Negative electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, the negative electrode film layer is located on at least one surface of the negative electrode current collector, the negative electrode film layer comprises first negative electrode active material particles and second negative electrode active material particles, the first negative electrode active material particles comprise a plurality of adsorption pores, the tap density of the first negative electrode active material particles is 0.4 g / cm 3 ~1.4 g / cm 3 ; the second negative electrode active material particles have a layered structure, and the tap density of the second negative electrode active material particles is 0.05 g / cm 3 ~1.5 g / cm 3 , wherein, based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 70%~95%, and the mass percentage of the second negative electrode active material particles is 5%~30%, and the compaction density PD of the negative electrode film satisfies: 0.8 g / cm 3 ≤PD≤1.3 g / cm 3 .

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] With the increasing prominence of energy and environmental issues, the new energy industry has received growing attention. Lithium-ion batteries, due to their high energy density and good cycle performance, have been widely used in recent years as an important new type of energy storage device. However, due to the scarcity of active materials for lithium-ion batteries, battery costs remain high, and the industry also faces serious challenges such as resource depletion. Therefore, there is a need to develop other low-cost metal-ion secondary battery systems.

[0003] Sodium-ion batteries have become a popular research area in recent years due to their advantages such as low cost, abundant resources, and manufacturing process similar to lithium-ion batteries.

[0004] However, limited by the relatively low specific capacity and voltage plateau of current sodium-ion battery cathode and anode materials, the energy density of sodium-ion batteries remains significantly lower than that of lithium-ion batteries, hindering their commercial application. Furthermore, the initial coulombic efficiency and rate performance of sodium-ion batteries also need improvement. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device that can effectively improve the energy density and rate performance of sodium-ion batteries.

[0006] A first aspect of this application provides a negative electrode sheet, comprising: a negative electrode current collector; and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer includes first negative electrode active material particles and second negative electrode active material particles. The first negative electrode active material particles include a plurality of adsorption pores, and the tap density of the first negative electrode active material particles is 0.4 g / cm³. 3 ~1.4g / cm 3 0.6g / cm³ is an option. 3 ~1.0g / cm 3 The second negative electrode active material particles have a layered structure, and the tap density of the second negative electrode active material particles is 0.05 g / cm³. 3 ~1.5g / cm 3 In this process, based on the total mass of the first and second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 70%–95%, optionally 80%–95%; the mass percentage of the second negative electrode active material particles is 5%–30%, optionally 5%–10%, and the compaction density PD of the negative electrode membrane satisfies: 0.8 g / cm³.3 ≤PD≤1.3g / cm 3 Optionally, 1.0 g / cm³ 3 ≤PD≤1.2g / cm 3 .

[0007] The first negative electrode active material particles contain multiple adsorption pores, and the tap density is within the aforementioned suitable range. After cold pressing, the interior of the first negative electrode active material particles still retains a sufficient number of adsorption pores. Therefore, Na... + The first negative electrode active material particles can be readily adsorbed and deintercalated during charging and discharging. Furthermore, the second negative electrode active material particles have a layered structure. During cold pressing, these particles can fill the gaps between multiple first active material particles or appear on the surface of the first particles. Through their layered structure, they exhibit a sliding effect, ensuring close contact between the particles during cold pressing and increasing the powder compaction density. This results in a suitable compaction density for the cold-pressed negative electrode film. Consequently, the close contact of the negative electrode active material particles in the negative electrode film improves the electron and sodium ion transport performance of the negative electrode, thereby enhancing the rate performance of the sodium-ion battery. However, due to their layered structure, the second negative electrode active material particles have a limited ability to adsorb and intercalate sodium ions compared to the first particles. Maintaining the appropriate content of the first and second negative electrode active material particles within the aforementioned range further ensures the high energy density of the sodium-ion battery.

[0008] In any embodiment, the median particle size D50 of the first negative electrode active material particles is 1 μm to 50 μm, and can be selected as 5 μm to 10 μm.

[0009] The median particle size of the first negative electrode active material particles is within the aforementioned suitable range. This not only improves the production capacity of the negative electrode sheet but also ensures that the surface of the first negative electrode active material particles has an appropriate number of active sites, thereby improving the coulombic efficiency of the sodium-ion battery. Furthermore, the suitable median particle size of the first negative electrode active material particles not only ensures good electron and sodium-ion transport performance within the particles but also results in low interparticle interface resistance. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion battery to possess high energy density, high coulombic efficiency, good rate performance, and good cycle performance.

[0010] In any embodiment, the elongation E of the negative electrode current collector satisfies: 0.1% ≤ E ≤ 0.2%, optionally, 0.1% ≤ E ≤ 0.15%. This application uses a compound of first and second negative electrode active material particles, utilizing the sliding function of the second negative electrode active material particles to ensure close contact between the particles during cold pressing, thereby achieving a high powder compaction density. Therefore, compared to negative electrode active material particles with lower compaction density, under the same cold pressing parameters, the negative electrode current collector of this application can have a lower elongation, thus maintaining good conductivity and mechanical strength.

[0011] In any embodiment, the negative electrode sheet according to any one of claims 1-3, wherein the single-sided coating weight CW of the negative electrode film is 2 mg / cm³. 2 ~13mg / cm 2 When the single-sided coating weight of the negative electrode film is within a suitable range, it not only ensures suitable migration paths for electrons and sodium ions within the negative electrode sheet, but also enables the negative electrode sheet to possess a suitable capacity. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion batteries to exhibit excellent rate performance and high energy density.

[0012] In any embodiment, the negative electrode film layer satisfies: 30% ≤ P ≤ 60%, optionally, 45% ≤ P ≤ 55%, where P = [1 - (CW) / (d*PA)] * 100%, d = d0 / (1 + E), CW represents the single-sided coating weight of the negative electrode film layer, PA represents the true density of the single-sided negative electrode film layer, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of the single-sided negative electrode film layer. When the parameter P of the negative electrode film layer satisfies the above conditions, it can be considered that the increase in the compaction density of the negative electrode film layer is mainly achieved through the slippage of the second negative electrode active material particles during cold pressing, and has no significant effect on the porosity of the negative electrode film layer. Thus, not only is the compaction density of the negative electrode film layer improved, but the electrolyte wettability of the negative electrode film layer is also maintained, thereby ensuring that the negative secondary battery has high energy density and good rate performance.

[0013] In any embodiment, the first negative electrode active material particles are selected from one or more of hard carbon, soft carbon, and mesophase carbon microspheres; the second negative electrode active material particles are selected from one or more of artificial graphite, natural graphite, and graphene. The aforementioned first and second negative electrode active material particles enable the negative electrode film to possess high compaction density and excellent electronic conductivity. When applied to sodium-ion batteries, this allows the sodium-ion battery to possess high compaction density and good cycle performance.

