Negative pole piece for sodium ion battery, preparation method of negative pole piece, battery and power utilization device

Abstract

The invention discloses a negative pole piece for a sodium-ion battery, a preparation method of the negative pole piece, the battery and a power utilization device, and the negative pole piece for the sodium-ion battery comprises a current collector; the negative electrode active material layer is arranged on at least one side of the current collector, the negative electrode active material layer comprises a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material is 2-20 [mu] m; and the dielectric layer is arranged on one side, far away from the current collector, of the negative electrode active material layer, the dielectric layer comprises first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles is 200nm-1500nm. The battery containing the negative pole piece for the sodium-ion battery is excellent in fast charging performance.

Description

Technical Field

[0001] This application belongs to the field of batteries, and specifically relates to a negative electrode sheet for a sodium-ion battery, a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Sodium-ion batteries have significant cost advantages that can be expected, and are superior in terms of safety and high and low temperature performance compared to lithium-ion batteries, and are attracting more and more attention. However, as the application scope of batteries becomes wider and wider, the requirements for the performance of sodium-ion batteries are gradually becoming more stringent. For example, they are required to have fast charging capabilities. However, the performance of the negative electrode active material in sodium-ion batteries plays a certain restrictive role in fast charging capabilities. Therefore, it is urgent to improve the performance of the negative electrode active material. Summary of the Invention

[0003] In view of the technical problems existing in the background art, this application provides a negative electrode sheet for a sodium-ion battery, aiming to improve the fast charging performance of a battery containing the same.

[0004] To achieve the above object, a first aspect of this application provides a negative electrode sheet for a sodium-ion battery, including:

[0005] A current collector;

[0006] A negative electrode active material layer provided on at least one side of the current collector, the negative electrode active material layer including a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material being 2 μm - 20 μm;

[0007] A dielectric layer provided on the side of the negative electrode active material layer away from the current collector, the dielectric layer including first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles being 200 nm - 1500 nm.

[0008] This application has at least the following beneficial effects: In the negative electrode sheet for a sodium-ion battery of this application, a dielectric layer containing a first dielectric material is provided on the side of the negative electrode active material layer away from the current collector, and the volume average particle sizes Dv50 of the negative electrode active material and the first dielectric material particles are controlled, which can significantly improve the fast charging performance of the battery.

[0009] In some embodiments, the volume average particle size Dv50 of the negative electrode active material is 3 μm - 10 μm. Thereby, the fast charging performance and cycle performance of the battery can be improved.

[0010] In some embodiments, the volume average particle size Dv50 of the first dielectric material particles is 600 nm - 800 nm. Thereby, the fast charging performance of the battery can be improved.

[0011] In some embodiments, the relative dielectric constant of the first dielectric material particles is 1000 - 10000. Thereby, the fast charging performance of the battery can be improved.

[0012] In some embodiments, the relative dielectric constant of the first dielectric material particles is 1500 - 5000. Thereby, the fast charging performance of the battery can be improved.

[0013] In some embodiments, the first dielectric material particles include at least one of barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, or barium lithium niobate. Thereby, the fast charging performance of the battery can be improved.

[0014] In some embodiments, the first dielectric material particles include doping ions, and the doping ions include trivalent rare earth metal ions, Nb 5+ 、W 5+ 、Mo 5+ 、Al 3+ 、Ga 3+ 、Cr 3+ 、Mn 3+ 、Mg 2+ 、Si 4+ or Ca 2+ and at least one of them. Thereby, the fast charging performance of the battery can be improved.

[0015] In some embodiments, the trivalent rare earth metal ions include at least one of Sc 3+ 、Y 3+ or Yb 3+ and at least one of them. Thereby, the fast charging performance of the battery can be improved.

[0016] In some embodiments, the barium titanate includes a tetragonal crystal form. Thereby, the fast charging performance of the battery can be improved.

[0017] In some embodiments, the negative electrode active material layer includes second dielectric material particles. Based on the total mass of the negative electrode active material layer, the mass ratio of the second dielectric material particles is a2, and based on the total mass of the dielectric layer, the mass ratio of the first dielectric material particles is a1, and a1 ≥ a2. Thereby, the fast charging performance of the battery can be improved.

[0018] In some embodiments, a1 ≥ 1%. Thereby, the fast charging performance of the battery can be improved.

[0019] In some embodiments, a2 ≤ 1%. Thereby, the fast charging performance of the battery can be improved.

[0020] In some embodiments, the dielectric layer includes the negative electrode active material. Thus, the fast charging performance of the battery can be improved.

[0021] In a second aspect of the present application, a method for preparing a negative electrode sheet for a sodium ion battery is provided, including:

[0022] Forming a negative electrode active material layer on at least one side of the current collector, the negative electrode active material layer including a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material being 2 μm - 20 μm;

[0023] Forming a dielectric layer on a side of the negative electrode active material layer away from the current collector, the dielectric layer including first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles being 200 nm - 1500 nm.

[0024] Thus, a battery containing the negative electrode sheet for a sodium ion battery obtained by this method has excellent fast charging performance.

[0025] In a third aspect of the present application, a battery is provided, including the negative electrode sheet for a sodium ion battery described in the first aspect of the present application or the negative electrode sheet for a sodium ion battery obtained by the method described in the second aspect of the present application. Thus, the battery has excellent fast charging performance.

[0026] In a fourth aspect of the present application, an electrical device is provided, including the battery described in the third aspect of the present application.

[0027] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present application. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0029] Figure 1 is a schematic structural diagram of a negative electrode sheet for a sodium ion battery according to an embodiment of the present application.

[0030] Figure 2 is an XRD pattern of barium titanate according to an embodiment of the present application.

[0031] Figure 3 is a schematic diagram of a battery according to an embodiment of the present application.

[0032] Figure 4 is Figure 3 exploded view of a battery according to an embodiment of the present application as shown.

[0033] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0034] Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0035] Figure 7 is Figure 6 exploded view of a battery pack according to an embodiment of the present application as shown.

[0036] Figure 8 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0037] Description of reference numerals:

[0038] 1000 negative electrode tab; 100 current collector; 200 negative electrode active material layer; 300 dielectric layer; 1 battery cell; 11 housing; 12 electrode assembly; 13 cover plate; 2 battery module; 3 battery pack; 31 upper box body; 32 lower box body. Detailed implementation manners

[0039] The embodiments of the technical solution of the present application will be described in detail below. The following embodiments are only used to illustrate the technical solution of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0040] Referring to "embodiment" herein means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0041] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] If there is no special instruction, all implementation manners and optional implementation manners of this application can be combined with each other to form new technical solutions.

