Positive electrode sheet and preparation method therefor, energy storage apparatus, and electric device

Abstract

A positive electrode sheet and a preparation method therefor, an energy storage apparatus, and an electric device. The positive electrode sheet comprises a current collector, a positive electrode active material layer, and a first additive, the positive electrode active material layer is arranged on at least one side of the current collector, and the first additive comprises sodium monofluorophosphate and / or sodium difluorophosphate.

Description

Positive electrode sheet and preparation method thereof, energy storage device, and electrical equipment Technical Field

[0001] The present application relates to the field of energy storage technology, and specifically to a positive electrode plate and a preparation method thereof, an energy storage device, and an electrical equipment. Background Art

[0002] During the cycle of sodium-ion batteries, the carbon negative electrode consumes the sodium element in the positive electrode active material to form a solid electrolyte interface (SEI) film. The irreversible consumption of sodium in the positive electrode active material greatly reduces the energy density of the sodium-ion battery. This problem has become one of the bottlenecks restricting the development of sodium-ion batteries. Pre-sodiumization technology can effectively supplement the irreversible sodium loss of the positive electrode active material during the cycle process, so it plays an important role in the practical application of sodium-ion batteries. The current sodium replenishment routes include the negative electrode sodium replenishment route and the positive electrode sodium replenishment route. Compared with the negative electrode sodium replenishment route, the positive electrode lithium replenishment route of adding a sodium replenisher to the positive electrode is safer and more compatible with the existing battery production process.

[0003] Currently used sodium supplements typically do not contain fluorine. Compared to non-fluorine-containing sodium supplements, fluorine in fluorine-containing sodium supplements facilitates the formation of solid electrolyte interface (CEI) films. However, existing fluorine-containing sodium supplements are highly toxic, hindering their commercial application.

[0004] Public content

[0005] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a positive electrode plate for a sodium battery, comprising a current collector, a positive electrode active material layer and a first additive, wherein the positive electrode active material layer is arranged on at least one side of the current collector, and the first additive comprises sodium monofluorophosphate and / or sodium difluorophosphate.

[0007] Compared with the prior art, the positive electrode plate of the present application includes at least the following beneficial effects: on the one hand, sodium monofluorophosphate and sodium difluorophosphate provide additional sodium ions, play the role of sodium supplement, and can effectively improve the first coulombic efficiency and first discharge capacity of the positive electrode, thereby improving the energy density of the sodium battery; on the other hand, sodium monofluorophosphate and sodium difluorophosphate also play the role of positive electrode film-forming additives, and can form by-products NaF and Na3PO3 in the process of replenishing sodium ions. NaF and Na3PO3 can form an interface layer on the surface of the positive electrode plate. The formation of the interface layer can reduce side reactions and reduce the self-discharge of the battery during high-temperature storage, thereby improving the high-temperature cycle stability of the sodium battery; sodium monofluorophosphate and sodium difluorophosphate are non-toxic, so the preparation process of the positive electrode plate is more environmentally friendly; sodium monofluorophosphate and sodium difluorophosphate are stable in nature, simple to obtain and low in cost, and are suitable for mass production.

[0008] The second aspect of the present application provides a method for preparing the aforementioned positive electrode sheet, comprising: forming a positive electrode active material layer on at least one side of a current collector; wherein a first additive is dispersed in the positive electrode active material layer, and the first additive comprises sodium monofluorophosphate and / or sodium difluorophosphate. This method for preparing the positive electrode sheet is not only simple in process and better meets the requirements of green environmental protection, but also does not require upgrading existing positive electrode sheet production equipment, making it suitable for mass production. The resulting positive electrode sheet has a high first coulombic efficiency and first discharge capacity, which can improve the energy density and cycle stability of sodium batteries.

[0009] The third aspect of the present application provides a method for preparing the aforementioned positive electrode sheet, comprising: forming a positive electrode active material layer on at least one side of a current collector; and forming a functional layer on a side of the positive electrode active material layer facing away from the current collector; wherein a first additive is dispersed in the positive electrode active material layer, and the first additive and / or a second additive is dispersed in the functional layer, and the second additive comprises at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2. This method for preparing the positive electrode sheet is not only simple in process and can better meet the requirements of green environmental protection, but also does not require upgrading existing positive electrode sheet production equipment, is suitable for mass production, and the prepared positive electrode sheet has high first coulombic efficiency and first discharge capacity, which can improve the energy density and cycle stability of sodium batteries.

[0010] A fourth aspect of the present application provides an energy storage device comprising the aforementioned positive electrode sheet. This energy storage device possesses all the features and advantages of the aforementioned positive electrode sheet, which are not further elaborated here. In general, this energy storage device has high energy density and cycle performance.

[0011] The fifth aspect of the present application provides an electrical device including the aforementioned energy storage device. The electrical device has all the features and advantages of the aforementioned energy storage device, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0013] FIG1 is a schematic structural diagram of a positive electrode sheet provided in an embodiment of the present application;

[0014] FIG2 is a schematic structural diagram of another positive electrode sheet provided in an embodiment of the present application;

[0015] FIG3 is a charge and discharge curve of the half-cells prepared in Example 1 and Comparative Example 1;

[0016] Reference numerals: 1 - current collector; 2 - positive electrode active material layer; 3 - functional layer. DETAILED DESCRIPTION

[0017] The technical solution of the present application is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present application. If specific techniques or conditions are not specified in the embodiments, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. The reagents used are not specified by the manufacturer and are all conventional products that can be obtained commercially.