[0014] In any embodiment, the first negative electrode active material particles include one or more of the following: irregularly shaped first negative electrode active material particles, spherical first negative electrode active material particles, or near-spherical first negative electrode active material particles. When the first negative electrode active material particles have the above-described morphology, the processing flexibility of the negative electrode sheet can be improved, and sodium-ion batteries can have high energy density.

[0015] In any embodiment, the first negative electrode active material particles include one or more of irregularly shaped hard carbon particles, spherical hard carbon particles, or near-spherical hard carbon particles. When the first negative electrode active material particles are selected from the hard carbon particles with the above-mentioned morphology, the negative electrode active material particles can have low cost and high theoretical specific capacity, thereby improving the energy density, rate performance, and cycle stability of sodium-ion batteries.

[0016] In any embodiment, the compaction density PD of the single-sided negative electrode film layer satisfies: 1.0 g / cm³ 3 ≤PD≤1.2g / cm 3 The negative electrode film layer satisfies the following conditions: 30% ≤ P ≤ 60%, optionally 45% ≤ P ≤ 55%, where P = [1 - (CW) / (d*PA)] * 100%, d = d0 / (1+E), CW represents the coating weight on one side of the negative electrode film layer, PA represents the true density of the single-sided negative electrode film layer, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of the single-sided negative electrode film layer. When the parameter P of the negative electrode film layer satisfies the above conditions, it can be considered that the increase in the compaction density of the negative electrode film layer is mainly achieved through the slippage function of the second negative electrode active material particles during cold pressing. Therefore, for hard carbon particles, they do not need to undergo deformation or slippage to enable the negative electrode film layer to have a high compaction density. Thus, hard carbon materials can be applied to sodium-ion batteries, giving sodium-ion batteries a broad application prospect.

[0017] In any embodiment, the negative electrode film layer further includes a flexible binder, which includes one or more of the following: styrene-acrylic emulsion, copolymer of vinylidene fluoride and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and acrylates, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber. The inclusion of the aforementioned flexible binder in the negative electrode film layer provides excellent flexibility. Therefore, during cold pressing, the negative electrode film layer exhibits lower stress, the negative electrode active material particles are more easily stacked, and the negative electrode current collector possesses lower elongation. This further increases the compaction density of the negative electrode film layer, thereby improving the energy density of the sodium-ion battery.

[0018] In any embodiment, based on the total mass of the negative electrode film, the negative electrode film comprises: 80wt% to 97wt% of negative electrode active material particles, 0wt% to 5wt% of conductive agent, 2wt% to 10wt% of binder, and 0.5wt% to 5wt% of dispersant, wherein the negative electrode active material particles include first negative electrode active material particles and second negative electrode active material particles. The negative electrode film includes the above components, and the content of each component is within the above-mentioned suitable range, which ensures that the negative electrode film has high compaction density and good electron and sodium ion transport performance. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion batteries to have high energy density and good cycle performance.

[0019] A second aspect of this application provides a secondary battery, including the negative electrode sheet of the first aspect of this application.

[0020] The secondary battery of this application includes the negative electrode sheet of the first aspect of this application, thereby enabling it to have high energy density and good rate performance.

[0021] A third aspect of this application provides a battery module, including the secondary battery of the second aspect of this application.

[0022] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0023] The fifth aspect of this application provides an electrical device, including at least one selected from the second aspect of this application, the third aspect of this application, or the fourth aspect of this application.

[0024] The battery module, battery pack, and power device of this application include the secondary battery of this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the elongation test of the negative electrode current collector according to one embodiment of this application.

[0026] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0027] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0028] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0030] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0031] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0032] Figure 8 This is a scanning electron microscope (SEM) image of the negative electrode sheet of Embodiment 1 of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate Detailed Implementation

[0035] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0039] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0041] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0042] In order to improve the energy density and rate performance of sodium-ion batteries, it is very important to select the negative electrode active material.

[0043] Through in-depth research, the inventors discovered that during the charging process, sodium-ion batteries undergo Na+ oxidation at the hard carbon negative electrode. + The intercalation or adsorption of Na+ occurs, and negative electrode active material particles with multiple adsorption pores are selected as the negative electrode of the sodium-ion battery. During charging, Na+ adsorption occurs. + The sodium-ion battery achieves its capacity through embedding or adsorption of adsorption pores. However, after the negative electrode active material particles with multiple adsorption pores are prepared into a negative electrode film, the compaction density of the negative electrode film decreases. This not only affects the energy density of the sodium-ion battery but also leads to an increase in the transport path of electrons and sodium ions in the negative electrode, thereby reducing the transport performance of electrons and sodium ions in the negative electrode and ultimately deteriorating the rate performance of the sodium-ion battery.

[0044] Based on this, after in-depth thinking and extensive experimentation, the inventor proposed a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device.

[0045] Negative electrode sheet

[0046] This application provides a negative electrode sheet, comprising a negative current collector and a negative electrode film. The negative electrode film is located on at least one surface of the negative current collector, and includes first negative electrode active material particles and second negative electrode active material particles. The first negative electrode active material particles include a plurality of adsorption pores, and the tap density of the first negative electrode active material particles is 0.4 g / cm³. 3 ~1.4g / cm 3 The second negative electrode active material particles have a layered structure, and their tap density is 0.05 g / cm³. 3 ~1.5g / cm 3 Based on the total mass of the first and second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 70%–95%, and the mass percentage of the second negative electrode active material particles is 5%–30%. The compaction density PD of the negative electrode film layer satisfies: 0.8 g / cm³. 3 ≤PD≤1.3g / cm 3 0.8g / cm 3 ≤PD≤1.2g / cm 3 0.8g / cm 3 ≤PD≤1.1g / cm 3 0.8g / cm 3 ≤PD≤1.0g / cm 3 1.0g / cm 3 ≤PD≤1.3g / cm 3 1.0g / cm 3 ≤PD≤1.2g / cm 3 Or 1.0g / cm 3 ≤PD≤1.1g / cm 3 Optionally, the tap density of the first negative electrode active material is 0.6 g / cm³. 3 ~1.0g / cm 3 Optionally, based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 80%–95%, and the mass percentage of the second negative electrode active material particles is 5%–20%. More preferably, based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 90%–95%, and the mass percentage of the second negative electrode active material particles is 5%–10%.

[0047] Although the mechanism is not yet clear, the inventors of this application unexpectedly discovered that the negative electrode film layer of this application includes first negative electrode active material particles and second negative electrode active material particles that meet the above conditions. The combination of the two negative electrode active material particles can enable the negative electrode film layer to have a high compaction density. Therefore, when the negative electrode sheet of this application is applied to sodium-ion batteries, it can enable sodium-ion batteries to have high energy density and good rate performance.

