Battery

Abstract

The invention belongs to the technical field of battery preparation, and particularly relates to a battery. The battery comprises a positive pole piece, an active substance layer in the positive pole piece comprises a first active substance layer located on the surface of a positive current collector and a second active substance layer located on the surface of the first active substance layer, the first active substance layer comprises O3-phase layered oxide particles, and the second active substance layer comprises P2-phase layered oxide particles; the pore diameter of the maximum pore in an area which is 0-10 microns away from the surface of the positive pole piece is 1-6 microns; the rubber coating layer in the diaphragm comprises rubber particles; the average particle size D1 of the O3-phase layered oxide particles is 4-5 [mu] m; the average particle size D2 of the P2-phase layered oxide particles, the average particle size D3 of the primary particles formed by the glue particles and the average particle size D4 of the secondary particles formed by the glue particles meet the relational expression 1, and D2 is 5-7.3 microns; d3 is in a range of 0.2 to 0.8 [mu] m; and D4 is 5-15 [mu] m. According to the invention, the rate capability and the cold start performance can be improved, the problem of overhigh temperature rise of the battery during high-rate discharge is reduced, the high-temperature storage is improved, and the side reaction is reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of battery preparation, and specifically relates to a battery. Background Art

[0002] Lithium-ion battery raw materials are in short supply and are rising rapidly in price. Sodium-ion battery raw materials are abundant and inexpensive, making them a growing trend in energy storage, two-wheeled vehicles, and start-stop systems. Conventional sodium-ion batteries suffer from a low platform voltage, making it difficult to start a vehicle with a low charge in low-temperature environments, and a high DCR. After cycling and storage, the capacity recovery rate is low, the DCR remains high, and safety is poor. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present application is to overcome the defects of the prior art sodium ion batteries, such as difficulty in starting the vehicle under low temperature conditions, thereby providing a battery.

[0004] To this end, this application provides the following technical solutions.

[0005] In a first aspect, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector; the active material layer comprises a first active material layer located on the surface of the positive electrode current collector and a second active material layer located on the surface of the first active material layer, the first active material layer comprises O3 phase layered oxide particles, and the second active material layer comprises P2 phase layered oxide particles; along the thickness direction of the positive electrode sheet, Any of the active material layers includes pores in a longitudinal cross-section, and the maximum pore size in the region of 0-10 μm from the surface of the positive electrode sheet is 1-6 μm; the separator includes a carrier layer and a coating layer provided on at least one surface of the carrier layer, the coating layer containing adhesive particles; the average particle size D1 of the O3 phase layered oxide particles satisfies: 4 μm ≤ D1 ≤ 5 μm; the average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the adhesive particles, and the average particle size D4 of the secondary particles formed by the adhesive particles satisfy the following relationship:

[0006] 7D3≤D2≤D4 Relationship 1

[0007] The D2 satisfies: 5 μm≤D2≤7.3 μm; the D3 satisfies: 0.2 μm≤D3≤0.8 μm; and the D4 satisfies: 5 μm≤D4≤15 μm.

[0008] As an optional embodiment, the maximum pore in the active material layer within a region of 0-10 μm from the surface of the positive electrode current collector is larger than the maximum pore in a region of 0-10 μm from the surface of the positive electrode sheet; and / or,

[0009] The average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloidal particles, and the average particle size D4 of the secondary particles formed by the colloidal particles satisfy the following relationship:

[0010] 7D3≤D2<D4 Relationship 1.

[0011] As an optional embodiment, the diameter of the largest pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector is 12-16 μm.

[0012] As an optional embodiment, the structural formula of the O3 phase layered oxide is Na x Fe y Ni z Mn r M p O2; wherein, the M includes at least one of Ti, Cu, Mg, Ca, Cr, Co, Ce, Zn, Pd, Al and Mo; the x satisfies: 0.8≤x<1, the y satisfies: 0.20≤y≤0.35, the z satisfies: 0.23≤z≤0.35, the r satisfies: 0.24≤r≤0.36, and the p satisfies: 0≤p≤0.2.

[0013] As an optional embodiment, the thickness of the first active material layer is 10-30 μm; and / or,

[0014] The porosity of the first active material layer is 24.2%-30.6%; and / or,

[0015] The specific surface area of ​​the O3 phase layered oxide particles is 0.45 m 2 / g-0.55m 2 / g.

[0016] As an optional embodiment, the structural formula of the P2 phase layered oxide is Na w Fe t Ni u Mn v Cu s N q O2, the N includes at least one of Mg, Ca, Cr, Co, Ce, Zn, Pd, Ti, Al and Mo; the w satisfies: 0.2≤w<0.8, the t satisfies: 0≤t≤0.3, the u satisfies: 0≤u≤0.3, the v satisfies: 0<v≤0.8, the s satisfies: 0.2≤s≤0.6, and the q satisfies: 0≤q≤0.2.

[0017] As an optional embodiment, the thickness of the second active material layer is 10-30 μm; and / or,

[0018] The porosity of the second active material layer is 20.5%-27.3%.

[0019] As an optional implementation manner, the thickness of the active material layer is 20-80 μm.

[0020] As an optional embodiment, the coverage of the adhesive layer on the carrier layer is 10%-60%; and / or,

[0021] The thickness of the adhesive layer is 0.3 μm-5 μm; and / or,

[0022] The carrier layer includes a base film and a heat-resistant layer optionally provided on at least one side surface of the base film, the heat-resistant layer includes heat-resistant particles, and the heat-resistant particles include one or more of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide (Y2O3), nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0023] As an optional embodiment, the active material layer further includes carbon nanotubes, and the aspect ratio B of the carbon nanotubes and the difference L between the maximum pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector and the maximum pore in the region of 0-10 μm from the surface of the positive electrode sheet satisfy the following relationship:

[0024]

[0025] The B satisfies: 450≤B≤2900.

