Positive pole piece, battery, energy storage device, power utilization system and energy storage system

Abstract

The invention provides a positive pole piece, a battery, an energy storage device, a power utilization system and an energy storage system. The invention provides a positive pole piece. The positive pole piece comprises a positive current collector; the positive electrode active layer is arranged on one side of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material, a binder and a conductive agent, in the positive electrode active layer, the average mass fraction of the positive electrode active material is x, the average mass fraction of the binder is y, and the average mass fraction of the conductive agent is y; the average mass fraction of the conductive agent is z, and the positive electrode active layer meets the relational expression that x / (y + z) is larger than or equal to 24.5 and smaller than or equal to 34.5. The positive electrode active layer of the positive electrode plate has good adhesiveness on the positive electrode current collector, and powder falling or material falling is not likely to happen.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to a positive electrode plate, a battery, an energy storage device, an electricity consumption system and an energy storage system. Background Art

[0002] With the continuous development of lithium-ion battery technology, lithium-ion batteries have the advantages of large specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, small size and light weight compared with other types of batteries such as lead-acid and cadmium nickel. At present, lithium ions have been widely used in mobile phones, laptops, electric vehicles, energy storage cabinets and other fields, and their application range is becoming more and more extensive. When preparing the electrode pole piece, the electrode slurry is coated on the collector, and it is completed after drying, rolling and other processes. However, the existing electrode pole pieces are prone to powder loss and material loss after rolling, which seriously affects the performance of the battery. Summary of the invention

[0003] In view of the above problems, an embodiment of the present application provides a positive electrode plate, wherein the positive electrode active layer has good adhesion on the positive electrode current collector and is not prone to powder or material loss.

[0004] In a first aspect, the present application provides a positive electrode sheet, comprising:

[0005] a positive electrode current collector; and

[0006] A positive electrode active layer, wherein the positive electrode active layer is arranged on one side of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material, a binder and a conductive agent, wherein in the positive electrode active layer, the average mass fraction of the positive electrode active material is x, the average mass fraction of the binder is y, and the average mass fraction of the conductive agent is z, wherein the positive electrode active layer satisfies the relationship: 24.5≤x / (y+z)≤34.5.

[0007] Optionally, the concentration of the binder gradually decreases from a side of the positive electrode active layer away from the positive electrode current collector to a side of the positive electrode active layer close to the positive electrode current collector.

[0008] Optionally, the difference between the mass fraction of the binder on the side of the positive electrode active layer away from the positive electrode current collector and the mass fraction of the binder on the side of the positive electrode active layer close to the positive electrode current collector is in the range of: 0.01%≤△y≤0.4%.

[0009] Optionally, along the stacking direction of the positive electrode current collector and the positive electrode active layer, the positive electrode active layer is divided into a first layer and a second layer of equal thickness, the first layer is farther away from the positive electrode current collector than the second layer, the average mass fraction of the binder in the first layer is y1, and the average mass fraction of the binder in the second layer is y2, then 1.01≤y1 / y2≤1.20.

[0010] Optionally, the concentration of the conductive agent gradually decreases from a side of the positive electrode active layer away from the positive electrode current collector to a side of the positive electrode active layer close to the positive electrode current collector.

[0011] Optionally, the difference between the mass fraction of the conductive agent on the side of the positive electrode active layer away from the positive electrode current collector and the mass fraction of the conductive agent on the side of the positive electrode active layer close to the positive electrode current collector is in the range of: 0.01%≤△z≤0.4%.

[0012] Optionally, along the stacking direction of the positive electrode current collector and the positive electrode active layer, the positive electrode active layer is divided into a first layer and a second layer of equal thickness, the first layer is farther away from the positive electrode current collector than the second layer, the average mass fraction of the conductive agent in the first layer is z1, and the average mass fraction of the conductive agent in the second layer is z2, then 1.01≤z1 / z2≤1.20.

[0013] Optionally, the positive electrode plate further includes a primer layer, and the primer layer is disposed between the positive electrode current collector and the positive electrode active layer.

[0014] Optionally, the mass fraction of the undercoat layer to the positive electrode active layer is b, wherein 4≤y / b≤8.

[0015] In a second aspect, the present application provides a battery, comprising:

[0016] Electrolyte;

[0017] The positive electrode sheet according to the first aspect of the present application, wherein the positive electrode sheet is at least partially immersed in the electrolyte;

[0018] a diaphragm, the diaphragm being located on one side of the positive electrode plate and at least partially immersed in the electrolyte, and

[0019] A negative electrode plate is disposed on a side of the diaphragm away from the positive electrode plate and is at least partially immersed in the electrolyte.

[0020] In a third aspect, the present application provides an energy storage device, comprising:

[0021] Box;

[0022] The battery described in the second aspect of the present application, the multiple batteries are accommodated in the box, and the connection method of the multiple batteries includes at least one of series connection and parallel connection.

[0023] In a fourth aspect, the present application provides a power consumption system, comprising:

[0024] Electrical equipment; and

[0025] The battery described in the second aspect of the present application is electrically connected to the electrical device and is used to supply power to the electrical device.

[0026] In a fifth aspect, the present application provides an energy storage system, comprising:

[0027] An electric energy conversion device, the electric energy conversion device is used to convert other forms of energy into electric energy;

[0028] The energy storage device according to the third aspect of the present application, the energy storage device is electrically connected to the electric energy conversion device and is used to store the electric energy of the electric energy conversion device; and

[0029] An electrical load, wherein the electrical load is electrically connected to the electric energy conversion device and the energy storage device respectively, and is used to work using the electric energy of the electric energy conversion device or the energy storage device.

[0030] The positive electrode active layer of the positive electrode plate of the embodiment of the present application includes a positive electrode active material, a binder and a conductive agent. In the positive electrode active layer, the mass fraction of the positive electrode active material is x, the mass fraction of the binder is y, and the mass fraction of the conductive agent is z. The positive electrode active layer satisfies 24.5≤x / (y+z)≤34.5. In this way, the positive electrode active layer has higher conductivity and lower impedance. At the same time, the positive electrode active layer is not prone to powder loss, material loss, rolling abnormality and the like, thereby avoiding powder loss or material loss of the positive electrode active layer, which affects the specific capacity or energy storage density of the battery using the positive electrode plate, as well as the cycle capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 It is an application scenario diagram of the energy storage system provided in the embodiment of the present application.

[0033] Figure 2 It is a structural schematic diagram of an energy storage system according to an embodiment of the present application.

[0034] Figure 3 It is a circuit block diagram of an energy storage system according to an embodiment of the present application.

[0035] Figure 4 It is a schematic diagram of the structure of an electric power system according to an embodiment of the present application, wherein the electric power equipment and the energy storage device are in a separated state.

[0036] Figure 5 It is a schematic diagram of the partial explosion structure of an energy storage device according to one embodiment of the present application.

[0037] Figure 6 It is a schematic diagram of the structure of a battery according to an embodiment of the present application.

[0038] Figure 7 It is a perspective structural diagram of a battery according to an embodiment of the present application.

[0039] Figure 8 It is a schematic diagram of the cross-sectional structure of a negative electrode plate according to an embodiment of the present application.

[0040] Fig. 9 It is a schematic diagram of the cross-sectional structure of a positive electrode plate according to an embodiment of the present application.

[0041] Fig.10 It is a schematic diagram of the cross-sectional structure of a positive electrode plate according to another embodiment of the present application.

