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

Abstract

The 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 base material Na x Ni a Fe b Mn c M d O2, the surface of the base material has a polyanion material, the polyanion material comprises at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound or a fluorinated phosphate compound; the base material Na x Ni a Fe b Mn c M d 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 The positive electrode material in the secondary battery provided by the application meets the above characteristics and can improve the electrochemical performance of the sodium-ion secondary battery.

Description

Technical Field

[0001] This 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 Technology

[0002] In recent years, secondary batteries such as sodium-ion secondary battery systems have attracted widespread attention due to their abundant resources, low price, environmental friendliness, and electrochemical properties similar to 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, making them an ideal cathode material. However, they have poor air stability. When stored in a certain humidity environment (e.g., RH 50% and above), the stability of the material decreases, affecting its electrochemical performance.

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

[0005] 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:

[0006] The first aspect of this application provides a cathode material comprising a matrix material Na. x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanionic material, the polyanionic material including at least one of phosphate compounds, NASICON compounds, pyrophosphate compounds, or fluorinated phosphate compounds; 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, with 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. Based on the mass of the cathode material, the mass percentage of the polyanionic material is 1% to 10%. By controlling the types of matrix material and polyanionic material in the cathode material and the mass percentage of polyanionic material within the scope of this application, the cathode material can have a higher specific capacity, thereby improving the electrochemical performance of sodium-ion secondary batteries.

[0007] In some embodiments of this application, the specific surface area of ​​the cathode material is BET m. 2 / g, 0.2≤BET≤20. By adjusting the BET value within the above range, it is possible to reduce the contact area between the cathode material and air, thereby reducing the hygroscopicity of the cathode material. On the other hand, it is possible to reduce the contact area between the cathode material and the electrolyte, thereby reducing the side reactions between the cathode material and the electrolyte, and thus reducing the gas production of sodium-ion secondary batteries.

[0008] In some embodiments of this application, the pH value of the positive electrode material is between 6 and 12. By adjusting 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 residual sodium and HF in the electrolyte and reducing the gas production.

[0009] In some embodiments of this application, at least a portion of the surface of the matrix material is coated with the polyanionic material, and the coating degree of the polyanionic material on the matrix material is ≥80%, which enables the coated matrix material to have better air stability and higher discharge specific capacity.

[0010] In some embodiments of this application, the matrix material is spherical or near-spherical secondary particles. By selecting matrix materials within the above-mentioned 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 energy density of Na. + The smaller the migration path, the better it is for the specific capacity to be realized. Furthermore, the high tap density of secondary particles formed by the close packing of primary particles is beneficial for increasing the compaction density of the matrix material. The energy density of the matrix material is positively correlated with both specific capacity and compaction density.

[0011] In some embodiments of this application, the matrix material is a single crystal or near-single crystal primary particle. By selecting a matrix material within the above-mentioned range, grain boundaries can be reduced, thereby reducing cracking at grain boundaries during cycling and improving the cycle performance of sodium-ion secondary batteries.

[0012] In some embodiments of this application, the primary particle size D of the polyanionic material is 20 nm to 200 nm, which can improve the charge and discharge speed, facilitate the electrochemical performance of the matrix material, and ensure the coating degree of the polyanionic material on the matrix material.

[0013] In some embodiments of this application, the cathode material satisfies at least one of the following characteristics: a) 0.65 ≤ BET ≤ 10; b) the polyanionic material has a coating degree of ≥ 90% over the matrix material; c) the primary particle size D of the polyanionic material is 20 nm to 100 nm.

[0014] In some embodiments of this application, the phosphate compound includes NaRPO4, where 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, and 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 the above, 0≤w≤1. By selecting phosphate compounds within the above range, the environmental stability of the matrix material can be improved, and the Na+ content of the matrix material during charge and discharge can also be reduced. + The effects of insertion / extraction are minimal. By selecting NASICON-type compounds within the aforementioned range, the environmental stability of the matrix material is improved while having minimal impact on its ionic conductivity, and its thermal stability is also enhanced. By selecting pyrophosphate compounds within the aforementioned range, the environmental stability of the matrix material is improved, as well as the cycle performance and thermal stability of the cathode material. By selecting fluorinated phosphate compounds within the aforementioned range, not only is the stability of the matrix material to air improved, but its energy density is also minimally affected.

[0015] A second aspect of this application provides a positive electrode sheet comprising the positive electrode material of any of the foregoing embodiments. Therefore, the positive electrode sheet provided by this application exhibits good electronic conductivity and ionic conductivity.

