Negative electrode plate, secondary battery, battery module, battery pack and electrical device

Abstract

This application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. The negative electrode sheet includes: a negative current collector; and a negative electrode film layer located on at least one surface of the negative 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 difference d between the median particle size of the first negative electrode active material particles and the second negative electrode active material particles satisfies the relationship: 3μm≤d≤19μm, and the compaction density PD of the negative electrode film layer satisfies: 0.8g / cm³. 3 ≤PD≤1.4g / cm 3 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] With the increasing prominence of energy and environmental problems, new energy industries have received more and more attention. In recent years, lithium ion batteries have been widely used as an important new type of energy storage device due to their high energy density and good cycle performance. However, due to the scarcity of resources of active materials related to lithium ion batteries, the cost of batteries is always high, and at the same time faces the serious problem of resource exhaustion, so it is necessary to develop other low-cost metal ion secondary battery systems.

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

[0004] However, due to the low specific capacity and voltage platform of the positive and negative electrode materials of the current sodium ion battery, the energy density of the sodium ion battery is always greatly different from that of the lithium ion battery, and it cannot be truly commercialized. In addition, the first coulombic efficiency and rate performance of the sodium ion battery also need to be improved. SUMMARY

[0005] The present application is made in view of the above-mentioned problems, and aims to provide a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device, which can effectively improve the energy density and rate performance of the sodium ion battery.

[0006] The first aspect of the present application provides a negative electrode sheet, comprising: a negative current collector; and a negative film layer located on at least one surface of the negative current collector, the negative film layer comprising first negative active material particles and second negative active material particles, the first negative active material particles comprising a plurality of adsorption pores, the tap density of the first negative active material particles being 0.4 g / cm 3 ~ 1.4 g / cm 3 , which can be 0.6 g / cm 3 ~ 1.0 g / cm 3 , wherein the difference d between the median particle sizes of the first negative active material particles and the second negative active material particles satisfies the relationship: 3 μm ≤ d ≤ 19 μm, and the compaction density PD of the negative film layer satisfies: 0.8 g / cm 3 ≤ PD ≤ 1.4 g / cm 3 , which can be 1.0 g / cm 3 ≤ PD ≤ 1.2 g / cm 3 .

[0007] Thus, the present application can make the negative electrode film layer have high porosity while making the negative electrode film layer have high tap density by compounding the first negative electrode active material particles and the second negative electrode active material particles satisfying the above conditions. Specifically, the first negative electrode active material particles include a plurality of adsorption pores, and the tap density is in the above suitable range, so that the first negative electrode active material particles can still have a sufficient number of adsorption pores after cold pressing. Thus, Na + can be smoothly adsorbed by the first negative electrode active material particles during charging and smoothly desorbed during discharging. Further, the difference between the median particle diameter of the first negative electrode active material particles and the median particle diameter of the second negative electrode active material particles is in the above suitable range, which is beneficial to the second negative electrode active material particles filling into the gaps between the plurality of first negative electrode active material particles, so that the negative electrode active material particles have high bulk density, and further so that the negative electrode film layer after cold pressing has a suitable tap density. Thus, the negative electrode active material particles in the negative electrode film layer are in close contact, so that the transport performance of electrons and sodium ions in the negative electrode sheet can be improved, and further the rate performance of the sodium ion battery can be improved.

[0008] In any embodiment, the median particle diameter D 1 50 is 4 μm to 50 μm, and can be 4 μm to 25 μm; and the median particle diameter D 2 50 of the second negative electrode active material particles is 1 μm to 40 μm, and can be 1 μm to 20 μm.

[0009] D 1 50, D 2 50 is in a suitable range, which is beneficial on one hand to control the difference between D 1 50 and D 2 50 in the range defined in the present application, so as to be beneficial to the second negative electrode active material particles filling into the gaps between the plurality of first negative electrode active material particles, and further beneficial to improving the tap density of the negative electrode film layer; and on the other hand, the particle interiors of the first negative electrode active material particles and the second negative electrode active material particles can have good transport performance of electrons and sodium ions, and the first negative electrode active material particles and the second negative electrode active material particles can have lower particle interface resistance. Thus, the negative electrode sheet of the present application applied to the sodium ion battery can allow the sodium ion battery to have high energy density and low impedance, so that the sodium ion battery has high capacity, good rate performance and cycle performance.

[0010] In any embodiment, the mass percentage content of the first negative electrode active material particles is 5% to 95%, and can be 70% to 95%, based on the total mass of the first negative electrode active material particles and the second negative electrode active material particles.

[0011] The mass percentage of the first negative electrode active material particles and the second negative electrode active material particles is within the above suitable range, which can ensure that the second negative electrode active material particles fill the gaps among the plurality of first negative electrode active material particles, while making the negative electrode active material particles have a suitable specific surface area. In this way, the contact area between the particles can be increased while improving the compaction density of the negative electrode film, the transmission path between the particles is improved, and the occurrence of particle bridging is avoided, so that the sodium ion battery has high energy density and cycle performance.

[0012] In any embodiment, the elongation E of the negative electrode sheet satisfies: 0.1%≤E≤0.2%, and optionally, 0.1%≤E≤0.15%.

[0013] The difference between the median particle diameters of the first negative electrode active material particles and the second negative electrode active material particles in the present application is within a suitable range, and the negative electrode active material particles can have a high bulk density. Therefore, compared with negative electrode active material particles with a lower bulk density, the negative electrode sheet of the present application can have a lower elongation under the same cold pressing parameters.

[0014] In any embodiment, the single-side coating weight CW of the negative electrode film layer is 2 mg / cm 2 ~ 13 mg / cm 2 , and optionally 5 mg / cm 2 ~ 12 mg / cm 2 .

