Positive plate and preparation method thereof, battery, battery pack and electric equipment

Abstract

The invention discloses a positive plate and a preparation method thereof, a battery, a battery pack and electric equipment, the positive plate comprises a current collector and a plurality of positive active layers, the plurality of positive active layers are sequentially arranged on at least one side surface of the current collector in the thickness direction, each positive active layer comprises a polymer and a plasticizer, and the polymer and the plasticizer are arranged in the direction away from the current collector. The weight-average molecular weights of the polymers of the plurality of positive electrode active layers are sequentially increased, and the molar molecular weights of the plasticizers of the plurality of positive electrode active layers are sequentially increased. According to the positive plate disclosed by the invention, the synergistic effect of the polymer and the plasticizer is favorably exerted, an ion path in the positive plate is optimized, the ionic conductivity of the positive plate is improved, meanwhile, the activity of a polymer molecular chain is suitable for the requirement of a corresponding positive active layer, the battery polarization can be effectively reduced, and the electrochemical performance of the positive plate is improved. Therefore, the gradient ionic conductivity of the positive plate is improved, the ionic conductivity of the positive plate is improved, polarization is reduced, an ion transmission path is optimized, and the ionic conductivity and rate capability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode sheets, and particularly to a positive electrode sheet, a preparation method thereof, a battery, a battery pack, and an electrical device. Background Art

[0002] The positive electrode material is one of the core components determining the battery performance. It not only affects the energy density of the battery, but also has a direct impact on the power density, cycle stability, and safety. An ideal positive electrode material needs to have a high theoretical specific capacity, good structural stability, and high electronic and ionic conductivity.

[0003] In related technologies, in order to improve the ionic conductivity of the positive electrode material and enhance the fast charge-discharge ability and overall performance of the battery, treatment methods such as nanotechnology, doping modification, and surface coating treatment are usually adopted. However, the above treatment methods have limited improvement in the ionic conductivity of the positive electrode sheet and are prone to cause the phenomenon of battery polarization (polarization is a phenomenon in which the charge distribution inside the dielectric changes under the action of an electric field, forming electric dipoles or changing the orientation of the original electric dipoles). Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first object of the present invention is to provide a positive electrode sheet, which improves the gradient ionic conductivity of the positive electrode sheet, enhances the ionic conductivity of the positive electrode sheet and reduces polarization, optimizes the ion transport path, and improves the ionic conductivity and rate performance.

[0005] The second object of the present invention is to provide a preparation method of a positive electrode sheet.

[0006] The third object of the present invention is to provide a battery.

[0007] The fourth object of the present invention is to provide a battery pack.

[0008] The fifth object of the present invention is to provide an electrical device.

[0009] The positive electrode sheet according to the first aspect embodiment of the present invention includes: a current collector; a plurality of positive electrode active layers, the plurality of positive electrode active layers are sequentially arranged on at least one surface in the thickness direction of the current collector, the positive electrode active layer includes a polymer and a plasticizer, and along the direction away from the current collector, the weight average molecular weight of the polymer of the plurality of positive electrode active layers increases sequentially, and the molar molecular weight of the plasticizer of the plurality of positive electrode active layers increases sequentially.

[0010] According to the positive electrode sheet of the embodiment of the present invention, by regulating the weight-average molecular weight of the polymer and the molar molecular weight of the plasticizer in multiple positive electrode active layers, it helps to exert the synergistic effect of the polymer and the plasticizer, optimize the ion pathway inside the positive electrode sheet, improve the ionic conductivity of the positive electrode sheet, and the gradient design of the plasticizer helps to adjust the interaction force between the corresponding polymer molecular chains, making the activity of the polymer molecular chains suitable for the needs of the corresponding positive electrode active layer, which can effectively reduce battery polarization and improve the electrochemical performance of the positive electrode sheet. Thereby, the gradient ionic conductance of the positive electrode sheet is improved, the ionic conductivity of the positive electrode sheet is increased and the polarization is reduced, the ion transport path is optimized, and the ionic conductivity and rate performance are improved.

[0011] According to some embodiments of the present invention, at least a first positive electrode active layer and a second positive electrode active layer are included in the multiple positive electrode active layers, wherein the weight-average molecular weight of the polymer in the first positive electrode active layer is 10,000 g / mol to 300,000 g / mol, preferably 50,000 g / mol to 150,000 g / mol; and / or the weight-average molecular weight of the polymer in the second positive electrode active layer is 400,000 g / mol to 1,000,000 g / mol, preferably 600,000 g / mol to 800,000 g / mol.

[0012] According to some embodiments of the present invention, the polymers in the multiple positive electrode active layers are independently selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyacrylonitrile, polypropylene carbonate, polyethylene oxide, and ethylene oxide-propylene oxide copolymer.

[0013] According to some embodiments of the present invention, at least a first positive electrode active layer and a second positive electrode active layer are included in the multiple positive electrode active layers, wherein the molar molecular weight of the plasticizer in the first positive electrode active layer is 40 g / mol to 250 g / mol, preferably 80 g / mol to 150 g / mol; and / or the molar molecular weight of the plasticizer in the second positive electrode active layer is 250 g / mol to 2,000 g / mol, preferably 500 g / mol to 1,000 g / mol.

[0014] According to some embodiments of the present invention, the plasticizers in the multiple positive electrode active layers are independently selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, succinonitrile, and polyethylene glycol dimethyl ether.

[0015] According to some embodiments of the present invention, the positive electrode active layer further includes at least one of an active material, a conductive agent, and an electrolyte salt, wherein the mass ratio of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer is (50-90):(1-10):(6-20):(0-10):(0-10).

[0016] According to some embodiments of the present invention, the active materials of the plurality of positive electrode active layers are independently selected from at least one of lithium cobaltate, lithium nickelate, lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium nickel iron phosphate, lithium manganate, xLi2MnO3·(1-x)LiMO2, LiNi y A (1-y) O2 and LiNimBnC (1-m-n) O2, where 0 < x < 1, M is selected from transition metals, A is selected from Co or Mn, 0 < y < 1, B and C are independently selected from Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1; and / or, the conductive agents of the plurality of positive electrode active layers are independently selected from at least one of conductive graphite, acetylene black, Super P, graphene, carbon fiber, carbon nanotube, Ketjen black, metal nanowire, and metal nanotube; and / or, the electrolyte salts of the plurality of positive electrode active layers are at least one of potassium salts, sodium salts, and lithium salts.