[0043] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0044] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0045] Currently, from the perspective of the development of the market situation, secondary batteries are more and more widely used. Secondary batteries are not only applied to energy storage power systems such as hydraulic, thermal, wind, and solar power stations, but also widely applied to electric transportation means such as electric bicycles, electric motorcycles, and electric vehicles, as well as multiple fields such as military equipment and aerospace.

[0046] Sodium-ion batteries are expected to have significant cost advantages, and are superior to lithium-ion batteries in terms of safety and high and low temperature performance, and are attracting increasing attention. As the application range of sodium-ion batteries becomes wider and wider, the requirements for the performance of sodium-ion batteries are gradually becoming more stringent, such as the requirement for fast charging ability. At present, the fast charging performance of sodium-ion batteries is improved by adding dielectric material particles to the negative electrode sheet for sodium-ion batteries. However, due to the mismatch between the particle size of the negative electrode active material and the particle size of the dielectric material particles in the negative electrode sheet, the contact area between the negative electrode active material and the dielectric material particles is small, and the dielectric material particles need to contact the negative electrode active material to better play the role of improving the fast charging performance of the battery. Therefore, the fast charging performance of sodium-ion batteries still needs to be improved.

[0047] The negative electrode sheet for sodium-ion batteries of the present application is provided with a negative electrode active material layer and a dielectric layer in sequence on a current collector. The dielectric layer is arranged on the outside of the negative electrode active material layer, and the volume average particle sizes Dv50 of the negative electrode active material and the first dielectric material particles are respectively controlled, which can improve the fast charging performance of sodium-ion batteries.

[0048] The negative electrode sheet for sodium-ion batteries disclosed in the embodiments of the present application is applicable to sodium-ion batteries, and the batteries disclosed in the embodiments of the present application can be used in electrical equipment using the battery as a power source or various energy storage systems using the battery as an energy storage element. The electrical equipment may include, but is not limited to, mobile phones, tablets, laptop computers, electric toys, power tools, battery cars, electric vehicles, ships, spacecraft, and the like. Among them, the electric toys may include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc., and the spacecraft may include airplanes, rockets, space shuttles, and spaceships, etc.

[0049] The first aspect of the present application proposes a negative electrode sheet 1000 for sodium-ion batteries. Refer to Figure 1 , the negative electrode sheet 1000 for sodium-ion batteries includes a current collector 100, a negative electrode active material layer 200, and a dielectric layer 300. The negative electrode active material layer 200 is disposed on at least one side of the current collector 100. The negative electrode active material layer 200 includes a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material is 2 μm - 20 μm; the dielectric layer 300 is disposed on the side of the negative electrode active material layer 200 away from the current collector 100. The dielectric layer 300 includes first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles is 200 nm - 1500 nm.

[0050] In the negative electrode sheet 1000 for a sodium-ion battery of the present application, a dielectric layer 300 containing a first dielectric material is provided on the side of the negative electrode active material layer 200 away from the current collector 100, and the volume average particle sizes Dv50 of the negative electrode active material and the first dielectric material particles are respectively controlled, which can significantly improve the fast charging performance of the sodium-ion battery containing the same.

[0051] The process of the above dielectric material particles exerting their performance is speculated as follows: The volume average particle sizes Dv50 of the negative electrode active material and the first dielectric material particles are respectively controlled to make their particle sizes match. On the one hand, the distribution density of the first dielectric material particles is high, and on the other hand, the compaction density of the negative electrode sheet is high, and the negative electrode active material and the first dielectric material particles are in full contact, which is beneficial for the dielectric material particles to play a role: In the battery containing the negative electrode sheet 1000 for a sodium-ion battery of the present application during the charging process, under the action of an electric field, the positive and negative charge centers in the first dielectric material particles will be separated, forming an excellent counter electric field on the surface of the negative electrode sheet. Under the action of this counter electric field, it may cause the electron concentration on the surface of the negative electrode sheet 1000 for a sodium-ion battery to decrease. Since the SEI film (solid electrolyte interface film) formed on the surface of the negative electrode active material is formed by the reduction of the electrolyte solvent after obtaining electrons at the negative electrode active material, the decrease in the electron concentration on the surface of the negative electrode sheet may cause a thinner SEI film to be generated at the three-phase interface of the first dielectric material particles, the negative electrode active material, and the electrolyte solvent, reducing the loss of sodium ions and the impedance of the SEI film, shortening the migration path of sodium ions in the SEI film, thereby improving the fast charging performance of the battery and reducing the consumption of the electrolyte. At the same time, the dielectric layer 300 containing the first dielectric material is provided on the side of the negative electrode active material layer 200 away from the current collector 100, and the counter electric field generated by the first dielectric material particles on the surface of the negative electrode sheet 1000 for a sodium-ion battery is negatively charged, which may attract the sodium ions aggregated on the surface of the negative electrode sheet 1000 for a sodium-ion battery and make them evenly distributed, thereby reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet. In addition, the addition of the above first dielectric material particles may also reduce the sodium ion desolvation barrier, thereby increasing the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film, further improving the fast charging performance of the battery.

[0052] In the present application, the "dielectric material particles" refer to materials that exhibit excellent insulating properties in an electric field, which are a class of substances that can separate charges and store electrical energy without losing charges.

[0053] In the present application, the volume average particle size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%. The test methods for the volume average particle size Dv50 of the first dielectric material particles and the volume average particle size Dv50 of the negative electrode active material in the negative electrode sheet for a sodium-ion battery are as follows:

[0054] (1) Use a ZEISS Sigma300 scanning electron microscope to obtain the ion-polished cross-sectional morphology (CP) image of the negative electrode sheet for sodium-ion batteries, determine the specific positions of the negative electrode active material layer and the dielectric layer, then scrape the powder sequentially along the direction from the dielectric layer to the current collector, record the number of times of powder scraping for the dielectric layer and the negative electrode active material layer respectively, and then sample the dried negative electrode sheet for sodium-ion batteries by powder scraping according to the number of times of powder scraping for the dielectric layer and the negative electrode active material layer above to obtain the upper-layer powder (powder in the dielectric layer), and then continue to scrape the powder to sample to obtain the bottom-layer powder (negative electrode active material layer);

[0055] (2) Calcinate the upper-layer powder and the bottom-layer powder to 600 °C respectively, sinter all the binder and negative electrode active substances completely (for the system containing silicon-based negative electrode active material, mix and react with sodium hydroxide solution after sintering), add water and filter. The upper-layer powder is calcined to obtain the first dielectric material particles, and the bottom-layer powder is calcined to obtain the negative electrode active material;

[0056] (3) Refer to GB / T 19077-2016, and use a laser particle size analyzer (such as Malvern Master Size3000) to measure the volume average particle size Dv50 of the first dielectric material particles and the volume average particle size Dv50 of the negative electrode active material for the filtered substances respectively.

