Positive pole piece and preparation method thereof, sodium ion battery and electric equipment

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a positive pole piece and a preparation method thereof, a sodium ion battery and electric equipment. The positive pole piece comprises a current collector, and a first active layer and a second active layer which are sequentially arranged on the surface of the current collector; the first active layer comprises a layered oxide positive electrode material; the second active layer comprises a polyanion positive electrode material and a honeycomb conductive agent; the honeycomb-shaped conductive agent comprises at least one of honeycomb-shaped carbon nanofibers, honeycomb-shaped graphene aerogel, honeycomb-shaped metal sulfide, a metal velvet network material and a carbon-based honeycomb composite material. The second active layer can ensure the cycle performance of the battery cell, and the polyanion positive electrode material can generate gas under thermal stimulation or mechanical action and can generate a gas buffer layer, so that the structural damage to the first active layer is reduced, and the contact between the positive electrode and the negative electrode is isolated; the honeycomb-shaped conductive agent is added into the second active layer, so that the conductivity can be improved, the contact short circuit of the positive electrode and the negative electrode can be isolated, and local stress is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode plate and a preparation method thereof, a sodium ion battery and an electrical device. Background Art

[0002] Currently, sodium-ion batteries (SIBs) are showing broad application prospects in the energy storage field due to their abundant sodium resources, low cost, and high safety. Their operating principle is similar to that of lithium-ion batteries, storing and releasing energy through the reversible insertion and deintercalation of sodium ions between the positive and negative electrodes.

[0003] The cathode material is a key factor in determining the performance of sodium-ion batteries. Layered oxide cathode materials have high energy density, but poor structural stability at high temperatures, leading to insufficient battery safety (such as the risk of needle puncture). Polyanion cathode materials offer good high-temperature stability and high safety, but their energy density is relatively low, making it difficult to meet high energy demands. Furthermore, polyanion cathode materials suffer from poor electrical conductivity. Conventional conductive agents form a point-connected conductive network with low electron transfer efficiency, increasing interfacial impedance and thus affecting the kinetics of sodium ion transport.

[0004] In terms of battery safety, sodium-ion batteries pose significant safety risks in situations like needle puncture. When sharp objects pierce the battery casing and separator, they can easily trigger an internal short circuit, leading to fire or even explosion. While existing technologies have optimized the structure of sodium-ion batteries, these efforts have sacrificed the energy density and cycle performance of the battery cells. Furthermore, in needle puncture scenarios, key safety mechanisms such as heat generation caused by short circuit contact between the positive and negative electrodes and stress dispersion remain inadequate.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a positive electrode sheet, wherein a first active layer containing a layered oxide positive electrode material can ensure the capacity of the battery cell; by providing a second active layer containing a polyanion positive electrode material on the surface of the first active layer, the thermal stability and cycle stability of the battery cell can be ensured. Moreover, due to the characteristic that the polyanion positive electrode material will generate gas when subjected to thermal stimulation or mechanical action, a gas buffer layer can be generated, which reduces structural damage to the first active layer and isolates the positive and negative electrodes from each other, preventing short circuits and significantly improving the safety performance of the battery cell. This solves the problems of poor high-temperature structural stability of layered oxide positive electrode materials leading to insufficient battery safety and low energy density of polyanion positive electrode materials. In addition, the addition of a honeycomb conductive agent to the second active layer can not only increase conductivity, but its honeycomb network structure can also provide gas diffusion channels, forming a directional gas buffer layer during acupuncture, isolating the positive and negative electrodes from short circuits and relieving local stress. This solves the problems of poor conductivity of polyanion positive electrode materials, low electron transmission efficiency of the point-connected conductive network formed by conventional conductive agents, and positive and negative electrode short circuits and stress dispersion during acupuncture. Therefore, the positive electrode plate provided by the present invention improves the battery acupuncture safety performance while ensuring the energy density and cycle performance of the sodium ion battery.

[0007] The second object of the present invention is to provide a method for preparing a positive electrode sheet, which has a simple process and is easy to implement in batch production.

[0008] A third object of the present invention is to provide a sodium ion battery having high capacity, good cycle performance and high safety performance.

[0009] A fourth object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] The present invention first provides a positive electrode plate, including a current collector, a first active layer arranged on the surface of the current collector, and a second active layer arranged on the surface of the first active layer; the first active layer includes a layered oxide positive electrode material; the second active layer includes a polyanion positive electrode material and a honeycomb conductive agent; the honeycomb conductive agent includes at least one of honeycomb carbon nanofibers, honeycomb graphene aerogels, honeycomb metal sulfides, metal velvet network materials and carbon-based honeycomb composite materials.

[0012] Furthermore, the mass of the honeycomb conductive agent accounts for 0.2% to 6% of the mass of the second active layer.

[0013] Furthermore, the ratio of the surface density of the first active layer to the surface density of the second active layer is 1.7 to 4.7:1.

[0014] Furthermore, the ratio of the thickness of the first active layer to the thickness of the second active layer is 1.01 to 4.10:1.

[0015] Furthermore, the compaction density of the first active layer is 2.5 to 3.5 g / cm 3 .

[0016] Furthermore, the compaction density of the second active layer is 1.7 to 2.4 g / cm 3 .