[0026] The technical solution of this application has the following advantages:

[0027] 1. The battery provided in the present application comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector; the active material layer comprises a first active material layer located on the surface of the positive electrode current collector and a second active material layer located on the surface of the first active material layer, the first active material layer comprising O3-phase layered oxide particles, and the second active material layer comprising P2-phase layered oxide particles; along the thickness direction of the positive electrode sheet, any longitudinal cross-section of the active material layer comprises pores, the distance from the surface of the positive electrode sheet to the active material layer is 0- The pore size of the maximum pores in the 10μm area is 1-6μm; the diaphragm includes a carrier layer and a glue layer arranged on at least one surface of the carrier layer, and the glue layer contains glue particles; the average particle size D1 of the O3 phase layered oxide particles satisfies: 4μm≤D1≤5μm; the average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the glue particles, and the average particle size D4 of the secondary particles formed by the glue particles satisfy the relationship 1, and the D2 satisfies: 5μm≤D2≤7.3μm; the D3 satisfies: 0.2μm≤D3≤0.8μm; and the D4 satisfies: 5μm≤D4≤15μm. In this application, small-particle O3-phase layered oxide particles are arranged in the inner layer of the positive electrode sheet, and large-particle P2-phase layered oxide particles are arranged in the surface layer of the positive electrode sheet. During the cycle, the small-particle O3-phase layered oxide particles in the inner layer are not easily broken; and the P2-phase layered oxide in the surface layer can give full play to the characteristics of rapid sodium ion deintercalation and high ionic conductivity, which can improve ion deintercalation and electron conduction, thereby improving the cold start and rate performance of the battery. Double-layer coating is performed on the positive electrode current collector. The active material layer containing the O3-phase layered oxide is directly in contact with the current collector, and the active material layer containing the P2-phase layered oxide is simultaneously coated on the surface of the first active material layer. The formed double-layer active material layer is beneficial to improving the ionic conductivity and overall voltage platform of the positive electrode sheet. The pore size of the largest pores in the area 0-10 μm away from the surface of the positive electrode plate is 1-6 μm, which makes the gaps between the active material particles in the positive electrode plate small, which is conducive to closer contact between the active material and the conductive agent in the positive electrode plate, facilitates the conduction of ions, reduces impedance, and thus improves rate performance and cold start performance.

[0028] Since the P2-phase layered oxide particles have a high residual alkali content, they are prone to side reactions with the electrolyte when located on the surface of the positive electrode. This application regulates the average particle size of the P2-phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloid particles, and the average particle size D4 of the secondary particles formed by the colloid particles to satisfy equation 1, which can make the adhesion between the diaphragm and the positive electrode plate and the electrolyte content appropriate. Appropriate adhesion is conducive to shortening the ion conduction path and reducing impedance; on the one hand, it promotes the formation of the CEI film on the surface of the P2-phase layered oxide and reduces side reactions; on the other hand, it can restrain the expansion of the P2-phase layered oxide particles and prevent the continuous rupture and formation of the CEI film during the cycle process, thereby improving the cycle performance of the battery and reducing the growth of DCR, thereby reducing the problem of excessive temperature rise when the battery is discharged at a high rate; at the same time, it improves the storage of the battery at high temperatures and reduces side reactions. An appropriate content of electrolyte can ensure that the battery cell is fully infiltrated, provide a liquid phase channel for ion migration, and at the same time take into account a longer cycle life; excessive electrolyte content will cause local swelling of the battery, and under the action of external force, the winding core will easily become soft, resulting in poor adhesion between the electrode and the diaphragm and more side reactions under high-temperature storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 This is the infrared spectrum of the positive electrode sheet of Example 1 of the present application;

[0031] Figure 2 This is a first charge curve diagram of the battery prepared in Example 1 of the present application;

[0032] Figure 3 This is the XRD diffraction pattern of the positive electrode sheet of Example 1 of the present application. DETAILED DESCRIPTION

[0033] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0034] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0035] Sodium-ion batteries have difficulty starting in low-temperature environments, have high DCR, low capacity recovery after cycling, and their safety performance needs to be further improved. To address the shortcomings of existing sodium-ion batteries, this application provides the following technical solutions.

[0036] In a first aspect, the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector; the active material layer comprises a first active material layer located on the surface of the positive electrode current collector and a second active material layer located on the surface of the first active material layer, the first active material layer comprises O3 phase layered oxide particles, and the second active material layer comprises P2 phase layered oxide particles; along the thickness direction of the positive electrode sheet, Any of the active material layers includes pores in a longitudinal cross-section, and the pore size of the maximum pore in the region of 0-10 μm from the surface of the positive electrode sheet is 1-6 μm. The separator includes a carrier layer and a coating layer provided on at least one surface of the carrier layer, the coating layer containing adhesive particles; the average particle size D1 of the O3 phase layered oxide particles satisfies: 4 μm ≤ D1 ≤ 5 μm; the average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the adhesive particles, and the average particle size D4 of the secondary particles formed by the adhesive particles satisfy the following relationship:

[0037] 7D3≤D2≤D4 Relationship 1

[0038] The D2 satisfies: 5 μm≤D2≤7.3 μm; the D3 satisfies: 0.2 μm≤D3≤0.8 μm; and the D4 satisfies: 5 μm≤D4≤15 μm.

[0039] The O3 phase layered oxide has a high proportion of sodium ions, which is beneficial to improving capacity; the P2 phase layered oxide has good electrical conductivity, which is beneficial to improving platform voltage and rate performance, thereby improving cold start performance. In this application, small-particle O3 phase layered oxide particles are arranged in the inner layer of the positive electrode sheet, and large-particle P2 phase layered oxide particles are arranged on the surface layer of the positive electrode sheet. During the cycle, the small-particle O3 phase layered oxide particles located in the inner layer are not easily broken; and the P2 phase layered oxide located on the surface layer can give full play to the characteristics of rapid deintercalation of sodium ions and high ionic conductivity, which can improve ion deintercalation and electron conduction, thereby helping to improve the cold start and rate performance of the battery. Double-layer coating is performed on the positive electrode current collector, and the active material layer containing the O3 phase layered oxide is directly in contact with the current collector. The active material layer containing the P2 phase layered oxide is simultaneously coated on the surface of the first active material layer. The double-layer active material layer formed is beneficial to improving the ionic conductivity and overall voltage platform of the positive electrode sheet. The pore size of the maximum pore in the area 0-10μm away from the surface of the positive electrode is 1-6μm, which makes the gaps between the active material particles in the positive electrode small, which is conducive to closer contact between the active material and the conductive agent in the positive electrode, conducive to ion conduction, and reduces impedance, thereby improving rate performance and cold start performance; when the pore size of the maximum pore is too high, on the one hand, the active material particles and the conductive agent cannot be effectively connected, resulting in a short circuit in the electronic conductivity and increased internal resistance; on the other hand, the mechanical strength of the electrode is weakened, and local expansion and other problems occur during long-term cycling; excessive pores will also lead to poor local adhesion to the diaphragm, making the ion transmission path larger, increasing internal resistance, and affecting rate performance.

