Positive electrode sheet for sodium ion battery, battery, battery pack, and electric device

Abstract

Embodiments of the present application provide a positive electrode sheet for a sodium ion battery, a battery, a battery pack, and an electric device. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a polyanionic positive electrode material, the cross-sectional porosity of the polyanionic positive electrode material is 1%-60%, the particle crush strength of the polyanionic positive electrode material is 0.2 mN-20 mN, and the powder disintegration ratio of the polyanionic positive electrode material satisfies: 1.2≤α≤48, wherein α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing. By using the polyanionic positive electrode material having the described characteristics to form the positive electrode active material layer on the current collector, the peel strength between the positive electrode active material layer and the current collector can be improved, thus the detachment of the positive electrode material from the current collector during calendering is reduced, thereby improving the compaction density of the positive electrode sheet, thus improving the volumetric energy density of the battery.

Description

Positive electrode sheets, batteries, battery packs, and electrical devices used in sodium-ion batteries.

[0001] This application claims priority to Chinese Patent Application No. 202510123529.0, filed on January 24, 2025, entitled "Positive electrode sheet, battery, battery pack and electrical device for sodium-ion batteries", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of batteries, and more particularly to a positive electrode sheet, battery, battery pack, and electrical device for sodium-ion batteries. Background Technology

[0003] Sodium has broad application prospects in sodium-ion batteries due to its abundant reserves and low cost. Existing cathode materials for sodium-ion batteries mainly include layered metal oxides, polyanionic compounds, and Prussian blue-like compounds.

[0004] Polyanionic cathode materials have attracted widespread attention due to their high rate performance, long cycle life, good thermal stability, and excellent safety performance, as well as their stable crystal structure, high voltage, and high safety.

[0005] After the polyanionic cathode material forms the cathode slurry, the cathode slurry is coated onto the current collector to form the cathode active material layer. Then, the cathode active material layer is rolled to compact the cathode active material layer on the current collector and increase the compaction density of the cathode sheet.

[0006] However, the peeling force between the positive electrode active material layer and the current collector is low, which can easily cause the positive electrode material to fall off the current collector during the rolling process, resulting in a reduction of the material on the current collector and thus affecting the compaction density of the positive electrode sheet. Summary of the Invention

[0007] The positive electrode sheet, battery, battery pack, and electrical equipment for sodium-ion batteries provided in this application are used to improve the compaction density of the positive electrode sheet.

[0008] The first aspect of this application provides a positive electrode sheet for a sodium-ion battery, including a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, the positive electrode active material layer containing a polyanionic positive electrode material;

[0009] The cross-sectional porosity of the polyanionic cathode material is 1%-60%;

[0010] The particle crushing force of the polyanionic cathode material is 0.2mN-20mN;

[0011] The powder collapse ratio of the polyanionic cathode material satisfies: 1.2≤α≤48, where α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing.

[0012] In one possible implementation, the cross-sectional porosity of the polyanionic cathode material is 2%-40%.

[0013] In one possible implementation, the cross-sectional porosity of the polyanionic cathode material is 5%-20%.

[0014] In one possible implementation, the particle crushing force of the polyanionic cathode material is 1mN-18mN.

[0015] In one possible implementation, the particle crushing force of the polyanionic cathode material is 3mN-10mN.

[0016] In one possible implementation, the powder collapse ratio of the polyanionic cathode material satisfies: 1.8 ≤ α ≤ 30.

[0017] In one possible implementation, the powder collapse ratio of the polyanionic cathode material satisfies: 2≤α≤26.

[0018] In one possible implementation, the chemical formula of the polyanionic cathode material is Na. x M y (PO4) w X a Z b Y c M is at least one of Ti, V, Cr, Mn, Fe, Co, and Ni; X is at least one of S, P, Si, W, and B; Z is at least one of F, O, and OH; and Y is at least one of C and Al.

[0019] Wherein, 2.8≤x≤4.2, 1.9≤y≤3.1, 1.8≤w≤2.2, 0≤a≤3.0, 0≤b≤8.0, 0≤c≤3.0.

[0020] In one possible implementation, the polyanionic cathode material is at least one of single crystal, quasi-single crystal, and polycrystalline.

[0021] Secondly, this application provides a battery including the positive electrode sheet described in the first aspect.

[0022] Thirdly, this application provides a battery pack including the battery described in the second aspect.

[0023] Fourthly, this application provides an electrical device including the battery described in the first aspect or the battery pack described in the second aspect.