[0017] Furthermore, the second active layer also includes a second conductive agent, which includes at least one of carbon black, graphite powder, graphene and carbon nanotubes, and the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:1.01-10.

[0018] Furthermore, the second active layer includes the following components in mass percentage: 82% to 97.5% of the polyanion positive electrode material, 0.2% to 6% of the honeycomb conductive agent, 0.1% to 2% of the second conductive agent, 0.1% to 5% of the second binder, 0% to 3% of the second acidic additive, and 0.1% to 2% of the second dispersant.

[0019] Furthermore, the polyanion cathode material includes at least one of a phosphate cathode material, a pyrophosphate cathode material, a sulfate cathode material and a composite phosphate cathode material.

[0020] Furthermore, the second binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin.

[0021] Furthermore, the second acidic additive includes at least one of oxalic acid, citric acid, acetic acid and phosphoric acid.

[0022] Furthermore, the second dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol and polyacrylic acid.

[0023] Furthermore, the first active layer includes the following components in mass percentage: 85% to 96% of the layered oxide positive electrode material, 0.1% to 5% of the first conductive agent, 0.1% to 5% of the first binder, 0% to 3% of the first acidic additive, and 0% to 3% of the first dispersant.

[0024] Furthermore, the first conductive agent includes at least one of carbon black, graphite powder, graphene and carbon nanotubes.

[0025] Furthermore, the first binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin.

[0026] Furthermore, the first acidic additive includes at least one of oxalic acid, citric acid, acetic acid and phosphoric acid.

[0027] Furthermore, the first dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol and polyacrylic acid.

[0028] The present invention also provides a method for preparing a positive electrode sheet, comprising the following steps: coating a first positive electrode slurry containing a layered oxide positive electrode material on the surface of a current collector, and forming a first active layer after drying; coating a second positive electrode slurry containing a polyanion positive electrode material and a honeycomb conductive agent on the surface of the first active layer, and forming a second active layer after drying to obtain the positive electrode sheet.

[0029] The present invention further provides a sodium ion battery comprising the above-mentioned positive electrode plate.

[0030] The present invention also provides an electrical device comprising the above-mentioned sodium ion battery.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: the positive electrode plate provided by the present invention, the first active layer containing the layered oxide positive electrode material can ensure the capacity of the battery core; the second active layer containing the polyanion positive electrode material can ensure the thermal stability and cycle stability of the battery core, and through the characteristic that the polyanion positive electrode material will produce gas when subjected to thermal stimulation or mechanical action, a gas buffer layer can be generated, reducing the structural damage to the first active layer, and isolating the positive and negative electrodes from each other, blocking the thermal runaway reaction chain, thereby improving the safety performance of the battery core and enabling the battery core to pass the needle test; adding a honeycomb conductive agent to the second active layer not only maintains conductivity, but also increases the gas release channel, forming a directional gas buffer layer during needle puncture, which can isolate the positive and negative electrodes from short circuiting and relieve local stress. Therefore, the positive electrode plate provided by the present invention improves the battery needle puncture safety performance while ensuring the energy density and cycle performance of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a schematic structural diagram of the positive electrode sheet provided by the present invention. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0035] Unless otherwise specified, in the present invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute closed-ended limitations on quantity.

[0036] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0037] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0038] In a first aspect, the present invention provides a positive electrode plate, which includes a current collector, a first active layer disposed on at least one surface of the current collector, and a second active layer disposed on a surface of the first active layer.

[0039] See also Figure 1 As shown, the structure of the positive electrode plate can be: a second active layer, a first active layer, a current collector, a first active layer, and a second active layer stacked in sequence.

[0040] In addition, the structure of the positive electrode sheet may also be: a current collector, a first active layer, and a second active layer stacked in sequence.

[0041] The first active layer includes a layered oxide positive electrode material. That is, the positive electrode active material in the first active layer includes a layered oxide positive electrode material.

[0042] The second active layer includes a polyanion cathode material and a honeycomb conductive agent. Specifically, the cathode active material in the second active layer includes a polyanion cathode material. The conductive agent in the second active layer includes a honeycomb conductive agent. The polyanion cathode material can improve the thermal stability and cycling stability of the battery cell.

[0043] The honeycomb conductive agent includes at least one of honeycomb carbon nanofibers, honeycomb graphene aerogels, honeycomb metal sulfides, metal velvet network materials and carbon-based honeycomb composite materials.

[0044] Among them, the metal velvet network material is a three-dimensional mesh material made of micron-level metal wires (such as copper, aluminum, molybdenum, with a diameter of about 0.1 mm) through a precision weaving process to form a velvet-like flexible grid structure.

[0045] Carbon-based honeycomb composite materials, such as Fe3O4@C honeycomb materials, MXene / carbon skeleton honeycomb materials, graphene-modified honeycomb (GNPs) materials, etc., but not limited thereto.

[0046] The positive electrode plate provided by the present invention comprises a first active layer containing a layered oxide positive electrode material, which can ensure the capacity of the battery core.

