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

Abstract

Provided in the embodiments of the present application are a positive electrode sheet for a sodium-ion battery, and 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 contains a polyanionic positive electrode material; the cross-sectional porosity of the polyanionic positive electrode material is 1%-60%; the powder resistivity of the polyanionic positive electrode material is denoted as ρ 104Ω·cm, where 2≤ρ≤100; the intensity ID of a D peak and the intensity IG of a G peak of the polyanionic positive electrode material satisfy: 0.3≤ID / IG≤1.8; and the polyanionic positive electrode material satisfies: ρ / (ID / IG)≥1.2. The use of the polyanionic positive electrode material satisfying the above characteristics can improve the conductivity of the polyanionic positive electrode material and the transmission rate of electrons inside the material, such that the reaction rate of the positive electrode material is increased, the energy stored by the positive electrode material per unit of mass is thus increased, and the gram capacity of the battery is increased.

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. 202510125336.9, 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] However, polyanionic cathode materials have poor conductivity, which limits the efficiency of electron transport within the material, reduces the reaction rate of the cathode material, and consequently reduces the energy that can be stored per unit mass of cathode material, thus reducing the specific capacity of the battery. Summary of the Invention

[0006] This application provides a positive electrode, a battery, a battery pack, and an electrical device for sodium-ion batteries to improve the specific capacity of the battery.

[0007] In a first aspect, embodiments of this application provide 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, wherein the positive electrode active material layer contains a polyanionic positive electrode material.

[0008] The cross-sectional porosity of the polyanionic cathode material is 1%-60%;

[0009] The resistivity of the polyanionic cathode material is denoted as ρ10. 4 Ω.cm, 2≤ρ≤100;

[0010] The intensity I of the D peak in the polyanionic cathode material D With the intensity of peak G I G Satisfy: 0.3≤I D / I G ≤1.8;

[0011] The polyanionic cathode material satisfies the following relationship: ρ / (I D / I G )≥1.2.

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

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

[0014] In one possible implementation, 2≤ρ≤60.

[0015] In one possible implementation, 0.5 ≤ I D / I G ≤1.6.

[0016] In one possible implementation, 0.7 ≤ I D / I G ≤1.4.

[0017] In one possible implementation, 1.2 ≤ ρ / (I D / I G )≤40.

[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] 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 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 second aspect or the battery pack described in the third 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. The cross-sectional porosity of the polyanionic positive electrode material is 1%-60%, and the powder resistivity of the polyanionic positive electrode material is denoted as ρ10. 4 Ω.cm, 2≤ρ≤100, the intensity of peak D in polyanionic cathode materials D With the intensity of peak G I G Satisfying 0.3≤I D / I G ≤1.8, polyanionic cathode materials satisfy ρ / (I D / I G ≥1.2. By using polyanionic cathode materials that meet the above characteristics, the conductivity of polyanionic cathode materials can be improved, the electron transport rate inside the material can be increased, thereby increasing the reaction rate of the cathode material, and thus increasing the energy that can be stored per unit mass of cathode material, and increasing the specific capacity of the battery. Detailed Implementation

[0025] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. 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 poor conductivity of polyanionic compounds limits the efficiency of electron transport within the material, which reduces the reaction rate of the cathode material and consequently reduces the energy that can be stored per unit mass of cathode material, thus reducing the specific capacity of the battery.

[0029] According to the inventor's research, the specific capacity of a battery 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 makes the contact between particles closer, which helps to form a continuous electron transport path, improves the conductivity of the cathode material, and thus increases the specific capacity of the battery. It can also improve the compressive strength of the particles, increase the compaction density of the cathode sheet, and thus increase the volumetric energy density of the battery.

[0032] However, excessive particle density in the cathode material can affect the solid-phase diffusion rate of sodium ions, reduce the conductivity of the cathode material, decrease the reaction rate of the cathode material, reduce the energy that can be stored per unit mass of cathode material, and thus reduce the specific capacity of the battery.