[0018] The first aspect of the present application provides a positive electrode plate for a sodium battery, see Figure 1, comprising: a current collector 1, a positive electrode active material layer 2 and a first additive, wherein the positive electrode active material layer 2 is arranged on at least one side of the current collector 1, and the first additive includes sodium monofluorophosphate (Na2PO3F) and / or sodium difluorophosphate (NaPO2F2). On the one hand, sodium monofluorophosphate and sodium difluorophosphate provide additional sodium ions, acting as sodium supplements, which can effectively improve the first coulombic efficiency and first discharge capacity of the positive electrode, thereby improving the energy density of the sodium battery; on the other hand, sodium monofluorophosphate and sodium difluorophosphate also play the role of positive electrode film-forming additives, which can form by-products NaF and Na3PO3 in the process of replenishing sodium ions. NaF and Na3PO3 can form an interface layer on the surface of the positive electrode. The main components of the interface layer include Na2O, Na2CO3, NaF, Na3PO3 and other substances. The formation of the interface layer can reduce side reactions and reduce the self-discharge of the battery during high-temperature storage, thereby improving the high-temperature cycle stability of the sodium battery; sodium monofluorophosphate and sodium difluorophosphate are non-toxic, so the preparation process of the positive electrode is more environmentally friendly; sodium monofluorophosphate and sodium difluorophosphate are stable in nature, simple to obtain and low in cost, and are suitable for mass production.

[0019] In some embodiments of the present application, the first additive may preferably be sodium monofluorophosphate (Na2PO3F). Compared with sodium difluorophosphate, sodium monofluorophosphate has a higher sodium content, which is beneficial for further reducing the amount of the additive while satisfying the sodium supplementation effect.

[0020] In some embodiments of the present application, the first additive (not shown) may be dispersed in the positive electrode active material layer 2. On the one hand, the dispersion of the first additive in the positive electrode active material layer facilitates the first additive to play a role in sodium replenishment, thereby facilitating the reduction of sodium consumption in the positive electrode active material, thereby facilitating the improvement of the initial coulombic efficiency of the positive electrode. On the other hand, the dispersion of the first additive in the positive electrode active material layer facilitates the formation of an interface layer on the surface of the positive electrode sheet, thereby facilitating the reduction of side reactions, thereby facilitating the improvement of the high-temperature cycling stability of the sodium battery.

[0021] In some embodiments of the present application, referring to FIG2 , the positive electrode plate may further include a functional layer 3 , the functional layer 3 being located on the side of the positive electrode active material layer 2 facing away from the current collector 1 . In this case, at least one of the positive electrode active material layer 2 and the functional layer 3 is dispersed with a first additive. For example, in some specific embodiments, the functional layer may be dispersed with the first additive. In this case, the positive electrode active material layer may or may not contain the first additive. In other specific embodiments, the functional layer may not contain the first additive. In this case, the positive electrode active material layer may be dispersed with the first additive. The functional layer can simply serve to supplement sodium. Compared with dispersing the first additive in the positive electrode active material layer, the functional layer not only allows for full contact with the electrolyte, allowing sodium to migrate faster to the vicinity of the negative electrode plate for film formation, but also helps reduce the consumption of sodium generated by the positive electrode active material, thereby improving the initial coulombic efficiency.

[0022] In some embodiments of the present application, the mass percentage of the first additive is 4.7wt%-20wt% based on the total mass of the positive electrode active material layer. If the mass percentage of the first additive is too large, on the one hand, the relative content of the positive electrode active material in the positive electrode plate is too small, which will have a certain negative impact on the energy density of the sodium battery. On the other hand, if the mass percentage of the first additive in the functional layer is too large, its thickness is also relatively large, which can easily lead to a significant increase in the polarization of the plate, affecting the electrochemical performance of the battery. If the mass percentage of the first additive is too small, it is difficult to achieve a significant sodium supplementation effect. By controlling the mass percentage of the first additive within the above range, the present application can better balance the sodium supplementation effect and the overall performance of the sodium battery. For example, the mass percentage of the first additive can be 4.7wt%, 5wt%, 7.5wt%, 9wt%, 10wt%, 11wt%, 12wt%, 12.5wt%, 13wt%, 14wt%, 15wt%, 17.5wt% or 20wt%, etc., and preferably can be 9wt%-15wt%. As some specific examples, when preparing the positive electrode active material layer, the total mass of the positive electrode active material, conductive agent and binder can be used as a benchmark to control the mass percentage of the first additive to be 5wt%-20wt%, preferably 10wt%-15wt%, to meet the mass percentage requirement of the first additive in the positive electrode sheet.

[0023] In some embodiments of the present application, the positive electrode plate may further include a second additive, which may include at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2. The second additive only has the function of replenishing sodium. Compared with the first additive, the second additive has a lower decomposition potential, which allows the sodium element to migrate to the vicinity of the negative electrode plate at a faster rate for film formation and consumption, thereby facilitating the first coulombic efficiency of the positive electrode.

[0024] In some embodiments of the present application, the second additive may preferably be NaF and / or NaHF2. NaF and NaHF2 have higher sodium content, so a smaller amount can achieve a certain sodium supplementation effect, and the sodium supplementation effect is higher.