[0016] In some embodiments of this application, the compaction density of the positive electrode sheet is CD g / cm³. 3 CD≥2.7. By adjusting the compaction density of the positive electrode within the above range, it is beneficial to obtain a sodium-ion secondary battery with high energy density.

[0017] A third aspect of this application provides a sodium-ion secondary battery, which includes the positive electrode sheet as described in any of the foregoing embodiments. Therefore, the sodium-ion secondary battery provided by this application has good electrochemical performance.

[0018] A fourth aspect of this application provides an electrical device comprising a sodium-ion secondary battery as described in any of the foregoing embodiments. Therefore, the electrical device provided by this application has excellent performance.

[0019] The beneficial effects of this application are:

[0020] This application provides a positive electrode material, a positive electrode sheet, a sodium-ion secondary battery, and an electrical device. The positive electrode material includes a matrix material Na. x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanionic material, the polyanionic material including at least one of phosphate compounds, NASICON compounds, pyrophosphate compounds or fluorinated phosphate compounds; 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, with 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. Based on the mass of the cathode material, the mass percentage of the polyanionic material is 1% to 10%. By controlling the types of matrix material and polyanionic material in the cathode material, as well as the mass percentage of the polyanionic material, within the scope of this application, the cathode material can have a higher specific capacity, thereby improving the electrochemical performance of sodium-ion secondary batteries.

[0021] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0022] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0023] Figure 1 This is a scanning electron microscope image of the matrix material in Example 1;

[0024] Figure 2 This is a scanning electron microscope image of the substrate material surface with polyanionic material in Example 1;

[0025] Figure 3 This is a comparison chart of water absorption and degradation degree when the substrate material surface in Example 1 has polyanionic material and when it has polyanionic material. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application.

[0027] The first aspect of this application provides a cathode material comprising a matrix material Na. x Ni a Fe b Mn c M d O2, the surface of the matrix material has a polyanionic material, the polyanionic material including at least one of phosphate compounds, NASICON compounds, pyrophosphate compounds or fluorinated phosphate compounds; 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, with 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. Based on the mass of the cathode material, the mass percentage of the polyanionic material is 1% to 10%. Specifically, the mass percentage of the polyanionic material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. Regardless of any specific theory, when the mass percentage of polyanionic material is too small (e.g., less than 1%), it 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 mass percentage of polyanionic material is too large (e.g., greater than 10%), it will affect the energy density of the sodium-ion secondary battery. By controlling the mass percentage of polyanionic material within the above-mentioned range, it is possible to effectively isolate the matrix material from air, improve material stability, and thus improve the electrochemical performance of the sodium-ion secondary battery.

[0028] The inventors discovered that when the surface of the matrix material contains a polyanionic material, the contact area between the matrix material and air can be minimized, thereby achieving the purpose of isolating the matrix material from H2O and CO2 in the air. This is mainly due to two reasons: firstly, the polyanionic material itself is not sensitive to humidity, and the influence of H2O and CO2 in the air is negligible; secondly, it is itself a positive electrode material for sodium-ion secondary batteries and can undergo Na+-ion exchange. + Normal insertion and extraction, affecting the Na matrix material + The insertion and extraction have a relatively small impact, thus achieving performance improvement of the matrix material while minimizing its impact on the specific capacity of the matrix material; secondly, polyanionic materials themselves have good thermal stability, and when the surface of the matrix material has polyanionic materials, the thermal stability of the matrix material can also be improved.

[0029] In the cathode material of this application, the matrix material Na x Ni a Fe b Mn c M d The surface of O2 contains polyanionic material because polyanionic material is also a positive electrode material in sodium-ion secondary batteries, possessing both electronic and ionic conductivity, and has minimal impact on the electronic and ionic conductivity of the substrate material. The presence of polyanionic material on the substrate material surface improves the insulation effect between the substrate material and air, thus resulting in better air stability. Furthermore, because polyanionic material can react with Na+... +Intercalation / deintercalation allows the material to function as an active cathode material with minimal impact on the specific capacity of the matrix material. Furthermore, using polyanionic materials helps reduce gas generation in sodium-ion batteries. Firstly, the strong covalent bonds between X and O in polyanionic materials stabilize the O in the crystal lattice, preventing oxygen release. Therefore, sodium-ion batteries do not oxidize the electrolyte and generate gas when charged to high voltage. Secondly, the matrix material itself releases oxygen, which oxidizes the electrolyte and causes gas generation. Polyanionic materials, to some extent, isolate the contact area between the electrolyte and the matrix material, thus reducing gas generation.

[0030] 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 polyanionic material, and when the mass percentage of the polyanionic material is controlled within the scope of this application, the electrochemical performance of sodium-ion secondary batteries can be improved.