[0033] Therefore, within a certain range, the particle density of polyanionic cathode materials helps improve the conductivity and reaction rate of the cathode material, thereby increasing the energy that can be stored per unit mass of cathode material and improving the specific capacity of the battery. It also helps improve the compressive strength of the particles, increasing the compaction density of the cathode sheet, thus improving 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. By coating polyanionic cathode materials with carbon materials, the conductivity of polyanionic cathode materials can be improved.

[0036] The higher the carbon coating amount, the better the conductivity. However, since carbon cannot contribute to capacity, it leads to a decrease in the specific capacity of polyanion cathode materials. After carbon coating, the higher the graphitization degree of the polyanion cathode material, the higher the carbon coating degree, and the better the intrinsic conductivity of the particles. Besides the intrinsic particle conductivity, the overall conductivity of the polyanion cathode material after contact between different particles must also be considered. The overall conductivity of the polyanion cathode material is related to the contact resistance; lower contact resistance results in higher overall conductivity. However, excessively low contact resistance will affect the ion transport rate after the cell is manufactured, increasing ion transport impedance and affecting the overall conductivity of the polyanion cathode material.

[0037] Therefore, within a certain range, the intrinsic conductivity of polyanionic cathode materials, their overall conductivity, and their contact resistance can help improve the conductivity of the cathode material, increase its reaction rate, thereby increasing the energy that can be stored per unit mass of cathode material and improving the battery's specific capacity.

[0038] Overall conductivity can be characterized by powder resistivity, while the intrinsic conductivity of particles can be measured by the intensity of the D peak in the Raman spectrum. D With the intensity of peak G I G The ratio between I D / I G Characterization, contact resistance can be achieved by comparing powder resistivity with I. D / I G The ratio is used to characterize the powder resistivity, I. D / I G Powder resistivity / (I D / I G It needs to be within a certain range.

[0039] 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 which is 1%-60%, and the powder resistivity of which is denoted as ρ10. 4 Ω.cm, 2≤ρ≤100, the intensity I of the D peak in the Raman spectrum of polyanionic cathode material D With the intensity of peak G I G Satisfying 0.3≤I D / I G ≤1.8, polyanionic cathode materials satisfy ρ / (I D / I G )≥1.2.

[0040] 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.

[0041] When the cross-sectional porosity of polyanionic cathode materials is between 1% and 60%, it helps to improve the conductivity and reaction rate of the cathode material, thereby increasing the energy that can be stored per unit mass of cathode material and improving the specific capacity of the battery. It also helps to improve the compressive strength of the particles and increase the compaction density of the cathode sheet, thus increasing the volumetric energy density of the battery.

[0042] The powder resistivity of polyanionic cathode materials is denoted as ρ10. 4 Ω.cm, 2≤ρ≤100, where ρ can be, for example, a range consisting of 2, 2.56, 10, 18, 31, 59, 60, 70, 80, 90, 100 or any two of these.

[0043] The powder resistivity of the polyanionic cathode material is 2×10⁻⁶. 4 Ω.cm-100×10 4 At a value of Ω·cm, it helps to improve the overall conductivity of polyanionic cathode materials, increase the reaction rate of cathode materials, thereby increasing the energy that can be stored per unit mass of cathode material and increasing the specific capacity of the battery.

[0044] Raman spectroscopy is a method for characterizing the microstructure and the degree of orderliness of carbon atoms in carbon materials. When using wavelengths of 514 nm, 532 nm, and 633 nm as excitation sources, carbon materials with ordered carbon atoms will exhibit two characteristic peaks in their Raman spectra: the D peak and the G peak. The D peak is located at approximately 1300 cm⁻¹. -1 -1360cm -1 Nearby, it represents the presence of defective structures in carbon materials (i.e., the presence of disordered carbon), with the G peak located at 1580 cm⁻¹. -1 -1600cm -1 Nearby, it represents the presence of sp2 hybridized carbon in the carbon material (that is, the presence of ordered carbon atoms), and the ratio between the intensity of the D peak and the intensity of the G peak is I. D / I G This can represent the degree of orderliness in the arrangement of carbon atoms in carbon materials.