[0042] Fig.11 It is a schematic diagram of the cross-sectional structure of a positive electrode plate according to another embodiment of the present application.

[0043] Fig.12 This is a peeling force test curve of the positive electrode sheet of Example 1 of the present application.

[0044] Fig.13 It is a peeling force test curve of the positive electrode sheet of comparative example 1 of the present application.

[0045] Fig.14 It is the Nyquist impedance spectrum of the positive electrode sheet of Example 1 and Comparative Example 1 of the present application.

[0046] Fig.15 It is a discharge curve diagram of the half-button battery composed of the positive electrode plates of Example 1 and Comparative Example 1 of the present application at 0.1P rate and 1P rate, wherein the left figure is the discharge curve diagram at 0.1P rate, and the right figure is the discharge curve diagram at 1P rate.

[0047] Description of reference numerals:

[0048] 300-energy storage system, 310-electric energy conversion device, 330-electric load, 200-electric system, 210-electric equipment, 100-energy storage device, 110-casing, 400-battery, 500-positive electrode plate, 410-diaphragm, 430-negative electrode plate, 431-negative current collector, 433-negative active layer, 450-casing, 510-positive current collector, 520-base coating, 530-positive active layer, 531-first layer, 533-second layer. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0051] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0052] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same figure marks represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0053] Since the energy people need is highly temporal and spatial, in order to rationally use energy and improve energy utilization, it is necessary to use a medium or device to store one form of energy in the same form or convert it into another form of energy, and then release it in a specific form based on future application needs. At present, the main way to generate green electricity is to develop green energy such as photovoltaics and wind power to replace fossil energy.

[0054] At present, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower, etc. However, wind and solar energy generally have problems of strong intermittency and large volatility, which will cause instability in the power grid, insufficient electricity during peak hours, and too much electricity during valley hours. Unstable voltage will also cause damage to electricity. Therefore, insufficient electricity demand or insufficient grid acceptance capacity may cause the problem of "abandoning wind and solar power". To solve these problems, we must rely on energy storage. That is, converting electrical energy into other forms of energy through physical or chemical means and storing it, and converting energy into electrical energy and releasing it when needed. In simple terms, energy storage is like a large "power bank". When photovoltaic and wind energy are sufficient, electrical energy is stored and the stored electricity is released when needed.

[0055] Taking the energy storage device that uses electrochemical energy storage as an example, a group of chemical batteries are installed in the energy storage device, which mainly uses the chemical elements in the battery as the energy storage medium. The charging and discharging process is accompanied by chemical reactions or changes in the energy storage medium. Simply put, the electricity generated by wind and solar energy is stored in chemical batteries. When the use of external electricity reaches its peak, the stored electricity is released for use, or transferred to places where electricity is scarce for use.

[0056] At present, energy storage (i.e. energy storage) has a wide range of application scenarios, including energy storage on the power generation side, energy storage on the grid side, and energy storage on the power consumption side. The corresponding types of energy storage devices include:

[0057] (1) Large-scale energy storage power stations applied to wind power and photovoltaic power stations can help renewable energy generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive regulating power source on the power supply side, energy storage power stations can achieve load matching of electric energy in time and space, enhance the ability to absorb renewable energy, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy generation, and are of great significance in power grid system backup, relieving peak load power supply pressure, and peak and frequency regulation.

[0058] (2) Energy storage containers used on the grid side mainly perform peak load regulation, frequency regulation, and grid congestion relief. They can achieve peak load shaving and valley filling of power loads, that is, charging the energy storage batteries when the power load is low and releasing the stored power during the peak load period, thereby achieving a balance between power production and consumption;

[0059] (3) Small energy storage cabinets (such as user energy storage systems) used on the power consumption side, mainly for self-generation and self-use of electricity, peak-valley price arbitrage, capacity cost management and improving power supply reliability. According to different application scenarios, energy storage on the power consumption side can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for valley-peak price arbitrage and capacity cost management. In the power market that implements peak-valley electricity prices, by charging the energy storage system at low electricity prices and discharging the energy storage system at high electricity prices, peak-valley electricity price arbitrage is achieved to reduce electricity costs. In addition, industrial enterprises that are subject to two-part electricity prices can use energy storage systems to store energy during low electricity consumption and discharge at peak loads, thereby reducing peak power and the maximum demand reported, and achieving the purpose of reducing capacity electricity charges. Household photovoltaic storage can improve the level of self-generation and self-use of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations has been driven. Considering that photovoltaic power is generated during the day, and users generally have higher loads at night, energy storage can be configured to better utilize photovoltaic power, improve the level of self-generation and self-use, and reduce electricity costs. In addition, communication base stations, data centers and other fields need to configure energy storage for backup power.

[0060] Figure 1 300 is an application scenario diagram of the energy storage system 300 provided in the embodiment of the present application. Figure 1 The embodiment is described by taking the household energy storage scenario in the user-side energy storage as an example, and the energy storage device 100 of the present application is not limited to the household energy storage scenario. Figure 2 Schematic diagram of the structure of an energy storage system 300 according to an embodiment of the present application. Figure 3 4 is a circuit block diagram of an energy storage system 300 according to an embodiment of the present application.

[0061] See also Figures 1 to 3The present application provides an energy storage system 300, which is a household energy storage system 300, and includes an electric energy conversion device 310, an energy storage device 100, and an electrical load 330. The electric energy conversion device 310 is used to convert other forms of energy into electric energy; the energy storage device 100 is electrically connected to the electric energy conversion device 310, and is used to store the electric energy of the electric energy conversion device 310; the electric load 330 is electrically connected to the electric energy conversion device 310 and the energy storage device 100, respectively, and is used to work with the electric energy of the electric energy conversion device 310 or the energy storage device 100. It can be understood that part of the electric energy converted by the electric energy conversion device 310 is stored in the energy storage device 100, and part is used to power the electric load 330. The energy storage device 100 is used to store electric energy and supply the electric load 330 when the electricity price is peak. The energy storage system 300 can convert other generated energy into electrical energy and store the electrical energy in the energy storage device 100 to supply the electrical load 330 with sufficient electrical energy.

[0062] Optionally, the electric energy conversion device 310 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy to provide a stable power supply for the electrical load 330 and the energy storage device 100 .

[0063] Optionally, the electric energy conversion device 310 may be a photovoltaic panel, which may convert solar energy into electric energy during the period of low electricity prices and store the electric energy in the energy storage device 100. In other embodiments, it may also be at least one of a wind power generation device, a thermal power generation device, a tidal power generation device, a biomass power generation device, and a mechanical power generation device.

[0064] Optionally, the energy storage device 100 is a small energy storage box that can be mounted on an outdoor wall by wall-mounting. In other embodiments, the energy storage device 100 can also be a large energy storage container, a battery used in electronic equipment, etc.

[0065] Optionally, the power load 330 may be a street lamp, household appliance, motor vehicle, etc. The energy storage device 100 is used to store the electric energy and supply it to street lamps and household appliances for use when the electricity price is at a peak, or to supply power when the power grid is off / power outage.

[0066] It is understandable that the energy storage device 100 may include but is not limited to at least one of a single cell, a battery module, a battery pack, a battery system, etc. The single cell may be but is not limited to at least one of a cylindrical battery, a square battery, etc.

[0067] It is understandable that the drawings in this embodiment illustrate only one form of the energy storage system 300 and should not be understood as a limitation on the energy storage system 300 provided in the present application, nor should they be understood as a limitation on the energy storage device 100 provided in each embodiment of the present application.