[0015] The single-side coating weight of the negative electrode film layer is within the above suitable range, which is beneficial to control the thickness of the negative electrode film layer within a suitable range. In this way, not only can the electrons and sodium ions have a suitable migration path in the negative electrode sheet, but also the negative electrode sheet can have a suitable capacity. Therefore, the negative electrode sheet of the present application applied to a sodium ion battery can allow the sodium ion battery to have good rate performance and high energy density

[0016] In any embodiment, the negative electrode film layer satisfies: 30%≤P≤60%, and optionally, 45%≤P≤55%, wherein P=[1-CW / (d1*PA)]*100%, d1=d2 / (1+E), CW represents the single-side coating weight of the negative electrode film layer, PA represents the true density of the single-side negative electrode film layer, E represents the elongation of the negative electrode sheet, and d2 represents the thickness of the single-side negative electrode film layer.

[0017] When the parameter P of the negative electrode film layer satisfies the above condition, it can be considered that the improvement of the compaction density of the negative electrode film layer is mainly realized by the improvement of the bulk density of the negative electrode active material particles, and has no significant effect on the porosity of the negative electrode film layer. In this way, not only is the compaction density of the negative electrode film layer improved, but also the electrolyte wettability of the negative electrode film layer is maintained, so that the negative secondary battery has high energy density and good rate performance.

[0018] In any embodiment, the pore size of the adsorption pores in the first negative electrode active material particles is 0.1 nm to 16 nm, and can be selected as 1 nm to 7 nm. The pore size distribution within the above-mentioned suitable range is beneficial for Na… + The adsorption and desorption of these substances help improve the rate performance of secondary batteries.

[0019] Optionally, the specific surface area of ​​the first negative electrode active material particles is 1 m². 3 / g~40m 3 / g, optional 1.5m 3 / g~10m 3 / g. When the specific surface area of ​​the first negative electrode active material particles is within a suitable range, it not only enables the negative electrode to possess good sodium ion transport performance but also reduces the loss of active ions caused by the solid electrolyte interface (SEI) film. This ensures the initial coulombic efficiency of the sodium-ion battery.

[0020] Optionally, the (002) interplanar spacing of the first negative electrode active material particles is 0.34 nm to 0.45 nm, and can be optionally 0.35 nm to 0.4 nm. The interplanar spacing of the first negative electrode active material particles is within a suitable range, which allows Na... + Successful insertion and extraction enable improved rate performance of sodium-ion batteries.

[0021] Optionally, the actual density of the first negative electrode active material particles is 1.3 g / cm³. 3 ~2.0g / cm 3 1.4g / cm³ is an optional value. 3 ~1.8g / cm 3 The actual density of the first negative electrode active material particles is within the aforementioned range, and the tap density is within the range defined in this application, indicating that the first negative electrode active material particles contain a sufficient number of adsorption pores. Therefore, Na... + It can be smoothly adsorbed and desorbed, thus enabling sodium-ion batteries to have good rate performance.

[0022] 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 hard carbon, soft carbon, and mesophase carbon microspheres. The particle production processes for materials selected from the above categories are mature, facilitating the processing to obtain the first and second negative electrode active material particles that meet the conditions of this application.

[0023] In any embodiment, the first negative electrode active material particles have an irregular shape and / or microspheres, and the second negative electrode active material particles have an irregular shape and / or microspheres.

[0024] 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 with irregular shapes is 5% to 95%, and optionally 70% to 95%.

[0025] When the difference in median particle size between the first and second negative electrode active material particles is within the range specified in this application, the negative electrode film can possess a high compaction density regardless of the morphology of the first and second negative electrode active material particles. This improves the processing flexibility of the negative electrode sheet and allows sodium-ion batteries to achieve high energy density.

[0026] In any embodiment, the first negative electrode active material particle is selected from irregularly shaped hard carbon particles, and the second negative electrode active material particle is selected from microspherical hard carbon particles. Based on the total mass of the first negative electrode active material particle and the second negative electrode active material particle, the mass percentage of the first negative electrode active material particle is 70% to 95%.

[0027] When the second negative electrode active material particles are microspherical hard carbon particles, they can not only fill the gaps between multiple first negative electrode active material particles, thereby improving the compaction density of the negative electrode film, the adhesion of the binder to the negative electrode active material particles, and the conductivity of the negative electrode film, but also play a certain role in slippage, further improving the compaction density of the negative electrode film. When the ratio of the first and second negative electrode active material particles is within a suitable range, the negative electrode active material particles can also possess a suitable specific surface area, resulting in an appropriate number of electrochemical reaction active sites on the surface of the negative electrode active material particles, ensuring the coulombic efficiency of the sodium-ion battery.

[0028] In any embodiment, the first negative electrode active material particles are selected from microspherical hard carbon particles, and the median particle size D of the first negative electrode active material particles is... 1 50 refers to particles ranging from 10μm to 50μm: the second negative electrode active material particles are selected from microspherical hard carbon particles, and the median particle size D of the second negative electrode active material particles is... 2 50 is 5μm to 40μm, 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 content of the first negative electrode active material particles is 5% to 95%, and can be selected as 70% to 95%.

[0029] Microspherical hard carbon particles inherently possess high packing density. Furthermore, the median particle size of both the first and second negative electrode active material particles meets the aforementioned range, further enhancing the packing density of the negative electrode active material particles. Moreover, the microspherical second negative electrode active material particles can simultaneously fill pores and facilitate slippage, thereby significantly improving the compaction density of the negative electrode film. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, can significantly improve the energy density, rate performance, and cycle stability of sodium-ion batteries.