[0045] The intensity of the D peak in polyanionic cathode materials D With the intensity of peak G I G Satisfy: 0.3≤I D / I G ≤1.8, I D / I G For example, the values ​​could be 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.4, 1.6, or 1.8.

[0046] The coating layer of the polyanionic cathode material includes carbon material, and the intensity of the D peak in the polyanionic cathode material is I. D With the intensity of peak G I G When the ratio of the two is 0.3-1.8, the ordered arrangement of carbon atoms is higher, the electronic conductivity of carbon materials is higher, thus effectively improving the intrinsic conductivity of polyanionic cathode materials, which helps to increase the reaction rate of cathode materials, thereby increasing the energy that can be stored per unit mass of cathode material and increasing the specific capacity of the battery.

[0047] The powder resistivity of polyanionic cathode materials is denoted as ρ10. 4 Ω.cm, the intensity of the D peak in polyanionic cathode materials D With the intensity of peak G I G The ratio is denoted as I. D / I G Polyanionic cathode materials satisfy the following relationship: ρ / (I D / I G ≥1.2 can effectively improve the overall conductivity of polyanionic cathode materials, increase the reaction rate of cathode materials, thereby increasing the energy that can be stored per unit mass of cathode material and increasing the specific capacity of the battery.

[0048] Therefore, by considering the cross-sectional porosity, powder resistivity, and the intensity I of the D peak in the polyanionic cathode material... D With the intensity of peak G I G The ratio of the two I D / I G And powder resistivity and I D / I G The ratio of [value] can better improve the conductivity of polyanionic cathode materials, increase the electron transport rate inside the material, thereby increasing the reaction rate of the cathode material, and thus increasing the energy that can be stored per unit mass of cathode material, and increasing the specific capacity of the battery.

[0049] In some embodiments of this application, the cross-sectional porosity of the polyanionic cathode material is 2%-40%. Within this range, the volumetric energy density of the polyanionic cathode material can reach or even exceed 615 Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.20 g / cm³. 3 The battery's specific capacity can reach 92mAh / g.

[0050] Therefore, the cross-sectional porosity of polyanionic cathode materials is 2%-40%, which helps to improve the conductivity of polyanionic cathode materials, thereby increasing the volumetric energy density of polyanionic cathode materials and the compaction density of cathode sheets, and thus improving the specific capacity and volumetric energy density of batteries.

[0051] In some embodiments of this application, the cross-sectional porosity of the polyanionic cathode material is 5%-20%. Within this range, the volumetric energy density of the polyanionic cathode material can reach or even exceed 660 Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.25 g / cm³. 3 The battery's specific capacity can reach or even exceed 98mAh / g.

[0052] Therefore, when the cross-sectional porosity of polyanionic cathode materials is 5%-20%, it helps to further improve the conductivity of polyanionic cathode materials, thereby increasing the volumetric energy density of polyanionic cathode materials and the compaction density of cathode sheets, and further improving the specific capacity and volumetric energy density of batteries.

[0053] In some embodiments of this application, the powder resistivity of the polyanionic cathode material is denoted as ρ10. 4 Within the specified range (Ω·cm, 2≤ρ≤60), the volumetric energy density of polyanionic cathode materials can reach or even exceed 640Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.20g / cm³. 3 The battery's specific capacity can reach or even exceed 97.5 mAh / g.

[0054] Therefore, the powder resistivity of polyanionic cathode material is 2×10⁻⁶. 4 Ω.cm-60×10 4 At a value of Ω·cm, it helps to improve the conductivity of polyanionic cathode materials, thereby increasing the volumetric energy density of polyanionic cathode materials, the compaction density of cathode sheets, and ultimately the specific capacity and volumetric energy density of the battery.

[0055] In some embodiments of this application, the intensity I of the D peak in the Raman spectrum of the polyanionic cathode material is... D With the intensity of peak G I G Satisfy: 0.5≤I D / I G ≤1.6. Within this range, the volumetric energy density of polyanionic cathode materials can reach or even exceed 655 Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.25 g / cm³. 3 The battery's specific capacity can reach or even exceed 97.5 mAh / g.