[0025] In some embodiments of the present application, the second additive (not shown) may be dispersed in the positive electrode active material layer 2. On this basis, the mass ratio of the first additive to the second additive may be (1-3):(1-3), and further may be 1:(1-3). This not only better balances the effects of graded sodium supplementation and the improvement of battery electrochemical performance, but also better meets the requirements of green environmental protection.

[0026] In some embodiments of the present application, the positive electrode sheet may further include a functional layer 3, and the second additive may be dispersed in the positive electrode active material layer 2 and / or the functional layer 3. For example, when the first additive is dispersed only in the positive electrode active material layer, the second additive may be dispersed in the positive electrode active material layer, the functional layer, or both. When the first additive is dispersed only in the functional layer, the second additive may be dispersed in the positive electrode active material layer, the functional layer, or both. When the first additive is dispersed in both the positive electrode active material layer and the functional layer, the second additive may be dispersed in the positive electrode active material layer, the functional layer, or both. That is, when the positive electrode sheet contains both the second additive and the functional layer 3, the second additive may be dispersed in the functional layer, or both the first and second additives may be dispersed in the functional layer. It should be noted that when the functional layer does not contain the first additive and the second additive, the positive electrode sheet may not be provided with a functional layer.

[0027] In some preferred embodiments, the positive electrode sheet may include both the positive electrode active material layer 2 and the functional layer 3. The first additive may be dispersed in the positive electrode active material layer 2, and the second additive may be dispersed in the functional layer. Compared to the second additive, the first additive is more stable. The combined use of the first and second additives not only achieves a graded sodium supplementation effect, but also reduces the impact of byproducts produced by the second additive on battery performance.

[0028] In some embodiments of the present application, when the positive electrode plate contains both a first additive and a second additive, the total mass percentage of the first additive and the second additive is 4.7 wt%-20 wt% based on the total mass of the positive electrode active material layer; for example, the total mass percentage of the first additive and the second additive can be 4.7 wt%, 5 wt%, 7.5 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 12.5 wt%, 13 wt%, 14 wt%, 15 wt%, 17.5 wt%, or 20 wt%, etc. The total mass percentage of the first additive and the second additive can preferably be 9 wt%-15 wt%. As some specific examples, when preparing the positive electrode active material layer, the total mass percentage of the first additive and the second additive can be controlled to be 5 wt%-20 wt%, preferably 10 wt%-15 wt%, based on the total mass of the positive electrode active material, the conductive agent, and the binder, to meet the total mass percentage requirement of the first additive and the second additive in the positive electrode plate.

[0029] In some embodiments of the present application, when the positive electrode plate contains both a first additive and a second additive, the mass ratio of the first additive to the second additive can be (1-3):(1-3), and further can be 1:(1-3). For example, on the basis of meeting the sodium supplement dosage requirements, the mass ratio of the first additive to the second additive can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc. In addition to supplementing sodium, the first additive also facilitates the formation of a stable CEI film on the surface of the positive electrode plate, but it is more stable than the second additive. If the mass of the first additive is too low relative to the second additive, on the one hand, it is not conducive to the formation of the CEI film, affecting the effect of improving the side reactions on the surface of the plate and improving the high-temperature cycling stability of the sodium battery, and on the other hand, it is not conducive to significantly reducing the use of the second additive with strong toxicity or corrosiveness. On the other hand, if the mass of the first additive is too high relative to the second additive, it is not conducive to rapid sodium supplementation during the formation process, making it difficult to achieve a good graded sodium supplementation effect. By controlling the mass of the first additive and the second additive within the given range, not only can the graded sodium supplementation effect and the improvement of the battery electrochemical performance be better balanced, but also more in line with the requirements of green environmental protection. Furthermore, the mass ratio of the first additive to the second additive can be 1:(1-2), which is not only conducive to achieving a better graded sodium supplementation effect, but also conducive to improving the energy density and high-temperature cycle stability of the battery, and is also conducive to further reducing the use of the second additive that is toxic or corrosive.

[0030] In some embodiments of the present application, the thickness range of the functional layer 3 can be 0.5μm to 5μm. In this case, the functional layer can be dispersed with the first additive but not the second additive, or with the second additive but not the first additive, or with the first additive and the second additive at the same time. Increasing the thickness of the functional layer is beneficial to improving the sodium supplementation effect, but if its thickness is too large, it is easy to cause the resistance of the functional layer to be higher than that of the positive electrode, causing the electrode to be polarized too much, affecting the electrochemical performance of the battery. By controlling the thickness of the functional layer within the above range, the present application can better balance the sodium supplementation effect and the overall performance of the battery. For example, on the basis of meeting the sodium supplementation dosage requirements, the thickness of the functional layer can be controlled to be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc.

[0031] For the convenience of subsequent description, this application introduces the concept of "additive", which refers to the first additive and / or the second additive; specifically, when the positive electrode active material layer or the functional layer contains only the first additive, the "additive" refers specifically to the first additive; when the positive electrode active material layer or the functional layer contains only the second additive, the "additive" refers specifically to the second additive; when the positive electrode active material layer or the functional layer contains only the first additive and the second additive, the "additive" refers to the first additive and the second additive. It should be noted that when only the positive electrode active material layer contains additives, the additives in the positive electrode active material layer need to meet the sodium supplement dosage requirements; when only the functional layer contains additives, the additives in the functional layer need to meet the sodium supplement dosage requirements; when the positive electrode active material layer contains additives and the functional layer contains additives, the sum of the additives in the positive electrode active material layer and the functional layer needs to meet the sodium supplement dosage requirements.