[0031] In some embodiments of this application, the specific surface area of ​​the cathode 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 of any two of the above values. In some embodiments of this application, 0.65≤BET≤10. By adjusting the value of BET within the above range, it is possible to reduce the contact area between the positive electrode material and air, thereby reducing the hygroscopicity of the positive electrode material; on the other hand, it is possible to reduce the contact area between the positive electrode material and the electrolyte, reducing side reactions between the positive electrode material and the electrolyte, thereby reducing gas production in the sodium-ion secondary battery.

[0032] In some embodiments of this application, the pH value of the positive electrode material is between 6 and 12. Exemplarily, 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 adjusting 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 residual sodium and HF in the electrolyte and lowering the gas production.

[0033] In some embodiments of this application, at least a portion of the surface of the matrix material is coated with a polyanionic material, and the coating degree of the polyanionic material on the matrix material is ≥80%. Exemplarily, the coating degree of the polyanionic material on the matrix material can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or a range of any two of the above values. In some embodiments of this application, the coating degree of the polyanionic material on the matrix material is ≥90%. The matrix material may have polyanionic material on a portion of its surface or on its entire surface. By controlling the coating degree of the polyanionic material on the matrix material within the above range, the area of ​​the matrix material in contact with air can be relatively small, resulting in better stability of the coated matrix material to air, lower hygroscopicity of the matrix material when stored in air, and reduced Na+ content in the products generated from the reaction with H2O and CO2 in the air. + The lower the content, the less Na + The less precipitation occurs in the bulk phase, the higher the discharge specific capacity of the matrix material.

[0034] In some embodiments of this application, the matrix material is spherical or near-spherical secondary particles. For example... Figure 1 As shown in the figure, the matrix material consists of near-spherical secondary particles. By selecting matrix materials within the aforementioned 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 energy density of Na. + The smaller the migration path, the better it is for the specific capacity to be realized. Furthermore, the high tap density of secondary particles formed by the close packing of primary particles is beneficial for increasing the compaction density of the matrix material. The energy density of the matrix material is positively correlated with both specific capacity and compaction density.

[0035] In some embodiments of this application, the matrix material is a single crystal or near-single crystal primary particle. By selecting a matrix material within the above-mentioned range, grain boundaries can be reduced, thereby reducing cracking at grain boundaries during cycling and improving the cycle performance of sodium-ion secondary batteries.

[0036] In some embodiments of this application, the primary particle size D of the polyanionic material is from 20 nm to 200 nm. Exemplarily, 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 of any two of the above values. In some embodiments of this application, D is from 20 nm to 100 nm. By adjusting D within the above range, the Na... + Migration pathways are improved, thereby increasing the charging and discharging speed. This also benefits the electrochemical performance of the polyanionic material itself and the electrochemical performance of the matrix material. Furthermore, the polyanionic material layer formed by the polyanionic material can be thinner while still having a high degree of coating on the matrix material.

[0037] In some embodiments of this application, the phosphate compound includes NaRPO4, where 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, and 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; fluorinated phosphate compounds include NaVPO4F or Na3(VO 1-w PO4)2F 1+2w At least one of the above, 0≤w≤1. By selecting phosphate compounds within the above range, the environmental stability of the matrix material can be improved, and the Na+ content of the matrix material during charge and discharge can also be reduced. + The effects of insertion / extraction are minimal. By selecting NASICON-type compounds within the aforementioned range—which are fast ion conductors of sodium—these compounds possess an open three-dimensional framework structure, high ionic conductivity, and good thermal stability. They not only enhance the environmental stability of the matrix material but also have minimal impact on its ionic conductivity and thermal stability. Similarly, by selecting pyrophosphate compounds within the aforementioned range, which exhibit good structural stability, thermal stability, and fast sodium ion mobility, the environmental stability of the matrix material can be improved, as well as the cycle performance and thermal stability of the cathode material. Finally, by selecting fluorinated phosphate compounds within the aforementioned range, which possess good air stability, these compounds are often used to replace PO4 due to the introduction of highly electronegative F into the material. 3- The presence of O in the matrix enhances its inductive effect, thereby increasing the voltage, resulting in a higher voltage plateau. When the surface of the matrix material has fluorinated phosphate compounds, it not only improves the stability of the matrix material to air but also has little impact on the energy density of the matrix material.