[0030] In any embodiment, the compaction density PD of the 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 / (d1 * PA)] * 100%, d1 = d2 / (1 + E), CW represents the coating weight of one side of the negative electrode film layer, PA represents the true density of the one side of the negative electrode film layer, E represents the elongation of the negative electrode sheet, and d2 represents the thickness of the one side of the negative electrode film layer.

[0031] When the parameter P of the negative electrode film satisfies the above conditions, it can be considered that the increase in the compaction density of the negative electrode film is mainly achieved through the increase in the packing density of the negative electrode active material particles. Therefore, for hard carbon particles, they do not need to undergo deformation or slippage to enable the negative electrode film to have a high compaction density. This allows hard carbon materials to be applied in sodium-ion batteries, giving sodium-ion batteries a broad application prospect.

[0032] In any embodiment, the negative electrode film layer further includes a slip increment component, wherein the ratio of the sum of the masses of the first negative electrode active material particles and the second negative electrode active material particles to the mass of the slip increment component is 100:2 to 100:1, and the slip increment component includes one or more of artificial graphite, natural graphite, and graphene.

[0033] The negative electrode film includes a small amount of slip increment component. During cold pressing, the slip increment component can exert a slipping effect, thereby further increasing the compaction density of the negative electrode film. In addition, the aforementioned slip increment component also has good electrical conductivity, and when applied to the negative electrode sheet, it can also improve the electron transport performance of the negative electrode sheet.

[0034] In any embodiment, the negative electrode film layer further includes a flexible binder, which includes one or more of 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.

[0035] The negative electrode film layer, including the aforementioned flexible binder, possesses excellent flexibility. Therefore, during cold pressing, the negative electrode film layer exhibits lower stress, and the negative electrode sheet achieves lower elongation. This further increases the compaction density of the negative electrode film layer, thereby improving the energy density of the sodium-ion battery.

[0036] A second aspect of this application provides a secondary battery, including the negative electrode sheet of the first aspect of this application.

[0037] 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.

[0038] A third aspect of this application provides a battery module, including the secondary battery of the second aspect of this application.

[0039] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0040] 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.

[0041] 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

[0042] Figure 1 This is a schematic diagram of the elongation test of the negative electrode sheet according to one embodiment of this application.

[0043] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0044] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0045] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0048] 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.

[0049] Figure 8 This is a scanning electron microscope (SEM) image of the negative electrode sheet of Embodiment 1 of this application.

[0050] Explanation of reference numerals in the attached figures:

[0051] 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

[0052] 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.

[0053] 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] Through in-depth research, the inventors discovered that, unlike the lithium intercalation reaction in lithium-ion batteries, during charging, the negative electrode of sodium-ion batteries not only undergoes Na+ intercalation... + The embedding of Na will also result in the negative electrode active material reacting with Na + The adsorption of Na is achieved by selecting negative electrode active material particles with multiple adsorption pores, which ensures that Na adsorption remains constant during long-term cycling. + The ability to smoothly enter and exit the negative electrode ensures the utilization of its capacity. 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 sheet, thereby reducing the transport performance of electrons and sodium ions in the negative electrode sheet and ultimately deteriorating the rate performance of the sodium-ion battery.

[0061] 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.

[0062] Negative electrode sheet

[0063] 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 0.6g / cm³ is an option. 3 ~1.0g / cm 3 The median particle size difference *d* between the first and second negative electrode active material particles satisfies the following relationships: 3μm≤d≤19μm, 3μm≤d≤15μm, 3μm≤d≤10μm, 3μm≤d≤5μm, 5μm≤d≤19μm, 5μm≤d≤15μm, 5μm≤d≤10μm, 10μm≤d≤19μm, 10μm≤d≤15μm, or 15μm≤d≤19μm. The compaction density *PD* of the negative electrode film layer satisfies: 0.8 g / cm³. 3 ≤PD≤1.4g / cm 3 0.8g / cm 3 ≤PD≤1.2g / cm 3 0.8g / cm 3 ≤PD≤1.0g / cm 3 1.0g / cm 3 ≤PD≤1.4g / cm 3 or 1.0g / cm 3 ≤PD≤1.2g / cm 3 .

[0064] 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 give the negative electrode film layer high compaction density while giving the negative electrode film layer high porosity. 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.

[0065] Specifically, not intended to be limited by any theory or explanation, 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 can still possess a sufficient number of adsorption pores. Therefore, Na... +The particles can be readily adsorbed by the first negative electrode active material particles during charging and readily desorbed during discharging. Furthermore, the difference between the median particle size of the first and second negative electrode active material particles is within the aforementioned suitable range, which facilitates the filling of the gaps between the multiple first negative electrode active material particles by the second negative electrode active material particles. This results in a high packing density of the negative electrode active material particles, leading to a suitable compaction density in the cold-pressed negative electrode film. Consequently, the negative electrode active material particles in the negative electrode film are in close contact, thereby improving the electron and sodium ion transport performance in the negative electrode sheet and thus enhancing the rate performance of the sodium-ion battery.

[0066] In some embodiments, the median particle size D of the first negative electrode active material particles 1 50 can be 4μm to 50μm, or optionally 4μm to 25μm; the median particle size D of the second negative electrode active material particles 2 50 can be 1μm to 40μm, or optionally 1μm to 20μm. For example, D 1 50 can be 4μm, 8μm, 10μm, 15μm, 20μm, 25μm, 35μm, 45μm, 50μm, or within any range of the above values; D 2 50 can be 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm or within any range of the above values.