[0048] Specifically, not intended to be limited by any theory or explanation, the first negative electrode active material particles include multiple adsorption pores, and the tap density is within the aforementioned suitable range. After cold pressing, the interior of the first negative electrode active material particles still retains a sufficient number of adsorption pores. Therefore, Na+ can be readily adsorbed and deintercalated by the first negative electrode active material particles during charge and discharge. Furthermore, the second negative electrode active material particles have a layered structure. During cold pressing, the second negative electrode active material particles can fill the gaps between multiple first active material particles or the surface of the first negative electrode active material particles. Through the layered structure, they exert a sliding effect, thereby ensuring close contact between the negative electrode active material particles during cold pressing, increasing the powder compaction density of the negative electrode active material particles, and thus ensuring that the cold-pressed negative electrode film has a suitable compaction density. Therefore, the close contact of the negative electrode active material particles in the negative electrode film improves the electron and sodium ion transport performance in the negative electrode sheet, thereby improving the rate performance of the sodium-ion battery. Furthermore, the second negative electrode active material particles have a layered structure, and compared to the first negative electrode active material particles, their ability to adsorb and intercalate sodium ions is limited. When the content of the first and second negative electrode active material particles is within the aforementioned suitable range, it can further ensure that the sodium-ion battery possesses high energy density.

[0049] In some embodiments, the median particle size D50 of the first negative electrode active material particles can be 1 μm to 50 μm, and can be selected as 5 μm to 10 μm. For example, D50 can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 35 μm, 45 μm, 50 μm, or within any range of the above values.

[0050] Not intended to be limited by any theory or explanation, the median particle size of the first negative electrode active material particles within the aforementioned suitable range can, on the one hand, reduce the difficulty of preparing the first negative electrode active material particles, thereby increasing the production capacity of the negative electrode sheet; on the other hand, it can have a suitable specific surface area, thus enabling the surface of the first negative electrode active material particles to have an appropriate number of active sites, thereby improving the coulombic efficiency of the sodium-ion battery. Furthermore, a suitable median particle size of the first negative electrode active material particles not only enables good electron and sodium-ion transport performance within the particles, but also results in low interparticle interface resistance. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion battery to possess high energy density, high coulombic efficiency, good rate performance, and good cycle performance.

[0051] In some implementations, the elongation E of the negative current collector may satisfy: 0.1% ≤ E ≤ 0.2%, and optionally, 0.1% ≤ E ≤ 0.15%. For example, E may be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or within any of the above values.

[0052] Not intended to be limited by any theory or explanation, this application uses a compound of first and second negative electrode active material particles. Utilizing the sliding function of the second negative electrode active material particles, the particles are brought into close contact during cold pressing, resulting in a high powder compaction density. Therefore, compared to negative electrode active material particles with lower compaction density, under the same cold pressing parameters, the negative electrode current collector of this application exhibits lower elongation, thus maintaining good conductivity and mechanical strength.

[0053] In some embodiments, the single-sided coating weight (CW) of the negative electrode film can be 2 mg / cm³. 2 ~13mg / cm 2 5mg / cm 2 ~12mg / cm 2 For example, CW can be 2 mg / cm³. 2 5mg / cm 2 8mg / cm 2 10mg / cm 2 12mg / cm 2 13mg / cm 2 Or it may fall within the range of any of the above values.

[0054] The single-sided coating weight of the aforementioned negative electrode film can represent the solid component content in the negative electrode slurry coated on a single-sided negative electrode film per unit area, and its numerical value can be equal to the areal density of the single-sided negative electrode film.

[0055] Not intended to be limited by any theory or explanation, the single-sided coating weight of the negative electrode film within the aforementioned suitable range is beneficial for controlling the thickness of the negative electrode film within a suitable range. This not only allows for suitable migration paths for electrons and sodium ions within the negative electrode sheet, but also enables the negative electrode sheet to have a suitable capacity. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion battery to possess good rate performance and high energy density.

[0056] In some embodiments, the negative electrode film layer may satisfy: 30% ≤ P ≤ 60%. Optionally, 45% ≤ P ≤ 55%.

[0057] Where P = [1-CW / (d*PA)]*100%, d = d0(1+E); CW represents the single-sided coating weight of the negative electrode film; PA represents the true density of the single-sided negative electrode film, which can be calculated by the following formula: PA = 1 / (∑x i / ρ i ), where x i ρi represents the mass percentage of the i-th component in the negative electrode film, ρi represents the density of the i-th component, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of the single-sided negative electrode film.

[0058] Not intending to be limited by any theory or explanation, the inventors unexpectedly discovered that when the parameter P of the negative electrode film meets the above conditions, the increase in the compaction density of the negative electrode film can be considered to be mainly achieved through the slippage of the second negative electrode active material particles during cold pressing, without significantly affecting the porosity of the negative electrode film. Therefore, not only is the compaction density of the negative electrode film improved, but the electrolyte wettability of the negative electrode film is also maintained, thus ensuring that the secondary battery possesses high energy density and good rate performance.

[0059] This application does not limit the materials of the first and second negative electrode active material particles. In some embodiments, the first negative electrode active material particles may be selected from one or more of hard carbon, soft carbon, and mesophase carbon microspheres (MCMB); the second negative electrode active material particles may be selected from one or more of artificial graphite, natural graphite, and graphene.

[0060] The particle production process of materials selected from the above-mentioned types is mature, facilitating the processing to obtain first and second negative electrode active material particles that meet the conditions of this application. Furthermore, when the second negative electrode active material particles are selected from the above-mentioned types of materials, the second negative electrode active material can not only fill the gaps between multiple first negative electrode active material particles or act as a sliding agent on the surface of the first negative electrode active material particles to increase the compaction density of the negative electrode active material, but also possess excellent electronic conductivity. Therefore, the negative electrode sheet of this application can possess high compaction density and excellent electronic conductivity, allowing sodium-ion batteries to achieve high compaction density and good cycle performance when applied in sodium-ion batteries.

[0061] This application does not limit the morphology of the first negative electrode active material particles. In some embodiments, the first negative electrode active material particles may include one or more of the following: irregularly shaped first negative electrode active material particles, spherical first negative electrode active material particles, or near-spherical first negative electrode active material particles.

[0062] In the negative electrode sheet of this application, first negative electrode active material particles and second negative electrode active material particles are compounded, and the content of the first negative electrode active material particles and the second negative electrode active material particles is within the range of this application. Regardless of the morphology of the first negative electrode active material particles, the negative electrode film layer can have a high compaction density. This improves the process flexibility of the negative electrode sheet and allows sodium-ion batteries to have high energy density.

[0063] In some embodiments, the first negative electrode active material particles can be hard carbon particles.

[0064] The inventors discovered that hard carbon materials possess low energy storage voltage, high capacity, and good cycle stability. Furthermore, hard carbon materials are abundant and their preparation process is simple. More importantly, the large lattice spacing and porosity of hard carbon particles make them an ideal choice for the first negative electrode active material particles in this application. Although conventional hard carbon materials are inherently hard and exhibit almost no deformation or slippage during cold pressing, resulting in typically low compaction density in negative electrode films, the second negative electrode active material particles with a layered structure in the negative electrode film of this application can fill the voids in the first negative electrode active material particles or act as slip particles on the surface of the first negative electrode active material particles. Therefore, the first negative electrode active material particles do not need to undergo deformation to achieve a high compaction density in the negative electrode film. Thus, when the first negative electrode active material particles are hard carbon particles, the negative electrode sheet of this application, when used in sodium-ion batteries, can reduce the cost of sodium-ion batteries and improve their energy density, rate performance, and cycle stability.