[0040] Since the P2-phase layered oxide particles have a high residual alkali content, they are prone to side reactions with the electrolyte when located on the surface of the positive electrode. This application regulates the average particle size of the P2-phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloid particles, and the average particle size D4 of the secondary particles formed by the colloid particles to satisfy equation 1, which can make the adhesion between the diaphragm and the positive electrode plate appropriate to the electrolyte content. Appropriate adhesion is conducive to shortening the ion conduction path and reducing impedance; on the one hand, it promotes the formation of the CEI film on the surface of the P2-phase layered oxide and reduces side reactions; on the other hand, it can restrain the expansion of the P2-phase layered oxide particles and prevent the continuous rupture and formation of the CEI film during the cycle process, thereby improving the cycle performance of the battery and reducing the growth of DCR, reducing the problem of excessive temperature rise when the battery is discharged at a high rate; at the same time, it improves the storage of the battery at high temperatures and reduces side reactions. An appropriate electrolyte content ensures full cell wetting, providing a liquid phase channel for ion migration while also ensuring a long cycle life. Excessive electrolyte content can cause local swelling of the battery, making the core soft under external forces, leading to poor adhesion between the electrode and diaphragm and more side reactions during high-temperature storage. If the active particle size is too small, the diaphragm adhesive layer adheres to the particle surface, blocking the ion transport channel, affecting ion transfer, increasing impedance, and reducing high-rate discharge and low-temperature cold start performance. If the active particle size is too large, the adhesive layer cannot effectively adhere to the active particle material, resulting in localized uneven electrolyte concentration and large local expansion after long-term cycling. This significantly increases the DCR, affecting the battery life, end-of-life rate, and cold start performance. If the particle size of the glue particles is too small, the adhesion is poor and they can only partially adhere to the active material. The adhesion between the diaphragm and the positive electrode is uneven, resulting in inconsistent ion transmission paths and increased polarization. If the particle size of the glue particles is too large, more active material particles will adhere to them, which may easily block the ion transmission channel, affect ion transmission and increase impedance.

[0041] In order to better understand the 0-10μm area, further explanation is given here. The 0-10μm area away from the surface of the positive current collector refers to the positive electrode active material layer with a thickness of 0-10μm located on the surface of the positive current collector, that is, the area with a thickness of 0-10μm in the first active material layer close to the positive current collector and close to the current collector. The 0-10μm area close to the surface of the positive electrode plate refers to the positive electrode active material layer with a thickness of 0-10μm located on one side of the surface of the positive electrode plate, that is, the area with a thickness of 0-10μm in the second active material layer away from the first active material layer and close to the plate surface. The active material layer also includes a third active material layer located between the first active material layer and the second active material layer. When the third active material layer is formed by the O3 phase layered oxide and the P2 phase layered oxide, the components of the two substances penetrate each other, and a transition layer is formed at the interface.

[0042] D1, D2, D3, and D4 are all obtained using existing test methods. Here's a test method for D1 and D2: Take a SEM image of the positive electrode active material layer within a 25μm x 25μm area of ​​any cross-section of the positive electrode sheet. Then, measure the particle size of 100 active material particles and take the average. If an SEM image shows fewer than 100 particles, repeat the cross-section and obtain SEM images until the number of active material particles reaches 100.

[0043] Here is a D3 test method: SEM images are taken within a 25μm×25μm area of ​​the rubber coating layer on any cross-section of the separator. The particle size of the primary particles formed by 100 rubber particles is measured and the average value is taken. Here is a D4 test method: SEM images are taken within a 25μm×25μm area of ​​the rubber coating layer on any cross-section of the separator. The particle size of the secondary particles formed by 100 rubber particles is measured and the average value is taken. When testing D3 and D4, if a single SEM image does not show 100 particles, repeat cross-sections and SEM images until the number of particles reaches 100.

[0044] Exemplarily, the D1 is 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm or within the range formed by any two of the above values; the D2 is 5 μm, 5.4 μm, 5.8 μm, 6.2 μm, 6.6 μm, 7.3 μm or within the range formed by any two of the above values; the D3 is 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm or within the range formed by any two of the above values; the D4 is 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm or within the range formed by any two of the above values; the pore size of the maximum pore in the region 0-10 μm from the surface of the positive electrode plate is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm or within the range formed by any two of the above values.

[0045] As an optional embodiment, the maximum pore in the active material layer within a region of 0-10 μm from the surface of the positive electrode current collector is larger than the maximum pore in a region of 0-10 μm from the surface of the positive electrode sheet; and / or,

[0046] The average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloidal particles, and the average particle size D4 of the secondary particles formed by the colloidal particles satisfy the following relationship:

[0047] 7D3≤D2<D4 Relationship 1.

[0048] This application regulates the pores at different positions in the active material layer to fully infiltrate the electrolyte. The inner layer has large pores, which can store sufficient electrolyte inside the electrode. The charge and discharge process is conducive to improving ion conductivity and achieving faster ion liquid phase transfer, thereby improving rate performance and cold start performance. The maximum pores on the surface are smaller than those in the inner layer, and the surface lithium ion transmission path is short, which is conducive to improving interfacial reaction kinetics. By regulating the relationship between the maximum pores in the inner layer and the maximum pores on the surface, this application can maximize the electrolyte retention while taking into account the higher interfacial dynamics on the surface, further improving the battery's rate performance, low temperature performance, and cycle performance.

[0049] As an optional embodiment, the pore size of the maximum pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector is 12-16 μm, which is conducive to the formation of an electrolyte reserve pool, has a suitable electrolyte holding capacity, can continuously replenish the electrolyte consumed by the surface layer, and is conducive to improving the overall life of the battery cell. The inner layer electrolyte holding capacity is high, providing a medium for ion liquid phase transfer, realizing seamless connection between the liquid phase and the solid phase in the ion transfer process, which is conducive to improving the ion transfer rate, reducing the overall impedance, and thus improving the rate performance and cold start performance. Exemplarily, the pore size of the maximum pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector is 12 μm, 14 μm, 16 μm or within the range of any two of the above values.

[0050] The pore size of the maximum pore is measured using methods known in the art. Here, one method is described: 10 cross-sections of the positive electrode sheet are taken as test samples, and SEM images of these 10 test sample cross-sections are obtained. The pore size of the maximum pore in the active layer within a region of 0-10 μm from the surface of the positive electrode current collector and the pore size of the maximum pore in the active layer within a region of 0-10 μm from the surface of the positive electrode sheet are measured in these 10 SEM images, and the average value is taken.

[0051] As an optional embodiment, the structural formula of the O3 phase layered oxide is Na x Fe y Ni z Mn r M p O2; wherein, the M includes at least one of Ti, Cu, Mg, Ca, Cr, Co, Ce, Zn, Pd, Al and Mo; the x satisfies: 0.8≤x<1, the y satisfies: 0.20≤y≤0.35, the z satisfies: 0.23≤z≤0.35, the r satisfies: 0.24≤r≤0.36, and the p satisfies: 0≤p≤0.2.

[0052] As an optional embodiment, the thickness of the first active material layer is 10-30 μm; and / or,

[0053] The porosity of the first active material layer is 24.2%-30.6%; and / or,

[0054] The specific surface area of ​​the O3 phase layered oxide particles is 0.45 m 2 / g-0.55m 2 The specific surface area of ​​the O3 phase layered oxide particles is measured according to a method known in the art. For example, the specific surface area of ​​the O3 phase layered oxide particles is measured using the BET method.