[0024] The positive electrode sheet, battery, battery pack, and electrical device for sodium-ion batteries provided in this application include a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector. The positive electrode active material layer contains a polyanionic positive electrode material with a cross-sectional porosity of 1%-60%, a particle crushing force of 0.2mN-20mN, and a powder collapse ratio satisfying 1.2≤α≤48, where α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing. By using the polyanionic positive electrode material with the above characteristics to form the positive electrode active material layer on the current collector, the peeling force between the positive electrode active material layer and the current collector can be improved, reducing the detachment of the positive electrode material from the current collector during rolling, thereby increasing the compaction density of the positive electrode sheet and thus increasing the volumetric energy density of the battery. Detailed Implementation

[0025] Exemplary embodiments will be described in detail below. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0026] The cathode materials of sodium-ion batteries mainly include layered metal oxides, polyanionic compounds, and Prussian blue compounds.

[0027] Layered metal oxides exhibit complex phase transitions, poor air and structural stability, stringent environmental requirements, and inherently poor material safety. Prussian blue compounds typically contain numerous vacancies and abundant water of crystallization, impacting the battery's actual specific capacity, stability, and safety. Polyanionic compounds, on the other hand, possess characteristics such as high rate performance, long cycle life, good thermal stability, and excellent safety performance. Furthermore, they exhibit stable crystal structures, high voltage, and high safety, thus attracting widespread attention.

[0028] However, the peeling force between the positive electrode active material layer formed by polyanionic compounds and the current collector is low, which can easily cause the positive electrode material to fall off the current collector during the rolling process, resulting in a reduction of the material on the current collector and thus affecting the compaction density of the positive electrode sheet.

[0029] According to the inventor's research, the compaction density of the positive electrode sheet can be increased through the following methods:

[0030] 1. Improve the internal density of polyanionic cathode materials.

[0031] Improving the particle density of polyanionic cathode materials can increase the amount of cathode material contained per unit volume, thereby improving the capacity and quality of the material per unit volume, increasing the specific capacity of the battery, enhancing the compressive strength of the particles, increasing the compaction density of the cathode sheet, and thus improving the volumetric energy density of the battery.

[0032] However, excessive particle density in the cathode material can affect the sodium ion solid-phase diffusion rate, leading to increased polarization and a decrease in the battery's specific capacity. Furthermore, excessive particle density in the cathode material makes the particles more prone to sedimentation, affecting the uniformity of the cathode slurry. This makes it difficult to uniformly coat the cathode slurry onto the current collector, impacting the coating effect and consequently affecting the uniformity of the cathode active material layer. Ultimately, this results in a lower compaction density of the cathode sheet, affecting the battery's volumetric energy density.

[0033] Therefore, within a certain range, the particle density of polyanionic cathode materials helps to increase the solid-phase diffusion rate of sodium ions, improve the specific capacity of the battery, reduce particle sedimentation, and improve the uniformity of the cathode slurry. This allows the cathode slurry to be coated more evenly on the current collector, improving the coating effect of the cathode slurry and the uniformity of the cathode active material layer. This, in turn, increases the compaction density of the cathode sheet and ultimately improves the volumetric energy density of the battery.

[0034] The particle density of polyanionic cathode materials can be characterized by cross-sectional porosity. Therefore, the cross-sectional porosity of polyanionic cathode materials needs to be within a certain range.

[0035] 2. Improve the crush resistance of polyanionic cathode material particles.

[0036] Improving the crush resistance of polyanionic cathode material particles can increase the pressure density of the polyanionic cathode material. Cathode material particles with higher crush resistance are less prone to breakage or deformation during rolling, helping to maintain particle integrity and thus ensuring cell lifespan. Furthermore, it facilitates the uniform distribution of binder between particles, enhancing the adhesion between the positive electrode active material layer and the current collector, thereby increasing the peel force between them and reducing the amount of cathode material detaching from the current collector during rolling. This increases the compaction density of the cathode sheet and ultimately improves the volumetric energy density of the battery.

[0037] However, excessively high crush resistance in cathode material particles can lead to excessively large particle sizes and slow nano-ion diffusion rates within the particles. Larger particle sizes result in excessively large inter-particle porosity, making it difficult for the cathode material particles to pack tightly after the cathode slurry is coated onto the current collector. This affects the compaction density of the cathode sheet and consequently, the volumetric energy density of the battery. Furthermore, the slow nano-ion diffusion rate within the cathode material particles increases stress in the cathode material, weakening the electrochemical activity of the cathode active material and reducing the battery's specific capacity. Therefore, excessively high crush resistance in the particles can actually reduce the battery's volumetric energy density and specific capacity.

[0038] Therefore, the crush resistance of polyanionic cathode materials, within a certain range, helps to improve the peeling force between the cathode active material layer and the current collector, reducing the shedding of cathode material from the current collector during rolling, thereby increasing the compaction density of the cathode sheet and thus improving the volumetric energy density of the battery. It also helps to tightly pack cathode material particles on the current collector, further increasing the compaction density of the cathode sheet and improving the volumetric energy density of the battery. Furthermore, it helps to improve the diffusion rate of sodium-ion batteries, increasing the specific capacity of the battery.