[0065] In some embodiments, the first negative electrode active material particles may include one or more of irregularly shaped hard carbon particles, spherical hard carbon particles, or near-spherical hard carbon particles.

[0066] Not intended to be limited by any theory or explanation, when the first negative electrode active material particles are selected from hard carbon particles with the above-mentioned morphology, the negative electrode active material particles can have low cost and high theoretical specific capacity, thereby improving the energy density, rate performance and cycle stability of sodium-ion batteries.

[0067] In some embodiments, the first negative electrode active material particles include one or more of irregularly shaped hard carbon particles, spherical hard carbon particles, or near-spherical hard carbon particles. The compaction density PD of the single-sided negative electrode film layer satisfies: 1.0 g / cm³. 3 ≤PD≤1.2g / cm 3 The negative electrode film layer satisfies: 30% ≤ P ≤ 60%, optionally, 45% ≤ P ≤ 55%, where P = [1 - (CW) / (d*PA)] * 100%, d = d0 / (1 + E), CW represents the single-sided coating weight of the negative electrode film layer, and PA represents the true density of the single-sided negative electrode film layer, which can be calculated by the following formula: PA = 1 / (∑x i / ρ i ), where x i ρi represents the mass percentage of the i-th component in the negative electrode film, ρi represents the density of the i-th component, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of the single-sided negative electrode film.

[0068] Not intended to be limited by any theory or explanation, when the parameter P of the negative electrode film satisfies the above conditions, the increase in the compaction density of the negative electrode film can be considered to be mainly achieved through the slippage function of the second negative electrode active material particles during cold pressing. Therefore, for hard carbon particles, deformation or slippage is not required to achieve a high compaction density in the negative electrode film. This allows for the application of hard carbon materials in sodium-ion batteries, giving sodium-ion batteries a broad application prospect.

[0069] In some embodiments, the negative electrode film layer may further include a flexible binder, which may include one or more of the following: styrene-acrylic emulsion, copolymer of vinylidene fluoride and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and acrylates, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber.

[0070] Not intended to be limited to any particular theory or explanation, the negative electrode film, including the aforementioned flexible binder, possesses excellent flexibility. Consequently, the negative electrode film exhibits lower stress during cold pressing, facilitates the deposition of negative electrode active material particles, and results in lower elongation of the negative electrode current collector. This further enhances the compaction density of the negative electrode film, thereby increasing the energy density of the sodium-ion battery.

[0071] In some embodiments, based on the total mass of the negative electrode film, the negative electrode film may include: 80wt% to 97wt% of negative electrode active material particles, 0wt% to 5wt% of conductive agent, 2wt% to 10wt% of binder and 0.5wt% to 5wt% of dispersant, wherein the negative electrode active material particles include first negative electrode active material particles and second negative electrode active material particles.

[0072] Not intended to be limited by any theory or explanation, the inclusion of the aforementioned components in the negative electrode film, with the content of each component within the aforementioned suitable range, ensures that the negative electrode film has a high compaction density and good electron and sodium ion transport performance. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, allows the sodium-ion batteries to possess high energy density and good cycle performance.

[0073] It should be noted that the parameters of each negative electrode film layer given in this application refer to the parameter range of a single negative electrode film layer. When the negative electrode film layer is disposed on both surfaces of the negative electrode current collector, if the parameters of the negative electrode film layer on either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0074] The first negative electrode active material particles in this application can be obtained in a variety of ways, and are not limited here. For example, the first negative electrode active material particles can be obtained by commercial purchase or self-production.

[0075] As an example, the first negative electrode active material particles can be hard carbon particles with irregular shapes. The first negative electrode active material particles can be prepared by the following steps: placing coconut shells at 300°C to pre-carbonize them; crushing the pre-carbonized coconut shells into particles with a diameter of about 2 mm using a roller mill, and removing impurities by sieving; heat-treating the particles at 400°C to 800°C, optionally introducing halogen or hydrogen halide gas to remove ash, obtaining particles that are easy to ball mill; ball milling the particles to obtain carbon particles with Dv50 = 50μm / 40μm / 25μm / 20μm / 9μm / 5μm / 3μm / 1μm; placing the ball-milled particles in an inert atmosphere and maintaining the temperature at 1150°C to carbonize the ball-milled particles, optionally introducing acetylene gas to perform vapor-phase deposition carbon coating on the ball-milled particles, thereby preparing the first negative electrode active material particles with irregular shapes.

[0076] As another example, the first negative electrode active material particles can be spherical hard carbon particles or near-spherical hard carbon particles. The first negative electrode active material particles can be prepared by the following steps: dehydrating and carbonizing starch and / or lignin at temperatures below 200°C to obtain pre-carbonized particles with a pre-fixed morphology (e.g., pre-carbonized particles obtained from papermaking lignin, potato starch, corn starch, and rice starch have Dv50 values ​​of 50 μm, 25 μm, 10 μm, and 6 μm, respectively, and are spherical or near-spherical in shape). Optionally, salts or polymeric dehydrating agents containing N, P, S, or halogens, such as ammonium salts, phosphates, sulfates, sulfites, persulfates, halides, or polymers of the above salts, can be added to the starch and / or lignin. The pre-carbonized particles are then heat-treated at 400–800°C to obtain carbonized particles that are easily pulverized by ball milling or air jet milling. The carbonized particles are then pulverized by ball milling or air jet milling to further obtain particles that are close to... Other particle sizes with spherical or truncated glass morphology (e.g., potato starch carbon particles with a particle size of 25 μm are ball-milled to 20 μm after primary ball milling, and the morphology is still close to spherical; after tertiary ball milling to 5 μm, the morphology is close to truncated glass morphology; rice starch with a particle size of 6 μm is ball-milled to 5 μm after primary ball milling, and the morphology is still close to spherical; after tertiary ball milling to 1.5 μm, the particle morphology is truncated glass morphology; corn starch carbon particles with a particle size of 10 μm can be obtained as 1 μm truncated glass morphology carbon particles by air jet milling); the above particles are placed in an inert atmosphere and the temperature is maintained at 1150℃ to carbonize the ball-milled particles. Optionally, acetylene gas can be introduced to perform vapor-phase deposition carbon coating on the ball-milled particles, thereby preparing spherical first negative electrode active material particles or near-spherical first negative electrode active material particles.

[0077] In this application, tap density has a meaning known in the art and can be determined by methods known in the art. For example, it can be tested using a powder tap density tester (such as Dandong Baite BT-310) with reference to standards GB / T 5162-2006 and GB / T 24533-2009.