[0056] Therefore, the intensity I of the D peak in polyanionic cathode materials D With the intensity of peak G I G The ratio between I D / I G When the value is 0.5-1.6, it helps to improve the conductivity of polyanionic cathode materials, thereby increasing the volumetric energy density of polyanionic cathode materials, increasing the compaction density of cathode sheets, and thus increasing the specific capacity and volumetric energy density of batteries.

[0057] In some embodiments of this application, the intensity I of the D peak in the Raman spectrum of the polyanionic cathode material is... D With the intensity of peak G I G Satisfy: 0.7≤I D / I G≤1.4. Within this range, the volumetric energy density of polyanionic cathode materials can reach or even exceed 665 Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.29 g / cm³. 3 The battery's specific capacity can reach or even exceed 98mAh / g.

[0058] Therefore, the intensity I of the D peak in polyanionic cathode materials D With the intensity of peak G I G The ratio between I D / I G When the value is 0.7-1.4, the conductivity of polyanionic cathode material can be further improved, thereby increasing the volumetric energy density of polyanionic cathode material, increasing the compaction density of cathode sheet, and further improving the specific capacity and volumetric energy density of battery.

[0059] In some embodiments of this application, the powder resistivity of the polyanionic cathode material is denoted as ρ10. 4 Ω.cm, the intensity of the D peak in polyanionic cathode materials D With the intensity of peak G I G The ratio is denoted as I. D / I G Polyanionic cathode materials satisfy 1.2≤ρ / (I D / I G ≤40. Within this range, the volumetric energy density of polyanionic cathode materials can reach or even exceed 630Wh / L, and the compaction density of the cathode sheet can reach or even exceed 2.28g / cm³. 3 The battery's specific capacity can reach or even exceed 96.0 mAh / g.

[0060] Therefore, the powder resistivity of polyanionic cathode materials is related to I. D / I G The ratio is 1.2 × 10 4 Ω.cm-4×10 5 At Ω.cm, it helps to improve the conductivity of polyanionic cathode materials, thereby increasing the volumetric energy density of polyanionic cathode materials, increasing the compaction density of cathode sheets, and thus increasing the specific capacity and volumetric energy density of the battery.

[0061] In some embodiments of this application, the chemical formula of the positive electrode material is Na. x M y (PO4) w X a Z b Y cM 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.

[0062] 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.

[0063] 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.

[0064] (PO4) w X a Z b Typically, 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.

[0065] 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.

[0066] Y (yet) can be used to enhance electrical conductivity, structural stability, and thermal stability. Y can be selected from at least one of C and Al. Carbon and aluminum have good electrical conductivity and are lightweight, and are used to improve conductivity and reduce weight.

[0067] 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.

[0068] In some embodiments of this application, the polyanionic cathode material is at least one of single crystal, quasi-single crystal, and polycrystalline.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In some embodiments of this application, the positive electrode active material is at least one of fully broken particle material, semi-broken particle material, and uncrushed particle material.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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 functional surface of the positive electrode current collector, and after drying, the positive electrode sheet of this application can be obtained.

[0077] The positive current collector in this application can be selected from positive current collectors conventionally used in the art, such as aluminum foil.

[0078] 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.

[0079] 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.

[0080] 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 specific capacity.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Batteries can be liquid batteries, solid-state batteries, or semi-solid-state batteries, and their shapes can be prismatic, cylindrical, or pouch batteries.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The present application will be further described below through specific embodiments.

[0090] It should be noted that the cross-sectional porosity, powder resistivity, and the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the polyanionic cathode material can be obtained by disassembling the product and conducting tests.

[0091] 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.

[0092] 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.

[0093] After cleaning and drying the positive electrode sheet, cross-sectional porosity testing can be performed. After cleaning and drying the scraped positive electrode powder material, powder resistivity testing can be performed. The ratio of the intensity of the D peak to the intensity of the G peak is I. D / I G test.

[0094] 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).