[0039] The crush resistance of polyanionic cathode materials can be characterized by particle crushing force and powder collapse ratio. Therefore, the particle crushing force and powder collapse ratio of polyanionic cathode materials need to be within a certain range.

[0040] Therefore, in a first aspect, embodiments of this application provide a positive electrode sheet for a sodium-ion battery, comprising a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector. The positive electrode active material layer contains a polyanionic positive electrode material, the cross-sectional porosity of the polyanionic positive electrode material is 1%-60%, the particle crushing force of the polyanionic positive electrode material is 0.2mN-20mN, and the powder crushing ratio of the polyanionic positive electrode material satisfies: 1.2≤α≤48, where α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing.

[0041] Specifically, the cross-sectional porosity of the polyanionic cathode material is 1%-60%, for example, it can be a range of 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any combination thereof.

[0042] When the cross-sectional porosity of polyanionic cathode materials is 1%-60%, it helps to improve the compaction of the cathode material, increasing the amount of cathode material contained per unit volume, thereby increasing the specific capacity of the battery. It also helps to increase the sodium ion diffusion rate, further improving the specific capacity. Furthermore, it helps to improve the compressive strength of the particles, increasing the compaction density of the cathode sheet, thus increasing the volumetric energy density of the battery. It also helps to reduce the sedimentation of cathode material particles, improving the uniformity of the cathode slurry, allowing the cathode slurry to be more evenly distributed on the current collector, improving the coating effect of the cathode slurry, thereby improving the uniformity of the cathode active material layer, further increasing the compaction density of the cathode sheet, and ultimately further increasing the volumetric energy density of the battery.

[0043] The particle crushing force of the polyanionic cathode material is 0.2mN-20mN, for example, it can be 0.2mN, 0.6mN, 1mN, 2mN, 3mN, 5mN, 7mN, 8mN, 10mN, 12mN, 15mN, 17mN, 18mN, 20mN or any combination thereof.

[0044] When the particle compaction force of polyanionic cathode materials is between 0.2 mN and 20 mN, it helps to improve the adhesion between the active cathode material layer and the current collector, increases the peeling force between them, and reduces the shedding of cathode material from the current collector during rolling, thereby increasing the compaction density of the cathode sheet and consequently the volumetric energy density of the battery. It also promotes the tight packing of cathode material particles on the current collector, further increasing the compaction density of the cathode sheet and the volumetric energy density of the battery. Furthermore, it helps to increase the sodium ion diffusion rate, thus improving the specific capacity of the battery.

[0045] The powder collapse ratio of the polyanionic cathode material satisfies 1.2≤α≤48, where α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing. The powder collapse ratio can be, for example, a range of 1.2, 1.8, 2, 5, 8, 10, 12, 14, 16, 18, 20, 13, 26, 28, 30, 35, 40, 45, 48 or any combination thereof.

[0046] When the powder dispersion ratio of polyanionic cathode materials is 1.2-48, it helps to improve the peeling force between the cathode active material layer and the current collector, reducing the shedding of cathode material from the current collector during rolling, thereby increasing the compaction density of the cathode sheet and thus improving the volumetric energy density of the battery. It also helps to tightly pack cathode material particles on the current collector, further increasing the compaction density of the cathode sheet and improving the volumetric energy density of the battery. Furthermore, it helps to increase the sodium ion diffusion rate, thereby increasing the specific capacity of the battery.

[0047] Therefore, when the cross-sectional porosity, particle crushing force, and powder dispersion ratio of polyanionic cathode materials are within a certain range, the bonding force between the active cathode material layer and the current collector formed by the polyanionic cathode material can be better improved, as can the peeling force between the active cathode material layer and the current collector. This reduces the shedding of cathode material from the current collector during rolling, thereby increasing the compaction density of the cathode sheet and thus improving the volumetric energy density of the battery. It can also better improve the compaction of cathode material particles, further increasing the compaction density of the cathode sheet and improving the volumetric energy density of the battery. Furthermore, it can better improve the diffusion rate of sodium ions, thereby increasing the specific capacity of the battery.

[0048] In some embodiments of this application, the cross-sectional porosity of the polyanionic cathode material is 2%-40%. Within this range, the compaction density of the cathode sheet can reach or even exceed 2.10 g / cm³. 3 The volumetric energy density of the cathode material can reach or even exceed 630Wh / L, and the specific capacity of the battery can reach or even exceed 96.0mAh / g.

[0049] Therefore, a cross-sectional porosity of 2%-40% for polyanionic cathode materials helps improve the compaction of the cathode material and the sodium ion diffusion rate, thereby increasing the specific capacity of the battery. It also helps improve the compressive strength of the cathode material particles, increasing the compaction density of the cathode sheet, thus improving the volumetric energy density of the battery. Furthermore, it helps reduce particle sedimentation, improves the uniformity of the cathode slurry, and enhances the coating effect of the cathode slurry, thereby improving the uniformity of the cathode active material layer, further increasing the compaction density of the cathode sheet and the volumetric energy density of the battery.