[0078] In this application, median particle size has a meaning known in the art, which can represent the particle size corresponding to a cumulative particle size distribution percentage of 50%. The median particle size can be determined using methods and instruments known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E) according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0079] In this application, the compaction density of the negative electrode film has a meaning known in the art and can be measured by methods known in the art. For example, after the negative electrode sheet is cold-pressed, several discs with an area of ​​S1, fully coated with slurry and uncoated with slurry, are punched out using a punching machine. The average masses W2 and W1 are obtained by weighing them respectively, and the average thicknesses T2 and T1 are obtained by measuring them respectively. The compaction density of the negative electrode film is PD = (W2-W1) / (T2-T1) / S1.

[0080] In this application, the elongation E of the negative electrode current collector has a meaning known in the art, which can represent the rate of change of the length of the negative electrode current collector in the mechanical direction before and after cold pressing. The elongation E can be measured using methods and instruments known in the art. As an example, such as... Figure 1 As shown, a 2m long negative electrode sheet after coating and drying can be taken, and two marking points A1 and A2 can be selected. The line connecting A1 and A2 is parallel to the length direction of the negative electrode sheet. The distance between marking points A1 and A2 can be accurately measured with a ruler and recorded as L1. After the negative electrode sheet is cold-pressed with a certain pressure, the distance between A1 and A2 can be measured again and recorded as L2. Then E=(L2-L1) / L1.

[0081] In this application, the single-sided coating weight of the negative electrode film has a meaning known in the art and can be determined by methods known in the art. For example, after the negative electrode sheet is cold-pressed, several discs with an area of ​​S2, fully coated with slurry and uncoated with slurry, are punched out using a punching machine. The average masses M2 and M1 are obtained by weighing them respectively. The single-sided coating weight of the negative electrode sheet is CW = (M2-M1) / nS2, where n represents the number of negative electrode film layers. When the negative electrode sheet is single-sided coated, n = 1, and when the negative electrode sheet is double-sided coated, n = 2.

[0082] In this application, the thickness d0 of the single-sided negative electrode film can be obtained by measuring with a micrometer. For example, after the negative electrode sheet is cold-pressed, the thickness d1 of the negative electrode sheet can be measured with a micrometer. After scraping off the negative electrode film on the surface of the negative electrode sheet and washing it with solvent, the thickness d2 of the negative current collector can be measured with a micrometer. d0 = (d1-d2) / n, where n represents the number of negative electrode film layers. When the negative electrode sheet is coated on one side, n = 1; when the negative electrode sheet is coated on both sides, n = 2.

[0083] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0084] Secondary batteries

[0085] A second aspect of this application provides a secondary battery. In some embodiments, it may be a sodium-ion battery.

[0086] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0087] [Positive electrode plate]

[0088] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0089] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0090] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0091] In some embodiments, when the secondary battery is a sodium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for sodium-ion batteries. As an example, the positive electrode active material can be a single material or a combination of two or more. The positive electrode active material can be selected from sodium-iron composite oxide (NaFeO2), sodium-cobalt composite oxide (NaCoO2), sodium-chromium composite oxide (NaCrO2), sodium-manganese composite oxide (NaMnO2), sodium-nickel composite oxide (NaNiO2), and sodium-nickel-titanium composite oxide (NaNiO2). 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi) 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na) 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate (NaFePO4), sodium manganese phosphate (NaMn)P The present application may use materials such as O4, sodium cobalt phosphate (NaCoPO4), Prussian blue materials, and polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), but this application is not limited to these materials. Other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0092] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0093] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0095] [Negative electrode plate]

[0096] In the secondary battery of this application, the negative electrode includes the negative electrode of the first aspect of this application.

[0097] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0098] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0099] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate 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 (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.).

[0100] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0102] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as first negative electrode active material particles, second negative electrode active material particles, optional slip increment components, conductive agents, binders and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0103] [Electrolytes]

[0104] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt may be selected from one or more of NaPF6, NaClO4, NaBCl4, NaSO3CF3 and Na(CH3)C6H4SO3.

[0107] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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, methyl ethyl sulfone, and diethyl sulfone.

[0108] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0109] [Isolation membrane]

[0110] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0111] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0112] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0113] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0114] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0116] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0117] Battery modules and battery packs

[0118] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0119] Figure 4This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0120] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0121] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0122] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0123] Electrical appliances

[0124] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0125] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0126] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0127] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0128] Example

[0129] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0130] Example 1

[0131] 1) Preparation of positive electrode sheet

[0132] The positive electrode active material is sodium-nickel-manganese composite oxide (NaNi). 1 / 2 Mn 1 / 2 O2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 92:5:3 to form a uniform positive electrode slurry. The positive electrode slurry is coated onto a 13μm thick positive electrode current collector aluminum foil, dried at 100℃, and then pressed to obtain a positive electrode sheet.

[0133] 2) Preparation of negative electrode sheet

[0134] The negative electrode active material particles, conductive agent acetylene black, binder styrene-acrylic emulsion, and thickener sodium carboxymethyl cellulose (CMC-Na) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 94:1:4:1 to form a uniform negative electrode slurry. The negative electrode slurry is coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8 μm, dried at 100°C, and then pressed to obtain a negative electrode sheet.

[0135] The negative electrode active material particles include first negative electrode active material particles and second negative electrode active material particles. The first negative electrode active material particles are irregularly shaped hard carbon particles, and the second negative electrode active material particles are artificial graphite particles. The median particle size D50 of the first negative electrode active material particles is 5 μm. Based on the total mass of the negative electrode active material particles, the mass percentage Q1 of the first negative electrode active material particles is 70%, and the mass percentage Q2 of the second negative electrode active material particles is 30%. The single-sided coating weight CW of the negative electrode sheet is 9 mg / cm³. 2 .

[0136] 3) Separating membrane

[0137] Polyethylene (PE) separator film (celgard) is used.

[0138] 4) Preparation of electrolyte

[0139] Equal volumes of ethylene carbonate (EC) and propylene carbonate (PC) were mixed evenly to obtain an organic solvent. Then, NaPF6 was uniformly dissolved in the organic solvent to obtain an electrolyte, wherein the concentration of NaPF6 was 1 mol / L.

[0140] 5) Battery manufacturing

[0141] The positive electrode, separator, and negative electrode are stacked in sequence, the electrolyte is added, and the container is sealed to obtain a sodium-ion battery.

[0142] Examples 2 to 6

[0143] Based on the preparation method of Example 1, sodium-ion batteries of Examples 2 to 6 were prepared by adjusting Q1 and Q2.

[0144] Examples 7 to 14

[0145] Based on the preparation method of Example 1, the median particle size D50 and Q1 and Q2 of the first negative electrode active material particles were adjusted to prepare sodium-ion batteries of Examples 7 to 14.

[0146] Examples 15 to 16

[0147] Based on the preparation method of Example 1, the morphology of the first negative electrode active material particles and Q1 and Q2 were adjusted to prepare sodium-ion batteries of Examples 15 and 16.