[0032] In some embodiments of the present application, the current collector may be aluminum foil. The type of positive electrode active material is not particularly limited, and those skilled in the art may flexibly select it within the relevant field according to actual needs. For example, the positive electrode active material may include at least one of layered transition metal oxides, polyanion compounds, and Prussian blue compounds; as some specific examples, layered transition metal oxides may include but are not limited to NaFeO2, Na 2 / 3 MnO2, polyanion compounds may include but are not limited to Na3V2(PO4)3, NaFePO4, and Prussian blue compounds may include but are not limited to Na2MnFe(CN)6·nH2O.

[0033] Based on the same application concept, the second aspect of this application provides a method for preparing the aforementioned positive electrode sheet, comprising: forming a positive electrode active material layer on at least one side of a current collector; wherein a first additive is dispersed in the positive electrode active material layer, and the first additive includes sodium monofluorophosphate and / or sodium difluorophosphate.

[0034] In some embodiments, a second additive may be dispersed in the positive electrode active material layer. The second additive may include at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2. It should be noted that the optional materials and mass percentages of the first and second additives in the positive electrode sheet have been described in detail in the previous section and will not be repeated here.

[0035] In some embodiments of the present application, the step of forming the positive electrode active material layer in which the additive is dispersed on the surface of the current collector includes:

[0036] Step S11, preparing a positive electrode slurry, in which the additives, positive electrode active material, conductive agent and binder are dispersed; specifically, the solvent of the positive electrode slurry includes but is not limited to at least one of NMP (N-methylpyrrolidone), DMF (N,N-dimethylformamide), acetone, and tetrahydrofuran. The types and relative amounts of the positive electrode active material, conductive agent and binder are not particularly limited, and those skilled in the art can flexibly select them according to actual needs.

[0037] Step S12: coating the positive electrode slurry on the surface of the current collector to obtain a positive electrode slurry layer; the coating process includes but is not limited to a slit coating process and a doctor blade coating process.

[0038] Step S13: Perform a first drying on the positive electrode slurry layer to obtain a positive electrode active material layer. It should be noted that the temperature and time of the first drying are not particularly limited and can be flexibly selected by those skilled in the art according to actual needs.

[0039] Based on the same application concept, the third aspect of the present application provides another method for preparing the aforementioned positive electrode sheet, comprising: forming a positive electrode active material layer on at least one side of a current collector; and forming a functional layer on a side of the positive electrode active material layer facing away from the current collector; wherein a first additive is dispersed in the positive electrode active material layer, and the first additive and / or a second additive are dispersed in the functional layer, the first additive comprising sodium monofluorophosphate and / or sodium difluorophosphate, and the second additive comprising at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2. It should be noted that the optional materials and mass percentages of the first and second additives in the positive electrode sheet have been described in detail in the previous section and will not be repeated here.

[0040] In some embodiments of the present application, the step of forming the positive electrode active material layer in which the additive is dispersed on the surface of the current collector may refer to steps S11 to S13; and the step of forming the functional layer on the surface of the positive electrode active material layer facing away from the current collector includes:

[0041] Step S21: preparing a sodium-supplementing suspension, wherein a first additive and / or a second additive is dispersed in the sodium-supplementing suspension. Whether to add the first additive to the sodium-supplementing suspension can be selected based on the type of additive in the positive electrode slurry layer; the solvent of the sodium-supplementing suspension can include but is not limited to at least one of NMP (N-methylpyrrolidone), DMF (N,N-dimethylformamide), acetone, and tetrahydrofuran. The concentration of the additive in the sodium-supplementing suspension can be flexibly selected according to actual needs.

[0042] Step S22: coating the sodium-supplementing suspension on the surface of the positive electrode active material layer to obtain a sodium-supplementing slurry layer; the coating process includes but is not limited to a slit coating process and a doctor blade coating process.

[0043] Step S23: performing a second drying on the sodium supplement slurry layer to obtain a functional layer. It should be noted that the temperature and time of the second drying are not particularly limited and can be flexibly selected by those skilled in the art according to actual needs.

[0044] In some embodiments, the functional layer may also be formed by other processes such as vacuum evaporation.

[0045] It should be noted that the preparation methods of the positive electrode sheets provided in the second and third aspects of this application are based on the same application concept as the positive electrode sheet of the first aspect of this application. The characteristics and effects described for the positive electrode sheets are also applicable to the preparation method of the positive electrode sheets, and will not be described in detail here. In general, the preparation method of the positive electrode sheets is not only simple in process and can better meet the needs of green environmental protection, but also does not require upgrading the existing production equipment of the positive electrode sheets, and is suitable for mass production. The prepared positive electrode sheets have high first coulombic efficiency and first discharge capacity, which can improve the energy density and cycle stability of sodium batteries.

[0046] The fourth aspect of the present application provides an energy storage device, which includes the positive electrode sheet mentioned above. The energy storage device can be a sodium battery, and the sodium battery includes a sodium metal battery and a sodium ion battery. It should be noted that the type of sodium battery is not particularly limited, and those skilled in the art can flexibly choose according to actual needs. For example, it can be a square battery, a cylindrical battery or a button battery, etc. The square battery can be a laminated battery or a wound battery. For another example, it can be a liquid battery or a semi-solid battery, etc. In addition, it should be noted that the energy storage device has all the characteristics and advantages of the positive electrode sheet mentioned above, which will not be repeated here. In general, the energy storage device has high energy density and cycle performance.

