Positive electrode material, positive electrode sheet, sodium-ion secondary battery, and electric device

Abstract

The present application provides a positive electrode material, a positive electrode sheet, a sodium-ion secondary battery, and an electric device. The positive electrode material comprises a matrix material NaxNiaFebMncMdO2; the surface of the matrix material is provided with a polyanionic material; the polyanionic material comprises at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; in the matrix material NaxNiaFebMncMdO2, M comprises at least one of Co, Mg, Ca, B, Al, Zr, Ti, W, Mo, Cr, Sr, Y, Cd, Sn, Sb, Ce, Li, K, Zn, La, F, Si or P, wherein 0.7≤x<1.0, 0.2<a≤0.5, 0.2<b≤0.5, 0.2<c≤0.7, 0≤d≤0.2, and 0.7≤x / (a+b+c+d)<1.0; and on the basis of the mass of the positive electrode material, the mass percentage of the polyanionic material is 1%-10%. The positive electrode material in a secondary battery provided by the present application satisfies the described characteristics, and thus can improve the electrochemical performance of sodium-ion secondary batteries.

Description

Positive electrode material, positive electrode sheet, sodium ion secondary battery and electrical device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a positive electrode material, a positive electrode sheet, a sodium ion secondary battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries such as sodium-ion secondary battery systems have attracted widespread attention due to their abundant resources, low prices, environmental friendliness, and electrochemical properties similar to those of lithium-ion batteries, providing a new option for electrochemical energy storage, especially large-scale energy storage.

[0003] Transition metal layered oxides have the advantage of high energy density and are ideal cathode materials. However, they have poor air stability. When stored in an environment with a certain humidity (e.g., RH 50% and above), the material's stability decreases, affecting its electrochemical performance.

[0004] Therefore, there is an urgent need for a new cathode material based on the above-mentioned transition metal layered oxides to improve the material stability and thus improve the electrochemical performance of secondary batteries.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a positive electrode material, a positive electrode sheet, a sodium ion secondary battery, and an electrical device to improve the electrochemical performance of the sodium ion secondary battery. The specific technical solution is as follows:

[0007] The first aspect of the present application provides a positive electrode material, which includes a matrix material Na x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanion material, and the polyanion material includes at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; the matrix material Na x Ni a Fe b Mn c M dIn O2, M includes at least one of Co, Mg, Ca, B, Al, Zr, Ti, W, Mo, Cr, Sr, Y, Cd, Sn, Sb, Ce, Li, K, Zn, La, F, Si or P, 0.7≤x<1.0, 0.2<a≤0.5, 0.2<b≤0.5, 0.2<c≤0.7, 0≤d≤0.2, 0.7≤x / (a+b+c+d)<1.0; based on the mass of the positive electrode material, the mass percentage of the polyanion material is 1% to 10%. By regulating the types of the matrix material and the polyanion material in the positive electrode material and the mass percentage of the polyanion material within the scope of this application, the positive electrode material can have a higher specific capacity, thereby improving the electrochemical performance of the sodium ion secondary battery.

[0008] In some embodiments of the present application, the specific surface area of ​​the cathode material is BET m 2 / g, 0.2≤BET≤20. By regulating the BET value within the above range, the contact area between the positive electrode material and the air can be reduced, thereby reducing the hygroscopicity of the positive electrode material. On the other hand, the contact area between the positive electrode material and the electrolyte can be reduced, reducing the side reactions between the positive electrode material and the electrolyte, thereby reducing the gas production of the sodium ion secondary battery.

[0009] In some embodiments of the present application, the pH value of the positive electrode material is 6 to 12. By regulating the pH value of the positive electrode material within the above range, the content of residual sodium (Na2CO3 / NaHCO3 / NaOH) in the positive electrode material can be reduced, thereby reducing the reaction between the residual sodium and HF in the electrolyte and reducing the gas production.

[0010] In some embodiments of the present application, at least a portion of the surface of the matrix material is coated with the polyanion material, and the degree of coverage of the polyanion material on the matrix material is ≥80%, which can make the coated matrix material more stable to air and have a higher discharge specific capacity of the matrix material.

[0011] In some embodiments of the present application, the matrix material is a spherical or quasi-spherical secondary particle. By selecting a matrix material within the above range, the energy density of the matrix material can be improved. The secondary particles are composed of primary particles. The smaller the primary particles, the higher the Na + The smaller the migration path, the more conducive it is to the utilization of specific capacity. Furthermore, the secondary particles, formed by the dense packing of primary particles, have a high tap density, which helps to increase the compaction density of the matrix material. The energy density of the matrix material is positively correlated with the specific capacity and compaction density.

[0012] In some embodiments of the present application, the matrix material is a single crystal or single crystal-like primary particle. By selecting a matrix material within the above range, the grain boundaries can be reduced, thereby reducing cracking at the grain boundaries during the cycle, which is beneficial to improving the cycle performance of the sodium ion secondary battery.

[0013] In some embodiments of the present application, the primary particle size D of the polyanion material is 20 nm to 200 nm, which can improve the charge and discharge speed, is beneficial to the electrochemical properties of the matrix material, and ensures the coverage of the polyanion material on the matrix material.

[0014] In some embodiments of the present application, the positive electrode material satisfies at least one of the following characteristics: a) 0.65≤BET≤10; b) the coverage of the polyanion material on the matrix material is ≥90%; c) the primary particle size D of the polyanion material is 20nm to 100nm.