[0148] Examples 17 to 19

[0149] Based on the preparation method of Example 1, the types of the second negative electrode active material and Q1 and Q2 were adjusted to prepare sodium-ion batteries of Examples 17 to 19. Among them, the second negative electrode active material used in Example 17 was natural graphite, the second negative electrode active material used in Example 18 was graphene, and the second negative electrode active material used in Example 19 was a material composed of a mixture of natural graphite and graphene in a 1:1 mass ratio.

[0150] Examples 20 to 23

[0151] Based on the preparation method of Example 1, the single-sided coating weight of the negative electrode film and Q1 and Q2 were adjusted to prepare sodium-ion batteries of Examples 20 to 23.

[0152] Examples 24 to 27

[0153] Based on the preparation method of Example 1, the tap density of the first negative electrode active material and Q1 and Q2 were adjusted to prepare sodium-ion batteries of Examples 24 to 27.

[0154] Examples 28 to 29

[0155] Based on the preparation method of Example 1, the tap density of the second negative electrode active material and Q1 and Q2 were adjusted to prepare sodium-ion batteries of Examples 28 to 29.

[0156] Examples 30 to 34

[0157] Based on the preparation method of Example 1, the types of binders used in Q1, Q2, and the negative electrode were adjusted to prepare sodium-ion batteries of Examples 30 to 34. Specifically, the binder used in the negative electrode of Example 30 was styrene-butadiene rubber (SBR); the binder used in the negative electrode of Example 31 was hydrogenated nitrile butadiene rubber; the binder used in the negative electrode of Example 32 was a copolymer of vinylidene fluoride and hexafluoropropylene; the binder used in the negative electrode of Example 33 was a copolymer of vinylidene fluoride and acrylates; and the binder used in the negative electrode of Example 34 was polytetrafluoroethylene (PTFE).

[0158] Comparative Examples 1 to 3

[0159] Based on the preparation method of Example 1, sodium-ion batteries of Comparative Examples 1 to 3 were prepared by adjusting the composition of the negative electrode active material particles. Specifically, the negative electrode active material particles of Comparative Example 1 consisted of irregularly shaped hard carbon particles with a D50 of 5 μm; the negative electrode active material particles of Comparative Example 2 consisted of spherical hard carbon particles with a D50 of 5 μm; and the negative electrode active material particles of Comparative Example 3 consisted of near-spherical hard carbon particles with a D50 of 5 μm.

[0160] Comparative examples 4 to 5

[0161] Based on the preparation method of Example 1, sodium-ion batteries of Comparative Examples 4 to 5 were prepared by adjusting Q1 and Q2.

[0162] The relevant preparation parameters of the negative electrode sheets of Examples 1-34 and Comparative Examples 1-5 are shown in Table 1 below. Wherein, Q1 represents the mass percentage of the first negative electrode active material particles based on the total mass of the negative electrode active material particles; Q2 represents the mass percentage of the second negative electrode active material particles based on the total mass of the negative electrode active material particles; the tap density ρ1 and D50 of the first negative electrode active material particles and the tap density ρ2 of the second negative electrode active material particles can be tested according to the methods described above in this specification, and PA can be calculated according to the methods described above in this specification.

[0163] The relevant test parameters of the negative electrode sheets of Examples 1-34 and Comparative Examples 1-5 are shown in Table 2 below. CW, d0, E, and PD can be tested according to the methods described above in this specification, and P can be calculated according to the methods described above in this specification.

[0164] The negative electrode sheet of Example 1 was subjected to SEM testing, and the obtained SEM image is shown below. Figure 8 As shown.

[0165] Table 1: Preparation parameters of negative electrode sheets in Examples 1-34 and Comparative Examples 1-5

[0166] Serial Number <![CDATA[ρ1 / (g / cm 3 )]]> <![CDATA[Q1 / %]]> D50 / μm <![CDATA[ρ2 / (g / cm 3 )]]> <![CDATA[Q2 / %]]> <![CDATA[PA / (g / cm 3 )]]> Example 1 0.85 70 5 1.15 30 2.07 Example 2 0.85 75 5 1.15 25 2.07 Example 3 0.85 80 5 1.15 20 2.07 Example 4 0.85 85 5 1.15 15 2.07 Example 5 0.85 90 5 1.15 10 2.07 Example 6 0.85 95 5 1.15 5 2.07 Example 7 0.85 90 1 1.15 10 2.07 Example 8 0.85 90 3 1.15 10 2.07 Example 9 0.85 90 8 1.15 10 2.07 Example 10 0.85 90 10 1.15 10 2.07 Example 11 0.85 90 20 1.15 10 2.07 Example 12 0.85 90 30 1.15 10 2.07 Example 13 0.85 90 50 1.15 10 2.07 Example 14 0.85 90 60 1.15 10 2.07 Example 15 0.85 90 5 1.15 10 2.07 Example 16 0.85 90 5 1.15 10 2.07 Example 17 0.85 90 5 1.15 10 2.07 Example 18 0.85 90 5 0.4 10 2.07 Example 19 0.85 90 5 1.15 10 2.07 Example 20 0.85 90 5 1.15 10 2.07 Example 21 0.85 90 5 1.15 10 2.07 Example 22 0.85 90 5 1.15 10 2.07 Example 23 0.85 90 5 1.15 10 2.07 Example 24 0.4 90 5 1.15 10 2.07 Example 25 0.6 90 5 1.15 10 2.07 Example 26 1.0 90 5 1.15 10 2.07 Example 27 1.4 90 5 1.15 10 2.07 Example 28 0.85 85 5 0.7 15 2.07 Example 29 0.85 85 5 1.3 15 2.07 Example 30 0.85 85 5 1.15 15 2.07 Example 31 0.85 85 5 1.15 15 2.07 Example 32 0.85 85 5 1.15 15 2.07 Example 33 0.85 85 5 1.15 15 2.07 Example 34 0.85 85 5 1.15 15 2.07 Comparative Example 1 0.85 100 5 1.15 0 2.07 Comparative Example 2 0.85 100 5 1.15 0 2.07 Comparative Example 3 0.85 100 5 1.15 0 2.07 Comparative Example 4 0.85 50 5 1.15 50 2.07 Comparative Example 5 0.85 98 5 1.15 2 2.07

[0167] Table 2: Test parameters of negative electrode sheets of Examples 1-34 and Comparative Examples 1-5