[0055] The present application regulates the thickness of the first active material layer to meet the above range, which is beneficial to improving the overall energy density and capacity of the battery. The porosity of the first active material layer to meet the above range is beneficial to increasing the electrolyte retention, achieving a seamless connection between the liquid and solid phases during the ion transfer process, and is beneficial to increasing the ion transfer rate and reducing the overall impedance, thereby improving the rate performance and cold start performance.

[0056] For example, the porosity of the first active material is 24.2%, 26%, 28%, 30.6% or within the range of any two of the above values. The specific surface area of ​​the O3 phase layered oxide particles is 0.45m 2 / g, 0.48m 2 / g, 0.52m 2 / g, 0.55m 2 / g or within the range formed by any two of the above values.

[0057] As an optional embodiment, the structural formula of the P2 phase layered oxide is Na w Fe t Ni u Mn v Cu s N q O2, the N includes at least one of Mg, Ca, Cr, Co, Ce, Zn, Pd, Ti, Al and Mo; the w satisfies: 0.2≤w<0.8, the t satisfies: 0≤t≤0.3, the u satisfies: 0≤u≤0.3, the v satisfies: 0<v≤0.8, the s satisfies: 0.2≤s≤0.6, and the q satisfies: 0≤q≤0.2.

[0058] It should be noted that the subscripts in the structural formulas of the O3 phase layered oxide and the P2 phase layered oxide represent the molar ratio of each element; the O3 phase layered oxide includes a technical solution that does not contain Cu, and the P2 phase layered oxide includes a technical solution that does not contain Fe and Ni.

[0059] O3 phase layered oxides are beneficial to improving capacity; P2 phase layered oxides have higher platform voltage and ionic conductivity, which are beneficial to improving the overall platform voltage and low-temperature starting performance of the battery. Adding Cu to the P2 phase layered oxide can significantly reduce costs, improve conductivity and material structure stability, and improve the overall voltage platform and conductivity, which is beneficial to further improve low-temperature starting performance.

[0060] As an optional embodiment, the thickness of the second active material layer is 10-30 μm; and / or,

[0061] The porosity of the second active material layer is 20.5%-27.3%.

[0062] The thickness of the second active material layer of the present application falls within the aforementioned range, facilitating rapid ion transfer while maintaining energy density and low impedance, resulting in long battery life while offering excellent high-rate discharge and low-temperature starting capabilities. The porosity of the second active material layer of the present application falls within the aforementioned range, facilitating closer contact between the active material particles and the conductive agent, enhancing ion conduction and reducing impedance, thereby improving rate and cold-start performance.

[0063] Illustratively, the porosity of the first active material is 20.5%, 22%, 24%, 26%, 27.3%, or within a range formed by any two of the above values.

[0064] As an optional embodiment, the thickness of the active material layer is 20-80 μm. If the active material layer of the present application meets the above range, the battery can have higher energy density, rate performance and low temperature performance, and improve long-term battery life.

[0065] Optionally, the thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is (0.5-2):1. Optionally, the thickness of the first active material layer is 15-20μm; and / or the thickness of the second active material layer is 15-20μm. Exemplarily, the thickness of the active material layer is 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 70μm, 80μm or within the range of any two of the above values. The thickness of the first active material layer is 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm or within the range of any two of the above values. The thickness of the second active material layer is 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, or within a range formed by any two of the above values.

[0066] As an optional embodiment, the coverage of the adhesive layer on the carrier layer is 10%-60%; and / or,

[0067] The thickness of the adhesive layer is 0.3 μm-5 μm; and / or,

[0068] The carrier layer includes a base film and a heat-resistant layer optionally provided on at least one side surface of the base film, the heat-resistant layer includes heat-resistant particles, and the heat-resistant particles include one or more of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0069] This application regulates the coverage and thickness of the coating layer to meet the above ranges, which can improve the electrolyte content at the interface between the diaphragm and the positive electrode and the siphon transport of the electrolyte in the thickness direction of the electrode, so that sufficient electrolyte participates in the film-forming reaction, which is beneficial to improving the CEI film stability on the surface of the active particles on the surface of the electrode, and is beneficial to reducing the growth of DCR, thereby improving the cycle performance and internal resistance, while reducing the temperature rise. Coverage refers to the area ratio of the coating layer on the carrier layer or heat-resistant layer.

[0070] Exemplarily, the coverage of the adhesive layer on the carrier layer is 10%, 20%, 30%, 40%, 50%, 60%, or within a range formed by any two of the above values; the coverage described in this application refers to the coverage of the adhesive layer on a single surface. The coverage refers to the ratio of the orthographic projection area of ​​the adhesive layer on the surface of the carrier layer to the surface area of ​​the carrier layer. It is understood that if the adhesive layer is provided on both sides of the carrier layer, the coverage of the adhesive layer on both sides will meet this range, but the actual values ​​can be the same or different. The coverage is obtained by a test method known in the art. Exemplarily, the test method includes: dividing any 10μm×10μm area on the surface of the carrier layer (specifically the heat-resistant layer or the base film) into 100×100 uniform squares, and calculating the total number X of squares occupied by the adhesive layer (when the adhesive layer occupies more than or equal to half of the square area, it is regarded as occupied; when the adhesive layer occupies less than half of the square area, it is regarded as unoccupied), then the coverage of the adhesive layer = X / (100×100)×100%, changing the selected position of the area to be tested, repeating the above operation 5 times, and taking the average value as the coverage of the adhesive layer on the surface of the carrier layer.

[0071] The thickness of the adhesive layer is 0.3 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or within a range formed by any two of the above values.

[0072] As an optional embodiment, the active material layer further includes carbon nanotubes, and the aspect ratio B of the carbon nanotubes and the difference L between the maximum pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector and the maximum pore in the region of 0-10 μm from the surface of the positive electrode sheet satisfy the following relationship:

[0073]

[0074] The B satisfies: 450≤B≤2900.

[0075] There is a difference in the compaction density of the first active material layer and the second active material layer, which easily leads to poor interface contact between the two layers and increases the internal resistance. In addition, the crystal structures of the O3 phase layered oxide and the P2 phase layered oxide are different, and the contact interface Na + The migration energy barrier increases. The present application satisfies the above-mentioned relationship 2. On the one hand, the winding effect and conductivity of carbon nanotubes are used to improve the problem of poor interface contact caused by the inconsistent compaction density and pores of the first active material layer and the second active material layer, thereby improving the internal resistance. The winding of carbon nanotubes is beneficial to reducing the overall expansion of the pole piece, facilitating effective contact of particles within the pole piece, reducing impedance, and improving rate and cold start performance. On the other hand, by regulating the difference in the maximum pores of the two active material layers, the difference in electrolyte content of the two active material layers is improved, so that the liquid retention of the inner layer of the positive electrode is higher than that of the outer layer. The inner layer has a large void, which can store sufficient electrolyte inside the pole piece. The charge and discharge process is beneficial to improving ionic conductivity and achieving faster ion liquid phase transfer, thereby improving rate performance and cold start performance. The present application utilizes carbon nanotubes and adjusts the difference in liquid retention of the two active material layers to reduce the interface Na + Migration resistance.