[0015] In some embodiments of the present application, the phosphate compound includes NaRPO4, R is selected from Fe or Mn; the NASICON compound includes Na y Q2(XO4)3, 1≤y≤4, Q includes at least one of V, Fe, Ni, Mn or Ti, X includes at least one of P, S or Si; the pyrophosphate compound includes Na m Z(PO4) n (P2O7) q , 2≤m<10, 0≤n≤4, 1≤q<10, Z includes at least one of Fe, Mn or Co; the fluorinated phosphate compound includes NaVPO4F or Na3(VO 1-w PO4)2F 1+2w At least one of 0≤w≤1. By selecting the phosphate compound within the above range, the environmental stability of the matrix material can be improved, and the Na + The effect of intercalation and deintercalation is small. By selecting NASICON compounds within the above range, while improving the environmental stability of the matrix material, it also has a small effect on the ionic conductivity of the matrix material and can also improve the thermal stability of the matrix material. By selecting pyrophosphate compounds within the above range, the environmental stability of the matrix material can be improved, and the cycle performance and thermal stability of the positive electrode material can also be improved. By selecting fluorinated phosphate compounds within the above range, not only can the stability of the matrix material to air be improved, but also the energy density of the matrix material can be less affected.

[0016] The second aspect of the present application provides a positive electrode plate, which includes the positive electrode material of any of the aforementioned embodiments. Therefore, the positive electrode plate provided by the present application has good electronic conductivity and ionic conductivity.

[0017] In some embodiments of the present application, the compacted density of the positive electrode sheet is CD g / cm 3 , CD ≥ 2.7. By regulating the compaction density of the positive electrode sheet within the above range, it is beneficial to obtain a sodium ion secondary battery with high energy density.

[0018] The third aspect of the present application provides a sodium ion secondary battery, which includes the positive electrode sheet of any of the aforementioned embodiments. Therefore, the sodium ion secondary battery provided by the present application has good electrochemical performance.

[0019] A fourth aspect of the present application provides an electrical device comprising the sodium ion secondary battery of any of the aforementioned embodiments. Therefore, the electrical device provided by the present application has good performance.

[0020] Beneficial effects of this application:

[0021] The present application provides a positive electrode material, a positive electrode sheet, a sodium ion secondary battery and an electric device. The positive electrode material includes a base material Na x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanion material, the polyanion material includes at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; the matrix material Na x Ni a Fe b Mn c M d In O2, M includes at least one of Co, Mg, Ca, B, Al, Zr, Ti, W, Mo, Cr, Sr, Y, Cd, Sn, Sb, Ce, Li, K, Zn, La, F, Si, or P, 0.7≤x<1.0, 0.2<a≤0.5, 0.2<b≤0.5, 0.2<c≤0.7, 0≤d≤0.2, 0.7≤x / (a+b+c+d)<1.0; based on the mass of the positive electrode material, the mass percentage of the polyanion material is 1% to 10%. By regulating the types of the matrix material and the polyanion material in the positive electrode material and the mass percentage of the polyanion material within the scope of this application, the positive electrode material can have a higher specific capacity, thereby improving the electrochemical performance of the sodium ion secondary battery.

[0022] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0024] FIG1 is a scanning electron microscope image of the base material in Example 1;

[0025] FIG2 is a scanning electron microscope image of the substrate material surface having a polyanion material in Example 1;

[0026] FIG3 is a comparison diagram of the water absorption and degradation degree of the substrate material surface in Example 1 when the substrate material surface does not have the polyanion material and when the substrate material surface has the polyanion material. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, and not all of them. All other embodiments derived by persons of ordinary skill in the art based on the examples in this application are intended to fall within the scope of protection of this application.

[0028] The first aspect of the present application provides a positive electrode material, which includes a matrix material Na x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanion material, the polyanion material includes at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; the matrix material Na x Ni a Fe b Mn c M dIn O2, M comprises at least one of Co, Mg, Ca, B, Al, Zr, Ti, W, Mo, Cr, Sr, Y, Cd, Sn, Sb, Ce, Li, K, Zn, La, F, Si, or P, 0.7 ≤ x < 1.0, 0.2 < a ≤ 0.5, 0.2 < b ≤ 0.5, 0.2 < c ≤ 0.7, 0 ≤ d ≤ 0.2, and 0.7 ≤ x / (a+b+c+d) < 1.0; and the weight percentage of the polyanion material is 1% to 10% based on the weight of the positive electrode material. Specifically, the weight percentage of the polyanion material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the foregoing values. Without being limited by theory, when the weight percentage of the polyanion material is too low (e.g., less than 1%), the polyanion material cannot effectively exist on the surface of the matrix material, cannot effectively isolate the matrix material from air, and cannot effectively improve the stability of the matrix material. When the weight percentage of the polyanion material is too high (e.g., greater than 10%), it can affect the energy density of the sodium-ion secondary battery. By regulating the weight percentage of the polyanion material within the above range, the matrix material can be effectively isolated from air, the material stability can be improved, and thus the electrochemical performance of the sodium-ion secondary battery can be improved.

[0029] The inventors have found that when the surface of the substrate material has a polyanion material, the contact area between the substrate material and the air can be minimized to achieve the purpose of isolating the substrate material from H2O and CO2 in the air. This is mainly due to the following two reasons: first, the polyanion material itself is not sensitive to humidity, and the influence of H2O and CO2 in the air on it is negligible; second, it is a positive electrode material for sodium ion secondary batteries, and can be used for Na + Normal deintercalation of the matrix material Na + The effect of embedding and de-embedding is small, thereby achieving the performance improvement of the matrix material under the premise of having little impact on the specific capacity of the matrix material; secondly, the polyanion material itself has good thermal stability. When the surface of the matrix material has a polyanion material, the thermal stability of the matrix material can also be improved.