[0057] In some embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material is 2 μm - 20 μm. For example, 2 μm - 19 μm, 3 μm - 18 μm, 4 μm - 17 μm, 5 μm - 16 μm, 6 μm - 15 μm, 7 μm - 14 μm, 8 μm - 13 μm, 9 μm - 12 μm, 10 μm - 11 μm, etc. Specifically, controlling the volume average particle size Dv50 of the negative electrode active material within the above range, on the one hand, the distribution density of the first dielectric material particles is high, and on the other hand, the compaction density of the negative electrode sheet is high. The negative electrode active material and the first dielectric material particles are in full contact, which can reduce the loss of sodium ions and the impedance of the SEI film, shorten the migration path of sodium ions in the SEI film, thereby improving the fast charging performance of the battery and reducing the consumption of the electrolyte, reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet, and improving the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film, further improving the fast charging performance of the battery. In other embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material is 3 μm - 10 μm.

[0058] In some embodiments of the present application, the volume average particle size Dv50 of the first dielectric material particles is 200 nm - 1500 nm, such as 300 nm - 1450 nm, 400 nm - 1400 nm, 500 nm - 1300 nm, 600 nm - 1200 nm, 700 nm - 1100 nm, 800 nm - 1000 nm, 900 nm - 1000 nm, etc. Specifically, by controlling the volume average particle size Dv50 of the first dielectric material particles within the above range, on the one hand, the distribution density of the first dielectric material particles is high, and on the other hand, the tap density of the negative electrode sheet is high. The negative electrode active material is in full contact with the first dielectric material particles, which can reduce the loss of sodium ions and the impedance of the SEI film, shorten the migration path of sodium ions in the SEI film, thereby improving the fast charging performance of the battery and reducing the consumption of the electrolyte, reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet, increasing the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film, and further improving the fast charging performance of the battery. In some other embodiments of the present application, the volume average particle size Dv50 of the first dielectric material particles is 600 nm - 800 nm.

[0059] In some embodiments of the present application, the BET specific surface area of the first dielectric material particles is 0.8 m 2 / g - 4 m 2 / g, such as 0.9 m 2 / g - 4 m 2 / g, 1 m 2 / g - 3.8 m 2 / g, 1.5 m 2 / g - 3.5 m 2 / g, 1.8 m 2 / g - 3 m 2 / g, 2 m 2 / g - 2.5 m 2 / g, etc. Thus, the combination of the first dielectric material particles with the above particle size range and the negative electrode active material is closer, which may further improve the desolvation effect of sodium ions and further improve the cycle performance and fast charging performance of the battery.

[0060] In the present application, the BET specific surface area of the first dielectric material particles has the meaning well-known in the art and can be tested by the instruments and methods well-known in the art. For example, first scrape the powder from the negative electrode sheet, take a sample and calcine it to 600 °C until all the binder and negative active material are sintered (for the system containing silicon negative active material, after sintering, it is mixed and reacted with sodium hydroxide solution), add water and filter. Then, referring to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis test method is used to test the filtered sample, and it is calculated by the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be carried out by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics, USA.

[0061] In some embodiments of the present application, the relative dielectric constant of the first dielectric material particles is 1000-10000, such as 1000-9500, 1100-9000, 1000-8500, 1200-8000, 1500-7500, 1600-7000, 1700-6000, 1800-5000, 1900-4000, 2000-3000, 2100-2500, etc. Thus, in the negative electrode sheet for a sodium-ion battery of the present application, the first dielectric material particles with such a relative dielectric constant are used, and an excellent reverse electric field effect can be formed on the surface of the negative electrode sheet during the charging process, so that a relatively thin SEI film may be formed on the surface of the negative electrode sheet, shortening the migration path of sodium ions in the SEI film, thereby improving the fast charging performance of the battery and reducing the consumption of the electrolyte. At the same time, the addition of the first dielectric material particles may reduce the desolvation barrier of sodium ions, thereby increasing the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film, further improving the fast charging performance of the battery. In some other embodiments of the present application, the relative dielectric constant of the first dielectric material particles is 1500-5000.

[0062] In the present application, the relative dielectric constant of the first dielectric material particles in the negative electrode sheet for a sodium-ion battery refers to the relative dielectric constant at room temperature (25 ± 5 °C), and the capacitance C can be measured by an LCR tester and calculated according to the formula relative dielectric constant ε = (C × d) / (ε0 × A). C represents the capacitance, with the unit of farad (F); d represents the thickness of the specimen, with the unit of cm; A represents the area of the specimen, with the unit of cm 2 ; ε0 represents the vacuum permittivity, ε0 = 8.854 × 10 -14 F / m. It has the meaning well-known in the art and can be tested by the instruments and methods known in the art. For example, the test method is as follows:

[0063] (1) Scrape the powder from the negative electrode sheet of the sodium-ion battery, take a sample and calcine it to 600 °C until all the binder and negative electrode active materials are sintered (for the system containing silicon-based negative electrode active materials, after sintering, mix and react with sodium hydroxide solution), add water and filter to obtain dielectric material particles; then prepare the dielectric material particles into circular specimens (the sample preparation process includes: adding 40 g of binder (the binder is compounded from acrylic acid (PAA) emulsion and alcohol amine plasticizer, and its decomposition temperature is less than 300 °C) to 200 g of the dielectric material particles to be measured, stirring evenly, and slowly adding it to an automatic roller press (the roller press is a pair-roller press, the roller wheels are made of stainless steel and surface polished; the gap between the two pairs of rollers is adjustable within the range of 0.5 mm to 2 mm), roll it into a green ceramic cake with a thickness of 1 mm ± 0.15 mm, and it is qualified with no color difference on the surface, uniform cross-section and no obvious delamination; then place the green ceramic cake under the pressure plate of a punching machine (the pressure plate of the punching machine is circular, with a size of The pressure plate is made of stainless steel and surface polished), and punch it into 10 thin-layer circular ceramic chips with a diameter of 11 ± 1 mm;