[0047] By providing a second active layer containing a polyanion positive electrode material on the surface of the first active layer, the thermal stability and cycle stability of the battery cell can be ensured; moreover, when subjected to certain thermal stimulation or mechanical action, the polyanion positive electrode material will undergo chemical reactions such as decomposition to produce gas, releasing gases such as carbon dioxide and water vapor. During the acupuncture process, these gases can form a gas buffer layer to reduce structural damage to the first active layer (protecting the layered oxide positive electrode material in the first active layer). At the same time, the gas expansion can isolate the contact between the positive and negative electrodes, thereby significantly improving the safety performance of the battery cell and enabling the battery cell to pass the acupuncture test.

[0048] At the same time, a honeycomb conductive agent is added to the second active layer, and its honeycomb skeleton structure is used to form a continuous three-dimensional conductive channel, which increases the continuous conductive transmission path and improves the electron transmission efficiency; at the same time, the porous network structure is used to optimize the gas release path (accelerates gas escape), and can provide a gas diffusion channel when acupuncture occurs, forming a directional gas buffer layer to isolate the contact between the positive and negative electrodes. The honeycomb cavity as a gas diffusion channel can also avoid local pressure accumulation.

[0049] Therefore, the positive electrode plate provided by the present invention improves the battery puncture safety performance while ensuring the energy density and cycle performance of the sodium ion battery, ensures battery safety, and solves the problem of poor safety performance.

[0050] In some specific embodiments, the mass of the honeycomb conductive agent accounts for 0.2% to 6% of the mass of the second active layer, including but not limited to any of 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, and 6%, or any range therebetween. This helps improve conductivity, isolate short circuits between the positive and negative electrodes, and relieve local stress.

[0051] In some specific embodiments, the ratio of the surface density of the first active layer to the surface density of the second active layer is 1.7 to 4.7:1, including but not limited to any point value of 1.7:1, 1.8:1, 2.0:1, 2.0:1, 2.3:1, 2.5:1, 2.8:1, 3.0:1, 3.3:1, 3.5:1, 3.8:1, 4.0:1, 4.3:1, 4.5:1, and 4.7:1, or a range of values ​​between any two of them. If the ratio of the surface density of the first active layer to the surface density of the second active layer is too high, that is, the surface density of the second active layer is relatively low, the active material in the second active layer is too little, and it is difficult to form a compact electrode structure, resulting in problems such as cracks and shedding during charging and discharging. If the ratio of the surface density of the first active layer to the surface density of the second active layer is too low, that is, the surface density of the second active layer is relatively high, the overall energy density of the battery cell will be reduced, and the first active layer will not be able to fully react with the electrolyte, thereby reducing the utilization rate of the active material in the first active layer.

[0052] Preferably, the ratio of the surface density of the first active layer to the surface density of the second active layer is 2.0 to 3.3:1.

[0053] In some specific embodiments, the ratio of the thickness of the first active layer to the thickness of the second active layer is 1.01 to 4.10:1, including but not limited to any one of 1.01:1, 1.05:1, 1.1:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, and 4.10:1, or a range of values ​​between any two of them. If the ratio of the thickness of the first active layer to the thickness of the second active layer is too high, that is, the thickness of the second active layer is relatively thin, the amount of gas produced by the active material in the second active layer after thermal stimulation or mechanical action is insufficient to form a gas buffer layer; if the ratio of the thickness of the first active layer to the thickness of the second active layer is too low, that is, the thickness of the second active layer is relatively thick, the diffusion path of sodium ions in the electrode will become longer, the diffusion resistance will increase, and the polarization phenomenon will be aggravated.

[0054] Preferably, the ratio of the thickness of the first active layer to the thickness of the second active layer is 1.1 to 3.0:1.

[0055] In some specific embodiments, the compaction density of the first active layer is 2.5 to 3.5 g / cm 3; Including but not limited to 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.5g / cm 3 Any point value in or any range of values ​​between them.

[0056] In some specific embodiments, the compaction density of the second active layer is 1.7 to 2.4 g / cm 3 , including but not limited to 1.7 g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 Any point value in or any range of values ​​between them.

[0057] A core-shell structure is constructed using the layered oxide of the first active layer and the polyanion positive electrode material of the second active layer. The polyanion of the second active layer has a low compaction density, high porosity, and larger pore size, exhibiting good ion transport properties, but poor conductivity; the layered oxide electrode of the first active layer is denser, has relatively less porosity, and has good electronic conductivity, but poor ion transport properties; the two layers cooperate with each other to construct a high-speed channel for ions and electrons, which can improve the battery's rate performance, and the second active layer can protect the first active layer from damage and reduce side reactions.

[0058] In some specific embodiments, the second active layer further includes a second conductive agent.

[0059] In some specific embodiments, the second conductive agent includes at least one of carbon black, graphite powder, graphene, and carbon nanotubes.

[0060] In some specific embodiments, the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:1.01 to 10, including but not limited to any one of 1:1.01, 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10, or a range of values ​​between any two of them. If the mass ratio of the second conductive agent to the honeycomb conductive agent is too high, i.e., the honeycomb conductive agent content is relatively low, then the porous network structure is insufficient and the gas diffusion channels are insufficient. If the content ratio of the second conductive agent to the honeycomb conductive agent is too low, i.e., the honeycomb conductive agent content is relatively high, then the electrode compaction will be reduced and the manufacturing cost will increase.

[0061] Preferably, the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:1.5-9.