[0030] In the positive electrode material of this application, the matrix material Na x Ni a Fe b Mn c M d The surface of O2 has polyanion material because polyanion material is also a positive electrode material of sodium ion secondary battery, which has electronic conductivity and ion conductivity and has little effect on the electronic conductivity and ion conductivity of the matrix material. The surface of the matrix material has polyanion material, which makes the matrix material more isolated from the air, thus having better air stability. In addition, since polyanion material can carry out Na +Deintercalation allows it to function as an active material in the positive electrode material, with minimal impact on the specific capacity of the matrix material. Furthermore, the use of polyanionic materials is also beneficial in reducing gassing in sodium-ion secondary batteries. This is because the strong covalent bond between X and O in the polyanion stabilizes the O in the crystal lattice, preventing oxygen release. Therefore, when the sodium-ion secondary battery is charged to a high voltage, it will not oxidize the electrolyte and cause gassing. Furthermore, the matrix material itself will release oxygen, which can oxidize the electrolyte and cause gassing. Polyanionic materials, to a certain extent, isolate the contact area between the electrolyte and the matrix material, thereby reducing gassing.

[0031] Based on the above research findings, in the cathode material of this application, the matrix material Na x Ni a Fe b Mn c M d The surface of O2 has a polyanion material, and when the mass percentage of the polyanion material is regulated within the scope of this application, the electrochemical performance of the sodium ion secondary battery can be improved.

[0032] In some embodiments of the present application, the specific surface area of ​​the positive electrode material is BET m 2 / g, 0.2≤BET≤20. Exemplarily, BET can be 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range consisting of any two of the above values. In some embodiments of the present application, 0.65≤BET≤10. By regulating the value of BET within the above range, on the one hand, the contact area between the positive electrode material and the air can be reduced, thereby reducing the hygroscopicity of the positive electrode material. On the other hand, the contact area between the positive electrode material and the electrolyte can be reduced, reducing the side reaction between the positive electrode material and the electrolyte, thereby reducing the gas production of the sodium ion secondary battery.

[0033] In some embodiments of the present application, the pH value of the positive electrode material is 6 to 12. For example, the pH value can be 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, or a range consisting of any two of the above values. By regulating the pH value of the positive electrode material within the above range, the content of residual sodium (Na2CO3 / NaHCO3 / NaOH) in the positive electrode material can be reduced, thereby reducing the reaction of residual sodium with HF in the electrolyte and reducing gas production.

[0034] In some embodiments of the present application, at least a portion of the surface of the substrate material is coated with a polyanion material, and the coverage of the polyanion material on the substrate material is ≥80%. For example, the coverage of the polyanion material on the substrate material can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100% or a range consisting of any two of the above values. In some embodiments of the present application, the coverage of the polyanion material on the substrate material is ≥90%. The polyanion material can be present on a portion of the surface of the substrate material, or on the entire surface of the substrate material. By regulating the coverage of the polyanion material on the substrate material within the above range, the area of ​​the substrate material in contact with the air can be made relatively small, the better the stability of the coated substrate material to air, the lower the hygroscopicity of the substrate material when stored in the air, and the Na in the product generated by the reaction with H2O and CO2 in the air. + The lower the content, the + The less precipitation from the bulk phase, the higher the discharge specific capacity of the matrix material.

[0035] In some embodiments of the present application, the matrix material is a spherical or quasi-spherical secondary particle. As shown in FIG1 , the matrix material in the figure is a quasi-spherical secondary particle. By selecting a matrix material within the above range, the energy density of the matrix material can be improved. The secondary particles are composed of primary particles. The smaller the primary particles, the higher the Na + The smaller the migration path, the more conducive it is to the utilization of specific capacity. Furthermore, the secondary particles, formed by the dense packing of primary particles, have a high tap density, which helps to increase the compaction density of the matrix material. The energy density of the matrix material is positively correlated with the specific capacity and compaction density.

[0036] In some embodiments of the present application, the matrix material is a single crystal or single crystal-like primary particle. By selecting a matrix material within the above range, the grain boundaries can be reduced, thereby reducing cracking at the grain boundaries during cycling, which is beneficial to improving the cycling performance of the sodium ion secondary battery.

[0037] In some embodiments of the present application, the primary particle size D of the polyanionic material is 20 nm to 200 nm. For example, D can be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm or a range consisting of any two of the above values. In some embodiments of the present application, D is 20 nm to 100 nm. By regulating D within the above range, the Na + The migration path is opened, thereby improving the charge and discharge speed, and is beneficial to the electrochemical properties of the polyanion material itself and the electrochemical properties of the matrix material. In addition, the polyanion material layer formed by the polyanion material can be thinner while still having a high degree of coverage on the matrix material.