[0064] (2) Debinding: Place the thin-layer circular ceramic chips obtained in step (1) on a clean and flat zirconia or alumina carrier plate, and put them into a muffle furnace together with the carrier plate. Debinding is carried out at a heating rate of 0.3 °C / min and holding at 300 °C for 6 h; after the front-side debinding is completed, take out the thin-layer circular ceramic chips, turn them over with the back side up, and repeat the above operation for back-side debinding;

[0065] (3) Silver coating: Place the thin-layer circular ceramic chips after debinding in step (2) on a clean and flat zirconia or alumina carrier plate, and use a fine brush to evenly brush the silver paste on the front side of the thin-layer circular ceramic chips. The silver paste is a high-temperature sintered conductive silver paste, and the silver paste is brushed unidirectionally 2 - 3 times with a thickness of 80 μm - 100 μm;

[0066] (4) Silver firing: First, gently scrape off the silver layer on the side of the thin-layer circular ceramic chips after silver coating in step (3) with a blade, then put the silver-coated thin-layer circular ceramic chips together with the carrier plate into a muffle furnace, and perform silver firing with a heating rate of 5 °C / min and holding at 800 °C for 2 h. After the front-side silver firing is completed, take out the thin-layer circular ceramic chips and the carrier plate, repeat steps (3) and (4) for back-side silver firing, and then use an LCR tester to measure the capacitance C and calculate according to the formula: relative dielectric constant ε = (C × d) / (ε0 × A). C represents the capacitance, with the unit of farad (F); d represents the sample thickness, with the unit of cm; A represents the sample area, with the unit of cm 2 ; ε0 represents the vacuum permittivity, ε0 = 8.854 × 10 -14F / cm. In this application, the test conditions can be 1 KHz, 1.0 V, and 25 ± 5 °C. The test standard can be based on GB / T 11297.11-2015.

[0067] In some embodiments of this application, the first dielectric material particles include at least one of barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, or barium lithium niobate. Thus, such first dielectric material particles can play an excellent role in the reverse electric field and reducing the desolvation barrier of sodium ions, thereby improving the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film, and improving the fast charging performance of the battery.

[0068] In some embodiments of this application, the first dielectric material particles include doping ions, and the doping ions include at least one of trivalent rare earth metal ions, Nb 5+ , W 5+ , Mo 5+ , Al 3+ , Ga 3+ , Cr 3+ , Mn 3+ , Mg 2+ , Si 4+ or Ca 2+ . By doping the above ions in the dielectric material particles of this application, the relative dielectric constant of the dielectric material particles can be adjusted, thereby improving the fast charging performance of the battery.

[0069] The process by which the above-doped dielectric material particles exert their performance is as follows: By doping the above ions in the dielectric material particles, the relative dielectric constant of the dielectric material particles can be adjusted, which may enable the dielectric material particles to play an excellent role in the reverse electric field and reducing the desolvation barrier of active ions, thereby improving the desolvation rate of active ions and the diffusion rate of active ions in the SEI film, and improving the fast charging performance of the battery.

[0070] As an example, the first dielectric material particles can include at least one of barium titanate doped with trivalent rare earth metal ions, barium titanate doped with pentavalent ions, lead titanate doped with pentavalent ions, or lead zirconate titanate doped with pentavalent ions. For example, the trivalent rare earth metal ions include at least one of Sc 3+ , Y 3+ or Yb 3+ , and the pentavalent ions include at least one of Nb 5+ , W 5+ or Mo 5+ . For example, the first dielectric material particles can include Ba x Ti y Al z O3 (x + y + z = 1), Ba a Yb Ti c O3 (a + b + c = 1), Pb m Ti n Nb p O3 (m + n + p = 1), etc.

[0071] In some embodiments of the present application, the first dielectric material particles are barium titanate, and the barium titanate includes a tetragonal crystal form.

[0072] In the present application, "tetragonal crystal form" refers to a crystal structure having a unit cell containing three axes, where two axes have the same length and are perpendicular to each other, and the third axis is perpendicular to the other two axes. The tetragonal crystal form of barium titanate can be obtained by XRD testing. Figure 2 is the XRD pattern of tetragonal barium titanate, and the 2θ positions of its X-ray diffraction peaks are at 22°, 31°, 38°, 45°, 56°, 66°.

[0073] Thus, using the above-mentioned tetragonal barium titanate as the dielectric material particles may further improve the desolvation rate of active ions and the diffusion rate of active ions in the SEI film, further reduce the thickness of the SEI film, and improve the cycling performance and fast charging performance of the secondary battery.

[0074] In some embodiments of the present application, the negative electrode active material layer includes second dielectric material particles. Based on the total mass of the negative electrode active material layer, the mass ratio of the second dielectric material particles is a2, and based on the total mass of the dielectric layer, the mass ratio of the first dielectric material particles is a1, where a1 ≥ a2. Thus, by adding the above-mentioned second dielectric material particles to the negative electrode active material layer and the content of the second dielectric material particles in the negative electrode active material layer is lower than or equal to the content of the first dielectric material particles in the dielectric layer, it may be beneficial to attract and uniformly distribute the sodium ions aggregated on the surface of the negative electrode sheet for sodium ion batteries, thereby reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet and improving the fast charging performance of the battery.

[0075] It can be understood that the parameters of the second dielectric material particles in the present application, such as volume average particle size Dv50, relative dielectric constant, specific surface area, etc., can refer to the first dielectric material particles and will not be elaborated here. And the composition of the first dielectric material particles and the composition of the second dielectric material particles can be the same or different.

[0076] In some embodiments of the present application, 2 ≤ a1 / a2 ≤ 10. For example, a1 / a2 can be 2 - 9, 3 - 8, 4 - 7, 5 - 6, etc. Controlling the ratio of the content of the first dielectric material particles in the dielectric layer to the content of the second dielectric material particles in the negative electrode active material layer within the above range is beneficial to giving full play to the role of the dielectric material, reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet, not only improving the fast charging performance of the battery, but also reducing the material cost. In some other embodiments of the present application, 5 ≤ a1 / a2 ≤ 8.