[0067] Not intended to be limited to any theory or explanation, D 1 50. D 2 Within the aforementioned suitable range, 50 not only improves the compaction density of the negative electrode film but also enhances interparticle contact and reduces the impedance of sodium-ion batteries. On one hand, D 1 50. D 2 50. Within the above-mentioned suitable range, it is beneficial to control D. 1 50 and D 2 The 50 difference, within the range defined in this application, facilitates the filling of the gaps between the multiple first negative electrode active material particles by the second negative electrode active material particles, thereby improving the compaction density of the negative electrode film. Furthermore, the suitable particle size of the first and second negative electrode active material particles not only ensures good electron and sodium ion transport performance within each particle but also results in low interparticle interface resistance. Therefore, when the negative electrode sheet of this application is applied to a sodium-ion battery, it allows the sodium-ion battery to possess high energy density and low impedance, thereby enabling the sodium-ion battery to exhibit high capacity, good rate performance, and good cycle performance.

[0068] In some embodiments, the mass percentage of the first negative electrode active material particles can be 5% to 95%, and optionally 70% to 95%, based on the total mass of the first and second negative electrode active material particles. For example, the mass percentage of the first negative electrode active material particles can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, or within any range of the above values, based on the total mass of the first and second negative electrode active material particles.

[0069] Not intended to be limited by any theory or explanation, the appropriate mass percentage of the first and second negative electrode active material particles, within the aforementioned suitable range, ensures that the second negative electrode active material particles fill the gaps between multiple first negative electrode active material particles while simultaneously giving the negative electrode active material particles a suitable specific surface area. This increases the compaction density of the negative electrode film, improves the contact area between particles, enhances the transport path between particles, and prevents interparticle bridging, thereby enabling the sodium-ion battery to possess high energy density and cycle performance.

[0070] In some implementations, the elongation E of the negative electrode sheet 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.

[0071] Not intended to be limited by any theory or explanation, the difference in median particle size between the first and second negative electrode active material particles in this application is within a suitable range, enabling the negative electrode active material particles to possess a high packing density. Therefore, compared to negative electrode active material particles with lower packing density, the negative electrode sheet of this application can possess a lower elongation under the same cold pressing parameters.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In some embodiments, the negative electrode film layer may satisfy: 30% ≤ P ≤ 60%. Optionally, 45% ≤ P ≤ 55%.

[0076] Where P = [1-CW / (d1*PA)]*100%, d1 = d2 / (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 sheet, and d2 represents the thickness of the single-sided negative electrode film.

[0077] 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 increase in the packing density of the negative electrode active material particles, 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.

[0078] In some embodiments, the pore size of the adsorption pores in the first negative electrode active material particles can be 0.1 nm to 16 nm, and optionally 1 nm to 7 nm. A pore size distribution within the aforementioned suitable range is beneficial for Na… + The adsorption and desorption of these substances help improve the rate performance of secondary batteries.

[0079] Optionally, the specific surface area of ​​the first negative electrode active material particles can be 1 m². 3 / g~40m 3 / g, optional 1.5m 3 / g~10m 3 / g. When the specific surface area of ​​the first negative electrode active material particles is within a suitable range, it not only enables the negative electrode to possess good sodium ion transport performance but also reduces the loss of active ions caused by the solid electrolyte interface (SEI) film. This ensures the initial coulombic efficiency of the sodium-ion battery.

[0080] Optionally, the (002) interplanar spacing of the first negative electrode active material particles can be 0.34 nm to 0.45 nm, and optionally 0.35 nm to 0.4 nm. When the interplanar spacing of the first negative electrode active material particles is within a suitable range, it allows Na... + Successful insertion and extraction enable improved rate performance of sodium-ion batteries.

[0081] Optionally, the actual density of the first negative electrode active material particles can be 1.3 g / cm³. 3 ~2.0g / cm 3 1.4g / cm³ is an optional value. 3 ~1.8g / cm 3 The actual density of the first negative electrode active material particles is within the aforementioned range, and the tap density is within the range defined in this application, indicating that the first negative electrode active material particles contain a sufficient number of adsorption pores. Therefore, Na... + It can be smoothly adsorbed and desorbed, thus enabling sodium-ion batteries to have good rate performance.

[0082] 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 hard carbon, soft carbon, and MCMB.

[0083] The particle production process of the materials selected from the above-mentioned types is mature and easy to process into first negative electrode active material particles and second negative electrode active material particles that meet the conditions of this application.

[0084] This application does not limit the morphology of the first negative electrode active material particles and the second negative electrode active material particles. In some embodiments, the first negative electrode active material particles may have an irregular shape and / or microspheres, and the second negative electrode active material particles may have an irregular shape and / or microspheres.

[0085] 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 with irregular shapes can be 5% to 95%, and optionally 70% to 95%.

[0086] The morphology of the first negative electrode active material particles can be the same as or different from that of the second negative electrode active material particles.

[0087] In the negative electrode sheet of this application, when the difference in median particle size between the first negative electrode active material particles and the second negative electrode active material particles is within the range specified in this application, the negative electrode film layer can possess a high compaction density regardless of the morphology of the first and second negative electrode active material particles. This improves the process flexibility of the negative electrode sheet and allows sodium-ion batteries to achieve high energy density.

[0088] In some embodiments, both the first negative electrode active material particles and the second negative electrode active material particles can be hard carbon particles.

[0089] 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 smaller second negative electrode active material particles in the negative electrode film of this application can fill the voids between the first negative electrode active material particles. This allows the first negative electrode active material particles to achieve a high compaction density without deformation, thus enabling the negative electrode film to achieve the desired compaction density. Therefore, when both the first and second 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.

[0090] In some embodiments, the first negative electrode active material particles may be selected from irregularly shaped hard carbon particles, and the second negative electrode active material particles may be selected from microspherical hard carbon particles. 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 may be 70% to 95%.