[0038] In some embodiments of the present application, the phosphate compound includes NaRPO4, R is selected from Fe or Mn; the NASICON compound includes Na y Q2(XO4)3, 1≤y≤4, Q includes at least one of V, Fe, Ni, Mn or Ti, X includes at least one of P, S or Si; pyrophosphate compounds include Na m Z(PO4) n (P2O7) q , 2≤m<10, 0≤n≤4, 1≤q<10, Z includes at least one of Fe, Mn or Co; the fluorinated phosphate compound includes NaVPO4F or Na3(VO 1-w PO4)2F 1+2w At least one of 0≤w≤1. By selecting the phosphate compound within the above range, the environmental stability of the matrix material can be improved, and the Na + The effect of intercalation and deintercalation is small. By selecting NASICON compounds within the above range, NASICON compounds are fast ion conductors of sodium. These compounds have an open three-dimensional skeleton structure, high ionic conductivity and good thermal stability. They not only have the effect of improving the environmental stability of the matrix material, but also have little effect on the ionic conductivity of the matrix material, and at the same time can also improve the thermal stability of the matrix material. By selecting pyrophosphate compounds within the above range, pyrophosphate compounds have good structural stability, thermal stability and fast sodium ion mobility, which can not only improve the environmental stability of the matrix material, but also improve the cycle performance and thermal stability of the positive electrode material. By selecting fluorinated phosphate compounds within the above range, fluorinated phosphate compounds have good air stability. In the material, F with strong electronegativity is usually used to replace PO4 3- The O in the substrate is used to enhance its inductive effect and thus increase the voltage, thus having a higher voltage platform; when the surface of the substrate material has a fluorinated phosphate compound, it can not only improve the stability of the substrate material to air, but also have little effect on the energy density of the substrate material.

[0039] In one embodiment of the present application, the polyanion material forms a polyanion material layer on the surface of the substrate material. The thickness of the polyanion material layer is 0.05 μm to 5 μm, which can improve the degree of coating on the substrate material and facilitate electron transport, thereby improving the kinetic performance of the sodium ion secondary battery. The present application does not particularly limit the number of layers of the polyanion material layer, as long as the purpose of the present application can be achieved. For example, the polyanion material layer can be a single layer or multiple layers. When it is a multiple layer, the thickness of the polyanion material layer is the total thickness of the multiple layers of polyanion material.

[0040] The present application has no particular restrictions on the preparation method of the positive electrode material, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode material may include but is not limited to the following steps:

[0041] Weighing matrix material raw materials according to a stoichiometric ratio, mixing the matrix material raw materials and grinding them uniformly, calcining them at 800° C. to 1000° C. for 12 h to 14 h, and crushing them to obtain a matrix material;

[0042] The polyanion material raw materials are weighed according to the stoichiometric ratio, and the polyanion material raw materials are uniformly mixed. Then, the matrix material is added and the mixture is further mixed. Then, the mixture is dried, sintered, and ground to obtain the positive electrode material.

[0043] The present application does not particularly limit the mixing method, as long as the purpose of the present application can be achieved, for example, wet mixing, such as wet ball milling. When the mixing method is wet ball milling, the ball milling time can be 3 hours to 5 hours, the ball mill speed can be 200 r / min to 400 r / min, and the ball milling medium can be acetone or ethanol. The present application does not particularly limit the sintering method. For example, sintering can be carried out in a vacuum tube furnace filled with nitrogen, the sintering temperature can be 350°C to 800°C, and the sintering time can be 6 hours to 24 hours.

[0044] Typically, the specific surface area of ​​the positive electrode material and the degree of polyanion coating on the matrix material can be controlled by adjusting the milling time after adding the matrix material and polyanion material. For example, increasing the milling time decreases the specific surface area; decreasing the milling time increases the specific surface area; increasing the milling time increases the degree of polyanion coating on the matrix material; decreasing the milling time decreases the degree of polyanion coating on the matrix material. The pH of the positive electrode material can be controlled by simultaneously varying the milling time after adding the matrix material and polyanion material, as well as the mass ratio of the matrix material to the polyanion material. The primary particle size D of the polyanion material can be controlled by varying the sintering temperature and time. For example, increasing the sintering temperature and time increases the primary particle size D of the polyanion material; decreasing the sintering temperature and time decreases the primary particle size D of the polyanion material.

[0045] The second aspect of the present application provides a positive electrode plate, which includes the positive electrode material of any of the aforementioned embodiments. Therefore, the positive electrode plate provided by the present application has good electronic conductivity and ionic conductivity.

[0046] In some embodiments of the present application, the compacted density of the positive electrode sheet is CD g / cm 3 , CD ≥ 2.7. In some embodiments of the present application, 2.8 ≤ CD ≤ 3.1. By regulating the compaction density of the positive electrode sheet within the above range, it is advantageous to obtain a sodium ion secondary battery with high energy density.

[0047] In this application, a positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its thickness direction, or on both surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire area of ​​the positive electrode current collector or a portion of the positive electrode current collector. This application does not specifically limit this, as long as the purpose of this application can be achieved.

[0048] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0049] The positive electrode material layer also includes a conductive agent and a binder. The present application does not particularly limit the types of conductive agent and binder, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose. The conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, metal material or conductive polymer. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fiber may include but is not limited to vapor-grown carbon fiber (VGCF) and / or nano-carbon fiber. The above-mentioned metal material may include but is not limited to metal powder and / or metal fiber. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include, but is not limited to, at least one of a polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art may select the ratio based on actual needs, as long as the objectives of the present application are achieved.

[0050] This application does not impose any particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. This application does not impose any particular restrictions on the thickness of the positive electrode sheet, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode sheet is 36 μm to 250 μm.

[0051] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer; it may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, it may be at least one of the above-mentioned conductive agents and binders.

[0052] The third aspect of the present application provides a sodium ion secondary battery, which includes the positive electrode sheet of any of the aforementioned embodiments. Therefore, the sodium ion secondary battery provided by the present application has good electrochemical performance.