[0050] In some embodiments of this application, the cross-sectional porosity of the polyanionic cathode material is 5%-20%. Within this range, the compaction density of the cathode sheet can reach or even exceed 2.20 g / cm³. 3 The volumetric energy density of the cathode material can reach or even exceed 655Wh / L, and the specific capacity of the battery can reach or even exceed 97.5mAh / g.

[0051] Therefore, when the cross-sectional porosity of polyanionic cathode materials is 5%-20%, the compaction density of the cathode sheet and the volumetric energy density of the cathode material can be further improved, thereby further improving the volumetric energy density and specific capacity of the battery.

[0052] In some embodiments of this application, the particle crushing force of the polyanionic cathode material is 1 mN-18 mN. Within this range, the peeling force between the positive electrode active material layer and the current collector formed by the polyanionic cathode material can reach or even exceed 0.7 N, and the compaction density of the cathode sheet can reach or even exceed 2.20 g / cm³. 3The volumetric energy density of the cathode material can reach or even exceed 630Wh / L, and the specific capacity of the battery can reach or even exceed 94.0mAh / g.

[0053] Therefore, when the particle crushing force of polyanionic cathode materials is between 1 mN and 18 mN, it helps to increase the peeling force between the active material layer and the current collector formed by the polyanionic cathode material, and improves the tight packing of the cathode material on the current collector, thereby increasing the compaction density of the cathode sheet and the volumetric energy density of the cathode material, and thus increasing the volumetric energy density of the battery. It also helps to increase the diffusion rate of sodium ions, thereby increasing the specific capacity of the battery.

[0054] In some implementations of this application, the particle crushing force of the polyanionic cathode material is 3mN-10mN. Within this range, the peeling force between the positive active material layer and the current collector formed by the polyanionic cathode material can reach or even exceed 1.18N, and the compaction density of the cathode sheet can reach or even exceed 2.28g / cm³. 3 The volumetric energy density of the cathode material can reach or even exceed 659Wh / L, and the specific capacity of the battery can reach or even exceed 97.8mAh / g.

[0055] Therefore, when the particle crushing force of polyanionic cathode material is 3mN-10mN, it can further improve the peeling force between the cathode active material layer and the current collector, increase the compaction density of the cathode sheet, and the volumetric energy density of the cathode material, thereby further improving the volumetric energy density and specific capacity of the battery.

[0056] In some embodiments of this application, the powder collapse ratio of the polyanionic cathode material satisfies 1.8 ≤ α ≤ 30, where α = S1 / S2, S1 is the powder area after collapse, and S2 is the powder area before collapse. Within this range, the peeling force between the positive electrode active material layer and the current collector formed by the polyanionic cathode material can reach or even exceed 1.4 N, and the compaction density of the cathode sheet can reach or even exceed 2.21 g / cm³. 3 The volumetric energy density of the cathode material can reach or even exceed 640Wh / L, and the specific capacity of the battery can reach or even exceed 97.5mAh / g.

[0057] Therefore, when the powder collapsibility ratio α of the polyanionic cathode material is 1.8-30, it can improve the peeling force between the positive active material layer and the current collector formed by the polyanionic cathode material, improve the compaction of the cathode material on the current collector, thereby increasing the compaction density of the cathode sheet and the volumetric energy density of the cathode material, and thus improving the volumetric energy density of the battery. It also helps to increase the diffusion rate of sodium ions, thereby increasing the specific capacity of the battery.

[0058] In some implementations of this application, the powder collapse ratio of the polyanionic cathode material satisfies: 2 ≤ α ≤ 26, where α = S1 / S2, S1 is the powder area after collapse, and S2 is the powder area before collapse. Within this range, the peeling force between the positive electrode active material layer and the current collector formed by the polyanionic cathode material can reach or even exceed 2.0 N, and the compaction density of the cathode sheet can reach or even exceed 2.26 g / cm³. 3 The volumetric energy density of the cathode material can reach or even exceed 655Wh / L, and the specific capacity of the battery can reach or even exceed 98.4mAh / g.

[0059] When the powder collapsibility ratio α of the polyanionic cathode material is 2-26, the peeling force between the cathode active material layer and the current collector is further improved, the compaction density of the cathode sheet is increased, and the volumetric energy density of the cathode material is increased, thereby further improving the volumetric energy density and specific capacity of the battery.

[0060] In some embodiments of this application, the chemical formula of the polyanionic cathode material is Na. x M y (PO4) w X a Z b Y c M is at least one of Ti, V, Cr, Mn, Fe, Co, and Ni; X is at least one of S, P, Si, W, and B; Z is at least one of F, O, and OH; and Y is at least one of C and Al.