[0091] Not intended to be limited by any theory or explanation, when the second negative electrode active material particles are microspherical hard carbon particles, they can not only fill the gaps between multiple first negative electrode active material particles, thereby improving the compaction density of the negative electrode film, the adhesion of the binder to the negative electrode active material particles, and the conductivity of the negative electrode film, but also play a certain role in slippage, thereby further improving the compaction density of the negative electrode film. When the ratio of the first and second negative electrode active material particles is within a suitable range, the negative electrode active material particles can also have a suitable specific surface area, thus ensuring that the surface of the negative electrode active material particles has an appropriate number of electrochemical reaction active sites, guaranteeing the coulombic efficiency of the sodium-ion battery.

[0092] In some embodiments, the first negative electrode active material particles may be selected from microspherical hard carbon particles, and the median particle size D of the first negative electrode active material particles is... 1 50 is 10μm~50μm; the second negative electrode active material particles can be selected from microspherical hard carbon particles, and the median particle size D of the second negative electrode active material particles is... 2 50 is 5μm to 40μm, 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 can be 5% to 95%, and can be selected as 70% to 95%.

[0093] Not intended to be limited by any theory or explanation, the microspherical hard carbon particles themselves possess a high packing density. Furthermore, the median particle size of both the first and second negative electrode active material particles meets the aforementioned range, further enhancing the packing density of the negative electrode active material particles. Moreover, the microspherical second negative electrode active material particles can simultaneously fill pores and facilitate slippage, thereby significantly improving the compaction density of the negative electrode film. Therefore, the negative electrode sheet of this application, when applied to sodium-ion batteries, can significantly improve the energy density, rate performance, and cycle stability of sodium-ion batteries.

[0094] In some embodiments, both the first and second negative electrode active material particles can be hard carbon particles. The compaction density (PD) of the negative electrode film can satisfy: 1.0 g / cm³. 3 ≤PD≤1.2g / cm 3 The negative electrode film layer can satisfy: 30% ≤ P ≤ 60%, optionally, 45% ≤ P ≤ 55%, where P = [1 - CW / (d1*PA)] * 100%, d1 = d2 / (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, 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 sheet, and d2 represents the thickness of the single-sided negative electrode film.

[0095] 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 increase in the packing density of the negative electrode active material particles. 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.

[0096] In some embodiments, the negative electrode film layer may further include a slip increment component, wherein the ratio of the sum of the masses of the first negative electrode active material particles and the second negative electrode active material particles to the mass of the slip increment component may be 100:2 to 100:1, and the slip increment component may include one or more of artificial graphite, natural graphite, and graphene.

[0097] Not intended to be limited to any theory or explanation, the inclusion of a small amount of slip increment component in the negative electrode film allows it to exert a slip effect during cold pressing, thereby further increasing the compaction density of the negative electrode film. Furthermore, this slip increment component also possesses good electrical conductivity, and when applied to the negative electrode sheet, it can enhance the electron transport performance of the negative electrode sheet.

[0098] 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.

[0099] 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, facilitating the accumulation of negative electrode active material particles and resulting in a lower elongation of the negative electrode sheet. This further enhances the compaction density of the negative electrode film, thereby increasing the energy density of the sodium-ion battery.

[0100] 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.

[0101] The first and second negative electrode active material particles in this application can be obtained in various ways, and are not limited here. For example, the first and second negative electrode active material particles can be obtained by commercial purchase or self-production.

[0102] As an example, the first and second negative electrode active material particles can be hard carbon particles with irregular shapes. The first and second negative electrode active material particles can be prepared by the following steps: placing coconut shells at 300°C for pre-carbonization; crushing the pre-carbonized coconut shells into particles with a diameter of approximately 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. The particles are easily ball-milled; the particles are ball-milled to obtain carbon particles with Dv50 = 50μm / 40μm / 25μm / 20μm / 9μm / 5μm / 3μm / 1μm; the ball-milled particles are placed in an inert atmosphere and kept at 1150℃ to carbonize the ball-milled particles. Optionally, acetylene gas can be introduced to perform vapor-phase carbon coating on the ball-milled particles, thereby preparing first negative electrode active material particles and second negative electrode active material particles with irregular shapes.

[0103] As another example, the first and second negative electrode active material particles can be microspherical hard carbon particles. The first and second negative electrode active material particles can be prepared by the following steps: dehydrating and carbonizing starch and / or lignin at below 200°C to obtain pre-carbonized particles with a pre-fixed morphology (e.g., the Dv50 of pre-carbonized particles obtained from papermaking lignin, potato starch, corn starch, and rice starch are 50μm, 25μm, 10μm, and 6μm, respectively, and the morphology is spherical or approximately spherical). 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. Other particle sizes with near-spherical or truncated glass morphologies can be obtained in one step (for example, 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 ball milling to 5 μm after tertiary ball milling, 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 ball milling to 1.5 μm after tertiary ball milling, 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 kept at a temperature of 1150°C to carbonize the ball-milled particles. Optionally, acetylene gas can be introduced to perform vapor-phase carbon coating on the ball-milled particles, thereby preparing first and second negative electrode active material particles with microspherical shapes.

[0104] 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.

[0105] 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) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0106] 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.

[0107] In this application, the elongation E of the negative electrode sheet has a meaning known in the art, representing the rate of change of the negative electrode sheet's length 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.

[0108] 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.

[0109] In this application, the thickness d2 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 d3 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 d4 of the negative current collector can be measured with a micrometer. d4 = (d3-d4) / 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.

[0110] In this application, the pore size and pore size distribution of the adsorption pores of the negative electrode material have meanings known in the art and can be determined by methods known in the art. For example, they can be measured by a specific surface area analyzer (e.g., Tristar II 3020M).

[0111] In this application, the specific surface area of ​​the negative electrode active material particles has a meaning known in the art and can be determined by methods known in the art. For example, a specific surface area analyzer (e.g., Tristar II 3020M) can be used to measure the specific surface area of ​​the negative electrode active material by nitrogen adsorption / desorption.