[0062] In some specific embodiments, the second active layer includes the following components in mass percentage: 82% to 97.5% of the polyanion positive electrode material, 0.2% to 6% of the honeycomb conductive agent, 0.1% to 2% of the second conductive agent, 0.1% to 5% of the second binder, 0% to 3% of the second acidic additive, and 0.1% to 2% of the second dispersant.

[0063] The polyanion positive electrode material includes but is not limited to any one of 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90%, 92%, 93%, 95%, 96%, 97.5% or any range between them; the honeycomb conductive agent includes but is not limited to any one of 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6% or any range between them; the second conductive agent includes but is not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2% or any range between them; the second binder includes but is not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2% or any range between them; %, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between them; the second acidic additive includes but is not limited to any one of 0, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3% or any range between them; the second dispersant includes but is not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2% or any range between them.

[0064] In some specific embodiments, the polyanion cathode material includes at least one of a phosphate cathode material, a pyrophosphate cathode material, a sulfate cathode material, and a composite phosphate cathode material.

[0065] In some specific embodiments, the second binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin.

[0066] In some specific embodiments, the second acidic additive includes at least one of oxalic acid, citric acid, acetic acid, and phosphoric acid.

[0067] In some specific embodiments, the second dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol, and polyacrylic acid.

[0068] In some specific embodiments, the first active layer includes the following components in mass percentage: 85% to 96% of the layered oxide positive electrode material, 0.1% to 5% of the first conductive agent, 0.1% to 5% of the first binder, 0% to 3% of the first acidic additive, and 0% to 3% of the first dispersant.

[0069] Wherein, the layered oxide positive electrode material includes but is not limited to any one of 85%, 86%, 87%, 88%, 90%, 92%, 93%, 95%, 96% or any range between two values; the first conductive agent includes but is not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between two values; the first binder includes but is not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between two values. 8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between them; the first acidic additive includes but is not limited to 0, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3% or any range between them; the first dispersant includes but is not limited to 0, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3% or any range between them.

[0070] In some specific embodiments, the layered oxide positive electrode material is selected from Na xMO2, wherein M comprises a transition metal element, 0<x≤2. Preferably, M comprises at least one of Cu, Fe, Mn, Co, Ni, Cr, Ru and Sn. For example, the chemical formula of the layered oxide positive electrode material is Na 1.03 Cu 0.31 Fe 0.15 Mn 0.35 Ni 0.19 O2.

[0071] In some specific embodiments, the first conductive agent includes at least one of carbon black, graphite powder, graphene, and carbon nanotubes.

[0072] In some specific embodiments, the first binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin.

[0073] In some specific embodiments, the first acidic additive includes at least one of oxalic acid, citric acid, acetic acid, and phosphoric acid.

[0074] In some specific embodiments, the first dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol, and polyacrylic acid.

[0075] In some specific embodiments, the current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, perforated aluminum foil, copper foil, carbon-coated copper foil and perforated copper foil.

[0076] In some specific embodiments, the thickness of the current collector is 8 to 16 μm, for example, 10 μm, 12 μm or 14 μm.

[0077] In a second aspect, the present invention provides a method for preparing a positive electrode sheet, comprising the following steps:

[0078] A first positive electrode slurry containing a layered oxide positive electrode material is coated on at least one surface of a current collector, and after drying, a first active layer is formed to obtain a current collector having the first active layer on its surface.

[0079] A second positive electrode slurry containing a polyanion positive electrode material and a honeycomb conductive agent is coated on the surface of the first active layer, and after drying, a second active layer is formed to obtain the positive electrode sheet.

[0080] The preparation method has simple process, high production efficiency and is easy to realize industrial production.

[0081] In some specific embodiments, a first positive electrode slurry containing a layered oxide positive electrode material is applied to both sides of a current collector and dried to form a first active layer. A second positive electrode slurry containing a polyanion positive electrode material and a honeycomb conductive agent is then applied to both sides of the first active layer and dried to form a second active layer, thereby obtaining the positive electrode sheet. Specifically, the positive electrode sheet comprises a second active layer, a first active layer, a current collector, a first active layer, and a second active layer, stacked in this order.

[0082] In some specific embodiments, the preparation method of the first positive electrode slurry includes: mixing a layered oxide positive electrode material, a first conductive agent, a first binder, a first acidic additive, and a first dispersant, and then stirring the mixture.

[0083] In some specific embodiments, the preparation method of the second positive electrode slurry includes: mixing a polyanion positive electrode material, a honeycomb conductive agent, a second conductive agent, a second binder, a second acidic additive, and a second dispersant, and then stirring the mixture.

[0084] In a third aspect, the present invention provides a sodium ion battery comprising the above-mentioned positive electrode plate.

[0085] The sodium ion battery has high capacity, good cycle performance and high safety performance.

[0086] In some specific embodiments, the sodium ion battery further includes a negative electrode plate, a separator and an electrolyte.

[0087] In a fourth aspect, the present invention provides an electrical device comprising the above-mentioned sodium ion battery.

[0088] It is understood that the above-mentioned electrical equipment includes any equipment, device or system using the above-mentioned sodium ion battery, including but not limited to: laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, and large household batteries.

[0089] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0090] It should be understood that the types of honeycomb conductive agents and their preparation methods in the following embodiments are only a part and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. The types of honeycomb conductive agents and their preparation methods are not limited to these.

