improving the power.

[0293] Table 5. List of Battery Cycle Performance Parameters

[0294] Hard-cased battery cell, tested at an ambient temperature of 60℃, subjected to continuous charge and discharge at a rate of 1C.

[0295] As shown in Table 5, the hard-shell battery cells were subjected to continuous charge-discharge tests at a rate of 1C under an ambient temperature of 60℃. The results indicate that activated carbon has no adverse effect on cycle performance.

[0296] The analysis in the table above shows that, regardless of whether it is a pouch cell or a rigid-shell cell, adding conductive porous material to the positive electrode coating results in a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g, all of which can improve the DC internal resistance (DCR) of the battery cell, thereby improving power. At low temperatures, the DC internal resistance (DCR) of the low state of charge (SOC) containing conductive porous materials is also improved, indicating that this application improves the DC internal resistance (DCR) by incorporating conductive porous materials into the positive electrode coating. The specific surface area of ​​the conductive porous materials is 1000m². 2 / g to 4000m 2 / g can reduce internal resistance and improve the power of secondary batteries.

[0297] The above are merely preferred embodiments of this application and do not limit the scope of this patent application. Any equivalent structural transformations made based on the inventive concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of this application.

Claims

1. A secondary battery, wherein, The secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector and a positive electrode coating disposed on at least one surface of the positive current collector. The positive electrode coating includes a conductive porous material with a specific surface area of ​​1000 m². 2 / g to 4000m 2 / g.

2. The secondary battery according to claim 1, wherein The mass percentage of the conductive porous material in the total mass of the positive electrode coating is 0.25% to 10%. And / or, the conductive porous material includes carbon materials.

3. The secondary battery according to claim 1 or 2, wherein The volume average particle size Dv50 of the conductive porous material is 0.1 μm to 7 μm; And / or, the resistivity of the conductive porous material powder is from 0.05 Ωcm to 0.8 Ωcm; and / or the compacted density of the electrically conductive porous material is 0.2 g / cm 3 to 0.7 g / cm 3 .

4. The secondary battery according to claim 2 or 3, wherein The mass percentage of the conductive porous material in the total mass of the positive electrode coating is 0.25% to 5%. And / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black.

5. The secondary battery according to any one of claims 1 to 4, wherein The positive electrode coating also includes a surfactant; And / or, the positive electrode coating further includes a surfactant, wherein the mass percentage of the surfactant is 0.1% to 1% of the total mass of the positive electrode coating; And / or, the positive electrode coating further includes a surfactant, the surfactant including at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid; And / or, the positive electrode coating further includes a positive electrode active material, wherein the mass percentage of the positive electrode active material is 93% to 98% of the total mass of the positive electrode coating; And / or, the positive electrode coating further includes a conductive agent, wherein the mass percentage of the conductive agent is 0.1% to 2% of the total mass of the positive electrode coating; And / or, the positive electrode coating further includes a binder, wherein the mass percentage of the binder is 1% to 3% of the total mass of the positive electrode coating; And / or, the positive electrode coating further includes a positive electrode active material, the positive electrode active material including at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide; And / or, the positive electrode coating further includes a conductive agent, the conductive agent including at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; And / or, the positive electrode coating further includes an adhesive, the adhesive comprising at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

6. The secondary battery according to any one of claims 1 to 5, wherein The positive electrode coating has an electrochemically active specific surface area of 5 m 2 / g to 12 m 2 / g; And / or, the resistance of the positive electrode coating is 0.1Ω to 0.2Ω; and / or the specific surface area of the positive electrode coating is 10 m 2 / g to 200 m 2 / g; and / or the positive electrode coating has a compacted density of 2.1 g / cm 3 to 2.65 g / cm 3 ; And / or, the thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

7. The secondary battery according to any one of claims 1 to 6, wherein The volumetric energy density of the secondary battery is 240Wh / L to 400Wh / L; And / or, the gravimetric energy density of the secondary battery is from 120Wh / Kg to 200Wh / Kg.