[0061] In this application, sodium ions can be reversibly inserted and extracted into the polyanionic cathode material, enabling sodium-ion batteries to achieve charge-discharge cycles.

[0062] Transition metal elements (M) contribute electrochemical activity, enhance structural stability, and improve conductivity and thermal stability in polyanionic cathode materials. By selecting and optimizing the type and proportion of transition metals, the battery's capacity, energy density, cycle life, and safety can be significantly improved. For example, titanium has good chemical stability and safety and is often used to improve the material's cycle life and thermal stability; vanadium has multiple oxidation states and can provide high capacity and good rate performance; chromium can improve the material's structural stability and corrosion resistance; manganese is inexpensive and environmentally friendly, and has good electrochemical stability; iron is abundant and low-cost, and has good safety and environmental friendliness; cobalt has high conductivity and good electrochemical performance; and nickel has high capacity and good rate performance.

[0063] (PO4) w X a Z bTypically, stable crystal frameworks are formed, such as phosphates or complex phosphates, providing structural support for the insertion and extraction of sodium ions and transition metal ions. This helps maintain the structural integrity of the material during charge and discharge, and can also provide higher energy and improve the electrochemical performance of the battery. X can be selected from at least one of S, P, Si, W, and B. Sulfur can provide high capacity, and sulfur-based compounds such as sulfides are used to improve energy density; phosphorus can improve the thermal stability and safety of the material, and phosphates such as lithium iron phosphate are used to provide high safety; silicon has high theoretical capacity, and silicon-based materials are used to improve capacity and energy density; tungsten has high density and good mechanical properties, and tungsten-based materials are used to enhance structural stability; boron can improve the conductivity and thermal stability of the material, and borides are used to improve conductivity and thermal stability.

[0064] Z can be used to improve chemical stability and ionic conductivity. Z can be selected from at least one of O, F, and OH. Oxygen can regulate the proportion of phosphates or complex phosphates in the crystal framework. Fluorine can improve the electrochemical stability and corrosion resistance of materials; fluorides are used to improve voltage and stability. Hydroxyl groups can improve the hydrophilicity and ionic conductivity of materials; hydroxyl compounds are used to improve ionic conductivity.

[0065] Wherein, 2.8≤x≤4.2, 1.9≤y≤3.1, 1.8≤w≤2.2, 0≤a≤3.0, 0≤b≤8.0, and 0≤c≤3.0. By adjusting these stoichiometric ratios, the electrochemical performance, structural stability, and other properties of the material can be optimized.

[0066] In some embodiments of this application, the polyanionic cathode material is at least one of single crystal, quasi-single crystal, and polycrystalline.

[0067] Single-crystal materials have a complete crystal structure, which reduces stress concentration points that may lead to material degradation during charging and discharging, and exhibits higher mechanical stability, which helps to extend the cycle life of the battery.

[0068] Polycrystalline materials can have their performance optimized by adjusting grain size and shape, offering greater design flexibility and a higher reaction rate, making them suitable for applications requiring rapid charge and discharge.

[0069] Single-crystal-like materials combine the advantages of single crystals and polycrystalline materials, exhibiting fewer grain boundaries and good structural integrity, as well as excellent stability and good rate performance during cycling.

[0070] In some embodiments of this application, the polyanionic cathode material is at least one of fully broken particles, partially broken particles, and uncrushed particles.

[0071] Completely broken particles refer to materials in which the original particles have been completely broken into smaller particles or powder. Completely broken particles have a larger specific surface area, which can increase the contact area with the electrolyte, thereby improving the electrochemical reaction rate.

[0072] Semi-crushed granular materials refer to materials in which the original particles are partially crushed to form a mixture of particles of varying sizes. While maintaining a certain degree of structural integrity, the semi-crushed particles increase the surface area, thereby achieving a balance between mechanical stability and reactivity.

[0073] Unbroken granular materials refer to materials in which the original granules retain their integrity without undergoing significant mechanical breakage. Unbroken granules maintain a complete crystal structure and typically have higher mechanical stability, making them suitable for long-life applications.

[0074] The positive electrode sheet for sodium-ion batteries of this application can be prepared using conventional techniques in the art. It can be prepared by wet or dry formulation. For example, the above-mentioned polyanionic positive electrode material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a positive electrode slurry. Then, the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, the positive electrode sheet of this application can be obtained.

[0075] The positive current collector in this application can be selected from positive current collectors conventionally used in the art, such as aluminum foil.

[0076] The conductive agent, adhesive, and other components can all be selected from conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black (SP), carbon nanotubes, carbon nanofibers, Ketjen black, graphyne, conductive graphite, and graphene. The adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), hydrogenated nitrile rubber (HNBR), sodium alginate (SA), polytetrafluoroethylene (PTEE), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber (SBR), and styrene-acrylic rubber.