[0091] Example 1

[0092] The method for preparing the positive electrode sheet provided in this embodiment includes the following steps:

[0093] (1) Preparation of the first positive electrode slurry: Weigh the following components in terms of mass percentage: layered oxide positive electrode material NaCu 0.22 Fe 0.3 Mn 0.48 O2 95.1%, a first conductive agent carbon black Super P 2.7%, a first binder polyvinylidene fluoride (PVDF) 1.3%, a first acidic additive oxalic acid 0.4% and a first dispersant polyvinyl pyrrolidone 0.5%, and the raw materials are uniformly mixed to obtain a first positive electrode slurry.

[0094] (2) Preparation of the Second Positive Electrode Slurry: The following components were weighed in percentage by mass: 93.8% of the polyanionic positive electrode material (composite phosphate positive electrode material) Na4Fe3(PO4)2P2O7, 0.5% of the second conductive agent, carbon black Super P, 3% of the honeycomb conductive agent, honeycomb carbon nanofiber (Tiannai Technology, FT900), 1.8% of the second binder, polyvinylidene fluoride (PVDF), 0.4% of the second acidic additive, and 0.5% of the second dispersant, polyvinyl pyrrolidone. The raw materials were mixed uniformly to obtain the second positive electrode slurry. That is, the mass ratio of the second conductive agent to the honeycomb conductive agent was 1:6.

[0095] (3) Preparation of positive electrode sheet: The first positive electrode slurry was coated on both sides of a 12 μm thick aluminum foil current collector, and the surface density was controlled to be 26 mg / cm 2 After drying, the first active layer is formed. Then the second positive electrode slurry is coated on the surface of the first active layer on both sides, and the surface density is controlled to 8mg / cm 3 After drying, the second active layer is formed to obtain a positive electrode sheet. That is, the positive electrode sheet includes the second active layer, the first active layer, the current collector, the first active layer and the second active layer stacked in sequence, such as Figure 1 The positive electrode sheet is rolled and cut, and the compaction density of the first active layer after rolling is 3.25g / cm 3 , thickness is 80μm; the compaction density of the second active layer is 1.8g / cm 3 , with a thickness of 44μm.

[0096] That is, the ratio of the area density of the first active layer to the area density of the second active layer is 3.25:1, and the ratio of the thickness of the first active layer to the thickness of the second active layer is 1.82:1.

[0097] This embodiment further provides a method for preparing a sodium ion battery, comprising the following steps: weighing the following components by mass percentage: 95.6% hard carbon HNA102 as a negative electrode active material, 1.4% carbon black Super P as a conductive agent, and 3% polyvinylidene fluoride (PVDF) as a binder; mixing the raw materials uniformly to obtain a negative electrode slurry; coating the negative electrode slurry on both sides of an aluminum foil current collector with a thickness of 12 μm, and controlling the surface density to 13.6 mg / cm 2 After drying, the negative electrode sheet is rolled and cut to obtain the negative electrode sheet. The positive electrode sheet, separator and negative electrode sheet are wound into a core, which is then placed in an aluminum shell and injected with electrolyte to produce a sodium ion battery.

[0098] Example 2

[0099] The preparation method of the positive electrode sheet provided in this embodiment is basically the same as that in Example 1, except that: in step (3), the coating surface density of the first positive electrode slurry is 22 mg / cm 2 The coating surface density of the second positive electrode slurry is 8 mg / cm 2 , and the thickness of the first active layer after rolling is 68 μm. That is, in this embodiment, the ratio of the surface density of the first active layer to the surface density of the second active layer is 2.75:1, and the ratio of the thickness of the first active layer to the thickness of the second active layer is 1.55:1.

[0100] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in Example 1, except that the positive electrode sheet prepared in this embodiment is used (instead of the positive electrode sheet prepared in Example 1), and the coating surface density of the negative electrode slurry is controlled to be 11.5 mg / cm 2 .

[0101] Example 3

[0102] The preparation method of the positive electrode provided in this embodiment is basically the same as that in embodiment 1, except that: step (2) is: weighing the following components in mass percentage: polyanion positive electrode material (sulfate positive electrode material) Na2Fe2(SO4)392.9%, second conductive agent carbon black Super P 1%, honeycomb conductive agent is honeycomb graphene aerogel 1.8%, second binder polyvinylidene fluoride (PVDF) 3.8% and second dispersant polyvinyl pyrrolidone 0.5%, and mixing the raw materials uniformly to obtain a second positive electrode slurry; that is, the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:1.8. At the same time, in step (3), the coating surface density of the first positive electrode slurry is 20 mg / cm2 The coating surface density of the second positive electrode slurry is 10 mg / cm 2 After rolling, the thickness of the first active layer was 61.5 μm, and the thickness of the second active layer was 55.5 μm. That is, in this embodiment, the ratio of the areal density of the first active layer to the areal density of the second active layer was 2:1, and the ratio of the thickness of the first active layer to the thickness of the second active layer was 1.11:1.