[0053] In the present application, the sodium-ion secondary battery further includes a negative electrode sheet, which may include a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The present application does not particularly limit the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. The negative electrode material layer in the present application includes a negative electrode active material, a conductive agent, and a thickener. The negative electrode active material in the present application may include at least one of a metal oxide, a metal sulfide, a metal phosphide, a Sb-based negative electrode material, hard carbon, soft carbon, and sodium metal. The metal oxide may include at least one of cobalt oxide, iron oxide, nickel oxide, or copper oxide; the metal sulfide may include at least one of tungsten disulfide, molybdenum disulfide, or tin disulfide; the metal phosphide may include at least one of lithium phosphide or sodium phosphide; and the Sb-based negative electrode material may include at least one of a Sb-C composite material, a NiSb alloy, Sb2O3, or Sb2O4. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode material layer is 30 μm to 120 μm. There is no particular limitation on the thickness of the negative electrode plate, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode plate is 36 μm to 250 μm.

[0054] In the present application, the sodium ion secondary battery also includes a separator to separate the positive electrode plate and the negative electrode plate, prevent the internal short circuit of the sodium ion secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0055] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer may include inorganic particles and a binder. The inorganic particles are not particularly limited and may, for example, include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited and may, for example, be at least one of the above binders. The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0056] In the present application, the sodium ion secondary battery also includes an electrolyte, and the electrolyte includes a sodium salt and a non-aqueous solvent. The sodium salt may include at least one of NaPF6, NaOTF, NaFSI, NaTFSI, NaBF4, NaBOB, NaDFOB or NaClO4. The present application does not particularly limit the concentration of the sodium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, the concentration of the sodium salt in the electrolyte is 0.9 mol / L to 1.5 mol / L. Exemplarily, the concentration of the sodium salt in the electrolyte can be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L or a range consisting of any two of the above values. The present application does not particularly limit the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0057] The sodium-ion secondary battery of this application also includes a packaging bag for accommodating the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0058] The preparation process of the sodium ion secondary battery of the present application is well known to those skilled in the art, and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a sodium ion secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a sodium ion secondary battery. In addition, as needed, an overcurrent protection element, a guide plate, etc. may be placed in the packaging bag to prevent the pressure inside the sodium ion secondary battery from rising and overcharging and discharging.

[0059] A fourth aspect of the present application provides an electrical device comprising the sodium ion secondary battery of any of the aforementioned embodiments. Therefore, the electrical device provided by the present application has good performance.

[0060] The electrical device of the present application is not particularly limited and can be any electrical device known in the prior art. In some embodiments, the electrical device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a sodium ion capacitor.

[0061] Example

[0062] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0063] Test methods and equipment:

[0064] Specific surface area test:

[0065] In accordance with the national standard "Determination of the specific surface area of ​​solid substances by gas adsorption BET method" (GB / T 19587-2017), a specific surface area analyzer (model: TristarⅡ3020M) was used to test the specific surface area of ​​the positive electrode materials in the original state described in each embodiment and comparative example by nitrogen adsorption or desorption method.

[0066] pH test:

[0067] Weigh 1g of the positive electrode material sample into a 100mL conical flask, add 20mL of ethylene glycol (purity of 99.999%), put in a magnetic rod and seal the bottle mouth with a sealing film, stir magnetically for 30 minutes and then filter, dilute the filtrate to 100mL with pure water, take 50mL of the filtrate and put it into a beaker for testing by potentiometric titration to obtain the residual sodium content in the positive electrode material.

[0068] The reaction formula is as follows:

[0069] Na2CO3+HCl=NaCl+NaHCO3

[0070] NaOH + HCl = NaCl + H2O

[0071] NaHCO3+HCl=NaCl+H2CO3

[0072] Coverage test:

[0073] The original positive electrode sheets described in each embodiment and comparative example were cut using an ion polisher (model JEOL-IB-09010CP) to obtain cross-sections. The cross-sections were observed using a scanning electron microscope (SEM, model Zeiss Sigma 02-33) at an appropriate magnification (e.g., 1000x to 30,000x). Image J software was used to identify the perimeter L1 of the substrate material and the total perimeter L2 of the uncoated area. The coverage M = 1-L2 / L1.

[0074] Testing of polyanion material particle size:

[0075] In accordance with the national standard "Particle Size Distribution Laser Diffraction Method" (GB / T19077-2016), the particle size distribution of polyanion materials was tested using a Malvern particle size tester.

[0076] Tests on material water absorption and material degradation:

[0077] In accordance with the "General Rules for Thermal Analysis Methods" (JY_T0589.1-2020 / JY_T0589.4-2020 / JY_T0589.5-2020), a thermogravimetric analyzer was used to test the change in the mass of the positive electrode material with temperature.

[0078] 10 mg of the positive electrode materials in different states in each embodiment and comparative example were taken and placed in a thermogravimetric analyzer. The test atmosphere was set to nitrogen, the test temperature was 35°C to 400°C, and the heating rate was 5°C / min to obtain a TG curve.

[0079] On the obtained TG curve, the weight loss from 35°C to 120°C is mainly due to the free water on the surface of the material, and the weight loss from 120°C to 400°C is due to the by-products generated after the material absorbs water and deteriorates. The weight loss ratio in the range of 35°C to 120°C is defined as the water absorption amount, and the weight loss ratio in the range of 120°C to 400°C is defined as the degree of degradation.