[0168] Serial Number <![CDATA[CW / (mg / cm 2 )]]> <![CDATA[d0 / μm]]> E / ％ <![CDATA[PD / (g / cm 3 )]]> P / ％ Example 1 9 85.7 0.12 1.05 48.8％ Example 2 9 86.5 0.12 1.04 49.3％ Example 3 9 87.4 0.12 1.03 49.8％ Example 4 9 88.2 0.12 1.02 50.2％ Example 5 9 89.1 0.12 1.01 50.7％ Example 6 9 90.0 0.12 1.00 51.2％ Example 7 9 91.8 0.12 0.98 52.2％ Example 8 9 90.9 0.12 0.99 51.7％ Example 9 9 89.1 0.12 1.01 50.7％ Example 10 9 88.2 0.12 1.02 50.2％ Example 11 9 86.5 0.12 1.04 49.3％ Example 12 9 84.1 0.12 1.07 47.8％ Example 13 9 82.6 0.12 1.09 46.8％ Example 14 9 85.7 0.12 1.05 48.8％ Example 15 9 78.3 0.12 1.15 43.9％ Example 16 9 78.3 0.12 1.15 43.9％ Example 17 9 89.1 0.12 1.01 50.7％ Example 18 9 89.1 0.12 1.01 50.7％ Example 19 9 89.1 0.12 1.01 50.7％ Example 20 3 28.6 0.12 1.05 48.8％ Example 21 5 48.5 0.12 1.03 49.8％ Example 22 7 68.6 0.12 1.02 50.2％ Example 23 13 132.7 0.12 0.98 52.2％ Example 24 9 91.8 0.12 0.98 52.2％ Example 25 9 90.0 0.12 1.00 51.2％ Example 26 9 89.1 0.12 1.01 50.7％ Example 27 9 88.2 0.12 1.02 50.2％ Example 28 9 89.1 0.12 1.01 50.7％ Example 29 9 89.1 0.12 1.01 50.7％ Example 30 9 95.7 0.9 0.94 54.1％ Example 31 9 89.1 0.12 1.01 50.4％ Example 32 9 89.1 0.12 1.01 50.8％ Example 33 9 89.1 0.12 1.01 50.8％ Example 34 9 89.1 0.12 1.01 50.8％ Comparative Example 1 9 105.9 1.6 0.85 58.6％ Comparative Example 2 9 90.0 0.3 1.00 51.2％ Comparative Example 3 9 91.8 0.3 0.98 51.2％ Comparative Example 4 9 81.8 0.12 1.10 46.4％ Comparative Example 5 9 103.4 1.5 0.87 57.6％

[0169] In addition, the sodium-ion batteries obtained in Examples 1-34 and Comparative Examples 1-5 were subjected to performance tests. The test results are shown in Table 3 below.

[0170] (1) Energy density test

[0171] At 25℃, the battery was charged at a constant current rate of 0.33C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V to a current of 0.05C, at which point the secondary battery reached a fully charged state. After resting for 5 minutes, it was discharged at a constant current rate of 0.33C to a voltage of 2.5V, and then rested for another 5 minutes. The capacity and voltage plateau of the secondary battery during the constant current discharge at a rate of 0.5C were recorded. Finally, the mass of the secondary battery was measured.

[0172] The energy density of a secondary battery (Wh / kg) = (the capacity of the secondary battery at a constant current discharge rate of 0.33C × the voltage plateau of the secondary battery at a constant current discharge rate of 0.33C) / the mass of the secondary battery.

[0173] (2) Cyclic life test

[0174] At 25°C, the secondary battery is charged to 4.2V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.2V. After resting for 5 minutes, it is discharged to 2.8V at 1 / 3C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity C of the battery after the nth cycle is recorded. n Then, the battery capacity retention rate P after each cycle n =C n / C0*100%, with P n The minimum n value corresponding to ≤80% is taken as the cycle life of the secondary battery.

[0175] Table 3: Performance test results of Examples 1-34 and Comparative Examples 1-5

[0176] Serial Number Energy density (Wh / kg) Cycle life / cycles Example 1 112 1902 Example 2 112 1911 Example 3 113 1912 Example 4 113 1900 Example 5 114 1984 Example 6 114 1978 Example 7 113.5 1650 Example 8 113.5 1866 Example 9 114 1900 Example 10 114 1901 Example 11 114.5 1904 Example 12 114.5 1811 Example 13 115 1764 Example 14 115 1065 Example 15 117 1795 Example 16 117 1790 Example 17 114 1997 Example 18 114 1980 Example 19 114 1998 Example 20 40 1993 Example 21 60 1996 Example 22 95 1992 Example 23 140 1805 Example 24 113.5 1945 Example 25 114 1954 Example 26 114 1930 Example 27 114.5 1923 Example 28 114 1941 Example 29 114 1925 Example 30 114 1911 Example 31 114 1797 Example 32 114 1691 Example 33 114 1696 Example 34 114 1593 Comparative Example 1 84 1021 Comparative Example 2 113 1322 Comparative Example 3 113 1209 Comparative Example 4 30 589 Comparative Example 5 84 1330

[0177] As can be seen from embodiments 1 to 34, when the negative electrode film layer includes first negative electrode active material particles and second negative electrode active material particles, and when the first negative electrode active material particles and second negative electrode active material particles meet the conditions of this application, the negative electrode film layer can have a high compaction density and a suitable parameter P, and the sodium-ion battery can have both high energy density and long cycle life. Figure 8 As shown, the second negative electrode active material particles can fill the gaps between the first negative electrode active material particles or the surface of the first negative electrode active material particles, and play a sliding function during cold pressing. Therefore, the negative electrode film layer can possess a high compaction density.

[0178] Specifically, as can be seen from Examples 1 to 6, under the same conditions, the higher the content of the first negative electrode active material particles and the lower the content of the second negative electrode active material particles, the higher the energy density of the sodium-ion battery; conversely, the lower the content of the first negative electrode active material particles and the higher the content of the second negative electrode active material particles, the higher the compaction density of the negative electrode film. Excessive compaction density may affect the electrolyte wetting performance of the negative electrode film; excessively low compaction density may affect the electron and sodium ion transport performance of the negative electrode film. Therefore, it is necessary to control the content of the first and second negative electrode active material particles within a suitable range.

[0179] As can be seen from Examples 5, 7 to 14, under the same conditions, as the median particle size D50 of the first negative electrode active material particles increases, the cycle life of the sodium-ion battery first increases and then decreases. This may be related to the number of active sites and the specific surface area on the surface of the first negative electrode active material particles.

[0180] Based on Examples 5, 15, and 16, it can be seen that, under the same conditions, compared to Example 5, Examples 15 and 16, which use spherical or near-spherical hard carbon particles as the first negative electrode active material particles, have a higher compaction density in the negative electrode film, but the corresponding sodium-ion battery has a shorter cycle life. This may be because the electrolyte wetting performance of the negative electrode film in Examples 15 and 16 is lower than that in Example 5.

[0181] As can be seen from Examples 5, 17 to 19, the second negative electrode active material particles with a layered structure can all play a sliding function, thereby increasing the compaction density of the negative electrode film.

[0182] Based on Examples 5, 20 to 23, it can be seen that, under the same conditions, the higher the single-sided coating weight of the negative electrode film, the lower the compaction density of the negative electrode film. This may be because when the negative electrode film is thicker, the sliding function of the second negative electrode active material under pressure is limited during the cold pressing process.