[0103] Among them, the preparation method of honeycomb graphene aerogel is as follows: using the biological template method, (1) GO solution and template (pollen particles, particle size 5-10 μm) are mixed at a ratio of 1:1 (w / w) and ultrasonically dispersed for 30 minutes; (2) the pH is adjusted to 7-8, and a reducing agent (ascorbic acid, accounting for 10% of the mass of GO) is added, and stirred in a 60°C water bath for 2 hours to induce GO reduction and wrap the template; (3) after freeze drying (-80°C pre-freezing for 12 hours, vacuum drying for 24 hours), the template is dissolved in ethanol or calcined (300°C, N2 atmosphere) to remove the template to form honeycomb pores.

[0104] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in Example 1, except that the positive electrode sheet prepared in this embodiment is used (instead of the positive electrode sheet prepared in Example 1), and the coating surface density of the negative electrode slurry is controlled to be 11.3 mg / cm 2 .

[0105] Example 4

[0106] The preparation method of the positive electrode provided in this embodiment is basically the same as that in embodiment 1, except that: step (2) is: weighing the following components in mass percentage: polyanion positive electrode material (pyrophosphate positive electrode material) Na2FeP2O7 95.2%, second conductive agent carbon black Super P 0.3%, honeycomb conductive agent is honeycomb carbon nanofiber 1.2%, second binder polyvinylidene fluoride (PVDF) 2.8%, and second dispersant polyvinyl pyrrolidone 0.5%, and mixing the raw materials uniformly to obtain a second positive electrode slurry; that is, the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:4. At the same time, in step (3), the coating surface density of the first positive electrode slurry is 27 mg / cm 2 The coating surface density of the second positive electrode slurry is 9 mg / cm 2 , and after rolling, the thickness of the first active layer was 83 μm, and the thickness of the second active layer was 50 μm. That is, in this embodiment, the ratio of the areal density of the first active layer to the areal density of the second active layer was 3:1, and the ratio of the thickness of the first active layer to the thickness of the second active layer was 1.66:1.

[0107] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in Example 1, except that the positive electrode sheet prepared in this embodiment is used (instead of the positive electrode sheet prepared in Example 1), and the coating surface density of the negative electrode slurry is controlled to be 10.3 mg / cm 2 .

[0108] Example 5

[0109] The preparation method of the positive electrode plate provided in this embodiment is basically the same as that in Example 1, except that: in step (2), the honeycomb carbon nanofibers are replaced with honeycomb metal sulfide of equal mass.

[0110] The preparation method of honeycomb metal sulfide is as follows: using the biological template method, (1) bacterial cellulose (BC, 1% w / v) and nickel nitrate (Ni(NO3)2, 0.3M) were mixed and allowed to stand for 12 hours to allow Ni 2+ Adsorbed on the BC fiber network, sodium sulfide (Na2S, 0.3M) was added and reacted at room temperature for 1 hour to form a NiS nanoparticle / BC complex; (2) carbonized at 600℃ for 2 hours in a N2 atmosphere, BC was converted into a carbon skeleton, and NiS maintained a honeycomb distribution, forming a NiS / carbon composite conductive agent (the conductivity can reach 800S / m).

[0111] A sodium ion battery was prepared using the positive electrode sheet prepared in this embodiment according to the preparation method of the sodium ion battery in Example 1.

[0112] Example 6

[0113] The preparation method of the positive electrode plate provided in this embodiment is basically the same as that in Example 1, except that: in step (2), the honeycomb carbon nanofibers are replaced with an equal mass of MXene / carbon skeleton honeycomb material.

[0114] The preparation method of MXene / carbon skeleton honeycomb material is as follows: using the impregnation-reduction method, (1) carbon nanotubes (CNT, 1 mg / mL) and graphene (1 mg / mL) were mixed, and Fe 3+ (1) The carbon skeleton was immersed in a MXene suspension (concentration 5-10 mg / mL) and ultrasonicated for 30 min to allow MXene to be uniformly adsorbed on the inner wall of the carbon pores; (2) a reducing agent (ascorbic acid, accounting for 20% of the MXene mass) was added and reacted at 60 °C for 4 h; (3) after freeze-drying (-50 °C, 24 h), the carbon skeleton was annealed at 500 °C in an Ar atmosphere for 1 h to improve the interfacial conductivity.

[0115] A sodium ion battery was prepared using the positive electrode sheet prepared in this embodiment according to the preparation method of the sodium ion battery in Example 1.

[0116] Example 7

[0117] The preparation method of the positive electrode provided in this embodiment is basically the same as that in Example 1, except that: in step (2), the mass percentage of the honeycomb carbon nanofiber is replaced by 6%, and the mass percentage of Na4Fe3(PO4)2P2O7 is replaced by 90.8%.

[0118] A sodium ion battery was prepared using the positive electrode sheet prepared in this embodiment according to the preparation method of the sodium ion battery in Example 1.

[0119] Example 8

[0120] The preparation method of the positive electrode sheet provided in this embodiment is basically the same as that in embodiment 1, except that: in step (3), the compaction density of the first active layer after roller pressing is controlled to be 2.8 g / cm 3 , and the compaction density of the second active layer is 2.2g / cm 3 .

[0121] A sodium ion battery was prepared using the positive electrode sheet prepared in this embodiment according to the preparation method of the sodium ion battery in Example 1.