[0080] Water absorption = 100% - mass percentage corresponding to TG curve at 120°C

[0081] Degradation degree = mass percentage corresponding to the TG curve at 120°C - mass percentage corresponding to the TG curve at 400°C.

[0082] The water absorption of the positive electrode material in the original state is recorded as W1, and the water absorption of the positive electrode material in the A2 state is recorded as W2; the degradation degree of the positive electrode material in the original state is recorded as T1, and the degradation degree of the positive electrode material in the A2 state is recorded as T2.

[0083] Specific capacity test:

[0084] In a dry room at 25°C and humidity ≤ 2%, the positive electrode materials described in the Examples and Comparative Examples, along with the binder polyvinylidene fluoride and the conductive agent acetylene black, were mixed in a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added and thoroughly stirred to form a uniform positive electrode slurry. The slurry was then coated onto a 10μm thick aluminum foil (positive electrode current collector), dried, and cold-pressed. The slurry was then punched into small discs with a diameter of 14mm for use as the positive electrode sheets. A button-type half-cell was assembled using a sodium sheet as the negative electrode sheet, a 12μm polypropylene separator, and a mixture of 1 mol / L NaPF6 and ethylene carbonate / propylene carbonate (EC / PC, volume ratio 1:1) as the electrolyte.

[0085] Half-cell charge and discharge tests were performed on a LAND CT2001A battery test system. The test was performed at an operating voltage range of 2.0V to 4.0V and a current density of 10mA / g, and the initial discharge specific capacity was recorded.

[0086] The discharge specific capacity of the positive electrode material in the original state is recorded as C1, and the discharge specific capacity of the positive electrode material in the A2 state is recorded as C2.

[0087] Example 1

[0088] <Preparation of positive electrode material>

[0089] According to Nani 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2(NFMA) was 6 μm for the precursor Ni 0.316 Fe 0.332 Mn 0.35 (OH)2, Na2CO3 and nano-Al2O3 were ground evenly, calcined at 900℃ for 12h and crushed to obtain the matrix material NFMA with a Dv50 of 6μm. The scanning electron microscope image of the matrix material is shown in Figure 1. The raw materials, Na₂CO₃, NH₄VO₃, and NH₄H₂PO₄, were weighed according to the stoichiometric ratio of Na₃V₂(PO₄)₃ (NVP). These materials were placed in a ball mill and wet-milled in a planetary ball mill (using acetone as the milling medium) at 300 r / min for 3 hours. NFMA was then added at a mass ratio of 95:5 to NVP, and milling continued for 3 hours. After milling, the mixture was dried in a vacuum drying oven at 60°C and sintered in a nitrogen-filled vacuum tube furnace. The temperature was first raised to 350°C for 4 hours, then to 800°C for 8 hours, and then ground for 4 hours to obtain a cathode material with NVP on the NFMA surface. This material is referred to as the "raw" state.

[0090] Take 10g of the above original material and spread it on a 100cm 2 The surface dish containing the material is then placed in a humidity box at a temperature of 25°C and RH50% for 10 days and then taken out. The material treated in the humidity box is recorded as state A2.

[0091] <Preparation of positive electrode sheet>

[0092] In a drying room at 25°C and humidity ≤RH2%, the above-mentioned original positive electrode material, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 80:10:10, N-methylpyrrolidone (NMP) solvent was added, and the mixture was fully stirred to form a positive electrode slurry with a solid content of 72%; a 200 μm coating (the thickness here refers to the coating thickness applied on one side of the aluminum foil) was applied on an aluminum foil with a thickness of 10 μm using a scraper, followed by drying at 70°C for 12 hours and then cold pressing; and then punched into small discs with a diameter of 14 mm for use as original positive electrode sheets.

[0093] In a drying room at 25°C and humidity ≤RH2%, the above-mentioned A2 state positive electrode material, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a mass ratio of 80:10:10, N-methylpyrrolidone (NMP) solvent is added, and the mixture is fully stirred to form a positive electrode slurry with a solid content of 72%; a 200 μm coating (the thickness here refers to the coating thickness applied on one side of the aluminum foil) is applied on an aluminum foil with a thickness of 10 μm using a scraper, followed by drying at 70°C for 12 hours and then cold pressing; and then punching out small discs with a diameter of 14 mm to be used as positive electrode sheets in the A2 state.

[0094] <Preparation of negative electrode sheet>

[0095] The sodium sheet is punched into a small disc with a diameter of 14 mm as the negative electrode.

[0096] <Preparation of Electrolyte>

[0097] In a dry room at 25°C and humidity ≤ RH2%, a non-aqueous solvent of ethylene carbonate and propylene carbonate was mixed in a volume ratio of 1:1. NaPF6 was then added to the non-aqueous solvent, dissolved, and mixed uniformly to obtain an electrolyte solution. The molar concentration of NaPF6 was 1 mol / L.

[0098] <Preparation of Separator>

[0099] A porous polyethylene film with a thickness of 12 μm (supplied by Celgard) was used.

[0100] <Preparation of Sodium Ion Batteries>

[0101] A button-type half-cell was assembled in a glove box in the order of the negative electrode sheet, the separator, and the original positive electrode sheet, which was recorded as the original button-type half-cell.

[0102] A button-type half-cell was assembled in the glove box in the order of the negative electrode sheet, the separator, and the positive electrode sheet in the A2 state, which was recorded as the button-type half-cell in the A2 state.

[0103] Example 2

[0104] Except for the difference in <Preparation of Positive Electrode Material> from Example 1, the rest is the same as Example 1.