[0076] The aspect ratio B of the carbon nanotubes is obtained according to a test method known in the art. Exemplarily, the test method includes: taking a positive electrode plate, using an SEM to find the area containing carbon nanotubes and photographing it to obtain an SEM image, measuring the length and diameter of the carbon nanotubes, and calculating the aspect ratio; testing 30 carbon nanotubes, taking the average value, and obtaining the carbon nanotube aspect ratio B. Exemplarily, the B satisfies 450, 600, 800, 1000, 1500, 2000, 2500, 2900, or is within the range of any two of the above values. Relational Equation 2 satisfies 40, 80, 120, 160, 200, 240, 280, 320, 360, or is within the range of any two of the above values.

[0077] As an optional embodiment, the positive electrode active material has a first peak in the infrared spectrum obtained by testing the positive electrode plate using Fourier transform infrared spectroscopy, and the wave number of the first peak is 1500-1550 cm -1The test results show that the first peak of the positive electrode active material helps to improve the overall conductivity of the electrode, reduce impedance, and improve low-temperature starting performance.

[0078] As an optional embodiment, an XRD diffraction pattern of the positive electrode is obtained, and the XRD diffraction pattern has 8 characteristic diffraction peaks between 14.5°≤2θ≤70°, which are the first diffraction peak, the second diffraction peak, the third diffraction peak, the fourth diffraction peak, the fifth diffraction peak, the sixth diffraction peak, the seventh diffraction peak, and the eighth diffraction peak in order of 2θ; the first diffraction peak is located at 14.9°≤2θ≤17°, the second diffraction peak is 24.6°≤2θ≤26.6°, the third diffraction peak is 31.11°≤2θ≤33.11°, the fourth diffraction peak is 34.72°≤2θ≤36.72°, the fifth diffraction peak is 36°≤2θ≤38°, the sixth diffraction peak is 44°≤2θ≤46.10°, the seventh diffraction peak is 47.9°≤2θ≤49°, and the eighth diffraction peak is 67.3°≤2θ≤69.5°. Specifically, the first diffraction peak 2θ is approximately 15.93°, the second diffraction peak 2θ is approximately 25.60°, the third diffraction peak 2θ is approximately 32.11°, the fourth diffraction peak 2θ is approximately 35.72°, the fifth diffraction peak 2θ is approximately 37.00°, the sixth diffraction peak 2θ is approximately 45.04°, the seventh diffraction peak 2θ is approximately 48.90°, and the eighth diffraction peak 2θ is approximately 68.39°.

[0079] The maximum intensities of the first diffraction peak, the second diffraction peak, the third diffraction peak, the fourth diffraction peak, the fifth diffraction peak, the sixth diffraction peak, the seventh diffraction peak and the eighth diffraction peak are 96547.4-96551.5, 753.5-757.7, 8655.5-8659.6, 708-712.3, 915.5-919.7, 396.1-400.2, 209.1-213.2, 896-900.5, respectively; specifically, they are 96549.42, 755.62, 8657.58, 710.24, 917.62, 398.13, 211.12, and 898.02, in units of cts.

[0080] The peak areas of the first diffraction peak, the second diffraction peak, the third diffraction peak, the fourth diffraction peak, the fifth diffraction peak, the sixth diffraction peak, the seventh diffraction peak and the eighth diffraction peak are 16363.3-16373.4, 170-180.5, 1443.4-1453.5, 330.5-340.5, 336.5-346.6, 260-270, 73-83.2, 830-840, respectively; specifically, they are 16368.38, 175.25, 1448.47, 335.83, 341.53, 264.96, 78.02, and 835.66, respectively.

[0081] As an optional embodiment, the first positive electrode active material layer further includes a binder and a conductive agent, etc.; the second positive electrode active material layer further includes a binder and a conductive agent, etc. It should be noted that the binder and the conductive agent adopt types and amounts known in the art. The first positive electrode active material layer includes 91-97wt% O3 phase layered oxide, 1-4wt% binder and 2-6wt% conductive agent. The second positive electrode active material layer includes 91-97wt% P2 phase layered oxide, 1-4wt% binder and 2-6wt% conductive agent. As an example, the binder includes at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) and polyacrylonitrile (PAN), and the positive electrode is preferably PVDF; the conductive agent also includes at least one of carbon black, conductive carbon fiber, carbon nanotubes, metal powder and carbon fiber.

[0082] As an optional embodiment, when preparing the positive electrode sheet, the specific surface area of ​​the O3 phase layered oxide raw material is 0.5-0.8m 2 / g; the particle size Dv50 of the O3 phase layered oxide raw material is 3.8-5.6 μm; and / or, Dv10 is 1.5-2.2 μm; and / or, Dv90 is 8-12 μm. The specific surface area of ​​the P2 phase layered oxide raw material is 0.43-0.75 m 2 / g; the P2-phase layered oxide raw material has a particle size Dv50 of 4.8-7.5μm; and / or a Dv10 of 1.6-3.0μm; and / or a Dv90 of 12-15μm. Selecting smaller particle sizes for O3-phase layered oxide raw materials and P2-phase layered oxide raw materials offers higher specific surface area, better ion intercalation and deintercalation capabilities, and more intercalation and deintercalation channels during charge and discharge, which is beneficial for rate performance and cycling performance, and helps improve cold start performance.

[0083] As an optional embodiment, the positive electrode sheet is prepared by a method known in the art. Here, a preparation method is listed, in which an O3-phase layered oxide, a binder, and a conductive agent are mixed to prepare a first positive electrode active material slurry; a P2-phase layered oxide, a binder, and a conductive agent are mixed to prepare a second positive electrode active material slurry; a double-layer coating process is used to coat the first positive electrode active material slurry on the positive electrode current collector to form a first positive electrode active material layer, and the second positive electrode active material slurry is coated on the first positive electrode active material layer, dried, and rolled with a certain pressure to obtain a positive electrode sheet. It should be noted that the positive electrode current collector is made of conventional materials in the art. As an example, the positive electrode current collector is one of other foils such as aluminum foil, composite aluminum foil, and lead foil. Before preparing the positive electrode sheet, the positive electrode current collector is also subjected to pretreatment such as corona treatment and coating to help improve the adhesion of the slurry. Specifically, the coating includes a conductive carbon layer, a ceramic layer, and other materials known in the art.