[0047] In some embodiments of the present application, the energy storage device further includes a negative electrode plate and a diaphragm, wherein the diaphragm is provided between the positive electrode plate and the negative electrode plate, and the diaphragm includes a main body and an aluminum oxide layer provided on at least one side of the main body, and the aluminum oxide can neutralize byproducts (such as HF or F2) that may be produced by fluorine-containing additives, thereby reducing the deterioration of the battery system and improving the stability of the battery.

[0048] As some specific examples, the aluminum oxide layer is located on the surface of at least one side of the body, that is, the aluminum oxide layer can be located in a partial area or the entire surface of one side of the body, or in a partial area or the entire surface of both sides of the body. Furthermore, the aluminum oxide layer is formed by, but not limited to, a coating method. For example, an aluminum oxide layer can be formed by coating an aluminum oxide slurry on the surface of the body. The prepared aluminum oxide layer includes, but is not limited to, aluminum oxide particles. For example, it can also include a small amount of binder, and the binder is used to fix the aluminum oxide particles on the surface of the body. Among them, the aluminum oxide particles have a small particle size and a large specific surface area. Fluorine-containing gas can be adsorbed onto the surface of the aluminum oxide particles by physical adsorption to generate a surface compound aluminum fluoride, which effectively neutralizes byproducts (such as HF or F2) that may be produced by fluorine-containing additives.

[0049] As some specific examples, the main body of the diaphragm may be a diaphragm base film, such as a polyethylene film, a polypropylene film, and the like.

[0050] In some embodiments of the present application, the diaphragm further includes a fiber mesh layer provided on at least one side of the body, the alumina layer includes alumina particles, and at least a portion of the alumina particles are distributed in the gaps of the fiber mesh layer. This structural arrangement can increase the contact area between the alumina particles and the electrolyte. When the electrolyte and the first additive accidentally react to generate fluorine-containing gas, the alumina particles can more promptly contact and neutralize the fluorine-containing gas, preventing the fluorine-containing gas from damaging the SEI film, thereby increasing the service life of the energy storage device. It should be noted that in this structural arrangement, the alumina layer may also include but is not limited to alumina particles. For example, the alumina layer may be composed solely of alumina particles, or may also include components such as a binder. The use of a binder is beneficial to improving the adhesion between the alumina particles and the fiber mesh layer. In addition, it should be noted that the material, thickness and mesh aperture of the fiber mesh layer are not particularly limited, as long as they can meet the embedding or fixation requirements of the alumina particles. For example, the material of the fiber mesh layer may include but is not limited to aramid. Preferably, the material of the fiber mesh layer may be an insulator or a poor conductor of electricity. For another example, the thickness of the fiber mesh layer may be no less than 0.5 times the particle size of the alumina particles, and may be 0.5 to 3 times, 0.8 times, 1 times, 1.2 times, 1.5 times, 2 times, 2.5 times, etc., of the particle size of the alumina particles, so that the thickness of the fiber mesh layer is The degree meets the requirements of the given range, which is beneficial to taking into account the thickness of the diaphragm on the basis of increasing the exposed area of ​​the alumina particles, and avoiding the excessive thickness affecting the performance of the battery such as energy density; for example, the mesh aperture of the fiber mesh layer can be no less than 0.5 times the particle size of the alumina particles, and can be selected from 0.5 to 5 times, 0.8 times, 1 times, 1.2 times, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, etc., so that the mesh aperture of the fiber mesh layer meets the requirements of the given range, which is beneficial to the effective embedding and dispersed distribution of the alumina particles. It can be understood that each alumina particle can be independently completely embedded in the gaps of the fiber mesh layer or partially embedded in the gaps of the fiber mesh layer, and the grid of each fiber mesh layer can independently distribute one or more alumina particles.

[0051] As some specific examples, the preparation of the above-mentioned diaphragm includes the following steps: preparing a coating slurry, the coating slurry containing alumina particles and a binder; attaching a fiber mesh cloth to at least one side of the body, applying the coating slurry to the surface of the fiber mesh cloth, and then drying it. After drying, an alumina layer is obtained in which the alumina particles are embedded in the gaps of the fiber mesh cloth. When the alumina layer is formed on both sides of the diaphragm, after attaching the fiber mesh cloth to both sides of the body, it can be directly double-sided coated by an equipment machine and then dried, or it can be coated and dried on one side first, and then coated and dried on the other side. It should be noted that the binder used in the coating slurry includes but is not limited to organic polymer materials, and the organic polymer materials include but are not limited to one or more of polyimide, aramid (preferably aramid micro-nanofiber), polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, and polyvinylidene fluoride. The form in which the organic polymer material is provided includes but is not limited to organic powder and suspension, and the fiber mesh cloth includes but is not limited to aramid mesh cloth.

[0052] Furthermore, the particle size Dv50 of the aluminum oxide particles satisfies: 2μm≤Dv50≤12μm, for example, Dv50 can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm, etc. The Dv50 of the alumina particles is not less than 2μm, which can ensure that there is sufficient gap between the particles, so that on the one hand, the fluorine-containing gas can contact the alumina particles faster and smoothly and undergo a neutralization reaction, and on the other hand, it also allows the active ions to smoothly pass through the alumina layer and the diaphragm body and shuttle between the positive and negative electrode sheets; while the Dv50 of the alumina particles is too large, it is not conducive to their firm embedding in the fiber mesh layer. When the diaphragm is wound together with the positive electrode sheet and the negative electrode sheet to form an electrode assembly, the alumina particles are easy to fall out of the fiber mesh layer, thereby scratching the surface of the positive electrode sheet or the negative electrode sheet, which is not conducive to the cycle life of the energy storage device; in this application, the Dv50 of the alumina particles is limited to no more than 12μm, which is more conducive to improving the firmness of their embedding in the fiber mesh layer, thereby improving the cycle life of the energy storage device.