[0112] In this application, the interplanar spacing has a meaning known in the art and can be determined by methods known in the art. For example, it can be obtained by analyzing the particles of the negative electrode active material using X-ray diffraction (e.g., Equinox 100).

[0113] In this application, the true density of the negative electrode active material particles has a meaning known in the art and can be determined by methods known in the art. For example, it can be determined using a true density meter (e.g., AccuPyc II 1340).

[0114] 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.

[0115] Secondary batteries

[0116] A second aspect of this application provides a secondary battery. In some embodiments, it may be a sodium-ion battery.

[0117] 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.

[0118] [Positive electrode plate]

[0119] 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.

[0120] 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.

[0121] 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.).

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] [Negative electrode plate]

[0127] In the secondary battery of this application, the negative electrode includes the negative electrode of the first aspect of this application.

[0128] 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.

[0129] 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.

[0130] 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.).

[0131] 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.

[0132] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0133] 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.

[0134] [Electrolytes]

[0135] 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.

[0136] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0137] In some embodiments, the electrolyte salt may be selected from one or more of NaPF6, NaClO4, NaBCl4, NaSO3CF3 and Na(CH3)C6H4SO3.

[0138] 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.

[0139] 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.

[0140] [Isolation membrane]

[0141] 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.

[0142] 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.

[0143] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0144] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] Battery modules and battery packs

[0149] 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.

[0150] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4In 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.

[0151] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0152] 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.

[0153] 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.

[0154] Electrical appliances

[0155] 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.

[0156] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0157] 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.

[0158] 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.

[0159] Example

[0160] 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.

[0161] Example 1

[0162] 1) Preparation of positive electrode sheet

[0163] 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 mixed thoroughly 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.

[0164] 2) Preparation of negative electrode sheet

[0165] 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.

[0166] The negative electrode active material particles include first negative electrode active material particles and second negative electrode active material particles. Both the first and second negative electrode active material particles are hard carbon particles with irregular shapes. The median particle size D of the first negative electrode active material is... 1 50 is 25μm, the median particle size D of the first negative electrode active material particles. 2 50 represents 22 μm. Based on the total mass of the negative electrode active material particles, the mass percentage of the first negative electrode active material particles, Q1, is 70%. The single-sided coating weight CW of the negative electrode sheet is 8 mg / cm³. 2 .

[0167] 3) Separating membrane

[0168] Polyethylene (PE) separator film (celgard) is used.

[0169] 4) Preparation of electrolyte

[0170] 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.

[0171] 5) Battery manufacturing

[0172] 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.

[0173] Examples 2 to 14

[0174] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. Sodium-ion batteries prepared in Examples 2 to 14.

[0175] Examples 15 to 22

[0176] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50 and Q1, sodium-ion batteries of Examples 15 to 22 were prepared.

[0177] Examples 23 to 26

[0178] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 Sodium-ion batteries of Examples 23 to 26 were prepared by adding 50 and Q1, and additionally adding slip increment components to the negative electrode slurry.

[0179] Examples 27 to 29

[0180] Based on the preparation method of Example 1, the CW of the negative electrode sheet was adjusted to prepare sodium-ion batteries of Examples 27 to 29.

[0181] Example 30

[0182] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The second negative electrode active material particles were replaced with microspherical hard carbon particles to prepare the sodium-ion battery of Example 30.

[0183] Example 31

[0184] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The first negative electrode active material particles and the second negative electrode active material particles were replaced with microspherical hard carbon particles to prepare the sodium-ion battery of Example 31.

[0185] Example 32

[0186] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The sodium-ion battery of Example 32 was prepared by replacing the first negative electrode active material particles with microspherical hard carbon particles.

[0187] Example 33

[0188] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The second negative electrode active material particles were replaced with soft carbon particles with irregular shapes to prepare the sodium-ion battery of Example 33.

[0189] Example 34

[0190] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The second negative electrode active material particles were replaced with spherical MCMB particles to prepare the sodium-ion battery of Example 34.

[0191] Example 35

[0192] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The first negative electrode active material particles were replaced with soft carbon particles with irregular shapes to prepare the sodium-ion battery of Example 35.

[0193] Example 36

[0194] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The first negative electrode active material particles were replaced with spherical MCMB particles to prepare the sodium-ion battery of Example 36.

[0195] Examples 37 to 41

[0196] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50. The types of binders used in the negative electrode sheets were used to prepare sodium-ion batteries in Examples 37 to 41. Specifically, the binder used in the negative electrode sheet of Example 37 was styrene-butadiene rubber (SBR); the binder used in the negative electrode sheet of Example 38 was hydrogenated nitrile butadiene rubber (NBR); the binder used in the negative electrode sheet of Example 39 was a copolymer of vinylidene fluoride and hexafluoropropylene; the binder used in the negative electrode sheet of Example 40 was a copolymer of vinylidene fluoride and acrylates; and the binder used in the negative electrode sheet of Example 41 was polytetrafluoroethylene (PTFE).

[0197] Examples 42 to 45

[0198] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 The sodium-ion batteries of Examples 32 to 45 were prepared by measuring the tap density of the first negative electrode active material particles and the 50.

[0199] Comparative Example 1

[0200] Based on the preparation method of Example 1, the negative electrode active material particles were replaced with hard carbon particles with an irregular shape and a median particle size of 5 μm to prepare a sodium-ion battery of Comparative Example 1.

[0201] Comparative Example 2

[0202] Based on the preparation method of Example 1, the negative electrode active material particles were replaced with microspherical hard carbon particles with a median particle size of 5 μm to prepare sodium-ion batteries of Comparative Example 2.