[0068] See also Figure 4 , Figure 4 The schematic diagram of the structure of the power system 200 of an embodiment of the present application is shown in FIG. The present application also provides a power system 200 , which includes: a power device 210 and an energy storage device 100 , wherein the energy storage device 100 supplies power to the power device 210 .

[0069] The power-consuming device 210 of the embodiment of the present application may be, but is not limited to, a portable electronic device such as a mobile phone, a tablet computer, a laptop computer, a desktop computer, a smart bracelet, a smart watch, an electronic reader, a game console, etc. It may also be a vehicle such as a car, a truck, a car, a truck, a truck, a motor vehicle, a high-speed train, an electric vehicle, etc. In addition, it may also be various household appliances such as a refrigerator, an electric light, an air conditioner, etc.

[0070] It can be understood that the power-consuming device 210 in the drawings of the present application is exemplified by a mobile phone, and the power-consuming system 200 illustrated in the drawings of the present application is only one form of the power-consuming device 210, and should not be understood as a limitation on the power-consuming system 200 and the power-consuming device 210 provided in the present application.

[0071] Figure 5 is a schematic diagram of a partial explosion structure of an energy storage device 100 according to an embodiment of the present application. Figure 5 The embodiment of the present application further provides an energy storage device 100, which includes a box 110 and a plurality of batteries 400. The plurality of batteries 400 are accommodated in the box 110, and the connection method of the plurality of batteries 400 includes at least one of series connection and parallel connection.

[0072] Optionally, the battery 400 may be, but is not limited to, a lithium ion secondary battery, a lithium ion primary battery, a lithium sulfur battery, a sodium lithium ion battery, a sodium ion battery or a magnesium ion battery, an energy storage battery, or the like.

[0073] The term "plurality" means greater than or equal to two.

[0074] It can be understood that the multiple batteries 400 of the energy storage device 100 can be connected in parallel; or in series; or partially in parallel and partially in series. This application does not specifically limit the connection method of the multiple batteries 400 of the same energy storage device 100.

[0075] It is understandable that the multiple batteries 400 are arranged in an array in the box 110, or arranged in sequence in a stacked manner, and this application does not make any specific limitation on this.

[0076] It can be understood that the box body 110 has a receiving cavity (not shown), and multiple batteries 400 are received in the receiving cavity. In some embodiments, each receiving cavity receives one battery 400. In other embodiments, each receiving cavity receives multiple batteries 400.

[0077] Figure 6 It is a schematic diagram of the structure of a battery according to an embodiment of the present application. Figure 7 It is a perspective structural diagram of a battery according to an embodiment of the present application.

[0078] See also Figure 6 and Figure 7 The present application also provides a battery 400, which includes: an electrolyte (not shown), a positive electrode sheet 500, a separator 410, and a negative electrode sheet 430. The positive electrode sheet 500 is at least partially immersed in the electrolyte; the separator 410 is located on one side of the positive electrode sheet 500 and is at least partially immersed in the electrolyte; the negative electrode sheet 430 is arranged on the side of the separator 410 away from the positive electrode sheet 500 and is at least partially immersed in the electrolyte.

[0079] Optionally, the electrolyte includes a lithium salt and an organic solvent. The lithium salt may be, but is not limited to, lithium hexafluorophosphate. The organic solvent may be, but is not limited to, at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and the like.

[0080] Optionally, it may be but is not limited to at least one of a polypropylene film (PP) and a polyethylene film (PE).

[0081] Optionally, in some embodiments, the battery 400 further includes a shell 450 , and the shell 450 is used to accommodate the electrolyte, the positive electrode plate 500 , the separator 410 and the negative electrode plate 430 .

[0082] See also Figure 8 Optionally, the negative electrode plate 430 includes a negative electrode current collector 431 and a negative electrode active layer 433 , and the negative electrode active layer 433 is disposed on one side of the negative electrode current collector 431 .

[0083] Optionally, the negative electrode current collector 431 may be, but is not limited to, a copper sheet. The negative electrode active layer 433 includes a negative electrode active material, which includes at least one of graphite, natural graphite, artificial graphite, silicon-carbon composite material, hard carbon, and the like.

[0084] See also Fig. 9, an embodiment of the present application provides a positive electrode plate 500, which includes a positive electrode collector 510 and a positive electrode active layer 530, wherein the positive electrode active layer 530 is arranged on one side of the positive electrode collector 510, and the positive electrode active layer 530 includes a positive electrode active material, a binder and a conductive agent. In the positive electrode active layer 530, the average mass fraction of the positive electrode active material is x, the average mass fraction of the binder is y, and the average mass fraction of the conductive agent is z, wherein the positive electrode active layer 530 satisfies the relationship: 24.5≤x / (y+z)≤34.5.

[0085] Specifically, x / (y+z) may be, but is not limited to, 24.5, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 34.5, etc. If x / (y+z) is too small, the proportion of the positive active material in the positive active layer 530 is low, and the capacity per unit volume or per unit mass is low. When applied to the battery 400, the energy storage density of the battery 400 is reduced; if x / (y+z) is too large, the content of the conductive agent may be too small, which reduces the conductivity of the positive active layer 530 and increases the impedance of the positive active layer 530, or the content of the binder is too small, and the bonding is insufficient, so that the positive active layer 530 is prone to powder loss, material loss, rolling abnormality, and the like.

[0086] The positive electrode active layer 530 of the positive electrode plate 500 of the embodiment of the present application includes a positive electrode active material, a binder and a conductive agent. In the positive electrode active layer 530, the mass fraction of the positive electrode active material is x, the mass fraction of the binder is y, and the mass fraction of the conductive agent is z. The positive electrode active layer 530 satisfies 24.5≤x / (y+z)≤34.5. In this way, the positive electrode active layer 530 can have higher conductivity and lower impedance. At the same time, the positive electrode active layer 530 is not prone to powder loss, material loss, rolling abnormality and the like, thereby avoiding powder loss or material loss of the positive electrode active layer 530, which affects the specific capacity or energy storage density, as well as the cycle capacity retention rate of the battery 400 using the positive electrode plate 500.

[0087] Optionally, the positive electrode current collector 510 may be, but is not limited to, an aluminum sheet.

[0088] Optionally, the positive electrode active material may be, but is not limited to, lithium iron phosphate (LiFePO4, LFP for short).

[0089] Optionally, the conductive agent may be, but is not limited to, at least one of conductive carbon black, carbon nanotubes, and the like.

[0090] Optionally, the binder may be, but is not limited to, polyvinylidene fluoride (PVDF). Polyvinylidene fluoride (PVDF) is a polymer material with a high dielectric constant, good chemical stability and temperature characteristics, excellent mechanical properties and processability, and has a positive effect on improving the bonding performance of the positive active layer 530 on the positive current collector 510.

[0091] Optionally, in the positive electrode active layer 530 , the average mass fraction of the positive electrode active material is in the range of 96.1%≤x≤97.2%.

[0092] Specifically, in the positive electrode active layer 530, the average mass fraction of the positive electrode active material can be but is not limited to 96.1%, 96.2%, 96.3%, 96.4%, 96.5%, 96.6%, 96.7%, 96.8%, 96.9%, 97.0%, 97.1%, 97.2%, etc.