[0038] In one embodiment of this application, a polyanion material layer is formed on the surface of a substrate material. The thickness of the polyanion material layer is 0.05 μm to 5 μm, which can improve the coating degree of the substrate material and facilitate electron transport, thereby improving the kinetic performance of the sodium-ion secondary battery. This application does not impose a particular limitation on the number of polyanion material layers, as long as the purpose of this application can be achieved. For example, the polyanion material layer can be a single layer or multiple layers. When multiple layers are used, the thickness of the polyanion material layer is the total thickness of the multiple polyanion materials.

[0039] This application does not impose any particular limitation on the preparation method of the cathode material, as long as it achieves the purpose of this application. For example, the preparation method of the cathode material may include, but is not limited to, the following steps:

[0040] Weigh the matrix material raw materials according to the stoichiometric ratio, mix the matrix material raw materials and grind them evenly, calcine them at 800℃ to 1000℃ for 12h to 14h, crush them, and obtain the matrix material;

[0041] Weigh the polyanionic material raw materials according to the stoichiometric ratio, mix the polyanionic material raw materials evenly, then add the matrix material and continue mixing, and then dry, sinter, and grind to obtain the cathode material.

[0042] This application does not impose any particular limitation on the mixing method, as long as it achieves the purpose of this application, such as wet mixing, like wet ball milling. When the mixing method is wet ball milling, the milling time can be 3 to 5 hours, the ball mill speed can be 200 r / min to 400 r / min, and the milling medium can be acetone or ethanol. This application does not impose any particular limitation on the sintering method. For example, sintering can be carried out in a nitrogen-filled vacuum tube furnace, the sintering temperature can be 350°C to 800°C, and the sintering time can be 6 to 24 hours.

[0043] Typically, the specific surface area of ​​the cathode material and the degree of coating of the polyanion material onto the matrix material are controlled by adjusting the grinding time after adding the matrix material and polyanion material. For example, increasing the grinding time decreases the specific surface area; decreasing the grinding time increases the specific surface area; increasing the grinding time increases the coating degree of the polyanion material onto the matrix material; decreasing the grinding time decreases the coating degree of the polyanion material onto the matrix material. The pH of the cathode material can be controlled by simultaneously changing the grinding 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 changing 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.

[0044] A second aspect of this application provides a positive electrode sheet comprising the positive electrode material of any of the foregoing embodiments. Therefore, the positive electrode sheet provided by this application exhibits good electronic conductivity and ionic conductivity.

[0045] In some embodiments of this application, the compaction density of the positive electrode sheet is CD g / cm³. 3 CD ≥ 2.7. In some embodiments of this application, 2.8 ≤ CD ≤ 3.1. By controlling 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.

[0046] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved.

[0047] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0048] The positive electrode material layer also includes a conductive agent and a binder. This application does not particularly limit the types of conductive agents and binders, as long as they can achieve the purpose of this application. For example, the binder may include, but is not limited to, one or more of the following: 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 carboxymethyl cellulose, or potassium carboxymethyl cellulose. The conductive agent may include, but is not limited to, at least one of the following: conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode material layer; those skilled in the art can select these ratios according to actual needs, as long as the purpose of this application is achieved.

[0049] This application does not impose any particular limitation on the thickness of the positive current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive 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 also does not impose any particular limitation on the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved; for example, the thickness of the positive electrode sheet is 36 μm to 250 μm.

[0050] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0051] A third aspect of this application provides a sodium-ion secondary battery, which includes the positive electrode sheet as described in any of the foregoing embodiments. Therefore, the sodium-ion secondary battery provided by this application has good electrochemical performance.

[0052] In this 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. This application does not have particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application; for example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors. The negative electrode material layer in this application includes a negative electrode active material, a conductive agent, and a thickener. The negative electrode active material in this application may include at least one of metal oxides, metal sulfides, metal phosphides, Sb-based negative electrode materials, hard carbon, soft carbon, and metallic sodium. The aforementioned metal oxides may include at least one of cobalt oxide, iron oxide, nickel oxide, or copper oxide; the aforementioned metal sulfides may include at least one of tungsten disulfide, molybdenum disulfide, or tin disulfide; the aforementioned metal phosphides may include at least one of lithium phosphide or sodium phosphide; the aforementioned Sb-based negative electrode materials may include at least one of Sb-C composite materials, NiSb alloys, Sb₂O₃, or Sb₂O₄. In this application, there are no particular limitations 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. Similarly, there are no particular limitations on the thickness of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode sheet is 36 μm to 250 μm.