[0053] Furthermore, the thickness of the aluminum oxide layer can be 0.1 μm to 10 μm. For example, the thickness of the aluminum oxide layer can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. An aluminum oxide layer with a thickness greater than or equal to 0.1 μm can effectively improve the insulation of the diaphragm and neutralize a large amount of fluorine-containing gas. An aluminum oxide layer with a thickness less than or equal to 10 μm can ensure the impregnation performance of the electrolyte.

[0054] Furthermore, the diaphragm may also meet at least one of the following conditions: the porosity of the diaphragm is ≥30%, the average pore size of the diaphragm is ≥25nm, the ionic conductivity of the diaphragm is ≥1.1mS / cm, and the thickness of the body is 2μm to 20μm. Making the diaphragm meet the given condition range is more conducive to the energy storage device obtaining better electrochemical performance.

[0055] The fifth aspect of the present application provides an electrical device, including the above-mentioned energy storage device, which is used to provide electrical energy. Specifically, the energy storage device can serve as a power source for the electrical device, and can also serve as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, an energy storage module, an energy storage cabinet or an energy storage container.

[0056] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0057] Example 1

[0058] (1) Preparation of positive electrode sheet

[0059] The positive electrode active material (Na 0.67 Ni 0.33 Mn 0.67 O2), a conductive agent (conductive carbon black SP) and a binder (polyvinylidene fluoride PVDF) are dispersed in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 95.5:2:2.5, and a first additive (Na2PO3F) is added to obtain a positive electrode slurry. The amount of the first additive is 5% based on the total mass of the positive electrode active material, the conductive agent and the binder. The positive electrode slurry is coated on the surface of the current collector to obtain a positive electrode slurry layer. The positive electrode slurry layer is dried and rolled to obtain a positive electrode active material layer with a thickness of 90 μm. The surface density of the positive electrode active material layer is 14 mg / cm 2 ;

[0060] The second additive (NaF) is dispersed in N-methylpyrrolidone (NMP) solvent to obtain a sodium-supplementing suspension; the sodium-supplementing suspension is coated on the surface of the positive electrode active material layer to obtain a sodium-supplementing slurry layer; the sodium-supplementing slurry layer is dried to obtain a functional layer with a thickness of 2 μm, and the mass ratio of the additive in the functional layer to the additive in the positive electrode active material layer is 1:1.

[0061] (2) Preparation of full battery

[0062] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the electrolyte is injected into the electrode assembly; then, after vacuum packaging, standing, forming, and shaping, a sodium battery is obtained. Among them, the negative electrode sheet includes a negative electrode collector and a negative electrode active material layer located on the surface of the negative electrode collector. The negative electrode active material layer is formed by a negative electrode active material (hard carbon), a conductive agent (conductive carbon black SP), carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR in a mass ratio of 95.5:1:1:2.5. The compacted density of the negative electrode active material layer is 0.95g / cm 3 , with a thickness of 150 μm; the diaphragm is a ceramic diaphragm with a single-sided Al2O3 coating (the ceramic diaphragm is formed by attaching an aramid fiber mesh cloth to one side of the base membrane, and coating the aramid fiber mesh cloth with a coating slurry including alumina particles and PVDF, and drying), the thickness of the Al2O3 coating is 2 μm, the base membrane is PP (polypropylene), and the thickness of the base membrane is 16 μm; the concentration of the electrolyte NaClO4 in the electrolyte is 1 mol / L, and the solvent is a composite solvent of polypropylene carbonate PC + polyvinyl carbonate EC + dimethyl carbonate DMC.

[0063] (3) Preparation of half-cell

[0064] Metal sodium sheet was selected as the negative electrode sheet, porous glass fiber was selected as the separator, the concentration of NaPF6 in the electrolyte was 1 mol / L, the solvent of the electrolyte was a mixed solvent, and the volume ratio of ethylene carbonate EC, propylene carbonate PC and dimethyl carbonate DMC in the mixed solvent was 1:1:1. The electrolyte also contained 5% by volume of fluoroethylene carbonate FEC. The button batteries were assembled in an argon glove box with a water oxygen value below 0.1 ppm.

[0065] Examples 2 to 19-Comparative Examples 1-2

[0066] The differences between Examples 2 to 19-Comparative Examples 1-2 and Example 1 are detailed in Table 1. It should be noted that the total amount of additives in the positive electrode plate in Table 1 is defined based on the total mass of the positive electrode active material, conductive agent, and binder, that is, the total amount of additives = total mass of additives / (mass of positive electrode active material + mass of conductive agent + mass of binder) × 100%. When the positive electrode plate contains only the first additive, the total amount of additives refers to the amount of the first additive; when the positive electrode plate contains only the second additive, the total amount of additives refers to the amount of the second additive; when the positive electrode plate contains the first additive and the second additive, the total amount of additives refers to the total amount of the first additive and the second additive; when the additive is dispersed only in the positive electrode active material layer, the "total amount of additives" refers to the amount of additives in the positive electrode active material layer; when the additive is dispersed in both the positive electrode active material layer and the functional layer, the "amount of additives" refers to the total amount of additives in the positive electrode active material layer and the functional layer.