[0084] Optionally, the battery is a sodium-ion battery. The sodium-ion battery provided herein has superior discharge capacity at low temperatures, better cold-start performance than conventional batteries, and superior rate performance. Furthermore, high-temperature stability, storage performance, and cell safety are further improved.

[0085] As an optional embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent. In this application, the negative electrode sheet is manufactured into a button-type battery with a negative electrode capacity of 280-330 mAh / g and a first efficiency of 85%-95%.

[0086] It should be noted that the negative electrode active material, binder, and conductive agent are selected from conventional types and amounts in the art. As an example, the negative electrode active material includes at least one of a carbon-based material, a polyanion negative electrode material, an alkaline metal negative electrode material, and a phosphorus negative electrode material; specifically, the negative electrode active material includes at least one of a biomass hard carbon, a resin-based hard carbon, a coal-based hard carbon, a red phosphorus material, and an alkaline metal material. The negative electrode active material is preferably hard carbon. The binder includes at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylonitrile (PAN), preferably one of a PAA binder, a composite binder of SBR and CMC, a composite binder of PAA, SBR, and CMC, and a PVDF binder; the conductive agent includes at least one of carbon black, carbon nanotubes, conductive carbon fibers, carbon nanotubes, metal powder, and carbon fibers, preferably at least one of carbon black and carbon nanotubes. Furthermore, the negative electrode active material layer comprises 91-97 wt% of negative electrode active material, 1-3 wt% of binder and 3-6 wt% of conductive agent. Furthermore, the compaction density of the negative electrode sheet is 0.8-1.5 g / cm 3 .

[0087] As an optional embodiment, the negative electrode plate is prepared by a method known in the art. Here is a preparation method, in which a negative electrode active material, a binder and a conductive agent are mixed to obtain a negative electrode slurry, which is then coated on a negative electrode current collector to obtain a negative electrode plate; wherein the negative electrode current collector is made of a material known in the art, for example, the negative electrode current collector is one of aluminum foil, composite aluminum foil, copper foil, composite copper foil, lead foil, etc.

[0088] As an optional embodiment, the negative electrode current collector may be pretreated by corona treatment or coating before preparing the negative electrode sheet to improve the adhesion of the slurry. Specifically, the coating may include a conductive carbon layer, a heat-resistant layer, or other materials known in the art.

[0089] As an optional embodiment, the sodium ion battery further comprises an electrolyte; the electrolyte is an organic solvent system, and the organic solvent comprises at least one of acetonitrile, tetrahydrofuran, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate, ethyl propionate, propyl acetate, ethyl acetate, ethyl acetate, ethyl methyl carbonate and dimethyl sulfoxide. The density M of the electrolyte is 1.1-1.3 g / cm 3 , with a conductivity of ρ of 8.5-9.5 ms / cm. Optionally, propylene sulfite (PS) has excellent high-temperature performance, and the propylene sulfite (PS) content in the electrolyte is 0.3-5%. Batteries can be assembled using electrolytes known in the art, and this application does not impose specific limitations thereon.

[0090] Furthermore, the electrolyte further comprises an additive, and the additive comprises at least one of sodium difluorophosphate, sodium bis(oxalatoborate), tris(trimethylsilyl)borate, vinylene carbonate and succinonitrile.

[0091] Furthermore, the electrolyte further comprises at least one of a sodium salt and a lithium salt; both the sodium salt and the lithium salt are selected from known salts in the art. For example, the sodium salt comprises at least one of NaPF6, NaBF4, NaClO4, NaAsF6, and NaCF3SO3; and the lithium salt comprises at least one of LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3.

[0092] As an optional embodiment, the thickness of the separator is 10-18 μm and the porosity is 40-55%.

[0093] As an optional embodiment, the diaphragm includes a carrier layer and an adhesive layer optionally disposed on at least one surface of the carrier layer. The carrier layer includes a base film layer and a heat-resistant layer disposed on at least one surface of the base film. The adhesive layer is disposed on the surface of the carrier layer and / or the heat-resistant layer. A heat-resistant layer may be disposed between the adhesive layer and the carrier layer, or alternatively, no heat-resistant layer may be disposed between the adhesive layer and the carrier layer.

[0094] As an optional embodiment, the base film has a thickness of 5-12 μm, and the heat-resistant layer has a thickness of 1-6 μm.

[0095] It should be noted that the materials of the base film (also known as the substrate layer), the heat-resistant layer, and the adhesive layer are selected from those known in the art. For example, the base film may be made of at least one of a woven film, a non-woven film, a polyolefin film, and a separator paper, and the polyolefin film may be made of at least one of polyethylene, polypropylene, polyethylene, and polypropylene.

[0096] The heat-resistant layer includes heat-resistant particles and a binder. The heat-resistant particles include one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate. The particle size Dv50 of the heat-resistant particles is 0.1μm-2.5μm. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene and polyhexafluoropropylene.

[0097] The coating layer includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene or polyhexafluoropropylene.

[0098] As an optional embodiment, the sodium-ion battery has characteristic peaks at 2.8-2.9V and 3.4-3.7V on the DQ / DV curve. During the first charge, the SEI film forms at around 1.7V. Earlier film formation is conducive to more stable film formation, and also indicates that the sodium-ion battery of the present application has better kinetic performance.

[0099] Example 1

[0100] This embodiment provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet; wherein:

[0101] The preparation method of the positive electrode plate includes: mixing O3 phase layered oxide, binder PVDF, conductive agent carbon black and conductive agent carbon nanotubes in a mass ratio of 93:2:4:1, adding solvent NMP to obtain slurry 1; mixing P2 phase layered oxide, binder PVDF and conductive agent carbon black in a mass ratio of 93:2:5, adding solvent to obtain slurry 2, coating slurry 1 and slurry 2 on aluminum foil in a thickness ratio of 1:1, wherein slurry 1 is located at the bottom layer and directly contacts the aluminum foil, and slurry 2 is located at the surface layer and contacts the slurry 1; after the slurry is evenly coated on both sides of the aluminum foil, it is dried and rolled to obtain a positive electrode plate, wherein the thickness of the active material layer in the positive electrode plate is 40 μm, the thickness of the first active material layer containing the O3 phase layered oxide is 20 μm, the average particle size D1 of the O3 phase layered oxide particles is shown in Table 1, the thickness of the second active material layer containing the P2 phase layered oxide is 20 μm, and the average particle size D2 of the P2 phase layered oxide is shown in Table 1. Among them, the structural formula of the O3 phase layered oxide is NaFe 0.28 Ni 0.32 Mn 0.33 Ti 0.07 O2; the structural formula of the P2 phase layered oxide is Na 0.63 Mn 0.68 Cu 0.32 O2.