[0053] In this application, the sodium-ion secondary battery also includes a separator membrane to separate the positive and negative electrode plates, prevent internal short circuits, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitations on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0054] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with 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 membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane 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 mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may include at least one of alumina, 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 be at least one of the binders described above. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0055] In this application, the sodium-ion secondary battery further includes an electrolyte, which comprises 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. This application does not impose any particular limitation on the concentration of the sodium salt in the electrolyte, as long as it achieves the purpose of this application. For example, the concentration of the sodium salt in the electrolyte may be from 0.9 mol / L to 1.5 mol / L. Exemplarily, the concentration of the sodium salt in the electrolyte may 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. This application does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application. For example, it may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include, but are 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 aforementioned carboxylic acid ester compounds may include, but are 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, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are 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 aforementioned 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-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0056] The sodium-ion secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, electrolyte, and other components known in the art for the secondary battery. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application.

[0057] The preparation process of the sodium-ion secondary battery of this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and winding or folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a sodium-ion secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a sodium-ion secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the sodium-ion secondary battery from rising and overcharging / discharging.

[0058] A fourth aspect of this application provides an electrical device comprising a sodium-ion secondary battery as described in any of the foregoing embodiments. Therefore, the electrical device provided by this application has excellent performance.

[0059] The electrical device used in this 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, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and sodium-ion capacitors, etc.

[0060] Example

[0061] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0062] Test methods and equipment :

[0063] Specific surface area test:

[0064] According to the national standard "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​the cathode materials in their original state as described in each example and comparative example was tested using a specific surface area analyzer (model TristarⅡ3020M) by nitrogen adsorption or desorption methods.

[0065] pH value test:

[0066] Weigh 1g of the positive electrode material sample into a 100mL conical flask, add 20mL of ethylene glycol (purity 99.999%), add a magnetic stir bar, seal the flask mouth with sealing film, stir magnetically for 30min, and then filter. Dilute the filtrate to 100mL with pure water, take 50mL of the filtrate and put it into a beaker for potentiometric titration to test the residual sodium content in the positive electrode material.

[0067] The reaction formula is as follows:

[0068] Na₂CO₃ + HCl → NaCl + NaHCO₃

[0069] NaOH + HCl = NaCl + H₂O

[0070] NaHCO3 + HCl = NaCl + H2CO3

[0071] Coverage test:

[0072] The original positive electrode sheets described in each embodiment and comparative example were cut using an ion polishing machine (JEOL-IB-09010CP) to obtain cross-sections. The cross-sections were observed using a scanning electron microscope (SEM, Zeiss Sigma02-33) at an appropriate magnification (e.g., 1000x to 30000x). The perimeter L1 of the matrix material was identified using ImageJ software, and the total perimeter L2 of the uncoated area was also identified. The coating degree M = 1 - L2 / L1.

[0073] Testing of particle size in polyanionic materials:

[0074] According to the national standard "Particle size distribution by laser diffraction" (GB / T19077-2016), the particle size distribution of polyanionic materials was tested using a Malvern particle size analyzer.

[0075] Testing of material water absorption and degree of material degradation:

[0076] 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 mass of the cathode material with temperature.

[0077] Take 10 mg of the cathode material in different states from each embodiment and comparative example, place it in a thermogravimetric analyzer, set the test atmosphere to nitrogen, test the temperature from 35℃ to 400℃, and the heating rate to 5℃ / min to obtain the TG curve.

[0078] On the obtained TG curve, the weight loss of free water on the material surface is mainly from 35℃ to 120℃, and the weight loss of by-products generated by the deterioration of the material after water absorption is from 120℃ to 400℃. The weight loss ratio in the range of 35℃ to 120℃ is defined as the water absorption, and the weight loss ratio in the range of 120℃ to 400℃ is defined as the degree of deterioration.

[0079] Water absorption = 100% - (mass percentage corresponding to the TG curve at 120℃)

[0080] Deterioration level = mass percentage corresponding to TG curve at 120℃ - mass percentage corresponding to TG curve at 400℃.

[0081] The amount of water absorbed by the cathode material in its original state is recorded as W1, and the amount of water absorbed by the cathode material in state A2 is recorded as W2; the degree of degradation of the cathode material in its original state is recorded as T1, and the degree of degradation of the cathode material in state A2 is recorded as T2.

[0082] Specific capacity test:

[0083] In a dry room at 25°C and RH ≤2%, the positive electrode materials, binder polyvinylidene fluoride, and conductive agent acetylene black in different states as described in the examples and comparative examples were mixed at a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to form a uniform positive electrode slurry. This positive electrode slurry was coated onto a 10 μm thick aluminum foil (positive electrode current collector), then dried and cold-pressed. It was then punched into small circular pieces with a diameter of 14 mm to be used as positive electrode sheets. A sodium sheet was used as the negative electrode sheet, a 12 μm polypropylene separator was used, and a mixture of 1 mol / L NaPF6 and ethylene carbonate / propylene carbonate (EC / PC, volume ratio 1:1) was used as the electrolyte to assemble a coin cell half-cell.