[0067] Among them, the difference between Examples 1-5 is that the amount of the second additive in the functional layer is different; the difference between Example 3, Examples 6-9, and Example 13 is that the thickness of the Al2O3 coating in the full battery separator is different; the difference between Example 10 and Example 3 is that the types of additives in the functional layer are different; the difference between Examples 11-12 and Example 3 is that the types of the first additives in the positive electrode active material layer are different; the difference between Examples 15, 16, 18, and 19 and Example 1 is that the types of additives in the functional layer are different; Example 14, Example 17, and Comparative Examples 1-2 do not contain a functional layer, and the difference between Example 14, Example 17, and Comparative Example 2 is that the types of additives in the positive electrode active material layer are different; Comparative Example 1 does not contain an additive.

[0068] The amounts of additives in the positive electrode active material layers of Examples 1-19 and Comparative Example 2 were the same; when the amount of additives in the positive electrode active material layer changed, the total mass of the additives and the positive electrode active material was kept unchanged by adjusting the amount of the positive electrode active material.

[0069] Table 1 Differences between Examples 2 to 19 and Comparative Examples 1-2 and Example 1

[0070] Performance testing:

[0071] (1) The half-cells prepared in Example 1 and Comparative Example 1 were subjected to charge and discharge capacity tests under the same conditions. The test method was as follows: The half-cell was mounted on a blue battery tester and placed in a test environment at 25±2°C. The following procedure was set: let it rest for 10 minutes → charge at a constant current of 0.1C to 4.2V → let it rest for 10 minutes → discharge at a constant current of 0.1C to 2.0V. The above steps were repeated three times as a repeating unit.

[0072] Figure 3 shows a comparison of the charge and discharge curves of the half-cells prepared in Example 1 and Comparative Example 1. As shown in Figure 3, the charge and discharge specific capacity of the half-cell prepared in Example 1 is higher than that of Comparative Example 1, indicating that adding additives to the positive electrode sheet can increase the initial charge and discharge specific capacity of the sodium battery, thereby improving the energy density of the sodium battery.

[0073] (2) The electrochemical performance of the full batteries prepared in Examples 1-19 and Comparative Examples 1-2 was tested under the same conditions. The test method is as follows. The results are shown in Table 2.

[0074] Initial discharge capacity test method: Clamp the full battery with a fixture and install it on the test instrument. After the full battery is formed and aged, place it in a test environment at 25±2℃. Set the procedure as follows: Let it stand for 10 minutes → discharge at a constant current of 0.1C to 2.0V → let it stand for 10 minutes → charge at a constant current of 0.1C to 4.0V → let it stand for 10 minutes → discharge at a constant current of 0.1C to 1.5V, then test the battery capacity.

[0075] The first coulombic efficiency test method is as follows: after the full battery formation is completed, stand for 30 minutes → 0.02C constant current charge to the voltage of 2.8V → 0.05C constant current charge to the voltage of 3.4V → 0.1C constant current charge to the voltage of 4.0V → stand for 20 minutes, perform battery capacity test to obtain charging capacity C1; then, 0.1C current constant current discharge to 1.5V, perform battery capacity test to obtain discharge capacity D1; then, 0.1C current constant current charge to 4.0V, perform battery capacity test to obtain charging capacity C2; then, 0.1C current constant current discharge to 1.5V, perform battery capacity test to obtain discharge capacity D2; calculate the first coulombic efficiency, first coulombic efficiency = D2 / (C1+C2-D1)*100%.

[0076] Cycle performance test method: 1) 25℃ battery cycle performance test: install the full battery on the test instrument, place it in a 25±2℃ environment, let it stand for 60min→1.0C constant current discharge to 1.5V→let it stand for 10min→1.0C constant current charge to 4.0V→let it stand for 10min→1.0C constant current discharge to 4.0V, use the above steps as a repeating unit, repeat the above steps 100 times, and perform a battery capacity test to obtain the battery capacity after 100 cycles at 25℃, and the capacity retention rate after 100 cycles at 25℃ = battery capacity after 100 cycles at 25℃ / first discharge capacity at 25℃ × 100%; 2) 45℃ battery cycle performance test: the difference between it and the 25℃ battery cycle performance test method is that the battery is placed in a 45±2℃ environment to obtain the battery capacity after 100 cycles at 45℃ and the first discharge capacity at 45℃, and then the capacity retention rate after 100 cycles at 45℃ is calculated.

[0077] Table 2 Test results of full batteries in Examples 1 to 19 and Comparative Examples 1-2

[0078] Results and Conclusions:

[0079] As can be seen from Table 2, at least one of the positive electrode active material layer and the functional layer in the positive electrode sheet contains sodium monofluorophosphate and / or sodium difluorophosphate, which can effectively improve the first coulombic efficiency and the first discharge capacity of the positive electrode, and improve the room temperature and high temperature cycle stability of the sodium battery; further, compared with only the positive electrode active material layer dispersed with the first additive, the surface of the positive electrode active material layer has a functional layer, and the material of the functional layer includes the first additive and / or the second additive, which can further improve the first coulombic efficiency; further, the material of the functional layer includes the second additive, which can further improve the first coulombic efficiency; from the comparison between Example 3 and Example 10, it can be seen that compared with the first additive dispersed in the functional layer, the second additive dispersed in the functional layer can further improve the first coulombic efficiency; from the comparison between Examples 14 and 17 and Comparative Example 2, it can be seen that compared with conventional fluorine-containing additives, the first additive can improve the cycle performance of the sodium battery; from the comparison between Example 13 and Example 3, From the comparison of Figures 6-9, it can be seen that compared with conventional diaphragms without Al2O3 coating, ceramic diaphragms with Al2O3 coating can improve the cycle performance of sodium batteries.