[0077] In the present application, the method for testing the mass ratio of the dielectric material particles (the first dielectric material particles and the second dielectric material particles) in the negative electrode active material layer and the dielectric layer of the negative electrode sheet for a sodium-ion battery includes: drying the negative electrode sheet for a sodium-ion battery, obtaining the cross-sectional morphology (CP) map of the ion-polished negative electrode sheet for a sodium-ion battery using a ZEISS Sigma300 scanning electron microscope, determining the specific positions of the negative electrode active material layer and the dielectric layer, then scraping the powder sequentially along the direction from the dielectric layer to the current collector, respectively recording the number of times of scraping the powder from the dielectric layer and the negative electrode active material layer, and then, according to the number of times of scraping the powder from the dielectric layer and the negative electrode active material layer above, scraping the powder from the dried negative electrode sheet for a sodium-ion battery to obtain the upper-layer powder (the powder in the dielectric layer), and then continuing to scrape the powder to obtain the bottom-layer powder (the negative electrode active material layer), and then respectively performing thermogravimetric tests on the upper-layer powder and the bottom-layer powder (for the system containing silicon negative electrode active material, sintering and then mixing with sodium hydroxide solution for reaction, and the filtered powder is the sample) (test conditions: oxygen atmosphere, heating from 25°C to 1000°C, heating rate of 5°C / min), and the thermogravimetric curves of the powder in the negative electrode active material layer and the thermogravimetric curve of the powder in the dielectric layer can be obtained respectively. The ordinate corresponding to the weight loss curve at 1000°C on the thermogravimetric curve of the powder in the negative electrode active material layer is the mass ratio of the first dielectric material particles in the negative electrode active material layer, and the ordinate corresponding to the weight loss curve at 1000°C on the thermogravimetric curve of the powder in the negative electrode active material layer is the mass ratio of the second dielectric material particles in the negative electrode active material layer.

[0078] In some embodiments of the present application, a1 ≥ 1%. For example, a1 can be 1% - 20%, 1.5% - 4.5%, 2% - 4%, 2.5% - 3.5%, 3% - 3.5%, etc. Specifically, controlling the content of the first dielectric material particles in the dielectric layer within the above range can give full play to the role of the first dielectric material particles, reducing the risk of dendrite formation due to the aggregation of sodium ions on the local surface of the negative electrode sheet, not only improving the fast charging performance of the battery, but also reducing the material cost. In some other embodiments of the present application, 1% ≤ a1 ≤ 5%.

[0079] In some embodiments of the present application, a2 ≤ 1%, for example, a2 can be 0.01% - 0.95%, 0.2% - 0.9%, 0.3% - 0.8%, 0.4% - 0.7%, 0.5% - 0.6%, etc. Specifically, by controlling the content of the second dielectric material particles in the negative electrode active material layer within the above range, the role of the second dielectric material particles can be fully exerted without affecting the capacity of the negative electrode sheet for sodium-ion batteries, and the risk of dendrite formation caused by the aggregation of sodium ions on the local surface of the negative electrode sheet can be reduced. This can not only improve the fast charging performance of the battery but also reduce the material cost. In some other embodiments of the present application, 0.1% ≤ a2 ≤ 1%.

[0080] In some embodiments of the present application, the thickness of the negative electrode active material layer is H2, and the thickness of the dielectric layer is H1, where H1 / H2 ≤ 1. For example, H1 / H2 can be 0.05 - 0.9, 0.1 - 0.8, 0.2 - 0.7, 0.3 - 0.6, 0.4 - 0.5, etc. Thus, with the thicknesses of the dielectric layer and the negative electrode active material layer in the above ratio, the influence of the introduction of the dielectric layer on the energy density of the battery can be reduced, and the energy density of the battery can be increased while improving the fast charging performance of the battery.

[0081] In the embodiments of the present application, the thickness is defined as known in the art and can be measured by methods and instruments known in the art. For example, the thicknesses of the negative electrode active material layer and the dielectric layer can be measured by the following method:

[0082] Dry the negative electrode sheet, use a ZEISS Sigma300 scanning electron microscope to obtain the cross-sectional morphology (CP) image of the ion-polished negative electrode sheet, and obtain the thicknesses of the negative electrode active material layer and the dielectric layer.

[0083] In some embodiments of the present application, 15μm ≤ H1 ≤ 50μm. For example, H1 can be 15μm - 49μm, 20μm - 45μm, 25μm - 40μm, 30μm - 35μm, etc. By controlling the thickness of the dielectric layer within the above range, the influence of the introduction of the dielectric layer on the energy density of the battery can be reduced, and the energy density of the battery can be increased while improving the fast charging performance of the battery. In some other embodiments of the present application, 15μm ≤ H1 ≤ 30μm.

[0084] In some embodiments of the present application, H2≥20μm. For example, H2 can be 20μm - 175μm, 30μm - 170μm, 40μm - 160μm, 50μm - 150μm, 60μm - 140μm, 70μm - 130μm, 80μm - 120μm, 90μm - 110μm, 100μm - 110μm, etc. Controlling the thickness of the negative electrode active material layer within the above range can improve the fast charging performance of the battery while increasing the energy density of the battery. In some other embodiments of the present application, H2≥30μm.

[0085] It can be understood that in the embodiments of the present application, the thickness H2 of the negative electrode active material layer and the thickness H1 of the dielectric layer both refer to the thickness on one side of the current collector.

[0086] In some embodiments of the present application, the dielectric layer includes the negative electrode active material. Specifically, by simultaneously providing a first dielectric material and a negative electrode active material in the dielectric layer, the loss of sodium ions and the impedance of the SEI film can be reduced, and the migration path of sodium ions in the SEI film can be shortened. Thereby, the fast charging performance of the battery can be improved, the consumption of the electrolyte can be reduced, the risk of dendrite formation caused by the aggregation of sodium ions on the local surface of the negative electrode sheet can be reduced, the desolvation rate of sodium ions and the diffusion rate of sodium ions in the SEI film can be increased, and the fast charging performance of the battery can be further improved.