[0084] The half-cell was charged and discharged using the LAND CT2001A battery testing system. The test was conducted within an operating voltage range of 2.0V to 4.0V, with a current density of 10mA / g, and the initial discharge specific capacity was recorded.

[0085] The discharge specific capacity of the cathode material in its original state is denoted as C1, and the discharge specific capacity of the cathode material in state A2 is denoted as C2.

[0086] Example 1

[0087] <Preparation of cathode materials>

[0088] According to NaNi 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2 (NFMA) was taken from the precursor Ni with a Dv50 of 6 μm. 0.316 Fe 0.332 Mn 0.35 (OH)₂, Na₂CO₃, and nano-Al₂O₃ were mixed, ground uniformly, calcined at 900℃ for 12 h, and then crushed to obtain NFMA matrix material with a Dv₅₀ of 6 μm. The scanning electron microscope image of the matrix material is shown below. Figure 1 As shown. Na₂CO₃, NH₄VO₃, and NH₄H₂PO₄ were weighed according to the stoichiometric ratio of Na₃V₂(PO₄)₃(NVP). The weighed raw materials were placed in a ball mill jar and wet-milled in a planetary ball mill (using acetone as the milling medium). The milling speed was set to 300 r / min, and the milling time was 3 h. Then, NFMA was added at a mass ratio of 95:5 to NVP, and milling continued for another 3 h. After milling, the material was dried in a vacuum drying oven at 60°C. Next, sintering was performed in a nitrogen-filled vacuum tube furnace. The temperature was first raised to 350°C and sintered for 4 h, then raised to 800°C and sintered for 8 h. Finally, the material was ground for 4 h to obtain a cathode material with NVP on the NFMA surface. This material at this point is recorded as the initial state.

[0089] Take 10g of the material in its original state and spread it evenly on a 100cm² surface. 2 The material was placed in a petri dish, and then placed in a humidity chamber at 25°C and 50% RH for 10 days. The material treated in the humidity chamber was then recorded as state A2.

[0090] <Preparation of the positive electrode>

[0091] In a drying room at 25°C and RH ≤2%, the above-mentioned original state positive electrode material, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed at a mass ratio of 80:10:10. N-methylpyrrolidone (NMP) solvent was added and the mixture was stirred thoroughly to form a positive electrode slurry with a solid content of 72%. A coating of 200 μm (here, thickness refers to the coating thickness on one side of the aluminum foil) was coated onto a 10 μm thick aluminum foil using a scraper. The coating was then dried at 70°C for 12 h and then cold-pressed. Finally, it was punched into small round pieces with a diameter of 14 mm to be used as the original state positive electrode sheet.

[0092] In a drying room at 25°C and RH ≤2%, the above-mentioned A2 state 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 stirred thoroughly to form a positive electrode slurry with a solid content of 72%. A 200μm coating (here, thickness refers to the coating thickness on one side of the aluminum foil) was coated onto a 10μm thick aluminum foil using a scraper. The coating was then dried at 70°C for 12 hours and then cold-pressed. Finally, it was punched into small round pieces with a diameter of 14mm to be used as A2 state positive electrode sheets.

[0093] <Preparation of Negative Electrode Sheets>

[0094] Sodium sheets are punched into small round pieces with a diameter of 14 mm to serve as negative electrode sheets.

[0095] <Preparation of Electrolyte>

[0096] In a dry room at 25℃ and humidity ≤RH2%, non-aqueous solvents ethylene carbonate and propylene carbonate were mixed at a volume ratio of 1:1. Then, NaPF6 was added to the non-aqueous solvent to dissolve and mix thoroughly to obtain the electrolyte. The molar concentration of NaPF6 was 1 mol / L.

[0097] <Preparation of the separating membrane>

[0098] A porous polyethylene film with a thickness of 12 μm (supplied by Celgard) was used.

[0099] <Preparation of Sodium-ion Batteries>

[0100] Assemble a button cell in the glove box in the following order: negative electrode, separator, and original positive electrode. This is referred to as the original button cell.

[0101] Assemble a button cell in the glove box in the following order: negative electrode, separator, and positive electrode in state A2. This button cell is denoted as state A2.

[0102] Example 2

[0103] Except for the preparation of the cathode material, which differs from Example 1, everything else is the same as in Example 1.