[0080] In the description of this application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B means that A exists alone, A and B exist at the same time, and B exists alone.

[0081] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0082] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limiting the present application. Persons skilled in the art may vary, modify, replace, and modify the above embodiments within the scope of the present application. Persons skilled in the art may combine and associate the different embodiments or examples described in this specification, as well as features of the different embodiments or examples, without conflicting with each other.

Claims

1. A positive electrode sheet for a sodium battery, wherein: include: A current collector, a positive electrode active material layer and a first additive, wherein the positive electrode active material layer is arranged on at least one side of the current collector, and the first additive comprises sodium monofluorophosphate and / or sodium difluorophosphate.

2. The positive electrode sheet according to claim 1, wherein: The first additive is dispersed in the positive electrode active material layer.

3. The positive electrode sheet according to claim 1 or 2, wherein: The device further comprises a functional layer, wherein the functional layer is located on a side of the positive electrode active material layer away from the current collector, and the first additive is dispersed in the functional layer.

4. The positive electrode sheet according to claim 3, wherein: The thickness of the functional layer ranges from 0.5 μm to 5 μm.

5. The positive electrode sheet according to claim 1 or 4, wherein: Based on the total mass of the positive electrode active material layer, the mass percentage of the first additive is 4.7wt%-20wt%.

6. The positive electrode sheet according to claim 5, wherein: The mass percentage of the first additive is 9wt%-15wt%.

7. The positive electrode sheet according to claim 1 or 2, wherein: It also includes a second additive, which includes at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2.

8. The positive electrode sheet according to claim 7, wherein: The second additive is dispersed in the positive electrode active material layer; and / or, The mass ratio of the first additive to the second additive is (1-3):(1-3).

9. The positive electrode sheet according to claim 7 or 8, wherein: The mass ratio of the first additive to the second additive is 1:(1-3).

10. The positive electrode sheet according to claim 7, wherein: Also includes: A functional layer, wherein the functional layer is located on a side of the positive electrode active material layer away from the current collector, the second additive is dispersed in the functional layer, or the first additive and the second additive are dispersed in the functional layer.

11. The positive electrode sheet according to claim 10, wherein: The first additive is dispersed in the positive electrode active material layer, and the second additive is dispersed in the functional layer.

12. The positive electrode sheet according to claim 10 or 11, wherein: At least one of the following three conditions is met: The thickness of the functional layer ranges from 0.5 μm to 5 μm; The mass ratio of the first additive to the second additive is (1-3):(1-3); Based on the total mass of the positive electrode active material layer, the total mass percentage of the first additive and the second additive is 4.7wt%-20wt%.

13. The positive electrode sheet according to claim 12, wherein: The total mass percentage of the first additive and the second additive is 9wt%-15wt%; and / or, The mass ratio of the first additive to the second additive is 1:(1-3).

14. A method for preparing a positive electrode sheet according to any one of claims 1 to 13, wherein: include: forming a positive electrode active material layer on at least one side of the current collector; Wherein, a first additive is dispersed in the positive electrode active material layer, and the first additive includes sodium monofluorophosphate and / or sodium difluorophosphate.

15. A method for preparing a positive electrode sheet according to any one of claims 1 to 13, wherein: include: forming a positive electrode active material layer on at least one side of the current collector; forming a functional layer on a side of the positive electrode active material layer away from the current collector; Among them, a first additive is dispersed in the positive electrode active material layer, the first additive and / or the second additive are dispersed in the functional layer, and the second additive includes at least one of Na2O, Na2O2, Na2CO3, Na2S, Na3P, NaN3, NaNiO2, NaCrO2, NaFeO2, Na3C6H5O7, Na2C6O6, NaF, and NaHF2.

16. An energy storage device, wherein: The invention comprises the positive electrode sheet according to any one of claims 1 to 13.

17. The energy storage device according to claim 16, wherein: It also includes a negative electrode plate and a separator. The separator is arranged between the positive electrode plate and the negative electrode plate. The separator includes a body and an aluminum oxide layer arranged on at least one side of the body.

18. The energy storage device according to claim 17, wherein: At least one of the following conditions is met: The diaphragm further comprises a fiber mesh layer disposed on at least one side of the body, the alumina layer comprises alumina particles, and at least a portion of the alumina particles are distributed in the gaps of the fiber mesh layer; The porosity of the diaphragm is ≥30%; The average pore size of the diaphragm is ≥25nm; The ionic conductivity of the diaphragm is ≥1.1 mS / cm; The thickness of the body is 2 μm to 20 μm.

19. The energy storage device according to claim 18, wherein: The particle size Dv50 of the aluminum oxide particles satisfies: 2 μm≤Dv50≤12 μm.

20. The energy storage device according to any one of claims 17 to 19, wherein: The thickness of the aluminum oxide layer is 0.1 μm to 10 μm.

21. An electrical equipment, characterized in that it comprises the energy storage device according to any one of claims 16 to 20.

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