[0017] According to some embodiments of the present invention, when the electrolyte salts of the plurality of positive electrode active layers are all lithium salts, the electrolyte salts of the plurality of positive electrode active layers are independently selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium tetrafluoro(oxalato)phosphate.

[0018] According to some embodiments of the present invention, the thickness of the current collector is 8 μm to 25 μm, preferably 10 μm to 15 μm; and / or, at least the first positive electrode active layer and the second positive electrode active layer are included in the plurality of positive electrode active layers, the thickness of the first positive electrode active layer is 100 μm to 200 μm, preferably 120 μm to 150 μm; and / or, the thickness of the second positive electrode active layer is 100 μm to 250 μm, preferably 150 μm to 200 μm.

[0019] A method for preparing a positive electrode sheet according to an embodiment of the second aspect of the present invention includes the following steps: Provide a variety of composite slurries, each of the composite slurries includes a polymer and a plasticizer, wherein the weight average molecular weights of the polymers in at least two of the composite slurries are different, and the molar molecular weights of the plasticizers are different; By means of coextrusion, the multiple composite slurries are coated on the surface of the current collector to form a plurality of positive electrode active layers. Among them, along the direction away from the current collector, the weight-average molecular weight of the polymer in the plurality of positive electrode active layers increases in sequence, and the molar molecular weight of the plasticizer decreases in sequence. After drying, the positive electrode sheet is obtained.

[0020] The battery according to the embodiment of the third aspect of the present invention includes: a positive electrode sheet, a negative electrode sheet and a separator; wherein, the positive electrode sheet is the positive electrode sheet according to the embodiment of the first aspect of the present invention or the positive electrode sheet prepared by using the preparation method of the embodiment of the first aspect of the present invention.

[0021] The battery pack according to the embodiment of the fourth aspect of the present invention includes: the positive electrode sheet according to the embodiment of the first aspect of the present invention or the positive electrode sheet prepared by using the preparation method of the embodiment of the first aspect of the present invention; or the battery according to the embodiment of the third aspect of the present invention.

[0022] The electrical equipment according to the embodiment of the fifth aspect of the present invention includes: the battery according to the embodiment of the third aspect of the present invention or the battery pack using the embodiment of the fourth aspect of the present invention.

[0023] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0024] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein: Figure 1 is a schematic diagram of a positive electrode sheet according to an embodiment of the present invention; Figure 2 is a schematic diagram of the preparation of a positive electrode sheet according to an embodiment of the present invention.

[0025] Reference Signs: 100: Positive electrode sheet; 1: Current collector; 2: First positive electrode active layer; 3: Second positive electrode active layer; 4: Composite slurry. Detailed Embodiments

[0026] Reference is made below to Figure 1 - Figure 2 describe the positive electrode sheet 100 according to the embodiment of the first aspect of the present invention.

[0027] As Figure 1 - Figure 2 shown, the positive electrode sheet 100 according to the embodiment of the first aspect of the present invention includes a current collector 1 and a plurality of positive electrode active layers.

[0028] Specifically, multiple positive electrode active layers are sequentially disposed on at least one surface of the current collector 1 in the thickness direction. The positive electrode active layer includes a polymer and a plasticizer. Along the direction away from the current collector 1, the weight-average molecular weight of the polymer in the multiple positive electrode active layers increases sequentially, and the molar molecular weight of the plasticizer in the multiple positive electrode active layers increases sequentially. In the description of the present invention, the meaning of "multiple" is two or more than two.

[0029] For example, in Figure 1 and Figure 2 example, multiple positive electrode active layers may be sequentially disposed only on one side of the current collector 1 in the thickness direction; or, multiple positive electrode active layers are sequentially provided on both sides of the current collector 1 in the thickness direction.

[0030] A polymer is introduced into each of the multiple positive electrode active layers, and the polymers form a three-dimensional network structure through a crosslinking reaction, which can not only improve the mechanical properties of the polymer but also promote ion conduction to a certain extent. The crosslinked structure can limit the excessive movement of polymer chains and at the same time provide channels for ion transport. The ion conduction of the polymer mainly depends on the segmental movement to provide migration channels for ions. The higher the segmental mobility, the easier it is for ions to move therein. For example, a polymer with more amorphous regions has freer segmental movement and better ion conduction performance.

[0031] Among them, along the direction away from the current collector 1, the weight-average molecular weight of the polymer in the multiple positive electrode active layers increases sequentially. The weight-average molecular weight of the polymer in the positive electrode active layer closer to the current collector 1 is smaller. Correspondingly, the polymer chain length is shorter, and it has better fluidity, which can provide higher ionic conductivity and is conducive to the transport of ions in the positive electrode active layer. The weight-average molecular weight of the polymer in the positive electrode active layer farther from the current collector 1 is larger, the polymer chain length is longer, and the fluidity of the polymer is smaller, which is thus conducive to improving the structural stability of the positive electrode active layer and reducing the risk of deformation and cracking of the above positive electrode active layer and the positive electrode sheet 100 using the same during the process, and further conducive to improving the use stability of the positive electrode sheet 100.

[0032] Thus, by adjusting and controlling the weight-average molecular weight of the polymer in the multiple positive electrode active layers, the polymer chain lengths in the multiple positive electrode active layers increase sequentially along the direction away from the current collector 1, which is conducive to realizing the gradient ionic conductivity of the multiple positive electrode active layers. The design of gradient ionic conductivity can improve the utilization rate of the active material on the side of the current collector 1 in the positive electrode sheet 100 and increase the capacity, balance the charge in the depth direction of the positive electrode sheet 100 and reduce polarization, optimize the ion transport path, and improve the ionic conductivity compared with the design of the existing positive electrode sheet, thereby enhancing the rate performance of the battery.