[0093] In this embodiment, when the average mass fraction of the positive electrode active material in the positive electrode active layer 530 is too small, the mass capacity and volume capacity of the battery 400 will be reduced when the positive electrode plate 500 is applied to the battery 400; when the average mass fraction of the positive electrode active material in the positive electrode active layer 530 is too large, it means that the binder and the conductive agent are too little, so that the conductivity of the positive electrode active layer 530 is insufficient, the impedance is large, and the adhesion is too low, resulting in the inability to coat or the positive electrode active layer 530 cracking and powdering.

[0094] Optionally, in the positive electrode active layer 530 , the average mass fraction of the binder is in the range of 0.8%≤y≤3.9%.

[0095] Specifically, in the positive electrode active layer 530, the average mass fraction of the binder can be but is not limited to 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 3.9%, etc.

[0096] In this embodiment, if the average mass fraction of the binder in the positive electrode active layer 530 is too small, the adhesiveness is insufficient, resulting in the inability to coat or the positive electrode sheet 500 cracking and falling off; if the average mass fraction of the binder in the positive electrode active layer 530 is too large, the shear viscosity of the positive electrode slurry formed by the mixture of the positive electrode active material, the binder and the conductive agent increases, the fluidity deteriorates, and the thixotropic recovery first increases and then decreases, making it difficult to coat normally. When the average mass fraction of the binder in the positive electrode active layer 530 is in the range of 0.8%≤y≤3.9%, the positive electrode active particles can form a uniform and stable dispersed structure in the positive electrode slurry, so that better coating can be performed and the phenomenon of falling off or dropping of the positive electrode sheet 500 can be reduced.

[0097] Optionally, in the positive electrode active layer 530 , the average mass fraction of the conductive agent is in the range of 0≤z≤2%.

[0098] Specifically, in the positive electrode active layer 530, the average mass fraction of the conductive agent may be, but is not limited to, 0, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.

[0099] It is understandable that the positive electrode active layer 530 may not have a conductive agent, but the absence of a conductive agent will have a certain impact on the dynamic performance of the positive electrode active layer 530 .

[0100] In this embodiment, if the average mass fraction of the conductive agent is too small, the conductive layer of the positive electrode active layer 530 will be too poor, which is not conducive to the dynamic performance of the positive electrode plate 500; if the average mass fraction of the conductive agent is too large, the positive electrode slurry formed by the positive electrode active material, the binder and the conductive agent will be difficult to disperse and the slurry will be easy to agglomerate, which is not conducive to the coating of the positive electrode slurry.

[0101] In some embodiments, in the positive electrode active layer 530, the average mass fraction of the positive electrode active material is in the range of 96.5%≤x≤97.0%, the average mass fraction of the binder is in the range of 2.2%≤y≤3.2%, and the average mass fraction of the conductive agent is in the range of 0.3%≤z≤0.8%. In this way, the positive electrode sheet 500 can have a higher specific capacity and better kinetic performance, and the positive electrode active layer 530 is not easy to crack and shed powder.

[0102] In some embodiments, the concentration of the binder gradually decreases from a side of the positive electrode active layer 530 away from the positive electrode current collector 510 to a side of the positive electrode active layer 530 close to the positive electrode current collector 510 .

[0103] It can be understood that the concentration of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is greater than the concentration of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 .

[0104] It can also be understood that the distribution of the binder in the positive electrode active layer 530 gradually increases from the side close to the positive electrode current collector 510 to the side away from the positive electrode current collector 510 .

[0105] In this embodiment, by making the binder distributed in the positive electrode active layer 530 in a gradient, the positive electrode active layer 530 has a higher concentration on the side away from the positive electrode current collector 510, which can better prevent the positive electrode active layer 530 of the positive electrode plate 500 from falling off or falling off. In addition, when the positive electrode plate 500 is applied to the battery 400, the positive electrode active layer 530 can be better swollen by the electrolyte and enter the inside of the positive electrode plate 500, which is beneficial to the liquid retention of the positive electrode active layer 530. Furthermore, the amount of surface binder of the positive electrode active layer 530 increases, which can increase the polarization effect of the positive electrode plate 500, improve the high-voltage stability of the positive electrode plate 500, and thus improve the safety of the battery 400 under overcharge voltage conditions.

[0106] In some embodiments, the difference between the mass fraction of the binder on the side of the positive active layer 530 away from the positive current collector 510 and the mass fraction of the binder on the side of the positive active layer 530 close to the positive current collector 510 is in the range of 0.01%≤△y≤0.4%.

[0107] In other words, the difference in mass concentration of the binder between the positive electrode active layer 530 at the side away from the positive electrode current collector 510 and the positive electrode active layer 530 at the side close to the positive electrode current collector 510 is in the range of 0.01%≤△y≤0.4%.

[0108] Specifically, the difference between the mass fraction of the binder on the side of the positive electrode active layer 530 facing away from the positive electrode current collector 510 and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 may be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0109] For example, the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 3.0%, and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 2.7%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the binder gradually decreases from 3.0% to 2.7%.

[0110] For another example, the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 3.5%, and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 3.1%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the binder gradually decreases from 3.5% to 3.1%.

[0111] For another example, the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 1.5%, and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 1.3%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the binder gradually decreases from 1.5% to 1.3%.

[0112] In this embodiment, the difference between the mass fraction of the binder on the side of the positive active layer 530 away from the positive current collector 510 and the mass fraction of the binder on the side of the positive active layer 530 close to the positive current collector 510 is too large, so the binder content of the positive active layer 530 close to the positive current collector 510 is too little, and the binder content of the position away from the positive current collector 510 is too much, which reduces the adhesion of the positive active layer 530 on the positive current collector 510, and the positive active layer 530 is prone to foil peeling, which increases the impedance and affects the performance of the battery 400 using the positive electrode sheet 500. Energy; if the difference between the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is too small, the bonding force of the surface of the positive electrode active layer 530 is insufficient, and the positive electrode active layer 530 is prone to powdering or slagging, which affects the capacity and cycle capacity retention rate of the positive electrode plate 500, and has poor swelling performance for the electrolyte, which is not conducive to the electrolyte entering the interior of the positive electrode plate 500, that is, the penetration ability of the electrolyte molecules into the interior of the positive electrode active layer 530 is reduced, which is not conducive to liquid retention.

[0113] Furthermore, the difference between the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is in the range of 0.05%≤△y≤0.3%. When the difference between the mass fraction of the binder on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 and the mass fraction of the binder on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is within this range, the bottom of the positive electrode active layer 530 (i.e., the part close to the positive electrode current collector 510) can have higher adhesion, so that the positive electrode active layer 530 and the positive electrode current collector 510 have higher bonding force; at the same time, the surface layer of the positive electrode active layer 530 (i.e., the part away from the positive electrode current collector 510) has sufficient adhesive, and is not prone to powdering or slag falling. In addition, the positive electrode active layer 530 can better absorb the electrolyte, which is conducive to the electrolyte entering the interior of the positive electrode plate 500.

[0114] See also Fig.10 In some embodiments, along the stacking direction of the positive electrode current collector 510 and the positive electrode active layer 530, the positive electrode active layer 530 is divided into a first layer 531 and a second layer 533 of equal thickness, the first layer 531 is farther away from the positive electrode current collector 510 than the second layer 533, the average mass fraction of the binder in the first layer 531 is y1, and the average mass fraction of the binder in the second layer 533 is y2, then 1.01≤y1 / y2≤1.20.

[0115] Specifically, y1 / y2 can be, but is not limited to, 1.01, 1.03, 1.05, 1.07, 1.1, 1.12, 1.14, 1.16, 1.18, 1.20, etc.