[0095] Powder resistivity test: The resistivity was tested using a PRCD3100 with a pressure range of 10-200 MPa, and the resistivity was recorded at a pressure of 90 MPa.

[0096] The ratio of the intensity of peak D to the intensity of peak G (I) D / I G Test: The cathode powder material was prepared according to the Raman test requirements. The change with light intensity at different wavelengths was measured. The ratio of the intensity of the D peak to the intensity of the G peak (I) was calculated using the area ratio or intensity ratio of the D peak to the G peak. D / I G .

[0097] 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, volumetric particle size distribution, and specific surface area are tested. The results may have slight differences compared to the test results of the raw material, which can be ignored.

[0098] Example 1

[0099] The method for preparing the sodium-ion battery in this embodiment includes the following steps:

[0100] (1) The cross-sectional porosity is 5%, and the powder resistivity is denoted as ρ10. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G A polyanionic cathode material with a strength of 28.75 and a chemical formula of Na 3.95 Fe 3.04 (PO4)2(P 1.98 O 7.02 The crystal 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 aluminum foil current collector. After drying, it is rolled to obtain positive electrode sheet.

[0101] (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.

[0102] (3) The positive electrode, negative electrode and separator are stacked sequentially in an orderly manner to obtain the electrode core;

[0103] (4) After the electrode core is encased, electrolyte is injected, and sodium-ion batteries are obtained through formation and capacity testing.

[0104] Example 2

[0105] The preparation method of the sodium-ion battery in Example 2 is basically the same as that in Example 1, except that a cross-sectional porosity of 1% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0106] Example 3

[0107] The preparation method of the sodium-ion battery in Example 3 is the same as that in Example 1, except that a cross-sectional porosity of 2% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0108] Example 4

[0109] The preparation method of the sodium-ion battery in Example 4 is the same as that in Example 1, except that a cross-sectional porosity of 4% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0110] Example 5

[0111] The preparation method of the sodium-ion battery in Example 5 is the same as that in Example 1, except that a cross-sectional porosity of 20% and a powder resistivity denoted as ρ10 are used. 4Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0112] Example 6

[0113] The preparation method of the sodium-ion battery in Example 6 is the same as that in Example 1, except that a cross-sectional porosity of 35% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0114] Example 7

[0115] The preparation method of the sodium-ion battery in Example 7 is the same as that in Example 1, except that a cross-sectional porosity of 40% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0116] Example 8

[0117] The preparation method of the sodium-ion battery in Example 8 is the same as that in Example 1, except that a cross-sectional porosity of 60% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0118] Example 9

[0119] The preparation method of the sodium-ion battery in Example 9 is the same as that in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ = 2, the ratio of the intensity of peak D to the intensity of peak G, I D / I G It is 1.10, and ρ / (ID / I G The polyanionic cathode material with a strength of 1.82 was prepared.

[0120] Example 10

[0121] The preparation method of the sodium-ion battery in Example 10 is the same as that in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω·cm, ρ is 2.56, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.88, and ρ / (I D / I G The polyanionic cathode material with a strength of 2.91 was prepared.

[0122] Example 11

[0123] Example 11 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ = 10, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.82, and ρ / (I D / I G The polyanionic cathode material with a strength of 12.20 was prepared.

[0124] Example 12

[0125] Example 12 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 18, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.64, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.13 was prepared.

[0126] Example 13

[0127] Example 13 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 31, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.83, and ρ / (I D / I G The polyanionic cathode material with a strength of 37.35 was prepared.

[0128] Example 14

[0129] Example 14 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 59, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 1.70, and ρ / (I D / I G The polyanionic cathode material with a strength of 34.71 was prepared.

[0130] Example 15

[0131] Example 15 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ = 100, the ratio of the intensity of peak D to the intensity of peak G, I D / I G It is 1.70, and ρ / (I D / I G The polyanionic cathode material with a strength of 58.82 was prepared.

[0132] Example 16

[0133] Example 16 uses the same method as Example 1 for preparing a sodium-ion battery, except that it uses a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10. 4 Ω.cm, ρ is 13, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.3, and ρ / (I D / I G The polyanionic cathode material with a strength of 43.33 was prepared.