[0033] Meanwhile, the molar molecular weight of the plasticizer in multiple positive electrode active layers is controlled so that along the direction away from the current collector 1, the molar molecular weight of the plasticizer in the multiple positive electrode active layers increases successively. Among them, the plasticizer with a low molar molecular weight has smaller molecules and can more easily insert between polymer molecular chains, weakening the intermolecular forces between polymer molecular chains, such as van der Waals forces and hydrogen bonds, enhancing the mobility of polymer molecular chains, and thus significantly reducing the glass transition temperature of the polymer at a lower addition amount, increasing the flexibility and plasticity of the polymer, and showing good plasticization effect; the plasticizer with a high molar molecular weight has larger molecules, slower diffusion rate in the polymer matrix, and stronger interaction with polymer molecular chains, so it has better migration resistance. It can remain stable in the polymer for a long time, is not easy to volatilize and migrate to the surface of the positive electrode sheet 100 or other substances, so that the plasticization effect has better persistence, can keep the positive electrode sheet 100 in good performance for a long time, and is conducive to ensuring reliable contact between the positive electrode sheet 100 and the electrolyte.

[0034] Thus, in the case of realizing gradient ionic conductivity by adjusting the polymer chain length, the design of adding plasticizers with different molecular weights is increased to give full play to the synergistic effect of the polymer and the plasticizer. The positive electrode sheet 100 with gradient ionic conductivity can be constructed through different electrolyte formulations. The positive electrode sheet 100 utilizes the synergistic effect of the polymer segment and the plasticizer. The positive electrode active layer close to the current collector 1 is paired with a short-chain polymer (the polymer has a smaller weight-average molecular weight) and a strong plasticizer (the plasticizer has a smaller molar molecular weight) to promote the migration of the polymer segment and facilitate lithium-ion transport, providing high ionic conductivity; the positive electrode active layer far from the current collector 1 is paired with a long-chain polymer (the polymer has a larger weight-average molecular weight) and a weak plasticizer (the plasticizer has a larger molar molecular weight) to ensure the viscosity and flexibility of each component in the above positive electrode active layer and the contact between the positive electrode sheet 100 and the electrolyte. The positive electrode sheet 100 designed by the above gradient ionic conductivity strategy can effectively improve the utilization rate of the active material on the current collector 1 side in the positive electrode sheet 100 and increase the capacity, balance the charge in the depth direction of the electrode plate and reduce polarization, optimize the ion transport path and improve the rate performance of the battery.

[0035] The positive electrode sheet 100 according to the embodiment of the present invention helps to exert the synergistic effect of the polymer and the plasticizer by regulating the weight-average molecular weight of the polymer and the molar molecular weight of the plasticizer in multiple positive electrode active layers, optimizes the ion path inside the positive electrode sheet 100, improves the ionic conductivity of the positive electrode sheet 100. The gradient design of the plasticizer helps to adjust the intermolecular force between the corresponding polymer molecular chains, making the mobility of the polymer molecular chains suitable for the needs of the corresponding positive electrode active layer, which can effectively reduce battery polarization and improve the electrochemical performance of the positive electrode sheet 100. Thus, the gradient ionic conductance of the positive electrode sheet 100 is improved, the ionic conductivity of the positive electrode sheet 100 is increased and the polarization is reduced, the ion transport path is optimized, and the ionic conductivity and rate performance are improved.

[0036] According to some embodiments of the present invention, referring to Figure 1 and Figure 2 , at least the first positive electrode active layer 2 and the second positive electrode active layer 3 are included in the multiple positive electrode active layers. Among them, the weight-average molecular weight of the polymer in the first positive electrode active layer 2 is 10,000 g / mol to 300,000 g / mol, preferably 50,000 g / mol to 150,000 g / mol. The weight-average molecular weight of the above polymer is relatively reasonable, the viscosity of the polymer is reasonable, and the fluidity is good, which is beneficial to improving the ionic conductance of the first positive electrode active layer 2.

[0037] The weight-average molecular weight of the polymer in the second positive electrode active layer 3 is 400,000 g / mol to 1,000,000 g / mol, preferably 600,000 g / mol to 800,000 g / mol. The weight-average molecular weight of the above polymer is relatively reasonable, which enhances the intermolecular force between the polymer molecular chains and also enhances the ability to resist external force damage. The strength, hardness and toughness of the polymer are reasonably increased, ensuring the viscosity of each component in the second positive electrode active layer 3, which is thus beneficial to improving the connection stability between the second positive electrode active layer 3 and the first positive electrode active layer 2 and ensuring the contact between the positive electrode sheet 100 and the electrolyte.

[0038] According to some embodiments of the present invention, the polymers of the plurality of positive electrode active layers are independently selected from at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polypropylene carbonate (PPC), polyethylene oxide (PEO), and ethylene oxide - propylene oxide copolymer (PEO - PO). Polyvinylidene fluoride is a homopolymer of vinylidene fluoride (VDF) or a copolymer of vinylidene fluoride and a small amount of fluorinated vinyl monomers, having good chemical corrosion resistance, high impact strength, abrasion resistance, creep resistance, high mechanical strength and toughness. At the same time, polyvinylidene fluoride also has a high dielectric strength. Vinylidene fluoride - hexafluoropropylene copolymer is copolymerized from vinylidene fluoride and hexafluoropropylene, with lower rigidity, better flexibility, higher fluidity and higher adhesion. Polytetrafluoroethylene has excellent corrosion resistance and weather resistance, good electrical insulation, low dielectric constant and high light transmittance. Polyacrylonitrile is obtained by free radical polymerization of the monomer acrylonitrile. Polypropylene carbonate is synthesized from carbon dioxide and propylene oxide as raw materials. Polyethylene oxide has a flexible chain segment, so polyethylene oxide has good flexibility. Ethylene oxide - propylene oxide copolymer has some characteristics of both ethylene oxide and propylene oxide, and its properties can be controlled by adjusting the ratio of ethylene oxide and propylene oxide, generally having good solubility, surface activity and softness, etc.

[0039] The polymers of the plurality of positive electrode active layers are independently selected from the above polymers, which is convenient for gradient regulation of the plurality of positive electrode active layers. At the same time, it is beneficial to ensure the flexibility of the plurality of positive electrode active layers, reduce the risk of deformation and cracking of the positive electrode sheet 100 during use, improve the use reliability of the positive electrode sheet 100, and extend the service life of the positive electrode sheet 100.

[0040] According to some other embodiments of the present invention, at least the first positive electrode active layer 2 and the second positive electrode active layer 3 are included in the plurality of positive electrode active layers. Among them, the molar molecular weight of the plasticizer in the first positive electrode active layer 2 is 40 g / mol to 250 g / mol, preferably 80 g / mol to 150 g / mol. The molar molecular weight of the above plasticizer is relatively reasonable, which helps to promote the migration of polymer chain segments, thereby facilitating the transport of ions and improving the ionic conductivity of the first positive electrode active layer 2.