[0116] In this embodiment, if y1 / y2 is too small, the bonding force of the surface of the positive electrode active layer 530 is insufficient, and the positive electrode active layer 530 is prone to powdering or slagging, which affects the capacity and cycle capacity retention rate of the positive electrode plate 500, and has poor swelling performance for the electrolyte, which is not conducive to the electrolyte entering the interior of the positive electrode plate 500; if y1 / y2 is too large, the positive electrode active layer 530 has too little binder near the positive electrode current collector 510, and the binder content is too much at the position away from the positive electrode current collector 510, which reduces the adhesion of the positive electrode active layer 530 to the positive electrode current collector 510, and the positive electrode active layer 530 is prone to foil peeling, which increases impedance and affects the performance of the battery 400 using the positive electrode plate 500. When y1 / y2 is 1.01 to 1.2, the positive electrode active layer 530 can have good adhesion on the positive electrode collector 510 and the positive electrode active layer 530 is not easy to fall off. At the same time, the binder on the surface of the positive electrode active layer 530 can be better swelled by the electrolyte, which is beneficial for the electrolyte to penetrate into the positive electrode plate 500, and is beneficial for improving the dynamic performance of the positive electrode plate 500; in addition, it can also increase the polarization effect on the side of the positive electrode plate 500, improve the high-voltage stability of the positive electrode plate 500, and thus improve the safety of the battery 400 under overcharge voltage conditions.

[0117] In some embodiments, the concentration of the conductive agent gradually decreases from a side of the positive electrode active layer 530 away from the positive electrode current collector 510 to a side of the positive electrode active layer 530 close to the positive electrode current collector 510 .

[0118] It can be understood that the concentration of the conductive agent on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is greater than the concentration of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 .

[0119] It can also be understood that the distribution of the conductive agent in the positive electrode active layer 530 gradually increases from the side close to the positive electrode current collector 510 to the side away from the positive electrode current collector 510 .

[0120] In this embodiment, by making the concentration of the conductive agent on the surface of the positive electrode active layer 530 larger and the concentration of the conductive agent in the bottom layer of the positive electrode active layer 530 smaller, and gradually reducing the concentration of the conductive agent from the surface layer to the bottom layer, the surface of the positive electrode active layer 530 can have a smaller contact impedance, thereby having better rate performance. In addition, the positive electrode active layer 530 can also have a more uniformly distributed current density.

[0121] In some embodiments, the difference between the mass fraction of the conductive agent on the side of the positive active layer 530 away from the positive current collector 510 and the mass fraction of the conductive agent on the side of the positive active layer 530 close to the positive current collector 510 is in the range of 0.01%≤Δz≤0.4%.

[0122] In other words, the mass concentration difference of the conductive agent in the positive electrode active layer 530 between the side of the positive electrode active layer 530 away from the positive electrode current collector 510 and the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is in the range of 0.01%≤△z≤0.4%.

[0123] Specifically, the difference between the mass fraction of the conductive agent on the side of the positive electrode active layer 530 facing away from the positive electrode current collector 510 and the mass fraction of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 may be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0124] For example, the mass fraction of the conductive agent on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 2%, and the mass fraction of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 1.6%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the conductive agent gradually decreases from 2.0% to 1.6%.

[0125] For another example, the mass fraction of the conductive agent on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 1.5%, and the mass fraction of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 1.25%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the conductive agent gradually decreases from 1.5% to 1.25%.

[0126] For another example, the mass fraction of the conductive agent on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 is 1%, and the mass fraction of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is 0.7%; from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, the concentration of the conductive agent gradually decreases from 10% to 0.7%.

[0127] In this embodiment, if the difference between the mass fraction of the conductive agent in the side of the positive active layer 530 away from the positive current collector 510 (also called the surface layer) and the mass fraction of the conductive agent in the side of the positive active layer 530 close to the positive current collector 510 (also called the bottom layer) is too small, the conductivity of the surface layer of the positive active layer 530 is less different from that of the bottom layer, so that the contact impedance of the surface of the positive active layer 530 away from the positive current collector 510 is large, and the rate performance of the positive electrode sheet 500 is poor; if the difference between the mass fraction of the conductive agent in the side of the positive active layer 530 away from the positive current collector 510 and the mass fraction of the conductive agent in the side of the positive active layer 530 close to the positive current collector 510 is too large, the conductivity of the side of the positive active layer 530 facing the positive current collector 510 is poor, so that the current distribution of the positive electrode sheet 500 is uneven, which affects the performance of the battery 400 using the positive electrode sheet 500. When the difference between the mass fraction of the conductive agent on the side of the positive electrode active layer 530 away from the positive electrode current collector 510 and the mass fraction of the conductive agent on the side of the positive electrode active layer 530 close to the positive electrode current collector 510 is in the range of: 0.01%≤△y≤0.4%, the surface of the positive electrode active layer 530 can have a smaller contact impedance, thereby having better rate performance. In addition, the positive electrode active layer 530 can also have a more uniformly distributed current density.

[0128] In some embodiments, along the stacking direction of the positive electrode current collector 510 and the positive electrode active layer 530, the positive electrode active layer 530 is divided into a first layer 531 and a second layer 533 of equal thickness, the first layer 531 is farther away from the positive electrode current collector 510 than the second layer 533, the average mass fraction of the conductive agent in the first layer 531 is z1, and the average mass fraction of the conductive agent in the second layer 533 is z2, then 1.01≤z1 / z2≤1.20.

[0129] Specifically, z1 / z2 can be, but is not limited to, 1.01, 1.03, 1.05, 1.07, 1.1, 1.12, 1.14, 1.16, 1.18, 1.20, etc.

[0130] In this embodiment, if z1 / z2 is too small, the difference in conductivity between the first layer 531 and the second layer 533 of the positive electrode active layer 530 is small, so that the contact impedance of the surface of the positive electrode active layer 530 away from the positive electrode current collector 510 is large, and the rate performance of the positive electrode plate 500 is poor; if z1 / z2 is too large, the conductivity of the side of the positive electrode active layer 530 facing the positive electrode current collector 510 (or the second layer 533) is poor, so that the current distribution of the positive electrode plate 500 is uneven, affecting the performance of the battery 400 using the positive electrode plate 500. When 1.01≤z1 / z2≤1.20, the surface of the positive electrode active layer 530 can have a small contact impedance, so as to have a better rate performance, and in addition, the positive electrode active layer 530 can also have a more uniformly distributed current density.

[0131] See also Fig.11 In some embodiments, the positive electrode plate 500 further includes a primer layer 520 , and the primer layer 520 is disposed between the positive current collector 510 and the positive active layer 530 , and the primer layer 520 is used to improve the adhesion of the positive active layer 530 on the positive current collector 510 .

[0132] In this embodiment, by providing a primer layer 520 between the positive current collector 510 and the positive active layer 530, the adhesion of the positive active layer 530 on the positive current collector 510 can be improved, thereby better preventing the positive electrode plate 500 from being delaminated or the positive active layer 530 from falling off during use, thereby improving the cycle performance of the battery 400 using the positive electrode plate 500.

[0133] In some embodiments, the mass fraction of the undercoat layer 520 in the positive electrode active layer 530 is b, wherein 4≤y / b≤8.

[0134] It can be understood that the ratio of the mass fraction y of the binder in the positive electrode active layer 530 to the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 is in the range of 4 to 8. Specifically, the ratio of the mass fraction y of the binder in the positive electrode active layer 530 to the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 is 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, etc.