[0087] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art for batteries. As an example, the negative electrode active material can include, but is not limited to, at least one of sodium metal, carbon materials, alloy materials, transition metal oxides and / or sulfides, phosphorus-based materials, and titanate materials. Specifically, the carbon materials can include at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials; the alloy materials can include alloy materials formed by at least one of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxides and sulfides is M x N y , where M includes at least one of Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based materials can include at least one of red phosphorus, white phosphorus, and black phosphorus; the titanate materials can include at least one of Na2Ti3O7, Na2Ti6O 13 , Na4Ti5O 12 , Li4Ti5O 12 , and NaTi2(PO4)3. These materials can all be obtained through commercial channels.

[0088] In some embodiments of the present application, the negative electrode active material layer and the dielectric layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS).

[0089] In some embodiments of the present application, the negative electrode active material layer and the dielectric layer may further optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0090] In some embodiments of the present application, the negative electrode active material layer and the dielectric layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0091] As an example, the current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer and the dielectric layer are disposed on any one or both of the two opposite surfaces of the current collector.

[0092] In some embodiments of the present application, the current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] In a second aspect of the present application, the present application proposes a method for preparing a negative electrode sheet for a sodium-ion battery, including:

[0094] Forming a negative electrode active material layer on at least one side of the current collector, the negative electrode active material layer including a negative electrode active material, and the volume average particle diameter Dv50 of the negative electrode active material being 2 μm - 20 μm;

[0095] Forming a dielectric layer on a side of the negative electrode active material layer away from the current collector, the dielectric layer including first dielectric material particles, and the volume average particle diameter Dv50 of the first dielectric material particles being 200 nm - 1500 nm.

[0096] Therefore, for the negative electrode sheet for sodium-ion batteries prepared in this application, a negative electrode active material layer and a dielectric layer are sequentially arranged on the current collector. The dielectric layer is arranged on the outer side of the negative electrode active material layer, and the volume average particle sizes Dv50 of the negative electrode active material and the first dielectric material particles are respectively controlled, which can improve the fast charging performance of the sodium-ion battery.

[0097] In some embodiments of this application, the negative electrode sheet for sodium-ion batteries can be prepared in the following manner: The components for preparing the negative electrode sheet for sodium-ion batteries described above, such as the negative electrode active material, the first dielectric material particles, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) according to a ratio to respectively form a negative electrode slurry and a dielectric layer slurry; then the negative electrode slurry and the dielectric layer slurry are sequentially coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet for sodium-ion batteries including the negative electrode active material layer and the dielectric layer can be obtained.

[0098] In some embodiments of this application, the dielectric layer slurry may also not contain the negative electrode active material.

[0099] In the third aspect of this application, this application proposes a battery, including the negative electrode sheet for sodium-ion batteries described in the first aspect of this application or the negative electrode sheet for sodium-ion batteries obtained by the method described in the second aspect of this application. Therefore, this battery has excellent fast charging performance.

[0100] Generally, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, sodium ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0101] In some embodiments of this application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material.

[0102] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0103] In some embodiments of the present application, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments of the present application, the positive electrode active material layer may further include a positive electrode active material, and the positive electrode active material can be a positive electrode active material for batteries known in the art.

[0105] As an example, the positive electrode plate is used for a sodium ion battery, and the positive electrode active material can be a positive electrode active material for sodium ion batteries known in the art. As an example, the positive electrode active material may include, but is not limited to, at least one of layered transition metal oxides, polyanion compounds, and Prussian blue analogs.

[0106] As an example of the above-mentioned layered transition metal oxides, for example, the following can be listed:

[0107] Na 1-x Cu h Fe k Mn l M 1 m O 2-y , where M 1 includes at least one of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, or Ba, 0 < x ≤ 0.33, 0 < h ≤ 0.24, 0 ≤ k ≤ 0.32, 0 < l ≤ 0.68, 0 ≤ m < 0.1, h + k + l + m = 1, 0 ≤ y < 0.2;

[0108] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 includes at least one of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, or Ba, 0 < z ≤ 0.1;

[0109] Na a Li b Ni c Mn d Fe eO2, where 0.67 < a ≤ 1, 0 < b < 0.2, 0 < c < 0.3, 0.67 < d + e < 0.8, and b + c + d + e = 1.

[0110] Examples of the above polyanion compounds include, for example:

[0111] A 1 f M 3 g (PO4) i O j X 1 3-j , where A 1 includes at least one of H, Li, Na, K, or NH4, M 3 includes at least one of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, or Zn, X 1 is at least one of F, Cl, or Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0112] Na n M 4 PO4X 2 , where M 4 includes at least one of Mn, Fe, Co, Ni, Cu, or Zn, X 2 is at least one of F, Cl, or Br, 0 < n ≤ 2;

[0113] Na p M 5 q (SO4)3, where M 5 includes at least one of Mn, Fe, Co, Ni, Cu, or Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0114] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0115] Examples of the above Prussian blue analogs include, for example:

[0116] A u M 6 v [M 7 (CN)6] w ·xH2O, where A includes H + 、NH4 + 、alkali metal cations or alkaline earth metal cations, M 6and M 7 each independently includes at least one of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A includes H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ or Ra 2+ and at least one of M 6 and M 7 each independently includes at least one of the cations of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn or W.

[0117] During the charge and discharge process of the battery, the deintercalation and consumption of Na will occur, and the molar content of Na is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Na is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Na will change.

[0118] In the listing of the positive electrode active material in this application, the molar content of oxygen is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0119] In some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer or fluorinated acrylate resin.

[0120] In some embodiments of the present application, based on the total mass of the active material layer, the mass ratio of the binder is 0.5% - 3%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0121] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers.

[0122] In some embodiments of the present application, based on the total mass of the positive electrode active material layer, the mass proportion of the conductive agent is 0.8% - 4%, such as 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0123] In some embodiments of the present application, the positive electrode plate can be prepared in the following manner: Dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; Coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0124] The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-state, or all-solid-state.

[0125] In some embodiments of the present application, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0126] In some embodiments of the present application, the battery is a sodium-ion battery, and the electrolyte salt may include at least one of sodium hexafluorophosphate, sodium difluoro(oxalato)borate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethylsulfonyl)imide.

[0127] In some embodiments of the present application, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0128] In some embodiments of the present application, the electrolytic solution may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0129] The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0130] In some embodiments, the material of the separator membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0131] The battery of the present application includes a battery cell form, a battery module form, and a battery pack form. The battery cell, battery module, and battery pack of the present application will be described below with reference to the accompanying drawings as appropriate.

[0132] In some embodiments, the positive electrode plate, negative electrode plate, and separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0133] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0134] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0135] The present application has no particular limitation on the shape of the battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 is a battery cell 1 with a square structure as an example.