[0122] Comparative Example 1

[0123] The preparation method of the positive electrode provided in this comparative example comprises the following steps: weighing the following components in terms of mass percentage: layered oxide positive electrode material NaCu 0.22 Fe 0.3 Mn 0.48 O2 95.1%, conductive agent carbon black Super P 2.7%, binder polyvinylidene fluoride (PVDF) 1.3%, acidic additive oxalic acid 0.4% and dispersant polyvinyl pyrrolidone 0.5% were mixed to obtain the positive electrode slurry. The positive electrode slurry was coated on both sides of the aluminum foil current collector with a thickness of 12μm, and the surface density was controlled to 30mg / cm 2 After drying, the positive electrode sheet is obtained. The positive electrode sheet is rolled and cut. The compaction density of the active layer after rolling is 3.25g / cm 3 , with a thickness of 92.3μm.

[0124] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that the positive electrode sheet prepared in this comparative example is used (instead of the positive electrode sheet prepared in Example 1), and the coating surface density of the negative electrode slurry is controlled to be 12.3 mg / cm 2 .

[0125] Comparative Example 2

[0126] The preparation method of the positive electrode sheet provided in this comparative example is basically the same as that of comparative example 1, except that the coating surface density of the positive electrode slurry is controlled to be 34 mg / cm 2 At the same time, the thickness of the active layer after rolling is controlled to be 104.6μm.

[0127] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that the positive electrode sheet prepared in this comparative example is used (instead of the positive electrode sheet prepared in Example 1), and the coating surface density of the negative electrode slurry is controlled to be 13.8 mg / cm 2 .

[0128] Comparative Example 3

[0129] The preparation method of the positive electrode provided in this comparative example is basically the same as that in Example 1, except that: honeycomb carbon nanofibers are not added in step (2), and the mass percentage of the second conductive agent carbon black Super P is replaced with 3.5%.

[0130] A sodium ion battery was prepared by using the positive electrode sheet prepared in this comparative example and following the preparation method of the sodium ion battery in Example 1.

[0131] Comparative Example 4

[0132] The preparation method of the positive electrode provided in this comparative example is basically the same as that in Example 1, except that: in step (2), the mass percentage of the honeycomb carbon nanofiber is replaced by 8%, and the mass percentage of Na4Fe3(PO4)2P2O7 is replaced by 88.8%.

[0133] A sodium ion battery was prepared by using the positive electrode sheet prepared in this comparative example and following the preparation method of the sodium ion battery in Example 1.

[0134] Comparative Example 5

[0135] The preparation method of the positive electrode sheet provided in this comparative example is basically the same as that in Example 1, except that: in step (3), the coating surface density of the first positive electrode slurry is 22 mg / cm 2 The coating surface density of the second positive electrode slurry is 15 mg / cm 2 That is, in this comparative example, the ratio of the surface density of the first active layer to the surface density of the second active layer is 1.47:1.

[0136] A sodium ion battery was prepared by using the positive electrode sheet prepared in this comparative example and following the preparation method of the sodium ion battery in Example 1.

[0137] Comparative Example 6

[0138] The preparation method of the positive electrode sheet provided in this comparative example is substantially the same as that in Example 1, except that in step (3), the thickness of the first active layer after rolling is 198 μm. That is, in this comparative example, the ratio of the thickness of the first active layer to the thickness of the second active layer is 4.5:1.

[0139] A sodium ion battery was prepared by using the positive electrode sheet prepared in this comparative example and following the preparation method of the sodium ion battery in Example 1.

[0140] Comparative Example 7

[0141] The preparation method of the positive electrode plate provided in this comparative example is basically the same as that in Example 1, except that: in step (2), the mass percentage of the second conductive agent carbon black Super P is 0.25%, and the mass percentage of the honeycomb carbon nanofiber is 3.25%, that is, the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:13.

[0142] A sodium ion battery was prepared by using the positive electrode sheet prepared in this comparative example and following the preparation method of the sodium ion battery in Example 1.

[0143] Experimental example

[0144] The sodium ion batteries prepared in each embodiment and each comparative example were subjected to a room temperature 1C / 1C cycle test, and a high-temperature resistant steel needle with a diameter of 5 to 8 mm was used to penetrate the battery plate at a speed of 25±5 mm / s in a direction perpendicular to the battery plate (the penetration direction should be close to the geometric center of the punctured surface, and the steel needle should remain in the battery for 1 hour to observe whether the battery catches fire or explodes). In addition, the diaphragm resistance was tested by a four-probe method. The test results are shown in Table 1.

[0145] Table 1 Test results of various sodium ion batteries

[0146]

[0147] It can be seen from Table 1 that the sodium ion batteries prepared in various embodiments have excellent cycle performance, good acupuncture safety performance, high energy density and low membrane resistance.

[0148] However, since the second active layer is not provided in Comparative Examples 1 and 2, the cycle performance is significantly reduced, the needle puncture safety performance is poor, and the membrane resistance is high.

[0149] In Comparative Example 3, since the honeycomb carbon nanofibers were not added, the battery cell failed the acupuncture safety test and the diaphragm resistance was high.

[0150] In Comparative Example 4, due to the excessive addition of honeycomb carbon nanofibers, the edge defects of the excess conductive agent catalyze the decomposition of the electrolyte, aggravate the side reaction, and the cycle capacity retention rate decays rapidly, and the energy density decreases.