[0077] This application does not specify the coating method; any coating method such as gravure coating, extrusion coating, spraying, or screen printing can be used to achieve the coating of the positive electrode active layer slurry.

[0078] The positive electrode sheet provided in this application includes the above-mentioned polyanionic positive electrode material. Therefore, when this positive electrode sheet is applied to a battery, the battery can have a good volumetric energy density.

[0079] Secondly, this application provides a battery including the positive electrode sheet for a sodium-ion battery as described above, which has advantages corresponding to the aforementioned positive electrode sheet, and will not be elaborated further.

[0080] In addition to the positive electrode, the battery of this application also includes a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as PP film, PE film, etc.

[0081] The battery of this application can be prepared using conventional methods in the art. Specifically, the positive electrode, separator and negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding. Then, the battery can be obtained by baking, liquid injection, formation and packaging.

[0082] Batteries can be liquid batteries, solid-state batteries, or semi-solid-state batteries, and their shapes can be prismatic, cylindrical, or pouch batteries.

[0083] Thirdly, this application provides a battery pack including the battery as described above, which has advantages corresponding to the above-mentioned positive electrode plate, which will not be elaborated further.

[0084] Fourthly, this application provides an electrical device, including the battery or battery pack described above, which has advantages corresponding to the positive electrode plate described above, and will not be elaborated further.

[0085] The electrical equipment used in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles), electronic equipment (e.g., computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (e.g., watches, wristbands, VR glasses, etc.), and household appliances (e.g., air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without any particular limitation.

[0086] For example, in addition to the battery mentioned above, the electrical device may also include control components, input components, output components, communication components, and storage components. Control components may include, for example, a microcontroller or processor, for handling the device's logic control and data processing; input components may include, for example, a keyboard or touchscreen, for user input; output components may include, for example, a speaker, for audio output; communication components may include, for example, Wi-Fi or Bluetooth, for communication; and storage components may include, for example, memory or storage devices, for storing data and programs.

[0087] The present application will be further described below through specific embodiments.

[0088] It should be noted that the cross-sectional porosity, particle crushing force, and powder collapse ratio of polyanionic cathode materials can be obtained by disassembling the product and conducting tests.

[0089] Specifically, the disassembly process involves the following: Battery cell types include, but are not limited to, pouch cells, prismatic cells, and cylindrical cells. The battery is discharged to 2.0V under a low current (e.g., 0.05C / 0.1C / 0.2C) and then disassembled in an inert environment. The positive electrode is removed, cleaned with an organic solvent, and the positive electrode powder material is scraped off. The organic solvent can be one or more types of alcohols, esters, or ethers.

[0090] Then, the scraped positive electrode powder material (such as the above-mentioned polyanionic positive electrode material, conductive agent, and binder) is ultrasonically cleaned for 10 minutes to remove the floating matter on the upper layer. Organic solvent is added again, and ultrasonic cleaning is performed for 10 minutes. The cleaning is repeated three times. The bottom layer material is taken and vacuum dried until the powder moisture content is below 500 ppm.

[0091] After cleaning and drying the positive electrode sheet, the cross-sectional porosity can be tested. After cleaning and drying the scraped positive electrode powder material, the particle crushing test can be performed.

[0092] Cross-sectional porosity test: The cross-section of the positive electrode is cut by plasma beam, magnified 1000 times, and 10 SEM images are taken. The proportion of particle porosity in the SEM images is counted (porosity = particle cross-sectional pore area / particle cross-sectional area).

[0093] Particle crushing test: The particles are crushed using a single-particle mechanical property testing system, with a pressure range of 10-400 MPa and a holding time of 10 seconds. The particle crushing force can be obtained from the single-particle crushing curve. The powder collapse ratio can be obtained from images of the powder before and after crushing.

[0094] In practical applications, the cathode material undergoes multiple steps such as mixing, coating, drying, and compaction during battery manufacturing. Therefore, after disassembling the product, the cross-sectional porosity, particle crushing force, and powder collapse ratio are tested. The results may have slight differences compared to the test results of the raw material, which can be ignored.

[0095] Example 1

[0096] The method for preparing the sodium-ion battery in this embodiment includes the following steps:

[0097] (1) A polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6, and the chemical formula Na... 3.95 Fe 3.04 (PO4)2(P 1.98 O 7.02The crystalline form is Pn21a. It is mixed with SP, PVDF and NMP (N-methylpyrrolidone) in a mass ratio of 93:4:3:60, and then coated on an aluminum foil current collector. After drying, it is rolled to obtain a positive electrode sheet. Wherein α=S1 / S2, S1 is the powder area after crushing and S2 is the powder area before crushing.

[0098] (2) Hard carbon, SP, CMC, SBR and deionized water are mixed evenly in a mass ratio of 90:4:3:3:50, and then coated on aluminum foil current collector. After drying, the negative electrode sheet is obtained by rolling.