[0135] Optionally, the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 ranges from 0.1% to 0.3%. Specifically, the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 may be, but is not limited to, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.28%, 0.3%. If the mass fraction of the undercoat layer 520 in the positive electrode active layer 530 is too small, the adhesion of the undercoat layer 520 is insufficient, which reduces the adhesion of the positive electrode active layer 530 on the positive electrode current collector 510, making the positive electrode active layer 530 easy to peel off; if the mass fraction of the undercoat layer 520 in the positive electrode active layer 530 is too large, the proportion of the positive electrode active layer 530 is reduced, the content of the positive electrode active material is reduced, and the energy density of the positive electrode sheet 500 is reduced.

[0136] In this embodiment, the ratio of the mass fraction y of the binder in the positive electrode active layer 530 to the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 is too small, and the mass fraction of the undercoat layer 520 in the positive electrode active layer 530 is too large, that is, the content of the undercoat layer 520 is too large, which will increase the thickness of the positive electrode plate 500, reduce the total proportion of the positive electrode active layer 530, and affect the volume capacity and mass capacity of the battery 400 using the positive electrode plate 500; the ratio of the mass fraction y of the binder in the positive electrode active layer 530 to the mass fraction b of the undercoat layer 520 in the positive electrode active layer 530 is too large, and the mass fraction of the undercoat layer 520 in the positive electrode active layer 530 is too small, that is, the content of the undercoat layer 520 is too small, which will reduce the adhesion between the active material layer and the positive current collector 510, easily cause foil peeling, reduce the conductivity of the positive electrode plate 500, increase the impedance, and affect the performance of the battery 400 using the positive electrode plate 500.

[0137] In some embodiments, the base coating 520 includes a binder and conductive particles. In the base coating 520 , the mass fraction of the conductive particles ranges from 0.01% to 0.1%.

[0138] Specifically, in the primer layer 520, the mass fraction of the conductive particles may be, but is not limited to, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, etc. If the mass fraction of the conductive particles is too small, the conductivity of the primer layer 520 is reduced and the impedance of the primer layer 520 is increased; if the mass fraction of the conductive particles is too large, the conductive particles are easily dispersed unevenly in the adhesive, so that the battery 400 using the positive electrode sheet 500 is prone to excessive local current during the subsequent charge and discharge process, affecting the performance of the battery 400.

[0139] Optionally, the adhesive may be, but is not limited to, at least one of polyacrylic acid (PAA for short), polymethyl acrylate (PMA for short), polymethyl methacrylate (PMMA for short), and polyacrylonitrile (PAN for short).

[0140] Optionally, the conductive particles may be, but are not limited to, at least one of conductive carbon black and carbon nanotubes.

[0141] In this embodiment, by adding conductive particles with a mass fraction of 0.01% to 0.1% to the base coating 520, the adhesion layer of the positive electrode active layer 530 on the surface of the positive electrode current collector 510 can be improved, the conductivity of the base coating 520 can be improved, the impedance of the base coating 520 can be reduced, and the problems of uneven dispersion of conductive particles and excessive local current caused by excessive conductive particle content can be avoided.

[0142] The resistivity of the positive electrode plate 500 of the present application is 60Ω·cm to 90Ω·cm; for example, 60Ω·cm, 65Ω·cm, 70Ω·cm, 75Ω·cm, 80Ω·cm, 85Ω·cm, 90Ω·cm, etc.

[0143] The charge transfer impedance Rct of the positive electrode plate 500 of the present application is 9Ω to 12Ω; for example, 9Ω, 10Ω, 11Ω, 112Ω, etc.

[0144] It is found through experiments that the positive electrode plate 500 of the present application that satisfies the relationship 24.5≤x / (y+z)≤34.5 has a lower resistivity and charge transfer impedance, which is beneficial to the dynamic performance of using the positive electrode plate 500.

[0145] The positive electrode plate 500 of the embodiment of the present application can be prepared by the method described in the following embodiments of the present application. In addition, it can also be prepared by other methods. The preparation method of the embodiment of the present application is only one or more preparation methods of the positive electrode plate 500 of the present application, and should not be understood as a limitation on the positive electrode plate 500 provided in the embodiment of the present application.

[0146] The present application also provides a method for preparing a positive electrode sheet 500, the method comprising:

[0147] 1) Weighing a positive electrode active material, a conductive agent and a binder according to a preset ratio, respectively, and stirring and dispersing the positive electrode active material, the conductive agent and the binder in an organic solvent (e.g., N-methylpyrrolidone, NMP), and stirring at a speed of 250 rpm to 450 rpm for 30 min to 90 min to prepare a positive electrode slurry;

[0148] 2) The positive electrode slurry is coated on the positive electrode current collector 510 (such as the aluminum foil) and dried to obtain the positive electrode sheet 500 .

[0149] Specifically, the positive electrode slurry is coated on the positive electrode collector 510 at a coating speed of 4 to 7.5 m / min, and moved in a vacuum drying oven at a temperature of 100° C. to 115° C. at a speed of 4 to 7.5 m / min to move from the head to the tail of the vacuum drying oven.

[0150] Optionally, the coating speed of the positive electrode slurry ranges from 4 m / min to 7.5 m / min; specifically, the coating speed of the positive electrode slurry may be, but is not limited to, 4 m / min, 4.5 m / min, 5 m / min, 5.5 m / min, 6 m / min, 6.5 m / min, 7 m / min, 7.5 m / min, etc.

[0151] Optionally, after coating, the coating is dried in a vacuum drying oven, and the temperature of the drying oven ranges from 100° C. to 115° C. Specifically, the temperature of the drying oven can be, but is not limited to, 100° C., 102° C., 104° C., 108° C., 110° C., 112° C., 114° C., 115° C., etc.

[0152] Optionally, the moving speed of the positive electrode sheet 500 during drying ranges from 4 m / min to 7.5 m / min; specifically, the moving speed of the positive electrode sheet 500 during drying can be but is not limited to 4 m / min, 4.5 m / min, 5 m / min, 5.5 m / min, 6 m / min, 6.5 m / min, 7 m / min, 7.5 m / min, etc.

[0153] It can be understood that when the positive electrode sheet 500 includes the primer layer 520 , the primer layer 520 is coated on the positive current collector 510 , and then the positive electrode slurry is coated on the primer layer 520 to form the positive electrode active layer 530 .

[0154] The preparation method of the positive electrode plate 500 of the present application controls the drying temperature and drying time of the positive electrode slurry so that the concentration of the binder in the positive electrode active layer 530 gradually decreases from the side of the positive electrode active layer 530 away from the positive electrode current collector 510 to the side of the positive electrode active layer 530 close to the positive electrode current collector 510, and the concentration of the conductive agent also gradually decreases, and the concentration gradient of the binder and the conductive agent is controlled within a certain range.

[0155] Any solid surface will appear uneven when magnified. To make the adhesive completely fit the morphology of the solid surface, the adhesive must be turned into liquid during the bonding process and completely wet the solid surface. If the wetness is incomplete, many bubbles will appear in the interface. Under the action of stress, stress concentration will occur around the bubbles, resulting in a decrease in strength. Since the surface tension of organic liquids does not differ too much, the time required for wetness mainly depends on the liquid viscosity and the contact angle. The lower the liquid viscosity, the shorter the wetness time, and the surface gaps can be fully wetted; the smaller the contact angle, the faster the wetness speed. When the adhesive is PVDF and the organic solvent is NMP, the free ammonia in NMP attacks the CF bond of PVDF, causing the CF and CH bonds to break and form double bonds on the PVDF chain. At the same time, the double bonds are very unstable and are easily attacked by other polar groups in the solution, causing PVDF to connect to other groups. Generally, this separation helps to improve the bonding performance of PVDF. Therefore, during the manufacturing process of the positive electrode plate 500, the reaction time is controlled to adjust the HF separation reaction so that the coating drying temperature and the surface viscosity remain unchanged, but the wetting effect is improved, thereby improving the dynamics and reducing the impedance.