[0151] In Comparative Example 5, due to the inappropriate ratio of the density of the first active layer surface to the density of the second active layer surface, there is too little active material to form a compact electrode structure, and problems such as cracks and shedding occur during the charge and discharge process, the cycle performance is reduced, and the membrane resistance is high.

[0152] In Comparative Example 6, due to an unsuitable ratio of the thickness of the first active layer to the thickness of the second active layer, the gas production of the second positive electrode active material after thermal stimulation or mechanical action was insufficient to form a gas buffer layer, and the battery cell failed the puncture test.

[0153] In Comparative Example 7, due to the inappropriate mass ratio of the second conductive agent to the honeycomb conductive agent, the honeycomb structure excessively accelerates heat transfer, causing the battery cell to explode after puncture. At the same time, the polyanion decomposition gas is excessively trapped, and local pressure accumulation causes the electrode to delaminate or rupture.

[0154] In summary, the present invention ensures the thermal stability and cycle stability of the battery cell by providing a second active layer containing a polyanion positive electrode material on the surface of the first active layer. Furthermore, due to the characteristic that the polyanion positive electrode material generates gas when subjected to thermal stimulation or mechanical action, a gas buffer layer can be generated, which reduces structural damage to the first active layer and isolates the positive and negative electrodes from contact, preventing short circuits and significantly improving the safety performance of the battery cell. At the same time, the addition of a honeycomb conductive agent to the second active layer not only increases conductivity, but its honeycomb mesh structure also provides a gas diffusion channel, forming a directional gas buffer layer during acupuncture, isolating the positive and negative electrodes from short circuits and relieving local stress.

[0155] Therefore, the positive electrode plate provided by the present invention can improve the battery acupuncture safety performance while ensuring the energy density and cycle performance of the sodium ion battery.

[0156] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A positive electrode plate, characterized in that: comprising a current collector, a first active layer disposed on a surface of the current collector, and a second active layer disposed on a surface of the first active layer; The first active layer includes a layered oxide positive electrode material; The second active layer includes a polyanion positive electrode material and a honeycomb conductive agent; the honeycomb conductive agent includes at least one of honeycomb carbon nanofibers, honeycomb graphene aerogels, honeycomb metal sulfides, metal velvet network materials and carbon-based honeycomb composite materials.

2. The positive electrode sheet according to claim 1, characterized in that: The mass of the honeycomb-shaped conductive agent accounts for 0.2% to 6% of the mass of the second active layer.

3. The positive electrode sheet according to claim 1, characterized in that: The ratio of the surface density of the first active layer to the surface density of the second active layer is 1.7 to 4.7:

1.

4. The positive electrode sheet according to claim 1, characterized in that: The ratio of the thickness of the first active layer to the thickness of the second active layer is 1.01 to 4.10:

1.

5. The positive electrode sheet according to claim 1, characterized in that: The compaction density of the first active layer is 2.5 to 3.5 g / cm 3 ; And / or, the compaction density of the second active layer is 1.7 to 2.4 g / cm 3 .

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The second active layer further includes a second conductive agent, the second conductive agent includes at least one of carbon black, graphite powder, graphene and carbon nanotubes, and the mass ratio of the second conductive agent to the honeycomb conductive agent is 1:1.01-10; Preferably, the second active layer comprises the following components by mass percentage: 82% to 97.5% of the polyanion positive electrode material, 0.2% to 6% of the honeycomb conductive agent, 0.1% to 2% of the second conductive agent, 0.1% to 5% of the second binder, 0% to 3% of the second acidic additive, and 0.1% to 2% of the second dispersant; Preferably, the polyanion cathode material includes at least one of a phosphate cathode material, a pyrophosphate cathode material, a sulfate cathode material and a composite phosphate cathode material; Preferably, the second binder comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin; Preferably, the second acidic additive includes at least one of oxalic acid, citric acid, acetic acid and phosphoric acid; Preferably, the second dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol and polyacrylic acid.

7. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The first active layer comprises the following components by mass percentage: 85% to 96% of the layered oxide positive electrode material, 0.1% to 5% of a first conductive agent, 0.1% to 5% of a first binder, 0% to 3% of a first acidic additive, and 0% to 3% of a first dispersant; Preferably, the first conductive agent comprises at least one of carbon black, graphite powder, graphene and carbon nanotubes; Preferably, the first binder comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin; Preferably, the first acidic additive includes at least one of oxalic acid, citric acid, acetic acid and phosphoric acid; Preferably, the first dispersant includes at least one of polyvinyl pyrrolidone, trisodium phosphate, sodium hexametaphosphate, polyethylene glycol and polyacrylic acid.

8. The method for preparing a positive electrode sheet according to any one of claims 1 to 7, wherein: The steps include: Coating a first positive electrode slurry containing a layered oxide positive electrode material on the surface of a current collector and forming a first active layer after drying; A second positive electrode slurry containing a polyanion positive electrode material and a honeycomb conductive agent is coated on the surface of the first active layer, and after drying, a second active layer is formed to obtain the positive electrode sheet.

9. A sodium ion battery, characterized in that: The invention comprises the positive electrode sheet as claimed in any one of claims 1 to 7.

10. An electrical device, characterized in that: Comprising the sodium ion battery as claimed in claim 9.

Images