[0041] The molar molecular weight of the plasticizer in the second positive electrode active layer 3 is 250 g / mol to 2000 g / mol, preferably 500 g / mol to 1000 g / mol. The molar molecular weight of the above plasticizer is relatively reasonable, which is beneficial to ensure the adhesion between the components in the positive electrode sheet 100 and the contact between the positive electrode sheet 100 and the electrolyte.

[0042] In some further embodiments of the present invention, the plasticizers in the plurality of positive electrode active layers are independently selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, succinonitrile, and polyethylene glycol dimethyl ether (PEGDM).

[0043] The plasticizers in the plurality of positive electrode active layers are independently selected from the above-mentioned organic substances. The above-mentioned plasticizers all have good compatibility with the polymer and can play a certain plasticizing role on the polymers in the plurality of positive electrode active layers, thereby helping to improve the ionic conduction performance of the corresponding positive electrode active layers and enhancing the flexibility and stability of the positive electrode active layers. A variety of plasticizers can be selected in each positive electrode active layer to increase the plasticizing effect and improve the gradient conductivity performance.

[0044] At the same time, during the preparation process of the positive electrode sheet 100, the plasticizer will coordinate with the polymer matrix and the electrolyte salt and will not completely volatilize during the subsequent preparation process, and can be measured at the finished end of the positive electrode sheet 100. For example, the above-mentioned plasticizer can be measured by Fourier-transform infrared spectroscopy (FIIR). By measuring the absorption degree of the sample to infrared light of different wavelengths, the vibration and rotation information of the molecules can be obtained, and then the chemical composition and functional group structure of the sample can be inferred. The slurry for preparing the above-mentioned plurality of positive electrode active layers can be extruded from the screw and collected on a PET (polyethylene terephthalate) film; after the film-forming positive electrode active layers are peeled off from the PET film and placed on a wiped clean sample stage, they can be tested, and the wavenumbers 4000nm -1 ~500nm -1 of the data are collected, and the types of plasticizers are distinguished according to the characteristic peaks.

[0045] At the same time, the increase in molecular weight usually causes the thermal performance parameters such as the glass transition temperature (Tg) and melting point (Tm) of the polymer to increase. This is because the longer the molecular chain, the stronger the intermolecular interaction, and higher energy is required to make the molecular chain segments start to move or to melt the crystal structure. Therefore, a differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TGA) can also be used in combination to distinguish the polymers in the plurality of positive electrode active layers.

[0046] A differential scanning calorimeter measures the heat flow difference between a sample and a reference by simultaneously heating or cooling them at a programmed rate. When a physical or chemical change occurs in the sample, such as a phase change, melting, crystallization, chemical reaction, etc., heat is absorbed or released, resulting in a heat flow difference from the reference. The instrument measures this heat flow difference and converts it into a temperature-heat change curve to obtain the thermal performance information of the sample. Among them, when the molecular weight of the polymer is small, its glass transition temperature is relatively low. Therefore, by comparing the endothermic and exothermic peak values, the use of the polymer in multiple positive electrode active layers can be distinguished.

[0047] By accurately measuring the change in the mass of a sample with temperature or time, a thermogravimetric analyzer can obtain information such as the thermal stability, thermal decomposition process, and reaction kinetics of the sample. When the analysis amount of the polymer is small, weight loss occurs most easily first. Therefore, the combination of a differential scanning calorimeter and a thermogravimetric analyzer is beneficial to improving the accuracy of identifying the polymer in the positive electrode active layer.

[0048] According to some embodiments of the present invention, the positive electrode active layer further includes at least one of an active material, a conductive agent, and an electrolyte salt, wherein the mass ratio of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer is (50-90):(1-10):(6-20):(0-10):(0-10). Thus, the mass ratio of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer is relatively reasonable, which is beneficial to giving full play to the roles of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer, and at the same time is suitable for improving the uniformity, stability, and structural integrity of the positive electrode active layer.

[0049] Among them, the active material, as the main substance for the redox reaction, realizes the charge and discharge process of the battery by gaining and losing electrons, and determines important parameters such as the energy density, voltage platform, and cycle performance of the battery. The conductive agent is beneficial to improving the electronic conductivity of the positive electrode material, ensuring the rapid transmission of electrons in the electrode material, thereby improving the charge and discharge efficiency and rate performance of the battery, and reducing the polarization phenomenon during the charge and discharge process of the battery. The electrolyte salt is used to provide mobile ions, and these ions migrate from the positive electrode to the negative electrode (during charging) or migrate in the reverse direction (during discharging) through the electrolyte, realizing the flow of current.

[0050] Further, the active materials of multiple positive electrode active layers are independently selected from lithium cobaltate, lithium nickelate, lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium nickel iron phosphate, lithium manganate, xLi2MnO3·(1-x)LiMO2, LiNi y A (1-y) O2 and LiNimBnC (1-m-n)At least one of O2, where 0 < x < 1, M is selected from transition metals, A is selected from Co or Mn, 0 < y < 1, B and C are independently selected from Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1. Among them, lithium cobalt oxide (LiCoO2) has a high energy density, good cycle stability, and a relatively high working voltage. Lithium nickel oxide (LiNiO2) has a high specific capacity. Lithium iron phosphate (LiFePO4) has excellent safety, long cycle life, stable chemical structure, low cost, and environmental friendliness. Lithium cobalt phosphate (LiCoPO4) has good chemical stability and a high working voltage. Lithium manganese phosphate (LiMnPO4) has a high specific capacity. Lithium nickel phosphate (LiNiPO4) is similar to lithium cobalt phosphate but has a higher theoretical energy density. Lithium manganese oxide (LiMn2O4) has a low cost and good thermal stability. Lithium manganese iron phosphate, lithium cobalt iron phosphate, and lithium nickel iron phosphate, xLi2MnO3·(1 - x)LiMO2 and LiNi y A (1-y) The energy densities of O2 are all relatively high, which is beneficial to reducing the volume of the positive electrode active layer while meeting the energy density requirements of the positive electrode active layer, thereby improving the applicability of the positive electrode active layer. Thus, the active materials of multiple positive electrode active layers independently adopt the above-mentioned active materials, which helps to improve the applicability of the positive electrode sheet 100 using the above-mentioned active materials, enhance the energy density and volume efficiency of the battery using the above-mentioned positive electrode sheet 100, improve the use safety of the battery, and extend the service life of the battery.