8. A positive electrode sheet, wherein, The positive electrode tab comprises a positive electrode current collector and a positive electrode coating provided on at least one surface of the positive electrode current collector, the positive electrode coating comprising a conductive porous material, the specific surface area of the conductive porous material being 1000 m 2 / g to 4000 m 2 / g.

9. The cathode sheet of claim 8, wherein, The mass percentage of the conductive porous material in the total mass of the positive electrode coating is 0.25% to 10%. And / or, the conductive porous material includes carbon materials; And / or, the positive electrode coating may further include a surfactant.

10. The cathode sheet of claim 8 or 9, wherein, The volume average particle size Dv50 of the conductive porous material is 0.1 μm to 7 μm; And / or, the resistivity of the conductive porous material powder is from 0.05 Ωcm to 0.8 Ωcm; and / or the compacted density of the electrically conductive porous material is 0.2 g / cm 3 to 0.7 g / cm 3 .

11. The cathode sheet of claim 9, wherein, The mass percentage of the conductive porous material in the total mass of the positive electrode coating is 0.25% to 5%. And / or, the carbon material includes at least one of activated carbon, ordered mesoporous carbon, disordered mesoporous carbon, carbon nanotubes, graphene, and porous carbon black; And / or, the mass percentage of the surfactant in the total mass of the positive electrode coating is 0.1% to 1%; And / or, the surfactant includes at least one of polyvinylpyrrolidone, polyethylene glycol, fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate, sodium stearate, hexadecyltrimethylammonium bromide, betaine, and polyacrylic acid.

12. The cathode sheet of any one of claims 8-11, wherein, At least one of the following conditions must be met: Condition A: The positive electrode coating further includes a positive electrode active material, and the mass percentage of the positive electrode active material in the total mass of the positive electrode coating is 93% to 98%. Condition B: The positive electrode coating further includes a conductive agent, and the mass percentage of the conductive agent in the total mass of the positive electrode coating is 0.1% to 2%. Condition C: The positive electrode coating further includes a binder, and the mass percentage of the binder to the total mass of the positive electrode coating is 1% to 3%. Condition D: The positive electrode coating further includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, lithium cobalt oxide, and lithium manganese oxide; Condition E: The positive electrode coating further includes a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Condition F: The positive electrode coating further includes a binder, which includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. Condition G: the positive electrode coating has an electrochemically active specific surface area of 5 m 2 / g to 12 m 2 / g; Condition H: The resistance of the positive electrode coating is 0.1Ω to 0.2Ω; Condition I: the specific surface area of the positive electrode coating is 10 m 2 / g to 200 m 2 / g; Condition J: the compacted density of the positive electrode coating is 2.1 g / cm 3 to 2.65 g / cm 3 ; Condition K: The thickness of the positive electrode coating is 0.13 mm to 0.24 mm.

13. A method of making a positive electrode sheet, wherein, include: The positive electrode active material, conductive agent, binder, conductive porous material and solvent are mixed and stirred to obtain a positive electrode slurry; The positive electrode slurry is coated on a current collector to obtain a positive electrode tab, the specific surface area of the conductive porous material being 1000 m 2 / g to 4000 m 2 / g.

14. The method of producing a cathode electrode piece according to claim 13, wherein The step of mixing and stirring the positive electrode active material, conductive agent, binder, conductive porous material and solvent to obtain a positive electrode slurry includes: A surfactant, a conductive agent, a conductive porous material, and a binder are added to a solvent and stirred to obtain a mixture. Add the positive electrode active material and solvent to the mixture, stir, and obtain the positive electrode slurry.

15. The method of producing a cathode electrode piece according to claim 14, wherein Based on 100 parts by weight, the positive electrode active material comprises 90 to 100 parts, the conductive agent comprises 0 to 3 parts, the binder comprises 0 to 3 parts, the surfactant comprises 0 to 3 parts, and the conductive porous material comprises 0 to 7 parts.

16. An electrical device, comprising: The electrical device includes a secondary battery as described in any one of claims 1 to 7.

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