[0134] Example 17

[0135] Example 17 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 13, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.5, and ρ / (I D / I G The preparation of a polyanionic cathode material with a strength of 26 was carried out.

[0136] Example 18

[0137] Example 18 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 13, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.7, and ρ / (I D / I G The polyanionic cathode material with a strength of 18.57 was prepared.

[0138] Example 19

[0139] Example 19 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 1.4, and ρ / (I D / I G The polyanionic cathode material with a strength of 16.43 was prepared.

[0140] Example 20

[0141] Example 20 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 1.6, and ρ / (I D / I G The polyanionic cathode material with a strength of 14.38 was prepared.

[0142] Example 21

[0143] Example 21 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 1.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 12.78 was prepared.

[0144] Example 22

[0145] Example 22 is prepared using the same method as the sodium-ion battery in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4Ω.cm, ρ is 80, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.5, and ρ / (I D / I G The preparation of a polyanionic cathode material with a strength of 40 is described.

[0146] Comparative Example 1

[0147] The sodium-ion battery in Comparative Example 1 was prepared using the same method as that in Example 1, except that a cross-sectional porosity of 65% and a powder resistivity denoted as ρ10 were used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0148] Comparative Example 2

[0149] The preparation method of the sodium-ion battery in Comparative Example 2 is the same as that in Example 1, except that a cross-sectional porosity of 0.1% and a powder resistivity denoted as ρ10 are used. 4 Ω.cm, ρ is 23, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.8, and ρ / (I D / I G The polyanionic cathode material with a strength of 28.75 was prepared.

[0150] Comparative Example 3

[0151] Comparative Example 3 was prepared using the same method as the sodium-ion battery in Example 1, except that it used a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10. 4 Ω.cm, ρ is 128, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 1.5, and ρ / (I D / I G The polyanionic cathode material with a strength of 85.33 was prepared.

[0152] Comparative Example 4

[0153] Comparative Example 4 was prepared using the same method as the sodium-ion battery in Example 1, except that it used a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10. 4 Ω·cm, ρ = 1.25, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.88, and ρ / (ID / I G The polyanionic cathode material with a strength of 1.42 was prepared.

[0154] Comparative Example 5

[0155] Comparative Example 5 was prepared using the same method as the sodium-ion battery in Example 1, except that it used a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10. 4 Ω·cm, ρ is 26.5, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 2.1, and ρ / (I D / I G The polyanionic cathode material with a strength of 12.62 was prepared.

[0156] Comparative Example 6

[0157] Comparative Example 6 and Example 1 were prepared using the same method, except that the cross-sectional porosity was 5% and the powder resistivity was denoted as ρ10. 4 Ω·cm, ρ = 7.4, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.2, and ρ / (I D / I G The polyanionic cathode material with a strength of 37 was prepared.

[0158] Comparative Example 7

[0159] Comparative Example 7 was prepared using the same method as the sodium-ion battery in Example 1, except that it used a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10. 4 Ω.cm, ρ is 47, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.64, and ρ / (I D / I G The polyanionic cathode material with a strength of 73.44 was prepared.

[0160] Comparative Example 8

[0161] The preparation method of the sodium-ion battery in Comparative Example 8 is the same as that in Example 1, except that a cross-sectional porosity of 5% and a powder resistivity denoted as ρ10 are used. 4 Ω·cm, ρ is 0.64, the ratio of the intensity of peak D to the intensity of peak G is I D / I G It is 0.67, and ρ / (I D / I G The preparation of polyanionic cathode material with a value of 0.96.

[0162] The specific volume, compacted density, and volumetric energy density of Examples 1-22 and Comparative Examples 1-8 were tested respectively, and the test results are shown in Table 1 below. The specific test methods are as follows:

[0163] 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.

[0164] 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.

[0165] 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.