[0156] The positive electrode plate 500 of the present application is further described below through specific embodiments.

[0157] Example 1

[0158] The positive electrode sheet 500 of this embodiment is prepared by the following steps:

[0159] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0160] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, and fully stirred and dispersed in NMP at a ratio of x / (y+z)=34.5. The slurry was stirred at a speed of 350 rpm for 60 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0161] 3) The positive electrode slurry is coated on the surface of the base coating 520 facing away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 6 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 110°C. The positive electrode slurry is moved in the vacuum drying oven at a speed of 6 m / min, and is rolled up at the tail of the vacuum drying oven to obtain the positive electrode sheet 500.

[0162] Example 2

[0163] The positive electrode sheet 500 of this embodiment is prepared by the following steps:

[0164] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0165] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, and fully stirred and dispersed in NMP at a ratio of x / (y+z)=32. The slurry was stirred at a speed of 350 rpm for 80 min to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0166] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 6.5 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 108°C. The positive electrode slurry is moved in the vacuum drying oven at a speed of 6.5 m / min, and rolled up at the tail of the vacuum drying oven to obtain the positive electrode sheet 500.

[0167] Example 3

[0168] The positive electrode sheet 500 of this embodiment is prepared by the following steps:

[0169] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0170] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, and fully stirred and dispersed in NMP at a ratio of x / (y+z)=30. The slurry was stirred at a speed of 350 rpm for 60 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0171] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 5.5 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 105°C. The device is moved in the vacuum drying oven at a speed of 6.5 m / min, and is rolled up at the tail of the vacuum drying oven to obtain a positive electrode sheet 500.

[0172] Example 4

[0173] The positive electrode sheet 500 of this embodiment is prepared by the following steps:

[0174] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0175] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, and fully stirred and dispersed in NMP at a ratio of x / (y+z)=28. The slurry was stirred at a speed of 350 rpm for 60 min to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0176] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 5.5 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 110°C. The device is moved in the vacuum drying oven at a speed of 6.5 m / min, and is rolled up at the tail of the vacuum drying oven to obtain a positive electrode sheet 500.

[0177] Example 5

[0178] The positive electrode sheet 500 of this embodiment is prepared by the following steps:

[0179] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0180] 1) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, fully stirred and dispersed in NMP at a ratio of x / (y+z)=24.5, and stirred at a speed of 350 rpm for 60 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0181] 3) The positive electrode slurry is coated on the surface of the base coating 520 facing away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 5.5 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 108°C. The device is moved in the vacuum drying oven at a speed of 6 m / min, and is rolled up at the tail of the vacuum drying oven to obtain a positive electrode sheet 500.

[0182] Comparative Example 1

[0183] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0184] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, fully stirred and dispersed in NMP at a ratio of x / (y+z)=34.5, and stirred at a speed of 350 rpm for 40 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0185] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 7 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 105°C. The positive electrode slurry is moved in the vacuum drying oven at a speed of 7 m / min, and rolled up at the tail of the vacuum drying oven to obtain the positive electrode sheet 500.

[0186] Comparative Example 2

[0187] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0188] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, fully stirred and dispersed in NMP at a ratio of x / (y+z)=34.5, and stirred at a speed of 350 rpm for 40 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0189] 3) The positive electrode slurry is coated on the surface of the base coating 520 facing away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 4.5 / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 105°C. The positive electrode slurry is moved in the vacuum drying oven at a speed of 4.5m / min, and rolled up at the tail of the vacuum drying oven to obtain the positive electrode sheet 500.

[0190] Comparative Example 3

[0191] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0192] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, fully stirred and dispersed in NMP at a ratio of x / (y+z)=36, and stirred at a speed of 350 rpm for 40 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0193] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 7 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 108°C. The device is moved in the vacuum drying oven at a speed of 6.5 m / min, and is rolled up at the tail of the vacuum drying oven to obtain a positive electrode sheet 500.

[0194] Comparative Example 4

[0195] 1) polymethyl methacrylate (PMMA, i.e., adhesive) and conductive carbon black (i.e., conductive particles) are placed in a stirring tank, fully stirred and dispersed in water at a certain ratio to prepare a primer slurry, and the primer slurry is coated on the aluminum foil (positive electrode current collector 510), and after drying, a positive electrode current collector 510 coated with a primer 520 (i.e., an aluminum foil coated with a primer 520) is obtained;

[0196] 2) Lithium iron phosphate (positive electrode active material LFP), conductive carbon black (conductive agent), and PVDF (binder) were placed in a stirring tank, fully stirred and dispersed in NMP at a ratio of x / (y+z)=22, and stirred at a speed of 350 rpm for 40 minutes to obtain a positive electrode slurry, wherein the value of y / b is shown in Table 1 below;

[0197] 3) The positive electrode slurry is coated on the surface of the base coating 520 away from the aluminum foil (positive electrode current collector 510), and the coating speed is controlled to be 7 m / min. Then, it is placed in a vacuum drying oven, and the temperature of the drying oven is set to 108°C. The device is moved in the vacuum drying oven at a speed of 6.5 m / min, and is rolled up at the tail of the vacuum drying oven to obtain a positive electrode sheet 500.

[0198] Performance Testing

[0199] (1) Peeling force test: The positive electrode sheet is cut into strips of 25 mm in width and 20 cm in length by a cutting machine. A steel plate and a 3M double-sided tape of 20 mm × 100 mm are taken, and the positive electrode sheet, the double-sided tape and the steel plate are overlapped in sequence. The positive electrode sheet and the steel plate are rolled back and forth 3 times with a roller to make the positive electrode sheet firmly bonded to the steel plate. The positive electrode sheet and the steel plate are manually separated for a certain length, and the steel plate at the separated end is fixed to the fixed fixture of the tensile machine. The positive electrode sheet at the separated end is fixed to the tensile fixture of the tensile machine, and the tensile machine is started for stretching. The stretching speed is 50 mm / min, and a tension-displacement curve (i.e., peeling force curve) is obtained. The tension with a displacement between 30 mm and 50 mm in the tension-displacement curve is selected, and the average value is calculated to obtain the peeling force between the positive current collector and the positive active layer of the positive electrode sheet.

[0200] The peeling force test curve of the positive electrode sheet of Example 1 is as follows: Fig.12 As shown, the peeling force test curve of the positive electrode sheet of comparative example 1 is as follows Fig.13 shown.

[0201] (2) Test of the mass fraction of the binder: The part of the positive electrode sheet containing the binder is scraped and powdered, placed in a crucible, and subjected to a thermogravimetric test (TGA). The temperature is raised from 25°C to 650°C in a N2 atmosphere at a rate of 10°C / min; the mass fraction of the binder = (weight change rate at 550°C - weight change rate at 300°C) / 65%, where 65% is the decomposition ratio of the binder at high temperature.