[0102] The preparation method of the negative electrode plate includes: mixing the negative electrode active material hard carbon, the binder (the mass ratio of SBR to CMC is 0.8:1) and the conductive agent carbon black in a mass ratio of 92.3:2.7:5.0, adding solvent water to obtain a slurry, coating it on both surfaces of the aluminum foil, and drying to obtain the negative electrode plate.

[0103] Electrolyte: The solvent in the electrolyte includes DMC and EC in a volume ratio of 1:1; the electrolyte also includes the additive PS, and the content of PS in the electrolyte is 3wt%; the electrolyte also includes 12wt% sodium salt NaPF6.

[0104] The diaphragm uses polyethylene (PE) as its substrate layer, with a thickness of 9±0.2μm. One side of the substrate layer is coated with a heat-resistant layer, and the surface of the heat-resistant layer away from the substrate layer and the other side of the substrate layer are coated with a rubber layer. The heat-resistant layer is 2±0.2μm thick, and the rubber layer is 2±0.2μm thick. The rubber layer contains rubber particles, which form primary particles and secondary particles. The average particle size D3 of the primary particles and the average particle size D4 of the secondary particles are shown in Table 1. The overall thickness of the diaphragm is 13±0.5μm. The heat-resistant layer is composed of heat-resistant aluminum oxide particles, and the rubber layer is acrylic resin glue.

[0105] The positive electrode sheet, negative electrode sheet and separator are stacked or wound into a core in a Z shape, encapsulated in an aluminum-plastic film, injected with electrolyte, and charged after standing. After the second sealing is completed, they are sorted and the laminated soft-pack battery is obtained after OCV testing.

[0106] Example 2-34

[0107] Example 2-34 provides a battery that is basically the same as Example 1, except that the positive electrode is different. The parameters of each example are shown in Table 1.

[0108] Comparative Examples 1-6

[0109] Comparative Examples 1-6 provide a battery that is basically the same as the embodiment, except that the positive electrode plates are different. The parameters of each comparative example are shown in Table 1.

[0110] Table 1 Parameters of Examples and Comparative Examples

[0111] Table 1-1 Parameter 1

[0112]

[0113]

[0114] Table 1-2 Parameter 2

[0115]

[0116]

[0117] Test Case

[0118] This test example provides the performance of the batteries prepared in each embodiment and comparative example, as follows:

[0119] Porosity: Cut the electrode according to the cutting board, and measure the cut sample to obtain the area A of the sample. Then measure the thickness of the sample 10 times, calculate the average value T, and then calculate its apparent volume V0 = A × T. Use an electronic balance to measure the weight of the electrode 3 times to obtain the average value M; use a true density meter to measure the true density ρ of the above material, and calculate the true volume V1 = M / ρ of the above material. Calculate the porosity of the electrode according to the following formula. This method is also applicable to testing the porosity of the diaphragm. Specifically for this application, first test the porosity of the entire positive electrode, and then remove the second active material layer on the surface of the electrode and test the porosity of the first active material layer. The porosity of the second active material layer can be calculated based on the above two porosities.

[0120] Porosity C (%) = (V0-V1) / V1×100%.

[0121] Peel force: Cut a 100mm long and 24mm wide positive electrode sheet coated with an active material layer as the test sample; secure it to the upper and lower fixtures of a universal tensile testing machine. Peel the sample 180° at a test speed of 100mm / min and a test displacement of 80mm. The peel force, i.e., the peel force between the active material layer and the positive current collector, is converted from the parameters measured by the tensile testing machine.

[0122] Surface resistance: Use a bulk resistance meter to test the surface resistance of the coating.

[0123] Internal resistance: Use a 1HZ voltage internal resistance tester to detect the battery's AC impedance.

[0124] 25℃ 3C / 3C Cycle Life: At 25±2℃, charge at 3C constant current and constant voltage to 3.9V, with a cutoff current of 0.05C, and hold for 10 minutes. Discharge at 3C constant current to 2.0V, and hold for 10 minutes. Repeat these charge and discharge steps for 450 cycles. Cycle life is the ratio of the 450th discharge capacity to the first discharge capacity.

[0125] -28℃ 50% SOC 4.25C 3s cold cranking voltage: Charge and discharge the battery cell at 25±2℃ at 1C to test the initial capacity, then discharge it at 1C to 50% SOC. Place the battery cell in a -28℃ constant temperature box for 4 hours, discharge it at 4.25C for 3 seconds, and record the lowest discharge voltage as the cold cranking voltage.

[0126] 25℃ 3C Rate Discharge Capacity: The battery cell is charged and discharged at 0.2C at 25±2℃ to test the initial capacity. The cell is then fully charged at 0.2C constant current and constant voltage, with a cutoff of 0.05C. The cell is then discharged at 3C to the lower voltage limit. The rate discharge capacity percentage is the ratio of the 3C rate discharge capacity to the 0.2C initial capacity.

[0127] Recovery rate after 14 days of high-temperature storage at 60°C: Charge and discharge the battery at 0.2C at 25±2°C to test the initial capacity. Then fully charge the battery at 0.2C constant current and constant voltage, with a cut-off value of 0.05C. Place the battery in a 60°C constant temperature box for 14 days. Take it out and measure the capacity recovery rate at 1C at 25°C.

[0128] Percentage of capacity above the 25°C platform voltage: Fully charge the cell at 25±2°C at 0.2C constant current and constant voltage, with a cutoff of 0.05C. Discharge at 0.2C to the lower voltage limit, and test the initial capacity (C0). The platform voltage is the ratio of discharge energy (Wh) to discharge capacity (Ah), expressed in V. From the discharge capacity and voltage data, find the capacity corresponding to the platform voltage, C1. The percentage of capacity above the platform voltage is C1 / C0 × 100%.

[0129] Voltage at 15% SOC: Fully charge the cell at 25±2°C at 0.2C constant current and constant voltage, with a cutoff of 0.05C. Discharge at 0.2C to the lower voltage limit to test the initial capacity. The voltage corresponding to the remaining 15% charge is used.

[0130] 130°C, 60-minute test: Fully charge the cell at 25±2°C using a constant current and voltage setting of 0.2°C, with a cutoff of 0.05°C. Measure the voltage after full charge. Attach a thermocouple to the cell surface and place the cell in an oven. Raise the temperature at a rate of 5±2°C / min to 130°C±2°C and hold the temperature constant for 60 minutes. Stop heating and observe for 1 hour or until the maximum surface temperature drops to or below the peak temperature by 10°C. Record the cell voltage after the test and observe the voltage change before and after the test. Observe the temperature change throughout the test and obtain the maximum temperature.