[0203] Comparative Example 3

[0204] Based on the preparation method of Example 1, D was adjusted 1 50. D 2 50, prepare sodium-ion batteries for Comparative Example 3.

[0205] The relevant preparation parameters of the negative electrode sheets of Examples 1-45 and Comparative Examples 1-3 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; Q3 represents the mass ratio of the slip increment component to the negative electrode active material particles. The tap density ρ and D of the first negative electrode active material particles are also shown. 1 50. D 2 50 can be tested according to the method described above in this instruction manual, and d and PA can be calculated according to the method described above in this instruction manual.

[0206] The relevant test parameters of the negative electrode sheets of Examples 1-45 and Comparative Examples 1-3 are shown in Table 2 below. CW, d2, 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.

[0207] The negative electrode sheet of Example 1 was subjected to SEM testing, and the obtained SEM image is shown below. Figure 8 As shown.

[0208] Table 1: Preparation parameters of negative electrode sheets in Examples 1-45 and Comparative Examples 1-3

[0209]

[0210]

[0211] Table 2: Test parameters of negative electrode sheets of Examples 1-45 and Comparative Examples 1-3

[0212]

[0213]

[0214] In addition, the sodium-ion batteries obtained in Examples 1-45 and Comparative Examples 1-3 were subjected to performance tests. The test results are shown in Table 3 below.

[0215] (1) Energy density test

[0216] 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.

[0217] 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.

[0218] (2) Cyclic life test

[0219] 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.

[0220] Table 3: Performance test results of Examples 1-45 and Comparative Examples 1-3

[0221]

[0222]

[0223] As can be seen from Examples 1 to 6, when the median particle size of the first negative electrode active material particles remains constant, as the median particle size of the second negative electrode active material particles decreases, the difference between the median particle sizes of the first and second negative electrode active material particles increases, and correspondingly, the packing density of the negative electrode active material particles also increases. Figure 8 As shown, the smaller median particle size of the second negative electrode active material particles can fill the gaps between the first negative electrode active material particles, thereby enabling the negative electrode film layer to have a high compaction density. Based on Examples 7 to 11, when the median particle size of the second negative electrode active material particles remains constant, as the median particle size of the first negative electrode active material particles increases, the difference between the median particle sizes of the first and second negative electrode active material particles increases, and correspondingly, the packing density of the negative electrode active material particles also increases. Therefore, the negative electrode film layer can also have a high compaction density. Based on Examples 4, 10, 12 to 13 and Examples 1, 7, 14, and 19, when the difference between the median particle size of the first and second negative electrode active material particles is constant, the median particle sizes of both the first and second negative electrode active material particles have a certain influence on the compaction density of the negative electrode film layer. As can be seen from Examples 1 to 14 and 19, the difference in median particle size between the first and second negative electrode active material particles, within the range specified in this application, can effectively increase the compaction density of the negative electrode film and keep the parameter P of the negative electrode film within a suitable range. This improves the energy density and cycle life of the sodium-ion battery.

[0224] As can be seen from Examples 15 to 22, as the mass percentage Q1 of the first negative electrode active material particles decreases, the compaction density of the negative electrode film generally shows a trend of first increasing and then decreasing. This may be because when Q1 is high, the mass percentage Q2 of the second negative electrode active material is relatively low, resulting in limited improvement in packing density after mixing and limited improvement in compaction density after cold pressing, thus leading to a low compaction density of the negative electrode film. When Q1 is low, Q2 is relatively high, and after the second negative electrode active material particles fill the gaps between the first negative electrode active material particles, there are still excess second negative electrode active material particles. The compaction density of these second negative electrode active material particles is also difficult to improve after cold pressing, and the median particle size of the second negative electrode active material particles is small, which also leads to a low compaction density of the negative electrode film. When the contents of Q1 and Q2 are within a suitable range, not only can the compaction density of the negative electrode film be effectively improved, but the corresponding parameter P of the negative electrode film can also be kept within a suitable range, thus enabling the sodium-ion battery to have both high energy density and long cycle life.

[0225] As can be seen from Examples 19, 23 to 26, adding a slip-increase component to the negative electrode slurry can further improve the compaction density of the negative electrode film. This may be because the slip-increase component can exert a slipping effect during the cold pressing of the negative electrode sheet, thereby allowing the second negative electrode active material particles to more fully fill the gaps between the first negative electrode active material particles. As can be seen from Examples 23 and 26, with the increase of the amount of slip-increase component added, the compaction density of the negative electrode film increases accordingly, but the energy density of the sodium-ion battery does not differ significantly. This may be because the slip-increase component itself is difficult to intercalate sodium ions; while increasing the compaction density of the negative electrode film, the slip-increase component also reduces the theoretical specific capacity of the negative electrode film.

[0226] As can be seen from Examples 19, 27 to 29, the single-sided coating weight of the negative electrode film layer has little effect on the compaction density of the negative electrode film layer. When the difference in median particle size between the first negative electrode active material particles and the second negative electrode active material particles is within the range of this application, negative electrode film layers with different single-sided coating weights can all have high compaction density and suitable parameter P, and have long cycle life.

[0227] As can be seen from Examples 19, 30 to 32, when at least one of the first negative electrode active material particles and the second active material particles is a microspherical hard carbon particle, the compaction density of the negative electrode film can be further improved.

[0228] As can be seen from Examples 33 to 36, compared with soft carbon and MCMB, hard carbon has a higher theoretical specific capacity and cycle stability for sodium-ion batteries.

[0229] As can be seen from Examples 19, 37 to 41, compared with conventional negative electrode binders SBR, flexible binders can improve 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.

[0230] As can be seen from Examples 19, 42 to 45, as the tap density of the first negative electrode active material particles increases, the compaction density of the negative electrode film also increases.