[0051] The conductive agents for multiple positive electrode active layers are independently selected from at least one of conductive graphite, acetylene black, Super P, graphene, carbon fiber, carbon nanotube, Ketjen black, metal nanowire, and metal nanotube. Conductive graphite has high electronic conductivity. Flaky graphite or granular graphite can form a continuous conductive network through physical contact, tightly connecting the active material particles and reducing the interruption of the electron transport path. At the same time, conductive graphite has a low cost and good chemical stability. Acetylene black has good conductivity, a large specific surface area, and excellent dispersibility, and can effectively increase the conductive network of the positive electrode sheet 100. Super P can provide a good conduction path, helping to improve the overall conductivity of the first positive electrode active layer 2 and the second positive electrode active layer 3. Super S has high conductivity and good dispersibility, and is suitable for enhancing the electron conduction ability of the positive electrode sheet 100. Graphene is a single-layer or multi-layer two-dimensional carbon nanomaterial with extremely high conductivity and mechanical strength. Due to its large specific surface area and excellent conductive performance, it can improve the conductivity and stability of the electrode, and at the same time can also improve the flexibility and mechanical strength of the electrode. Carbon fiber is a fibrous material composed of carbon atoms, with high strength and high modulus. In addition to excellent conductivity, it also has good mechanical properties and can be used to enhance the structural stability and conductive network of the electrode material. Carbon nanotubes (CNTs) are tubular one-dimensional nanomaterials, divided into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). They have an ultra-high aspect ratio and excellent conductivity, can form an efficient three-dimensional conductive network, and greatly improve the conductivity and cycle stability of the positive electrode sheet 100. Ketjen black is a special type of high-structured carbon black with a very large specific surface area and a highly branched structure. Due to its unique structure, it has excellent conductivity and dispersibility, and can build an efficient conductive network inside the electrode, thereby improving the battery performance. Metal nanowires and metal nanotubes have high conductive performance, good conductive network construction ability, low contact resistance, and efficient charge transport. Therefore, the conductive agents for multiple positive electrode active layers are independently selected from at least one of the above conductive agents, which helps to improve the conductivity and structural stability of the positive electrode sheet 100 using the first positive electrode active layer 2 and the second positive electrode active layer 3 containing the above conductive agents.

[0052] The electrolyte salts for multiple positive electrode active layers are at least one of potassium salts, sodium salts, and lithium salts. That is to say, the electrolyte salts of multiple positive electrode active layers can all be potassium salts; or, the electrolyte salts of multiple positive electrode active layers can all be sodium salts; or, the electrolyte salts of multiple positive electrode active layers can all be lithium salts. In addition, a variety of composite salts of potassium salts, sodium salts, and lithium salts can also be selected as the electrolyte salts for multiple positive electrode active layers. Thus, ensuring the unity of ions in the positive electrode sheet 100, the electrolyte salts of multiple positive electrode active layers can all provide mobile ions, increasing the ion concentration, and thereby enhancing the ionic conductance of the positive electrode sheet 100.

[0053] Furthermore, when the electrolyte salts of the multiple positive electrode active layers are lithium salts, the electrolyte salts of the multiple positive electrode active layers are independently selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), and lithium tetrafluoro(oxalato)phosphate (LiTFOP). The above-mentioned electrolyte salts all have good thermal stability and electrochemical window. Using at least one of the above-mentioned electrolyte salts helps to improve the ionic conductivity of the positive electrode sheet 100, and at the same time helps to improve the safety of the battery using the above-mentioned positive electrode sheet 100 and extend the service life of the battery.

[0054] According to some embodiments of the present invention, the thickness of the current collector 1 is 8 um to 25 um, preferably 10 um to 15 um. The current collector 1 plays a role of carrying active substances, collecting and conducting current in the battery. The selection of its thickness has an important impact on the overall performance of the battery, including energy density, power density, cycle life, and cost, etc. The thickness of the above-mentioned current collector 1 is relatively reasonable, which helps to provide a better conduction path, reduce resistance loss, effectively control the total weight and volume of the positive electrode sheet 100 and the battery using the above-mentioned positive electrode sheet 100, ensure the energy density of the battery, and in addition, can also ensure the mechanical strength of the positive electrode sheet 100 and prevent cracking or damage during the manufacturing process or use process.

[0055] The thickness of the first positive electrode active layer 2 is 100 um to 200 um, preferably 120 um to 150 um; and / or, the thickness of the second positive electrode active layer 3 is 100 um to 250 um, preferably 150 um to 200 um. The thickness of the above-mentioned first positive electrode active layer 2 and / or second positive electrode active layer 3 is relatively reasonable, which helps to achieve high-power output, reduce internal resistance, improve power density, and at the same time helps to avoid the shedding or cracking of the first positive electrode active layer 2 and / or second positive electrode active layer 3 caused by the increase in mechanical stress of the first positive electrode active layer 2 and / or second positive electrode active layer 3 due to volume change during charge and discharge, thereby facilitating the extension of the cycle life of the positive electrode sheet 100 and the battery using the above-mentioned positive electrode sheet 100. In addition, the molecular chains of the polymer in the first positive electrode active layer 2 are shorter, avoiding cracks in the positive electrode sheet 100 during the manufacturing and use processes caused by a higher thickness.

[0056] Among them, the thickness of the first positive electrode active layer 2 and the thickness of the second positive electrode active layer 3 can be equal, or the thickness of the first positive electrode active layer 2 can be greater than the thickness of the second positive electrode active layer 3; or the thickness of the first positive electrode active layer 2 can be less than the thickness of the second positive electrode active layer 3. No specific limitation is made here.

[0057] According to some specific embodiments of the present invention, the current collector 1 is aluminum foil, aluminum foam, carbon-coated aluminum foil, carbon mesh or carbon cloth.

[0058] A method for preparing the positive electrode sheet 100 according to an embodiment of the second aspect of the present invention includes the following steps: Provide a plurality of composite slurries 4, each composite slurry 4 includes a polymer and a plasticizer. Among them, the weight average molecular weights of the polymers in at least two composite slurries 4 are different, and the molar molecular weights of the plasticizers are different; By means of co-extrusion, coat a plurality of composite slurries 4 on the surface of the current collector 1 to form a plurality of positive electrode active layers. Among them, along the direction away from the current collector 1, the weight average molecular weight of the polymer in the plurality of positive electrode active layers increases in sequence, and the molar molecular weight of the plasticizer decreases in sequence, and then dry to obtain the positive electrode sheet 100.