[0104] <Preparation of cathode materials>

[0105] According to NaNi 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2 (NFMA) was taken from the precursor Ni with a Dv50 of 6 μm. 0.316 Fe 0.332 Mn0.35 (OH)2, Na2CO3, and nano-Al2O3 were ground uniformly and calcined at 900℃ for 12 hours. The resulting material was then crushed to obtain NFMA matrix material 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 jar 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 N4FPP, and milling continued for another 3 hours. After milling, the material was dried in a vacuum drying oven at 60℃, followed by sintering in a nitrogen-filled vacuum tube furnace at 500℃ for 10 hours. Finally, the material was ground for 4 hours to obtain a cathode material with N4FPP on the NFMA surface. This material is referred to as the initial state.

[0106] Take 10g of the material in its original state and spread it evenly on a 100cm² surface. 2 The material was placed in a petri dish, and then placed in a humidity chamber at 25°C and 50% RH for 10 days. The material treated in the humidity chamber was then recorded as state A2.

[0107] Example 3

[0108] Except for the preparation of the cathode material, which differs from Example 1, everything else is the same as in Example 1.

[0109] <Preparation of cathode materials>

[0110] According to NaNi 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2 (NFMA) was taken from the precursor Ni with a Dv50 of 6 μm. 0.316 Fe 0.332 Mn 0.35(OH)2, Na2CO3, and nano-Al2O3 were ground uniformly and calcined at 900℃ for 12 hours. The resulting material was then crushed to obtain NFMA matrix material 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 jar 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 N3FPP, and milling continued for another 3 hours. After milling, the material was dried in a vacuum drying oven at 60℃, followed by sintering in a nitrogen-filled vacuum tube furnace at 500℃ for 24 hours. Finally, the material was ground for 4 hours to obtain a cathode material with N3FPP on the NFMA surface. This material is referred to as the initial state.

[0111] Take 10g of the material in its original state and spread it evenly on a 100cm² surface. 2 The material was placed in a petri dish, and then placed in a humidity chamber at 25°C and 50% RH for 10 days. The material treated in the humidity chamber was then recorded as state A2.

[0112] Example 4

[0113] Except for adjusting the mass ratio of NFMA to N4FPP to 97:3 in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0114] Example 5

[0115] Except for adjusting the mass ratio of NFMA to N4FPP to 90:10 in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0116] Example 6

[0117] Except for adjusting the grinding time after adding NFMA and N4FPP to 6h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0118] Example 7

[0119] Except for adjusting the grinding time after adding NFMA and N4FPP to 2h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0120] Example 8

[0121] Except for adjusting the grinding time after adding NFMA and N4FPP to 1 hour in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0122] Example 9

[0123] Except for adjusting the mass ratio of NFMA to N4FPP to 99:1 and the grinding time after adding NFMA and N4FPP to 1 hour in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0124] Example 10

[0125] Except for adjusting the grinding time after adding NFMA and N4FPP to 0.5h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0126] Example 11

[0127] Except for adjusting the grinding time after adding NFMA and N4FPP to 2.5h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0128] Example 12

[0129] Except for adjusting the grinding time after adding NFMA and N4FPP to 5h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0130] Example 13

[0131] Except for adjusting the sintering temperature to 400°C and the sintering time to 8h in the <Preparation of Cathode Material> section, the rest is the same as in Example 2.

[0132] Example 14

[0133] Except for adjusting the sintering temperature to 580°C and the sintering time to 12h in the <Preparation of Cathode Material> section, the rest is the same as in Example 2.

[0134] Example 15

[0135] Except for adjusting the sintering temperature to 650°C and the sintering time to 16h in the <Preparation of Cathode Material> section, the rest is the same as in Example 2.

[0136] Example 16

[0137] Except for adjusting the Dv50 of the NFMA precursor to 10 μm and the grinding time after adding NFMA and N4FPP to 6 h in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0138] Example 17

[0139] Except for adjusting the Dv50 of the NFMA precursor to 3 μm and the grinding time after adding NFMA and N4FPP to 0.5 h in the <Preparation of Cathode Material>, the rest is the same as in Example 5.

[0140] Comparative Example 1

[0141] Except for the preparation of the cathode material, which differs from Example 1, everything else is the same as in Example 1.

[0142] <Preparation of cathode materials>

[0143] According to NaNi 0.316 Fe 0.332 Mn 0.35 Al 0.002 The stoichiometric ratio of O2 (NFMA) was taken from the precursor Ni with a Dv50 of 6 μm. 0.316 Fe 0.332 Mn 0.35 (OH)2, Na2CO3, and nano-Al2O3 were mixed and ground evenly, then calcined at 900℃ for 12 hours and crushed to obtain NFMA matrix material with a Dv50 of 6 μm. This material is referred to as the original state.