[0099] (3) The positive electrode, negative electrode and separator are stacked sequentially in an orderly manner to obtain the electrode core;

[0100] (4) After the electrode core is encased, electrolyte is injected, and sodium-ion batteries are obtained through formation and capacity testing.

[0101] Example 2

[0102] The preparation method of the sodium-ion battery in Example 2 is basically the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 1%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6 is used.

[0103] Example 3

[0104] The preparation method of the sodium-ion battery in Example 3 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 2%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6 is used.

[0105] Example 4

[0106] Example 4 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 5%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6.

[0107] Example 5

[0108] Example 5 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 20%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6.

[0109] Example 6

[0110] The preparation method of the sodium-ion battery in Example 6 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 23%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6 is used.

[0111] Example 7

[0112] The preparation method of the sodium-ion battery in Example 7 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 40%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6 is used.

[0113] Example 8

[0114] The preparation method of the sodium-ion battery in Example 8 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 60%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6 is used.

[0115] Example 9

[0116] The preparation method of the sodium-ion battery in Example 9 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 0.2 mN, and a powder collapse ratio α of 17.8 is used.

[0117] Example 10

[0118] The preparation method of the sodium-ion battery in Example 10 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 1 mN, and a powder collapse ratio α of 12.3 is used.

[0119] Example 11

[0120] The preparation method of the sodium-ion battery in Example 11 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 2.8 mN, and a powder collapse ratio α of 19.2 is used.

[0121] Example 12

[0122] Example 12 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 3.0 mN, and a powder collapse ratio α of 9.6.

[0123] Example 13

[0124] Example 13 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 5.8 mN, and a powder collapse ratio α of 32.1.

[0125] Example 14

[0126] Example 14 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 10.2 mN, and a powder collapse ratio α of 9.7.

[0127] Example 15

[0128] Example 15 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 12.7 mN, and a powder collapse ratio α of 14.7.

[0129] Example 16

[0130] Example 16 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 18 mN, and a powder collapse ratio α of 15.2.

[0131] Example 17

[0132] Example 17 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 20 mN, and a powder collapse ratio α of 16.2.

[0133] Example 18

[0134] The preparation method of the sodium-ion battery in Example 18 is the same as that in Example 1, except that a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 1.2 is used.

[0135] Example 19

[0136] Example 19 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 1.8.

[0137] Example 20

[0138] Example 20 uses the same method as Example 1 for preparing a sodium-ion battery, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 2.

[0139] Example 21

[0140] Example 21 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 26.

[0141] Example 22

[0142] Example 22 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 30.

[0143] Example 23

[0144] Example 23 is prepared using the same method as the sodium-ion battery in Example 1, except that it is prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 48.

[0145] Comparative Example 1

[0146] The sodium-ion battery of Comparative Example 1 was prepared using the same method as that of Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 68%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6.

[0147] Comparative Example 2

[0148] Comparative Example 2 was prepared using the same method as the sodium-ion battery in Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 0.08%, a particle crushing force of 6.3 mN, and a powder collapse ratio α of 15.6.

[0149] Comparative Example 3

[0150] The sodium-ion battery of Comparative Example 3 was prepared using the same method as that of Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 28.9 mN, and a powder collapse ratio α of 15.4.

[0151] Comparative Example 4

[0152] The sodium-ion battery of Comparative Example 4 was prepared using the same method as that of Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 0.01 mN, and a powder collapse ratio α of 39.5.

[0153] Comparative Example 5

[0154] Comparative Example 5 was prepared using the same method as the sodium-ion battery in Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 1.5 mN, and a powder collapse ratio α of 54.4.

[0155] Comparative Example 6

[0156] The sodium-ion battery of Comparative Example 6 was prepared using the same method as that of Example 1, except that it was prepared using a polyanionic cathode material with a cross-sectional porosity of 7%, a particle crushing force of 18.8, and a powder collapse ratio α of 1.14.

[0157] The specific volume, compacted density, and volumetric energy density of Examples 1-23 and Comparative Examples 1-6 were tested respectively, and the test results are shown in Table 1 below. The specific test methods are as follows:

[0158] Compacted density test: The weight and thickness of a fixed area of ​​positive electrode sheet are measured, and then the compacted density is obtained based on the ratio of the mass of the dressing to the volume of the dressing.

[0159] Specific capacity test: The battery is charged to 3.8V under 1 / 3C conditions and discharged to 2.0V under 1 / 3C conditions, and the cycle is repeated 3 times. The specific capacity is calculated based on the capacity of the last test.

[0160] Volumetric energy density test: The battery is charged to 3.8V under 1 / 3C conditions and discharged to 2.0V under 1 / 3C conditions for 3 cycles. The specific capacity and average voltage of the last test are taken, and the volumetric energy density of the cathode material is calculated in combination with the electrode compaction density.