[0059] By using the co-extrusion coating method, coat a plurality of composite slurries 4 on the surface of the current collector 1 together, and after drying and rolling, the positive electrode sheet 100 with gradient ionic conductivity can be obtained. Among them, the co-extrusion coating method can simplify the coating process and does not require multiple coating steps. Among them, the composite slurry 4 containing the plasticizer has high fluidity, so that the simultaneous coating of the above two composite slurries 4 can prevent cracks from occurring during the drying (such as baking) process.

[0060] After the coating is completed, the solvent can be removed by vacuum drying at 60 °C to 120 °C for 4 to 16 hours, and after rolling, the positive electrode sheet 100 with gradient ionic conductivity can be obtained.

[0061] The above preparation method has low cost and simple process, and is suitable for large-scale production and commercialization.

[0062] The preparation method of the positive electrode sheet 100 according to the embodiment of the present invention can produce the positive electrode sheet 100 with gradient ionic conductivity with a simple preparation process, and has low cost, high structural strength and long service life of the produced positive electrode sheet 100.

[0063] A battery according to an embodiment of the third aspect of the present invention includes: a positive electrode sheet 100, a negative electrode sheet and a separator; wherein, the positive electrode sheet 100 is the positive electrode sheet 100 according to the above first aspect embodiment of the present invention or the positive electrode sheet 100 prepared by using the preparation method of the above first aspect embodiment of the present invention.

[0064] For the battery according to the embodiment of the present invention, adopting the above positive electrode sheet 100 helps to improve the charging efficiency and discharging efficiency of the battery, enables the battery to output a larger current, and meets the requirements of high-power devices; at the same time, the conductivity of the positive electrode sheet 100 is improved, which helps to reduce the energy loss of the battery and improve the energy utilization rate of the battery; in addition, by improving the conductivity, the reaction inside the battery becomes more uniform, reducing the irreversible change of the electrode material, thereby prolonging the cycle service life of the battery.

[0065] The battery pack according to the embodiment of the fourth aspect of the present invention includes: the positive electrode sheet 100 according to the embodiment of the first aspect of the present invention above or the positive electrode sheet 100 prepared by using the preparation method according to the embodiment of the first aspect of the present invention above; or the battery according to the embodiment of the third aspect of the present invention above.

[0066] The battery pack according to the embodiment of the fourth aspect of the present invention helps to improve the conductivity of the battery pack and extend the service life of the battery pack.

[0067] The electrical equipment according to the embodiment of the fifth aspect of the present invention includes: the battery according to the embodiment of the third aspect of the present invention above or the battery pack according to the embodiment of the fourth aspect of the present invention above.

[0068] The electrical equipment according to the embodiment of the present invention helps to improve the energy supply stability and reliability of the electrical equipment, thereby facilitating the improvement of the operation stability of the electrical equipment, and further facilitating the improvement of the market competitiveness of the electrical equipment.

[0069] The embodiments of the present invention will be described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and cannot be understood as a limitation of the present invention. In addition, if not specified explicitly, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described in this article or known methods. For the reaction conditions not listed, they are also easily obtained by those skilled in the art.

[0070] Example 1 Lithium iron phosphate is selected as the active material, SuperP is selected as the conductive agent, and lithium bis(trifluoromethanesulfonyl)imide is selected as the electrolyte salt. The above substances are dissolved in N,N-dimethylformamide together with the polymer and the plasticizer to form the first composite slurry and the second composite slurry.

[0071] (1) Among them, the polymer in the first composite slurry is polyethylene oxide with a weight average molecular weight of 100,000 g / mol, and the polymer in the second composite slurry is polyethylene oxide with a weight average molecular weight of 600,000 g / mol; the plasticizer in the first composite slurry is succinonitrile (SN, Mw = 80 g / mol), and the plasticizer in the second composite slurry is polyethylene glycol dimethyl ether (Mw = 1000 g / mol, that is, the plasticizer is PEGDM-1000).

[0072] (2) In the first composite slurry and the second composite slurry, the mass ratios of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer are all 79:3:9:4.5:4.5. Calculated by mass fraction, the mass fraction of the active material in the first composite slurry is 13 parts, and the mass fraction of the active material in the second composite slurry is 17 parts.

[0073] (3) By using the co-extrusion coating method, the first composite slurry and the second composite slurry are coated on the surface of the current collector 1 together, where the first composite slurry is on the side close to the current collector 1, and the second composite slurry is on the side close to the solid electrolyte, that is, away from the current collector 1. The prepared solid-state battery cathode precursor is placed under vacuum drying at 80 °C for 8 hours, and after roll pressing, the cathode sheet 100 with gradient ionic conductivity performance is obtained.

[0074] (4) The tap density of the cathode sheet 100 of the prepared solid-state battery is 2.35 g / cm 3 , the thickness of the first cathode active layer 2 prepared from the first composite slurry is 130 μm, and the thickness of the second cathode active layer 3 prepared from the second composite slurry is 170 μm.

[0075] Example 2 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is SN, and the plasticizer in the second composite slurry is PEGDM-2000.

[0076] Example 3 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is acetonitrile ((Mw = 41 g / mol), and the plasticizer in the second composite slurry is PEGDM-1000.

[0077] Example 4 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is SN, and the plasticizer in the second composite slurry is PEGDM-250.

[0078] Example 5 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is SN, and the plasticizer in the second composite slurry is PEGDM-500 and PEGDM-1000. The mass ratio of PEGDM-500 and PEGDM-1000 is 2:8.

[0079] Example 6 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is acetonitrile, and the plasticizer in the second composite slurry is PEGDM-3000.

[0080] Example 7 The preparation method of this example is generally the same as that of Example 1, except that in step (1), the polymer in the first composite slurry is polyethylene oxide with a weight average molecular weight of 100000 g / mol, and the polymer in the second composite slurry is polyethylene oxide with a weight average molecular weight of 700000 g / mol.

[0081] Example 8 The preparation method of this example is generally the same as that of Example 1, except that in step (1), the polymer in the first composite slurry is polyethylene oxide with a weight average molecular weight of 10000 g / mol, and the polymer in the second composite slurry is polyethylene oxide with a weight average molecular weight of 700000 g / mol.