[0105] <Preparation of positive electrode material>

[0106] According to Nani 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2(NFMA) was 6 μm for the precursor Ni 0.316 Fe 0.332 Mn0.35 (OH)2, Na2CO3, and nano-Al2O3 were ground uniformly, calcined at 900°C for 12 hours, and crushed to produce a NFMA substrate with a Dv50 of 6 μm. FePO4 and dehydrated Na3PO4 were weighed according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7 (N4FPP). The weighed raw materials were placed in a ball mill and wet-milled in a planetary ball mill (using acetone as the milling medium) at 300 rpm for 3 hours. NFMA was then added at a mass ratio of 95:5 to N4FPP. Milling continued for 3 hours. After milling, the product was dried in a vacuum drying oven at 60°C and sintered in a nitrogen-filled vacuum tube furnace at 500°C for 10 hours. The resulting NFMA cathode material had N4FPP on its surface. This material is referred to as the "raw" state.

[0107] Take 10g of the above original material and spread it on a 100cm 2 The surface dish containing the material is then placed in a humidity box at a temperature of 25°C and RH50% for 10 days and then taken out. The material treated in the humidity box is recorded as state A2.

[0108] Example 3

[0109] Except for the difference in <Preparation of Positive Electrode Material> from Example 1, the rest is the same as Example 1.

[0110] <Preparation of positive electrode material>

[0111] According to Nani 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2(NFMA) was 6 μm for the precursor Ni 0.316 Fe 0.332 Mn 0.35(OH)2, Na2CO3, and nano-Al2O3 were ground uniformly, calcined at 900°C for 12 hours, and crushed to produce a NFMA substrate with a Dv50 of 6 μm. FePO4 and dehydrated Na3PO4 were weighed according to the stoichiometric ratio of Na3Fe2(PO4)P2O7 (N3FPP). The weighed raw materials were placed in a ball mill and wet-milled in a planetary ball mill (using acetone as the milling medium) at 300 rpm for 3 hours. NFMA was then added at a mass ratio of 95:5 to N3FPP. Milling was continued for 3 hours. After milling, the product was dried in a vacuum drying oven at 60°C and sintered in a nitrogen-filled vacuum tube furnace at 500°C for 24 hours. The resulting NFMA cathode material had N3FPP on its surface. This material is referred to as the "raw" state.

[0112] Take 10g of the above original material and spread it on a 100cm 2 The surface dish containing the material is then placed in a humidity box at a temperature of 25°C and RH50% for 10 days and then taken out. The material treated in the humidity box is recorded as state A2.

[0113] Example 4

[0114] The process was the same as in Example 2 except that the mass ratio of NFMA to N4FPP was adjusted to 97:3 in the preparation of positive electrode material.

[0115] Example 5

[0116] The process was the same as in Example 2 except that the mass ratio of NFMA to N4FPP was adjusted to 90:10 in the preparation of positive electrode material.

[0117] Example 6

[0118] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 6 h in <Preparation of Positive Electrode Material>.

[0119] Example 7

[0120] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 2 h in the preparation of positive electrode materials.

[0121] Example 8

[0122] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 1 h in <Preparation of Positive Electrode Material>.

[0123] Example 9

[0124] The process was the same as in Example 2 except that the mass ratio of NFMA to N4FPP was adjusted to 99:1 and the milling time after adding NFMA and N4FPP was adjusted to 1 h in the preparation of positive electrode material.

[0125] Example 10

[0126] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 0.5 h in <Preparation of Positive Electrode Material>.

[0127] Example 11

[0128] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 2.5 h in <Preparation of Positive Electrode Material>.

[0129] Example 12

[0130] The process was the same as in Example 2 except that the milling time after adding NFMA and N4FPP was adjusted to 5 h in <Preparation of Positive Electrode Material>.

[0131] Example 13

[0132] The process was the same as in Example 2 except that the sintering temperature was adjusted to 400° C. and the sintering time was adjusted to 8 h in the preparation of the positive electrode material.

[0133] Example 14

[0134] The process was the same as in Example 2 except that the sintering temperature was adjusted to 580° C. and the sintering time was adjusted to 12 h in the preparation of the positive electrode material.

[0135] Example 15

[0136] The process was the same as in Example 2 except that the sintering temperature was adjusted to 650° C. and the sintering time was adjusted to 16 h in the preparation of the positive electrode material.

[0137] Example 16

[0138] The process was the same as in Example 2 except that the Dv50 of the precursor of the matrix material NFMA was adjusted to 10 μm and the milling time after adding NFMA and N4FPP was adjusted to 6 h in <Preparation of positive electrode material>.

[0139] Example 17

[0140] The process was the same as in Example 5 except that the Dv50 of the precursor of the matrix material NFMA was adjusted to 3 μm and the milling time after adding NFMA and N4FPP was adjusted to 0.5 h in <Preparation of positive electrode material>.

[0141] Comparative Example 1

[0142] Except for the difference in <Preparation of Positive Electrode Material> from Example 1, the rest is the same as Example 1.

[0143] <Preparation of positive electrode material>

[0144] According to Nani 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2(NFMA) was 6 μm for the precursor Ni 0.316 Fe 0.332 Mn 0.35 (OH)2, Na2CO3 and nano-Al2O3 were ground evenly, calcined at 900℃ for 12h, and crushed to obtain the matrix material NFMA with Dv50 of 6μm. The material at this time was recorded as the original state.

[0145] Take 10g of the above original material and spread it on a 100cm 2 The surface dish containing the material is then placed in a humidity box at a temperature of 25°C and RH50% for 10 days and then taken out. The material treated in the humidity box is recorded as state A2.