[0161] Electrode peeling force test: Take the rolled positive electrode sheet, fix the positive electrode sheet on the fixture of the testing machine, and pull the positive active material layer on the current collector at a constant speed to test the force required to peel the positive active material layer from the current collector.

[0162] Table 1

[0163] The following conclusions can be drawn from Table 1:

[0164] 1) As can be seen from Examples 1 to 23 and Comparative Examples 1 to 8, when the cross-sectional porosity, particle crushing force and powder dispersion ratio of the polyanionic cathode material are within the range of the embodiments of this application, it helps to improve the electrode peeling force and volumetric energy density of the cathode material, the compaction density of the cathode sheet, thereby improving the volumetric energy density and specific capacity of the battery.

[0165] 2) As can be seen from Example 1 and Comparative Example 1, if the cross-sectional porosity of the polyanionic cathode material is too high, it will reduce the electrode peeling force and volumetric energy density of the cathode material, the compaction density of the cathode sheet, and the volumetric energy density and specific capacity of the battery.

[0166] 3) As can be seen from Example 1 and Comparative Example 2, the cross-sectional porosity of the polyanionic cathode material is too low. Although it can improve the electrode peeling force of the cathode material, it will reduce the volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the volumetric energy density and specific capacity of the battery.

[0167] 4) As can be seen from Example 1 and Comparative Example 3, the particle crushing force of the polyanionic cathode material is too high. Although it can improve the electrode peeling force of the cathode material, it will reduce the volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity and volumetric energy density of the battery.

[0168] 5) As can be seen from Example 1 and Comparative Example 4, if the particle crushing force of the polyanionic cathode material is too low, it will reduce the electrode peeling force and volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity and volumetric energy density of the battery.

[0169] 6) As can be seen from Example 1 and Comparative Example 5, if the powder collapse ratio of the polyanionic cathode material is too high, it will reduce the electrode peeling force and volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity and volumetric energy density of the battery.

[0170] 7) As can be seen from Example 1 and Comparative Example 6, if the powder collapse ratio of the polyanionic cathode material is too low, it will reduce the electrode peeling force and volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity and volumetric energy density of the battery.

[0171] By using polyanionic cathode materials with specific ranges of cross-sectional porosity, particle crushing force, and powder dispersion ratio to prepare sodium-ion batteries, the electrode peeling force and volumetric energy density of the cathode material can be improved, as well as the compaction density of the cathode sheet, thereby increasing the volumetric energy density and specific capacity of the battery.

[0172] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A positive electrode for a sodium-ion battery, wherein, It includes a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer containing a polyanionic positive electrode material; The cross-sectional porosity of the polyanionic cathode material is 1%-60%; The particle crushing force of the polyanionic cathode material is 0.2mN-20mN; The powder collapse ratio of the polyanionic cathode material satisfies: 1.2≤α≤48, where α=S1 / S2, S1 is the powder area after crushing, and S2 is the powder area before crushing.

2. The positive electrode according to claim 1, wherein, The cross-sectional porosity of the polyanionic cathode material is 2%-40%.

3. The positive electrode according to claim 1 or 2, wherein, The cross-sectional porosity of the polyanionic cathode material is 5%-20%.

4. The positive electrode according to any one of claims 1-3, wherein, The particle crushing force of the polyanionic cathode material is 1mN-18mN.

5. The positive electrode according to any one of claims 1-4, wherein, The particle crushing force of the polyanionic cathode material is 3mN-10mN.

6. The positive electrode according to any one of claims 1-5, wherein, The powder collapse ratio of the polyanionic cathode material satisfies: 1.8≤α≤30.

7. The positive electrode according to any one of claims 1-6, wherein, The powder collapse ratio of the polyanionic cathode material satisfies: 2≤α≤26.

8. The positive electrode according to any one of claims 1-7, wherein, The chemical formula of the polyanionic cathode material is Na. x M y (PO4) w X a Z b Y c M is at least one of Ti, V, Cr, Mn, Fe, Co, and Ni; X is at least one of S, P, Si, W, and B; Z is at least one of F, O, and OH; and Y is at least one of C and Al. Wherein, 2.8≤x≤4.2, 1.9≤y≤3.1, 1.8≤w≤2.2, 0≤a≤3.0, 0≤b≤8.0, 0≤c≤3.

0.

9. The positive electrode according to any one of claims 1-8, wherein, The polyanionic cathode material is at least one of single crystal, quasi-single crystal, and polycrystalline.

10. A battery, wherein, Includes the positive electrode sheet as described in any one of claims 1-9.

11. A battery pack, wherein, Includes the battery as described in claim 10.

12. An electrical appliance, wherein, Includes the battery of claim 10 or the battery pack of claim 11.

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