[0082] Example 9 The preparation method of this example is generally the same as that of Example 1, except that in step (1), the polymer in the first composite slurry is polyethylene oxide with a weight average molecular weight of 100000 g / mol, and the polymer in the second composite slurry is polyethylene oxide with a weight average molecular weight of 1000000 g / mol.

[0083] Example 10 (1) Lithium iron phosphate is selected as the active material, SuperP as the conductive agent, polyethylene oxide as the polymer, lithium bis(trifluoromethanesulfonyl)imide as the electrolyte salt, and a plasticizer are dissolved in N,N-dimethylformamide together to prepare the first composite slurry, the second composite slurry and the third composite slurry.

[0084] (2) The polymer in the first composite slurry is polyethylene oxide with a weight average molecular weight of 100000 g / mol, the polymer in the second composite slurry is polyethylene oxide with a weight average molecular weight of 300000 g / mol, and the polymer in the third composite slurry is polyethylene oxide with a weight average molecular weight of 700000 g / mol.

[0085] (3) The plasticizer in the first composite slurry is acetonitrile, the plasticizer in the second composite slurry is PEGDM-250, and the third plasticizer in the third composite slurry is PEGDM-1000.

[0086] (4) In the first composite slurry, the second composite slurry and the third composite slurry, the mass ratios of the active material, the conductive agent, the polymer, the electrolyte salt and the plasticizer are all 79:3:9:4.5:4.5. By mass fraction, the fraction of the active material in the first composite slurry is 10 parts, the fraction of the active material in the second composite slurry is 6 parts, and the fraction of the third active material in the third composite slurry is 14 parts.

[0087] (5) By using the co-extrusion coating method, the first composite slurry, the second composite slurry, and the third composite slurry are coated on the surface of the current collector 1 together. In the direction from the current collector 1 to the solid electrolyte, they are the first composite slurry, the second composite slurry, and the third composite slurry in sequence. The obtained solid-state battery cathode precursor is placed under vacuum drying at 80 °C for 8 hours, and after roll pressing, the cathode sheet 100 with gradient ionic conductivity performance is obtained.

[0088] (6) The compaction density of the obtained solid-state battery cathode is 2.35 g / cm 3 , the thickness of the first cathode active layer 2 made of the first composite slurry is 100 μm, the thickness of the second cathode active layer 3 made of the second composite slurry is 60 μm, and the thickness of the third cathode active layer made of the third composite slurry is 140 μm.

[0089] Example 11 The preparation method of this example is roughly the same as that of Example 10. The difference is that in step (3), the plasticizer in the first composite slurry is SN, the plasticizer in the second composite slurry is SN, and the third plasticizer in the third composite slurry is PEGDM-500.

[0090] Comparative Example 1 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is SN, and the plasticizer in the second composite slurry is also SN.

[0091] Comparative Example 2 The preparation method of this example is roughly the same as that of Example 1. The difference is that in step (2), the plasticizer in the first composite slurry is PEGDM-1000, and the plasticizer in the second composite slurry is PEGDM-1000.

[0092] Comparative Example 3 The preparation method of this example is roughly the same as that of Example 10. The difference is that in step (3), the plasticizer in the first composite slurry is SN, the plasticizer in the second composite slurry is SN, and the third plasticizer in the third composite slurry is SN.

[0093] Performance Test The cathode sheets 100 prepared in Examples 1-7 and Comparative Examples 1-3 are subjected to ionic conductivity tests at 60 °C. And using the cathode sheets 100 of the solid-state batteries prepared in Examples 1-7 and Comparative Examples 1-3, polyethylene oxide as the polymer electrolyte, lithium bis(trifluoromethanesulfonyl)imide as the electrolyte salt, acetonitrile as the plasticizer, and metallic lithium as the anode, soft-pack batteries are assembled and over-potential tests are carried out on them at 60 °C. Among them, the mass ratio of polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, and acetonitrile is 2:1:1, and the measured results are shown in Table 1.

[0094] Table 1 Electrochemical properties of the positive electrode sheet 100 prepared in Examples 1-11 and Comparative Examples 1-3 and the soft-packaged battery assembled therefrom

[0095] Analysis of test results It can be seen from the comparison between Comparative Examples 1-3 and Examples 1-6 that in Examples 1-6, by controlling the plasticization strength of the plasticizer in the composite slurry, the fluidity of the polymer electrolyte inside the positive electrode sheet 100 is regulated, so as to prepare the positive electrode sheet 100 of a solid-state battery with gradient ion conductivity performance. It can be seen from the comparison between Comparative Examples 1-3 and Examples 7-9 that the gradient design of the polymer segments can effectively optimize the ion path inside the positive electrode sheet 100 and improve the ion conductivity of the positive electrode sheet 100. It can be seen from the comparison between Comparative Examples 1-3 and Examples 10-11 that on the basis of the gradient design of the polymer segments, the design of increasing the molecular weight of the plasticizer can further improve the ion conductivity of the positive electrode sheet 100, reduce polarization, and thus improve the rate performance of the battery.

[0096] It can be seen from Examples 1-4 that the plasticization strength of the plasticizer has an important influence on the performance of the positive electrode sheet 100 of the solid-state battery. Compared with Example 1, the plasticization strength of the plasticizer in Example 2 is relatively low, the movement degree of the polymer segments in the electrolyte decreases, and the lithium ion transmission speed slows down; the plasticization strength of the plasticizer in Example 3 is relatively high, the adhesion of the polymer segments decreases, and the plasticizer easily flows out of the target active sub-layer, resulting in a decrease in the plasticization effect of this active sub-layer and a decrease in ion conductivity; the plasticization strength of the plasticizer in Example 4 is relatively high, the overall adhesion of the positive electrode sheet 100 is poor, and cracking is likely to occur, resulting in a decrease in ion conductivity. Therefore, in order to make the positive electrode sheet 100 have better electrochemical performance, the molar molecular weight of the plasticizer is controlled within a suitable range in this application.

[0097] It can be seen from Example 1 and Example 5 that the composite plasticizer can combine the advantages of the two plasticizers and can optimize the plasticization effect of the plasticizer to a certain extent, thereby enhancing the effect of gradient ion conductivity.