[0136] In some embodiments, referring to Figure 4 , the outer package may include a housing 11 and a cover plate 13. Among them, the housing 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates enclose to form a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode plate, negative electrode plate, and separator membrane can form an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 included in the battery cell 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0137] In some embodiments, the battery can be assembled into a battery module. The number of batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0138] Figure 5 is a battery module 2 as an example. Referring to Figure 5, in the battery module 2, a plurality of battery cells 1 may be arranged in sequence along the length direction of the battery module 2. Of course, they may also be arranged in any other arbitrary manner. Further, the plurality of battery cells 1 may be fixed by fasteners.

[0139] Optionally, the battery module 2 may further include a housing having an accommodation space, and the plurality of battery cells 1 are accommodated in the accommodation space.

[0140] In some embodiments, the above battery module may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0141] Figure 6 and Figure 7 is a battery pack 3 as an example. Refer to Figure 6 and Figure 7 , in the battery pack 3, a battery box and a plurality of battery modules 2 disposed in the battery box may be included. The battery box includes an upper box body 31 and a lower box body 32. The upper box body 31 can cover the lower box body 32 and form a closed space for accommodating the battery modules 2. The plurality of battery modules 2 may be arranged in the battery box in any manner.

[0142] In addition, the present application also provides an electrical device. The electrical device includes the battery provided by the present application. The battery cell, battery module, or battery pack may be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0143] As the electrical device, the battery cell, battery module, or battery pack may be selected according to its usage requirements.

[0144] Figure 8 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or a battery module may be adopted.

[0145] Another example of the device may be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinness and lightness, and a battery may be used as the power source.

[0146] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technical or conditions noted in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For those reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchases.

[0147] Example 1

[0148] 1. Preparation of the positive electrode sheet

[0149] The positive electrode active material NaNi 0.33 Fe 0.33 Mn 0.34 O2, the conductive agent acetylene black, and the binder polyvinylidene fluoride are fully stirred and mixed evenly in an N-methylpyrrolidone solvent system according to a mass ratio of 95:3:2 to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 13 μm at a coating density of 13.6 mg / cm 2 . After drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0150] 2. Preparation of the negative electrode sheet

[0151] (1) The negative electrode active material hard carbon material, the conductive agent acetylene black, the composite binder SBR (styrene-butadiene rubber), and the dispersant sodium carboxymethyl cellulose (CMC-Na) are dispersed in deionized water as the solvent according to a weight ratio of 97:1:1:1, and after being stirred and mixed evenly, a negative electrode slurry is prepared. The negative electrode slurry is uniformly coated on the current collector aluminum foil at a coating density of 7 mg / cm 2 . After drying, a negative electrode active material layer is obtained, and the thickness of the negative electrode active material layer on one side of the current collector is 40 μm.

[0152] (2) The negative electrode active material hard carbon material, the conductive agent acetylene black, the composite binder SBR, the dispersant sodium carboxymethyl cellulose (CMC-Na), and barium titanate are dispersed in deionized water as the solvent according to a weight ratio of 96.5:1:1:1:0.5, and after being stirred and mixed evenly, a dielectric layer slurry is prepared. The dielectric layer slurry is uniformly coated on the negative electrode active material layer at a coating density of 7 mg / cm 2 . After drying, cold pressing, and slitting, the negative electrode sheet is obtained, and the thickness of the dielectric layer on one side of the current collector is 20 μm.

[0153] 3. Preparation of the electrolyte

[0154] Prepare the electrolyte in an argon - atmosphere glove box (H₂O < 0.1 ppm, O₂ < 0.1 ppm). The volume ratio of the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) is 2:2:4:2; the dosage of vinylene sulfate (DTD) is 0.5 wt% of the total mass of the electrolyte, the dosage of NaPF₆ is 6 wt% of the total mass of the electrolyte, and the dosage of NaFSI is 6 wt% of the total mass of the electrolyte.

[0155] 4. Separator

[0156] Use polyethylene with a thickness of 7 μm as the base film, and coat nano - boehmite with a thickness of 3 μm on the base film to obtain the separator.

[0157] 5. Preparation of secondary battery

[0158] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrodes to play a role in isolation, and wind them to obtain a bare battery core. Place the bare battery core in the outer package, inject the above - mentioned electrolyte and seal it to obtain the secondary battery.

[0159] The preparation methods of the sodium - ion batteries in Examples 2 - 20 and Comparative Examples 1 - 5 are the same as that in Example 1, except that the process of preparing the negative electrode sheet is different, as shown in Table 1 specifically. In Examples 1 - 20 and Comparative Examples 1 - 4, in the negative electrode paste and the dielectric layer paste, the mass ratios of the conductive agent acetylene black, the composite binder SBR, and the dispersant sodium carboxymethyl cellulose (CMC - Na) in the paste are all 1%, 1%, and 1% respectively. If the addition amount of the first dielectric material changes, the addition amount of the negative electrode active material also changes accordingly.

[0160] In Examples 14 - 16, the second dielectric material particles are exactly the same as the first dielectric material particles.

[0161] In Examples 19 - 20, except that no negative electrode active material is added to the dielectric layer paste, and the conductive agent acetylene black, the composite binder SBR, the dispersant sodium carboxymethyl cellulose (CMC - Na), and barium titanate are in a weight ratio of 1:1:1:1, the other conditions and preparation methods are the same as those in Example 1.

[0162] Table 1

[0163]

[0164] Characterize the sodium - evolution situation, charging time, and cycling performance of the batteries in Examples 1 - 20 and Comparative Examples 1 - 5. The characterization results are shown in Table 2.

[0165] (1) 25 °C fast - charge cycling performance test:

[0166] The capacity retention performance of the secondary battery was evaluated by the fast charge cycle life / cycles at 25 °C. At 25 °C, the sodium-ion batteries prepared in the examples and comparative examples were charged at a rate of 2C and discharged at a rate of 1C, and continuous cycle tests were carried out in the SOC range of 3% - 97% until the capacity of the sodium-ion battery was less than 80% of the initial capacity. The number of cycles was recorded and denoted as the cycle performance.