[0144] Take 10g of the material in its original state and spread it evenly on a 100cm² surface. 2 The material was placed in a petri dish, and then placed in a humidity chamber at 25°C and 50% RH for 10 days. The material treated in the humidity chamber was then recorded as state A2.

[0145] Comparative Example 2

[0146] Except for adjusting the mass ratio of NFMA to N4FPP to 99.9:0.1 in the <Preparation of Cathode Material> section, the rest is the same as in Example 2.

[0147] Comparative Example 3

[0148] Except for adjusting the mass ratio of NFMA to N4FPP to 80:20 in the <Preparation of Cathode Material>, the rest is the same as in Example 2.

[0149] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Table 1.

[0150]

[0151]

[0152] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0153] Referring to Table 1, it can be seen from Examples 1 to 17 and Comparative Examples 1 to 3 that by controlling the types of matrix materials and polyanionic materials in the cathode material and the mass percentage of polyanionic materials within the scope of this application, the cathode material has a lower water absorption and degradation degree, and the prepared sodium-ion secondary battery has a higher specific capacity. This indicates that the cathode material provided in this application has good stability, and the sodium-ion secondary battery made using the cathode material provided in this application has good electrochemical performance.

[0154] The specific surface area of ​​the cathode material, the coating degree of the polyanion material onto the matrix material, the primary particle size of the polyanion material, and the compaction density of the cathode sheet typically affect the electrochemical performance of sodium-ion secondary batteries. As can be seen from Examples 1 to 17, by controlling the specific surface area of ​​the cathode material, the pH value of the cathode material, the coating degree of the polyanion material onto 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 cathode material and the electrochemical performance of the sodium-ion secondary battery.

[0155] The pH value of the cathode material typically affects the electrochemical performance of sodium-ion secondary batteries. As can be seen from Examples 2 and 4, adjusting the pH value of the cathode material within the range specified in this application is beneficial for further improving the stability of the cathode material and the electrochemical performance of the sodium-ion secondary battery.

[0156] from Figure 2 It can be seen that the positive electrode material prepared in Example 1 has a polyanionic material on the surface of its matrix material, and the matrix material is relatively completely wrapped by the polyanionic material.

[0157] Figure 3 This is a comparison chart of water absorption and degradation degree when the matrix material surface has and does not contain polyanionic materials. The curves within the rectangular dashed boxes represent the temperature range of 35℃ to 120℃, while the curves outside the rectangular dashed boxes represent the temperature range of 120℃ to 400℃. Figure 3 As can be seen, the water absorption and degradation degree of the A2 state in Example 2 are much smaller than those of the A2 state in Comparative Example 1, indicating that the cathode material provided in this application has better stability.

[0158] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode sheet, wherein, The positive electrode tab includes a positive electrode material, the positive electrode material including a base material Na x Ni a Fe b Mn c M d O2, a surface of the base material having a polyanion material, the polyanion material including at least one of a phosphate compound, a NASICON compound, a pyrophosphate compound, or a fluorinated phosphate compound; The base material Na x Ni a Fe b Mn c M d 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 The coating degree of the polyanionic material on the base material is ≥80%; The mass percentage of the polyanionic material is 1% to 10% based on the mass of the positive electrode material; The compacted density of the positive electrode plate is CD g / cm 3 , CD≥2.

7.

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

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

4. The cathode sheet of claim 1, wherein, The base material is a spherical or spherical-like secondary particle.

5. The cathode sheet of Claim 1, wherein, The base material is a single-crystal or single-crystal-like primary particle.

6. The cathode sheet of Claim 1, wherein, The primary particle size D of the polyanionic material is 20 nm to 200 nm.

7. The cathode sheet of Claim 1, wherein, The positive electrode material satisfies at least one of the following characteristics: a) the specific surface area of the positive electrode material is BET m 2 / g, 0.65 < BET < 10; b) The coating degree of the polyanionic material on the base material is ≥90%; c) The primary particle size D of the polyanionic material is 20 nm to 100 nm.

8. The cathode sheet of Claim 1, wherein, The phosphate-based compounds include NaRPO4, R selected from Fe or Mn; the NASICON-based compounds include 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-based 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 fluorophosphate-based compounds include NaVPO4F or Na3(VO 1-w PO4)2F 1+2w , 0≤w≤1.

9. A sodium-ion secondary battery comprising the positive electrode sheet of any one of claims 1 to 8.

10. An electric device comprising the sodium-ion secondary battery of claim 9.

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