[0146] Comparative Example 2

[0147] The process was the same as in Example 2 except that the mass ratio of NFMA to N4FPP was adjusted to 99.9:0.1 in the preparation of positive electrode material.

[0148] Comparative Example 3

[0149] The process was the same as in Example 2 except that the mass ratio of NFMA to N4FPP was adjusted to 80:20 in the preparation of positive electrode material.

[0150] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Table 1.

[0151] Note: In Table 1, / ” indicates no relevant preparation parameters.

[0152] Referring to Table 1, it can be seen from Examples 1 to 17 and Comparative Examples 1 to 3 that by regulating the types of the matrix material and the polyanion material in the positive electrode material and the mass percentage of the polyanion material within the scope of this application, the positive electrode material has a lower water absorption and degree of deterioration, and the prepared sodium ion secondary battery has a higher specific capacity, which indicates that the positive electrode material provided in this application has good stability, and the sodium ion secondary battery prepared using the positive electrode material provided in this application has good electrochemical properties.

[0153] The specific surface area of ​​the positive electrode material, the degree of coverage of the polyanion material on the matrix material, the primary particle size of the polyanion material, and the compaction density of the positive electrode sheet generally affect the electrochemical performance of the sodium ion secondary battery. From Examples 1 to 17, it can be seen that by regulating the specific surface area of ​​the positive electrode material, the pH value of the positive electrode material, the degree of coverage of the polyanion material on the matrix material, the primary particle size of the polyanion material, and the compaction density of the electrode sheet within the scope of this application, it is beneficial to further improve the stability of the positive electrode material and the electrochemical performance of the sodium ion secondary battery.

[0154] The pH value of the positive electrode material generally affects the electrochemical performance of the sodium ion secondary battery. As can be seen from Examples 2 and 4, by adjusting the pH value of the positive electrode material within the range of this application, it is beneficial to further improve the stability of the positive electrode material and the electrochemical performance of the sodium ion secondary battery.

[0155] As can be seen from FIG2 , in the positive electrode material prepared in Example 1, the surface of the base material has the polyanion material, and the base material is relatively completely wrapped by the polyanion material.

[0156] Figure 3 compares the water absorption and degradation of the substrate material surface without and with the polyanionic material. The curve within the dashed rectangular frame represents the curve in the range of 35°C to 120°C, and the curve outside the dashed rectangular frame represents the curve in the range of 120°C to 400°C. As can be seen from Figure 3, the water absorption and degradation in state A2 of Example 2 are much lower than those in state A2 of Comparative Example 1, indicating that the positive electrode material provided by this application has good stability.

[0157] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A positive electrode material comprising a matrix material Na x Ni a Fe b Mn c M d O2, the surface of the substrate material has a polyanion material, and the polyanion material includes at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; The matrix material Na x Ni a Fe b Mn c M d In O2, M includes at least one of Co, Mg, Ca, B, Al, Zr, Ti, W, Mo, Cr, Sr, Y, Cd, Sn, Sb, Ce, Li, K, Zn, La, F, Si or P, 0.7≤x<1.0, 0.2<a≤0.5, 0.2<b≤0.5, 0.2<c≤0.7, 0≤d≤0.2, 0.7≤x / (a+b+c+d)<1.0; Based on the mass of the positive electrode material, the mass percentage of the polyanion material is 1% to 10%.

2. The positive electrode material according to claim 1, wherein The specific surface area of ​​the positive electrode material is BET m 2 / g, 0.2≤BET≤20.

3. The positive electrode material according to claim 1, wherein The pH value of the positive electrode material is 6 to 12.

4. The positive electrode material according to claim 1, wherein At least a portion of the surface of the matrix material is coated by the polyanion material, and the degree of coating of the matrix material by the polyanion material is ≥80%.

5. The positive electrode material according to claim 1, wherein The matrix material is spherical or quasi-spherical secondary particles.

6. The positive electrode material according to claim 1, wherein The matrix material is single crystal or single crystal-like primary particles.

7. The positive electrode material according to claim 1, wherein The primary particle size D of the polyanion material is 20 nm to 200 nm.

8. The positive electrode material according to claim 1, wherein The positive electrode material satisfies at least one of the following characteristics: a) 0.65≤BET≤10; b) the coverage degree of the polyanion material on the matrix material is ≥ 90%; c) The primary particle size D of the polyanion material is 20 nm to 100 nm.

9. The positive electrode material according to claim 1, wherein The phosphate compound includes NaRPO4, R is selected from Fe or Mn; the NASICON compound includes Na y Q2(XO4)3, 1≤y≤4, Q includes at least one of V, Fe, Ni, Mn or Ti, X includes at least one of P, S or Si; the pyrophosphate compound includes Na m Z(PO4) n (P2O7) q , 2≤m<10, 0≤n≤4, 1≤q<10, Z includes at least one of Fe, Mn or Co; the fluorinated phosphate compound includes NaVPO4F or Na3(VO 1-w PO4)2F 1+2w At least one of , 0≤w≤1. 10 . A positive electrode sheet comprising the positive electrode material according to claim 1 .

11. The positive electrode sheet according to claim 10, wherein: The compaction density of the positive electrode sheet is CD g / cm 3 , CD≥2.

7. 12 . A sodium ion secondary battery comprising the positive electrode sheet according to claim 11 .

13. An electrical device comprising the sodium ion secondary battery according to claim 12.

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