[0167] (2) Sodium deposition test during fast charge cycles at 25 °C:

[0168] The battery was charged to 4.2V at a rate of 4C, left standing for 5 min, then discharged to 2.5V at a rate of 1C, left standing for 5 min, and cycled 500 times according to the above charge-discharge process. Then, the negative electrode sheet was disassembled, and the surface of the disassembled negative electrode sheet was scanned under vacuum conditions using electron backscatter diffraction (EBSD) technology (where a scanning electron microscope (SEM) was used). The sodium deposition area signal and the non-sodium deposition area signal were collected respectively. The proportion of sodium deposition area = intensity of sodium deposition area signal / (intensity of sodium deposition area signal + intensity of non-sodium deposition area signal).

[0169] (3) Charge time test:

[0170] At 25 °C, the battery was charged at a constant current of 0.33C to the charge cut-off voltage of 4.2V, then charged at a constant voltage until the current was 0.05C, left standing for 5 min, and then discharged at a constant current of 0.33C to the discharge cut-off voltage of 2.5V. Its actual capacity was recorded as C0.

[0171] Then the battery is successively charged at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, 4.5C0 until the full battery charging cut-off voltage of 4.2V or the 0V negative electrode cut-off potential (whichever is reached first). After each charging is completed, it needs to be discharged at 1C0 until the full battery discharge cut-off voltage of 2.5V. Record the negative electrode potentials corresponding to 10%, 20%, 30%... 80% SOC (State of Charge) at different charging rates, plot the rate-negative electrode potential curve under different SOC states, and obtain the charging rate corresponding to 0V of the negative electrode potential under different SOC states after linear fitting. This charging rate is the charging window under this SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC respectively. According to the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC)×10%, calculate the charging time T of the battery from 10% SOC to 80% SOC. The shorter the charging time T, the better the fast charging performance of the secondary battery.

[0172] Table 2

[0173]

[0174]

[0175] Conclusion: As can be seen from Table 2, compared with Comparative Examples 1-5, for the negative electrode plates of the batteries used in Examples 1-20 of sodium-ion batteries, the volume average particle size Dv50 of the negative electrode active material and the volume average particle size Dv50 of the first dielectric material particles are simultaneously controlled. In Comparative Examples 1-4, the above two volume average particle sizes Dv50 are not simultaneously controlled, and in Comparative Example 5, no dielectric layer is provided. The sodium precipitation area of the negative electrode plates of the batteries in Examples 1-20 after cyclic disassembly is significantly smaller than that of Comparative Examples 1-5, and the charging time of the batteries in Examples 1-20 is also significantly lower than that of Comparative Examples 1-5, and the cyclic performance of the batteries in Examples 1-20 is also higher than that of Comparative Examples 1-5.

[0176] It can be seen that in the embodiments of the present application, by simultaneously controlling the volume average particle size Dv50 of the negative electrode active material and the first dielectric material particles, the negative electrode active material and the first dielectric material particles are in full contact, which can not only reduce the loss of active sodium ions and the risk of sodium precipitation, but also improve the cyclic performance and fast charging performance of the battery.

[0177] It should be noted that this application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having the same composition and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other forms constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A negative electrode sheet for a sodium ion battery, characterized in that, Comprising: Current collector; Negative electrode active material layer provided on at least one side of the current collector, the negative electrode active material layer comprising a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material being 2 μm - 20 μm; Dielectric layer provided on the side of the negative electrode active material layer away from the current collector, the dielectric layer comprising first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles being 200 nm - 1500 nm.

2. The negative electrode sheet for a sodium ion battery according to claim 1, characterized in that The volume average particle size Dv50 of the negative electrode active material is 3 μm - 10 μm.

3. The negative electrode sheet for a sodium-ion battery according to claim 1 or 2, characterized in that, The volume average particle size Dv50 of the first dielectric material particles is 600 nm - 800 nm.

4. The negative electrode sheet for a sodium ion battery according to any one of claims 1-3, characterized in that, The relative dielectric constant of the first dielectric material particles is 1000 - 10000.

5. The negative electrode sheet for a sodium ion battery according to any one of claims 1-4, characterized in that The relative dielectric constant of the first dielectric material particles is 1500 - 5000.

6. The negative electrode sheet for a sodium ion battery according to any one of claims 1-5, characterized in that, The first dielectric material particles include at least one of barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, or lithium barium lead niobate.

7. The negative electrode sheet for a sodium-ion battery according to claim 6, wherein The first dielectric material particles include doped ions, and the doped ions include at least one of trivalent rare earth metal ions, Nb 5+ , W 5+ , Mo 5+ , Al 3+ , Ga 3+ , Cr 3+ , Mn 3+ , Mg 2+ , Si 4+ or Ca 2+ .

8. The negative electrode sheet for a sodium ion battery according to claim 7, characterized in that, The trivalent rare earth metal ions include Sc 3+ , Y 3+ or Yb 3+ and at least one of them.

9. The negative electrode sheet for a sodium ion battery according to any one of claims 6-8, characterized in that, The barium titanate includes a tetragonal crystal form.

10. The negative electrode sheet for a sodium - ion battery according to any one of claims 1 - 9, characterized in that, The negative electrode active material layer includes second dielectric material particles, and based on the total mass of the negative electrode active material layer, the mass percentage of the second dielectric material particles is a2, and based on the total mass of the dielectric layer, the mass percentage of the first dielectric material particles is a1, and a1 ≥ a2.

11. The negative electrode sheet for a sodium ion battery according to claim 10, characterized in that, a1≥1％。 12. The negative electrode sheet for a sodium-ion battery according to claim 10 or 11, characterized in that, a2≤1％。 13. The negative electrode sheet for a sodium ion battery according to any one of claims 1-12, characterized in that, The dielectric layer includes the negative electrode active material.

14. A method for preparing a negative electrode sheet for a sodium-ion battery, characterized in that, Comprising: Forming a negative electrode active material layer on at least one side of the current collector, the negative electrode active material layer comprising a negative electrode active material, and the volume average particle size Dv50 of the negative electrode active material being 2 μm - 20 μm; Forming a dielectric layer on the side of the negative electrode active material layer away from the current collector, the dielectric layer comprising first dielectric material particles, and the volume average particle size Dv50 of the first dielectric material particles being 200 nm - 1500 nm.

15. A battery, characterized in that, Comprising the negative electrode sheet for a sodium ion battery according to any one of claims 1 - 13 or the negative electrode sheet for a sodium ion battery prepared by the method according to claim 14.

16. An electrical device, characterized in that, Comprising the battery according to claim 15.

Images