[0098] It can be seen from Example 1 and Example 6 that the molecular weight of the plasticizer has an important influence on the performance of the positive electrode sheet 100 of the solid-state battery. Selecting a suitable molecular weight of the plasticizer can effectively improve the ion transport rate inside the positive electrode sheet 100.

[0099] It can be seen from Example 1 and Examples 7-9 that the gradient design of the polymer segments can effectively optimize the ion path inside the positive electrode sheet 100. If the polymer segments are too short, cracking and other phenomena are likely to occur during the manufacturing process and use of the positive electrode sheet 100; if the polymer segments are too long, the lithium ion migration resistance is large, which is likely to reduce the ion transport rate.

[0100] Compared with Comparative Example 3, Examples 10-11 changed the plasticizing strength of the plasticizer in different cathode active layers. Through the synergistic effect of the plasticizer, the deficiencies of a single plasticizer in the ion transport path were improved. At the same time, by adjusting the plasticizing strength of the plasticizer between different active sub-layers, the battery polarization could be effectively reduced.

[0101] The other configurations and operations of the battery and the electrical equipment according to the embodiments of the present invention are known to those of ordinary skill in the art and will not be described in detail here.

[0102] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0103] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example.

[0104] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A positive electrode sheet, characterized in that, Comprising: Current collector; A plurality of positive electrode active layers, which are sequentially arranged on at least one surface in the thickness direction of the current collector. The positive electrode active layer includes a polymer and a plasticizer. Along the direction away from the current collector, the weight-average molecular weight of the polymer in the plurality of positive electrode active layers increases sequentially, and the molar molecular weight of the plasticizer in the plurality of positive electrode active layers increases sequentially.

2. The positive electrode sheet according to claim 1, characterized in that, At least the first positive electrode active layer and the second positive electrode active layer are included in the plurality of positive electrode active layers. Among them, the weight-average molecular weight of the polymer in the first positive electrode active layer is 10,000 g / mol to 300,000 g / mol, preferably 50,000 g / mol to 150,000 g / mol; and / or, The weight-average molecular weight of the polymer in the second positive electrode active layer is 400,000 g / mol to 1,000,000 g / mol, preferably 600,000 g / mol to 800,000 g / mol.

3. The positive electrode sheet according to claim 1, characterized in that, The polymers in the plurality of positive electrode active layers are independently selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyacrylonitrile, polypropylene carbonate, polyethylene oxide, and ethylene oxide-propylene oxide copolymer.

4. The positive electrode sheet according to claim 1, wherein At least the first positive electrode active layer and the second positive electrode active layer are included in the plurality of positive electrode active layers. Among them, the molar molecular weight of the plasticizer in the first positive electrode active layer is 40 g / mol to 250 g / mol, preferably 80 g / mol to 150 g / mol; and / or, The molar molecular weight of the plasticizer in the second positive electrode active layer is 250 g / mol to 2,000 g / mol, preferably 500 g / mol to 1,000 g / mol.

5. The positive electrode sheet according to claim 1, wherein, The plasticizers in the plurality of positive electrode active layers are independently selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, succinonitrile, and polyethylene glycol dimethyl ether.

6. The positive electrode sheet according to claim 1, wherein, The positive electrode active layer further includes at least one of an active material, a conductive agent, and an electrolyte salt. Among them, the mass ratio of the active material, the conductive agent, the polymer, the electrolyte salt, and the plasticizer is (50-90):(1-10):(6-20):(0-10):(0-10).

7. The positive electrode sheet according to claim 6, characterized in that, The active materials of the plurality of the positive electrode active layers are independently selected from at least one of lithium cobaltate, lithium nickelate, lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium nickel iron phosphate, lithium manganate, xLi2MnO3·(1-x)LiMO2, LiNi y A (1-y) O2 and LiNimBnC (1-m-n) O2, where 0 < x < 1, M is selected from transition metals, A is selected from Co or Mn, 0 < y < 1, B and C are independently selected from Co, Al, and Mn, and B and C are different, 0 < m < 1, 0 < n < 1; and / or, The conductive agents in the plurality of positive electrode active layers are independently selected from at least one of conductive graphite, acetylene black, Super P, graphene, carbon fiber, carbon nanotube, Ketjen black, metal nanowire, and metal nanotube; and / or, The electrolyte salts in the plurality of positive electrode active layers are at least one of potassium salts, sodium salts, and lithium salts.

8. The positive electrode sheet according to claim 7, wherein When the electrolyte salts of the multiple positive electrode active layers are all lithium salts, the electrolyte salts of the multiple positive electrode active layers are independently selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium tetrafluoro(oxalato)phosphate.

9. The positive electrode sheet according to any one of claims 1-8, characterized in that, The thickness of the current collector is 8 μm to 25 μm, preferably 10 μm to 15 μm; and / or, At least a first positive electrode active layer and a second positive electrode active layer are included in the multiple positive electrode active layers. The thickness of the first positive electrode active layer is 100 μm to 200 μm, preferably 120 μm to 150 μm; and / or, the thickness of the second positive electrode active layer is 100 μm to 250 μm, preferably 150 μm to 200 μm.

10. The method for preparing a positive electrode sheet according to any one of claims 1-9, characterized in that, Comprising the following steps: Providing a plurality of composite slurries, each of the composite slurries comprising a polymer and a plasticizer, wherein the weight average molecular weights of the polymers in at least two of the composite slurries are different, and the molar molecular weights of the plasticizers are different; By means of co-extrusion, coating the plurality of composite slurries on the surface of the current collector to form a plurality of positive electrode active layers, wherein, along the direction away from the current collector, the weight average molecular weight of the polymer in the plurality of positive electrode active layers increases in sequence, and the molar molecular weight of the plasticizer decreases in sequence, and then drying to obtain the positive electrode sheet.

11. A battery, characterized in that, Comprising: A positive electrode sheet, a negative electrode sheet, and a separator; wherein, the positive electrode sheet is the positive electrode sheet according to any one of claims 1-9 or the positive electrode sheet prepared by using the preparation method described in claim 10.

12. A battery pack, characterized in that, Comprising: The positive electrode sheet according to any one of claims 1-9 or the positive electrode sheet prepared by using the preparation method described in claim 10; or the battery according to claim 11.

13. An electrical device, characterized in that, Comprising: The battery according to claim 11 or the battery pack according to claim 12.

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