[0202] (3) Symmetrical battery EIS impedance test of positive electrode sheet: After the small soft-pack symmetrical battery assembled with the positive electrode sheet is clamped, it is placed in a high-temperature box at 25°C for 10 minutes. The test line is connected to the test board in the high-temperature box, and the battery is clamped on the test board. Open the Mulistat test software, click the Pstat button, set the protection voltage to 4V and the protection current to 1A, select the test item interface, and click Impedance to enter the impedance test interface, and set the disturbance voltage to 5mV, set the high frequency to 1MHz and the low frequency to 0.01Hz for testing. The Nyquist impedance spectra of the positive electrode sheets of Example 1 and Comparative Example 1 are shown in Figure 1. Fig.14 shown.

[0203] (4) Discharge capacity test: The positive electrode sheets 500 of the above-mentioned embodiments and comparative examples are used as the counter electrode to form a half-button battery 400, and the discharge capacity of the half-button battery 400 at room temperature (i.e., 25° C.) at 0.1P rate and 1P rate is measured. The discharge curves of the half-button battery composed of the positive electrode sheets of Embodiment 1 and Comparative Example 1 at 0.1P rate and 1P rate are shown in the figure below: Fig.15 As shown, the left figure is a discharge curve diagram at a 0.1P rate, and the right figure is a discharge curve diagram at a 1P rate.

[0204] Table 1 Parameters of each embodiment and each comparative example

[0205]

[0206]

[0207] From the test data of Examples 1 to 5, Comparative Examples 1 and 2, it can be seen that when 1.01≤y1 / y2≤1.20, as y1 / y2 increases, the resistivity and charge transfer impedance of the positive electrode sheet 500 first gradually decrease, and then gradually increase. When y1 / y2=1.15, the resistivity and charge transfer impedance of the positive electrode sheet 500 reach the minimum.

[0208] It can be seen from the test results of Example 1 and Comparative Example 1 that when the material composition and ratio of the positive electrode active layer 530 are the same (i.e., x / (y+z)=34.5), when 1.01≤y1 / y2≤1.20 (y1 / y2=1.15 in Example 1), the positive electrode sheet 500 has a lower resistivity and a lower charge transfer impedance. When y1 / y2 is greater than 1.2, the resistivity and charge transfer impedance of the positive electrode sheet 500 are greatly increased. Compared with Comparative Example 1, the resistivity of the positive electrode sheet 500 in Example 1 is reduced by nearly 30%, and the charge transfer impedance is reduced by nearly 25%. In addition, the peeling force, 0.1P and 1P discharge capacity of the positive electrode active layer 530 in Example 1 are slightly increased compared with Comparative Example 1, but the increase is not much.

[0209] From the test data of Examples 1 to 5, Comparative Examples 3 and 4, it can be seen that when 24.5≤x / (y+z)≤34.5, the positive electrode active layer 530 has a high bonding force or peeling force, is not easy to drop powder or material, and the resistivity and charge transfer impedance of the positive electrode sheet 500 are both small; from the test results of Comparative Example 4, it can be seen that when x / (y+z)=22<24.5, the bonding force of the positive electrode active layer 530 is greatly reduced, and the resistivity and charge transfer impedance of the positive electrode sheet 500 also increase. From the test results of Comparative Example 3, it can be seen that when x / (y+z)=36>34.5, although the bonding force of the positive electrode active layer 530 increases, the resistivity and charge transfer impedance of the positive electrode sheet 500 are both large, which is not conducive to the dynamics of the positive electrode sheet 500.

[0210] Mentioning "embodiment" and "implementation method" in this application means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should also be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, provided that there is no contradiction between them.

[0211] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the above preferred implementation modes, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A positive electrode sheet, characterized in that: include: Positive electrode current collector; as well as A positive electrode active layer, wherein the positive electrode active layer is arranged on one side of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material, a binder and a conductive agent, wherein in the positive electrode active layer, the average mass fraction of the positive electrode active material is x, the average mass fraction of the binder is y, and the average mass fraction of the conductive agent is z, wherein the positive electrode active layer satisfies the relationship: 24.5≤x / (y+z)≤34.

5.

2. The positive electrode sheet according to claim 1, characterized in that: The concentration of the binder gradually decreases from a side of the positive electrode active layer away from the positive electrode current collector to a side of the positive electrode active layer close to the positive electrode current collector.

3. The positive electrode sheet according to claim 2, characterized in that: The difference between the mass fraction of the binder on the side of the positive electrode active layer away from the positive electrode current collector and the mass fraction of the binder on the side of the positive electrode active layer close to the positive electrode current collector is in the range of 0.01%≤△y≤0.4%.

4. The positive electrode sheet according to claim 1, characterized in that: Along the stacking direction of the positive electrode current collector and the positive electrode active layer, the positive electrode active layer is divided into a first layer and a second layer of equal thickness, the first layer is farther away from the positive electrode current collector than the second layer, the average mass fraction of the binder in the first layer is y1, and the average mass fraction of the binder in the second layer is y2, then 1.01≤y1 / y2≤1.

20.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The concentration of the conductive agent gradually decreases from a side of the positive electrode active layer away from the positive electrode current collector to a side of the positive electrode active layer close to the positive electrode current collector.

6. The positive electrode sheet according to claim 5, characterized in that: The difference between the mass fraction of the conductive agent on the side of the positive electrode active layer away from the positive electrode current collector and the mass fraction of the conductive agent on the side of the positive electrode active layer close to the positive electrode current collector is in the range of 0.01%≤Δz≤0.4%.

7. The positive electrode sheet according to claim 5, characterized in that: Along the stacking direction of the positive electrode current collector and the positive electrode active layer, the positive electrode active layer is divided into a first layer and a second layer of equal thickness, the first layer is farther away from the positive electrode current collector than the second layer, the average mass fraction of the conductive agent in the first layer is z1, and the average mass fraction of the conductive agent in the second layer is z2, then 1.01≤z1 / z2≤1.

20.

8. The positive electrode sheet according to any one of claims 1 to 4, 6 and 7, characterized in that: The positive electrode plate further includes a primer layer, which is disposed between the positive electrode current collector and the positive electrode active layer.

9. The positive electrode sheet according to claim 8, characterized in that: The mass fraction of the undercoat layer to the positive electrode active layer is b, wherein 4≤y / b≤8.

10. A battery, It is characterized by; including: Electrolyte; The positive electrode sheet according to any one of claims 1 to 9, wherein the positive electrode sheet is at least partially immersed in the electrolyte; a diaphragm, the diaphragm being located on one side of the positive electrode plate and at least partially immersed in the electrolyte, and A negative electrode plate is disposed on a side of the diaphragm away from the positive electrode plate and is at least partially immersed in the electrolyte.

11. An energy storage device, characterized in that: include: Box; A plurality of batteries according to claim 10, wherein the plurality of batteries are housed in the housing, and the plurality of batteries are connected in at least one of series connection and parallel connection.

12. An electricity system, characterized in that: include: Electrical equipment; as well as The battery according to claim 10, wherein the battery is electrically connected to the electrical device and is used to supply power to the electrical device.

13. An energy storage system, characterized in that: include: An electric energy conversion device, the electric energy conversion device is used to convert other forms of energy into electric energy; The energy storage device of claim 11, wherein the energy storage device is electrically connected to the electric energy conversion device and is used to store the electric energy of the electric energy conversion device; and An electrical load, wherein the electrical load is electrically connected to the electric energy conversion device and the energy storage device respectively, and is used to work using the electric energy of the electric energy conversion device or the energy storage device.

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