[0131] 25°C 5mΩ External Short-Circuit: Fully charge the cell at 25±2°C using a constant current and constant voltage test at 0.2C, with a cutoff of 0.05C. Measure the internal resistance R1 before the short-circuit. At 25°C, attach a thermocouple to the cell surface. Externally short-circuit the positive and negative terminals for 10 minutes. The external circuit resistance should be less than 5mΩ. Observe for 1 hour. Record the temperature rise (°C) and the internal resistance R2 after the test. The change in internal resistance before and after the short-circuit is (R2-R1) / R1×100%.

[0132] The test results are as follows:

[0133] Figure 1 This is the infrared spectrum of the positive electrode of Example 1 and Comparative Example 1. It can be seen from the figure that Example 1 has an infrared spectrum of 1159 cm -1 and 1525cm -1 There are characteristic peaks at all points, which are unique to this system.

[0134] Figure 2 This is the first charge curve of the battery prepared in Example 1. According to the characteristic peak 2 of Example 1, it shows that it has excellent kinetic performance and small polarization. Peak 3 is sharp, which is a unique property of this system. It has higher capacity contribution in the higher voltage range and the overall platform voltage is high, which further indicates that the battery prepared in this application has excellent cold start performance.

[0135] Figure 3It is the XRD diffraction pattern of the positive electrode piece of Example 1. It can be seen from the figure that the XRD diffraction pattern has 8 characteristic diffraction peaks. In the order of 2θ size, the first diffraction peak 2θ is about 15.93°, the second diffraction peak 2θ is about 25.60°, the third diffraction peak 2θ is about 32.11°, the fourth diffraction peak 2θ is about 35.72°, the fifth diffraction peak 2θ is about 37.00°, the sixth diffraction peak 2θ is about 45.04°, and the seventh diffraction peak 2θ is about 48. .90°, the eighth diffraction peak 2θ is about 68.39°, the maximum intensities are 96549.42, 755.62, 8657.58, 710.24, 917.62, 398.13, 211.12, and 898.02, respectively, in cts, and the peak areas are 16368.38, 175.25, 1448.47, 335.83, 341.53, 264.96, 78.02, and 835.66, respectively.

[0136] Table 2 Test results of various embodiments and comparative examples

[0137] Table 2-1 Test results

[0138]

[0139]

[0140] Table 2-2 Test results

[0141]

[0142] It can be seen from the above results that the present application regulates the positive electrode plate to have a first active material layer and a second active material layer, and makes the pore size of the maximum pore in the area 0-10μm away from the surface of the positive electrode plate be 1-6μm, and the average particle size D1 of the O3 phase layered oxide particles satisfies: 4μm≤D1≤5μm; the average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloid particles, and the average particle size D4 of the secondary particles formed by the colloid particles satisfy the relationship 1, D2 satisfies: 5μm≤D2≤7.3μm; D3 satisfies: 0.2μm≤D3≤0.8μm; D4 satisfies: 5μm≤D4≤15μm, which can improve the cold start performance and rate performance of the battery.

[0143] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector; the active material layer comprises a first active material layer located on the surface of the positive electrode current collector and a second active material layer located on the surface of the first active material layer, the first active material layer comprises O3 phase layered oxide particles, and the second active material layer comprises P2 phase layered oxide particles; along the thickness direction of the positive electrode sheet, any of the active material The longitudinal cross-section of the layer includes pores, and the pore size of the largest pore in the area 0-10 μm away from the surface of the positive electrode plate is 1-6 μm; the separator includes a carrier layer and a glue layer provided on at least one surface of the carrier layer, and the glue layer contains glue particles; the average particle size D1 of the O3 phase layered oxide particles satisfies: 4 μm≤D1≤5 μm; the average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the glue particles, and the average particle size D4 of the secondary particles formed by the glue particles satisfy the following relationship: 7D3≤D2≤D4 Relationship 1 The D2 satisfies: 5 μm≤D2≤7.3 μm; the D3 satisfies: 0.2 μm≤D3≤0.8 μm; and the D4 satisfies: 5 μm≤D4≤15 μm.

2. The battery according to claim 1, characterized in that The maximum pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector is larger than the maximum pore in the region of 0-10 μm from the surface of the positive electrode sheet; and / or, The average particle size D2 of the P2 phase layered oxide particles, the average particle size D3 of the primary particles formed by the colloidal particles, and the average particle size D4 of the secondary particles formed by the colloidal particles satisfy the following relationship: 7D3≤D2<D4 Relationship 1.

3. The battery according to claim 1 or 2, characterized in that The diameter of the largest pore in the active material layer within the region of 0-10 μm from the surface of the positive electrode current collector is 12-16 μm.

4. The battery according to claim 1, characterized in that The structural formula of the O3 phase layered oxide is Na x Fe y Ni z Mn r M p O2; wherein, the M includes at least one of Ti, Cu, Mg, Ca, Cr, Co, Ce, Zn, Pd, Al and Mo; the x satisfies: 0.8≤x<1, the y satisfies: 0.20≤y≤0.35, the z satisfies: 0.23≤z≤0.35, the r satisfies: 0.24≤r≤0.36, and the p satisfies: 0≤p≤0.

2.

5. The battery according to claim 4, characterized in that The thickness of the first active material layer is 10-30 μm; and / or, The porosity of the first active material layer is 24.2%-30.6%; and / or, The specific surface area of ​​the O3 phase layered oxide particles is 0.45 m 2 / g-0.55m 2 / g.

6. The battery according to claim 1, characterized in that The structural formula of the P2 phase layered oxide is Na w Fe t Ni u Mn v Cu s N q O2, the N includes at least one of Mg, Ca, Cr, Co, Ce, Zn, Pd, Ti, Al and Mo; the w satisfies: 0.2≤w<0.8, the t satisfies: 0≤t≤0.3, the u satisfies: 0≤u≤0.3, the v satisfies: 0<v≤0.8, the s satisfies: 0.2≤s≤0.6, and the q satisfies: 0≤q≤0.

2.

7. The battery according to claim 1, characterized in that The thickness of the second active material layer is 10-30 μm; and / or, The porosity of the second active material layer is 20.5%-27.3%.

8. The battery according to claim 1, characterized in that The thickness of the active material layer is 20-80 μm.

9. The battery according to claim 1, characterized in that The coverage of the adhesive layer on the carrier layer is 10%-60%; and / or, The thickness of the adhesive layer is 0.3 μm-5 μm; and / or, The carrier layer includes a base film and a heat-resistant layer optionally provided on at least one side surface of the base film, the heat-resistant layer includes heat-resistant particles, and the heat-resistant particles include one or more of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

10. The battery according to claim 1, characterized in that The active material layer further includes carbon nanotubes, and the aspect ratio B of the carbon nanotubes and the difference L between the maximum pore in the active material layer within a region of 0-10 μm from the surface of the positive electrode current collector and the maximum pore in the region of 0-10 μm from the surface of the positive electrode sheet satisfy the following relationship: The B satisfies: 450≤B≤2900.

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