[0166] Table 1

[0167] The following conclusions can be drawn from Table 1:

[0168] 1) As can be seen from Examples 1 to 22 and Comparative Examples 1 to 8, the cross-sectional porosity and powder resistivity ρ10 of the polyanionic cathode material are relatively high. 4 Ω.cm, the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum. D / I G and ρ / (I D / I G When within the scope of the embodiments of this application, it helps to improve the volumetric energy density of polyanionic cathode materials and the compaction density of cathode sheets, thereby improving the specific capacity and volumetric energy density of the battery.

[0169] 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 volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity of the battery.

[0170] 3) As can be seen from Example 1 and Comparative Example 2, if the cross-sectional porosity of the polyanionic cathode material is too low, it will reduce the volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity of the battery.

[0171] 4) As can be seen from Example 1 and Comparative Example 3, if the powder resistivity of the polyanionic cathode material is too high, it will reduce the volumetric energy density of the cathode material, reduce the compaction density of the cathode sheet, and reduce the specific capacity of the battery.

[0172] 5) As can be seen from Example 1 and Comparative Example 4, the powder resistivity of polyanionic cathode material is too low. Although it can increase the specific capacity of the battery, it will reduce the volumetric energy density of polyanionic cathode material and the compaction density of cathode sheet.

[0173] 6) As can be seen from Example 1 and Comparative Example 5, the I of the polyanionic cathode material D / I G If the density is too low, it will reduce the volumetric energy density of the cathode material, the compaction density of the cathode sheet, and the specific capacity of the battery.

[0174] 7) As can be seen from Example 1 and Comparative Example 6, the I of the polyanionic cathode material D / I G Excessive energy density will reduce the volumetric energy density of the cathode material, the compaction density of the cathode sheet, and the specific capacity of the battery.

[0175] 8) As can be seen from Example 1 and Comparative Example 7, the ρ / (I) ratio of the polyanionic cathode material is... D / I G Excessive energy density will reduce the volumetric energy density of the cathode material, the compaction density of the cathode sheet, and the specific capacity of the battery.

[0176] 9) As can be seen from Example 1 and Comparative Example 8, the ρ / (I) ratio of the polyanionic cathode material is... D / I G If the density is too low, it will reduce the volumetric energy density of the cathode material, the compaction density of the cathode sheet, and the specific capacity of the battery.

[0177] By using cross-sectional porosity, powder resistivity, and the ratio of the intensity of the D peak to the intensity of G within a specific range, I... D / I G and powder resistivity / (I D / I G Polyanionic cathode materials can improve the volumetric energy density of cathode materials and the compaction density of cathode sheets, thereby increasing the volumetric energy density and specific capacity of batteries.

[0178] 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 shown in the accompanying drawings, 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 sheet for sodium-ion batteries, characterized in that, 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 resistivity of the polyanionic cathode material is denoted as ρ10. 4 Ω.cm, 2≤ρ≤100; The intensity I of the D peak in the polyanionic cathode material D With the intensity of peak G I G Satisfy: 0.3≤I D / I G ≤1.8; The polyanionic cathode material satisfies the following relationship: ρ / (I D / I G )≥1.

2.

2. The positive electrode sheet according to claim 1, characterized in that, The cross-sectional porosity of the polyanionic cathode material is between 2% and 40%.

3. The positive electrode sheet according to claim 2, characterized in that, The cross-sectional porosity of the polyanionic cathode material is between 5% and 20%.

4. The positive electrode sheet according to claim 1, characterized in that, 2≤ρ≤60.

5. The positive electrode sheet according to claim 1, characterized in that, 0.5≤I D / I G ≤1.6。 6. The positive electrode sheet according to claim 5, characterized in that, 0.7≤I D / I G ≤1.4。 7. The positive electrode sheet according to claim 1, characterized in that, 1.2≤ρ / (I D / I G )≤40。 8. The positive electrode sheet according to any one of claims 1-7, characterized in that, 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. 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 sheet according to any one of claims 1-7, characterized in that, The polyanionic cathode material is at least one of single crystal, quasi-single crystal, and polycrystalline.

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

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

12. An electrical appliance, characterized in that, Includes the battery of claim 10 or the battery pack of claim 11.

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