[0183] As can be seen from Examples 5, 24 to 27, under the same conditions, as the tap density of the first negative electrode active material particles increases, the compaction density of the negative electrode film also increases, and the cycle life of the sodium-ion battery is shortened accordingly. This may be because: as the tap density of the first negative electrode active material particles increases, the number of adsorption pores inside the first negative electrode active material particles decreases, thereby allowing the negative electrode film to have a higher compaction density. Correspondingly, as the number of adsorption pores inside the first negative electrode active material particles decreases, the sodium storage space inside the first negative electrode active material particles also decreases, thus shortening the cycle life of the sodium-ion battery.

[0184] As can be seen from Examples 5, 28 to 29, when the tap density of the second negative electrode active material particles is within a suitable range, the negative electrode film layer can have a high tap density, and the sodium-ion battery can have a high tap density and a long cycle life.

[0185] As can be seen from Examples 5, 30 to 34, compared with conventional negative electrode binders SBR, flexible binders can increase the compaction density of the negative electrode film, improve the long-term cycle performance of sodium-ion batteries, and increase the energy density and cycle life of sodium-ion batteries.

[0186] In contrast, Comparative Examples 1 to 3 used only hard carbon particles with different morphologies and a median particle size of 5 μm as the negative electrode active material particles, resulting in a lower compaction density of the negative electrode film. Consequently, the negative electrode not only has a lower energy density but also a longer electron and sodium ion transport path, leading to lower energy density and cycle life in the sodium-ion battery. Although Comparative Examples 4 and 5 utilized a combination of first negative electrode active material particles and second negative electrode active material particles with a layered structure, in Comparative Example 4, the content of the first negative electrode active material particles was below the range specified in this application, significantly reducing the energy density of the sodium-ion battery. In Comparative Example 5, the content of the first negative electrode active material particles was above the range specified in this application, limiting the effect of the second negative electrode active material particles on improving the compaction density of the negative electrode film. Therefore, the energy density and cycle life of the sodium-ion battery in Comparative Example 5 were also unsatisfactory.

[0187] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode plate, comprising: Negative electrode current collector; as well as A negative electrode film layer is located on at least one surface of the negative electrode current collector. The negative electrode film layer includes first negative electrode active material particles and second negative electrode active material particles. The first negative electrode active material particles include multiple adsorption pores, and the tap density of the first negative electrode active material particles is 0.4 g / cm³. 3 ~1.4g / cm 3 The second negative electrode active material particles have a layered structure, and the tap density of the second negative electrode active material particles is 0.05 g / cm³. 3 ~1.5g / cm 3 ; Wherein, based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 70% to 95%; and the mass percentage of the second negative electrode active material particles is 5% to 30%. The compaction density PD of the negative electrode film layer satisfies: 0.8 g / cm³ 3 ≤PD≤1.3g / cm 3 .

2. The negative electrode sheet according to claim 1, wherein, The tap density of the first negative electrode active material particles is 0.6 g / cm³. 3 ~1.0g / cm 3 .

3. The negative electrode sheet according to claim 1, wherein, Based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the first negative electrode active material particles is 80% to 95%.

4. The negative electrode sheet according to claim 1, wherein, Based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles, the mass percentage of the second negative electrode active material particles is 5% to 10%.

5. The negative electrode sheet according to claim 1, wherein, The compaction density PD of the negative electrode film layer satisfies: 1.0 g / cm³ 3 ≤PD≤1.2g / cm 3 .

6. The negative electrode sheet according to any one of claims 1-5, wherein, The median particle size D50 of the first negative electrode active material particles is 1 μm to 50 μm.

7. The negative electrode sheet according to claim 6, wherein, The median particle size D50 of the first negative electrode active material particles is 5 μm to 10 μm.

8. The negative electrode sheet according to any one of claims 1-7, wherein, The elongation E of the negative electrode current collector satisfies: 0.1% ≤ E ≤ 0.2%.

9. The negative electrode sheet according to claim 8, wherein, The elongation E of the negative electrode current collector satisfies: 0.1% ≤ E ≤ 0.15%.

10. The negative electrode sheet according to any one of claims 1-9, wherein, The single-sided coating weight (CW) of the negative electrode film is 2 mg / cm³. 2 ~13mg / cm 2 .

11. The negative electrode sheet according to any one of claims 1-10, wherein, The negative electrode film layer satisfies: 30% ≤ P ≤ 60%. Where P = [1-(CW) / (d*PA)]*100%, d = d0 / (1+E), CW represents the coating weight of one side of the negative electrode film, PA represents the true density of one side of the negative electrode film, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of one side of the negative electrode film.

12. The negative electrode sheet according to claim 11, wherein, The negative electrode film layer satisfies the following condition: 45% ≤ P ≤ 55%.

13. The negative electrode sheet according to any one of claims 1-12, wherein, The first negative electrode active material particles are selected from one or more of hard carbon, soft carbon, and mesophase carbon microspheres; the second negative electrode active material particles are selected from one or more of artificial graphite, natural graphite, and graphene.

14. The negative electrode sheet according to any one of claims 1-13, wherein, The first negative electrode active material particles include one or more of the following: irregularly shaped first negative electrode active material particles, spherical first negative electrode active material particles, or near-spherical first negative electrode active material particles.

15. The negative electrode sheet according to any one of claims 1-14, wherein, The first negative electrode active material particles include one or more of the following: irregularly shaped hard carbon particles, spherical hard carbon particles, or near-spherical hard carbon particles.

16. The negative electrode sheet according to claim 15, wherein, The compaction density PD of the negative electrode film layer on one side satisfies: 1.0 g / cm³ 3 ≤PD≤1.2g / cm 3 ; The negative electrode film layer satisfies: 30% ≤ P ≤ 60%, where P = [1 - (CW) / (d * PA)] * 100%, d = d0 / (1 + E), CW represents the coating weight of one side of the negative electrode film layer, PA represents the true density of one side of the negative electrode film layer, E represents the elongation of the negative electrode current collector, and d0 represents the thickness of one side of the negative electrode film layer.

17. The negative electrode sheet according to claim 16, wherein, The negative electrode film layer satisfies the following condition: 45% ≤ P ≤ 55%.

18. The negative electrode sheet according to any one of claims 1-17, wherein, The negative electrode film layer also includes a flexible binder, which includes one or more of the following: styrene-acrylic emulsion, copolymer of vinylidene fluoride and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and acrylates, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber.

19. The negative electrode sheet according to any one of claims 1-18, wherein, Based on the total mass of the negative electrode film, the negative electrode film comprises: 80wt% to 97wt% of negative electrode active material particles, 0wt% to 5wt% of conductive agent, 2wt% to 10wt% of binder, and 0.5wt% to 5wt% of dispersant, wherein the negative electrode active material particles comprise the first negative electrode active material particles and the second negative electrode active material particles.

20. A secondary battery comprising a negative electrode sheet according to any one of claims 1-19.

21. A battery module comprising the secondary battery of claim 20.

22. A battery pack comprising the battery module of claim 21.

23. An electrical device comprising at least one selected from the secondary battery of claim 20, the battery module of claim 21, or the battery pack of claim 22.

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