[0231] In contrast, Comparative Examples 1 and 2 used only hard carbon particles with 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 Example 3 utilized a blend of negative electrode active material particles with different median particle sizes, the difference in median particle size between the first and second negative electrode active material particles was below the range defined in this application, limiting its effect 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 3 were also unsatisfactory.

[0232] 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 sheet for a sodium-ion battery, comprising: a negative electrode current collector; and a negative electrode film layer on at least one surface of the negative electrode current collector, the negative electrode film layer including first negative electrode active material particles and second negative electrode active material particles, the first negative electrode active material particles including a plurality of adsorption pores, the first negative electrode active material particles having a tap density of 0.4 g / cm 3 1.4 g / cm 3 , the adsorption pores having a pore diameter of 0.1 nm to 16 nm, wherein a difference d between the median particle diameters of the first and second negative electrode active material particles satisfies the relationship: 3 pm≤d≤19 pm, The compaction density PD of the negative electrode film layer satisfies: 0.8 g / cm 3 ≤ PD ≤ 1.4 g / 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 / cm 3 1.0 g / cm 3 .

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

4. The negative electrode sheet according to any one of claims 1 to 3, wherein The median particle diameter D of the first negative electrode active material particles 1 50 is 4 to 50 μm; The median particle diameter D of the second negative electrode active material particles 2 50 is 1 to 40 μm.

5. The negative electrode sheet according to claim 4, wherein The median particle diameter D of the first negative electrode active material particles 1 50 is 4 to 25 μm; The median particle diameter D of the second negative electrode active material particles 2 50 is 1 to 20 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein a mass percentage of the first negative electrode active material particles is 5% to 95% based on the total mass of the first and second negative electrode active material particles.

7. The negative electrode sheet according to claim 6, wherein a mass percentage of the first negative electrode active material particles is 70% to 95% based on the total mass of the first and second negative electrode active material particles.

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

9. The negative electrode sheet according to claim 8, wherein 0.1%≤E≤0.15%。 10. The negative electrode sheet according to any one of claims 1 to 9, wherein The single-side coating weight CW of the negative electrode film layer is 2 mg / cm 2 13 mg / cm 2 .

11. The negative electrode sheet according to claim 10, wherein The single-side coating weight CW of the negative electrode film layer is 5 mg / cm 2 12 mg / cm 2 .

12. The negative electrode sheet according to any one of claims 1 to 11, wherein the negative electrode film layer satisfies: 30%≤P≤60%, wherein P=[1-CW / (d1*PA) ]*100%, d1=d2 / (1+E), CW represents a single-side coating weight of the negative electrode film layer, PA represents a true density of the single-side negative electrode film layer, E represents an elongation of the negative electrode sheet, and d2 represents a thickness of the single-side negative electrode film layer.

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

14. The negative electrode sheet according to any one of claims 1 to 13, wherein the first negative electrode active material particles satisfy at least one of the following: (1) the pore size of the adsorption pores is 1 nm to 7 nm; (2) the specific surface area of the first negative electrode active material particle is 1 m 3 / g ~ 40 m 3 / g; (3) the (002) interplanar spacing of the first negative electrode active material particles is 0.34 nm to 0.45 nm; (4) the first negative electrode active material particle has a true density of 1.3 g / cm 3 2.0 g / cm 3 .

15. The negative electrode sheet according to claim 14, wherein the first negative electrode active material particles satisfy at least one of the following: (1) the specific surface area of the first negative electrode active material particles is 1.5 m 3 / g ~ 10 m 3 / g; (2) the (002) interplanar spacing of the first negative electrode active material particles is 0.35 nm to 0.4 nm; (3) the first negative electrode active material particle has a true density of 1.4 g / cm 3 1.8 g / cm 3 .

16. The negative electrode sheet according to any one of claims 1-15, wherein the first negative electrode active material particles are selected from one or more of hard carbon, soft carbon, and mesocarbon microbeads; and the second negative electrode active material particles are selected from one or more of hard carbon, soft carbon, and mesocarbon microbeads.

17. The negative electrode sheet according to any one of claims 1-16, wherein, the first negative electrode active material particles have an irregular shape and / or a microspherical shape, and the second negative electrode active material particles have an irregular shape and / or a microspherical shape. 18.The negative electrode sheet of claim 17, wherein a mass percentage of the first negative electrode active material particles having an irregular shape is 5% to 95% based on the total mass of the first and second negative electrode active material particles. 19.The negative electrode sheet of claim 18, wherein a mass percentage of the first negative electrode active material particles having an irregular shape is 70% to 95% based on the total mass of the first and second negative electrode active material particles.

20. The negative electrode sheet according to any one of claims 1-19, wherein, the first negative electrode active material particles are selected from irregularly-shaped hard carbon particles, the second negative electrode active material particles are selected from microspherically-shaped hard carbon particles, and a mass percentage of the first negative electrode active material particles is 70% to 95% based on the total mass of the first and second negative electrode active material particles.

21. The negative electrode sheet according to any one of claims 1-20, wherein, The first negative electrode active material particles are selected from microspheroidal hard carbon particles, the median particle diameter D50 of the first negative electrode active material particles is in the range of 0.5 μm to 10 μm, and the first negative electrode active material particles have a specific surface area of at least 200 m2 / g. 1 50 is 10 μm to 50 μm; The second negative electrode active material particles are selected from microspheroidal hard carbon particles, the median particle diameter D50 of the second negative electrode active material particles is in the range of 5 μm to 40 μm, and the median particle diameter D50 of the first negative electrode active material particles is in the range of 0.1 μm to 5 μm. 2 50 is 5 μm to 40 μm, wherein a mass percentage of the first negative electrode active material particles is 5% to 95% based on the total mass of the first and second negative electrode active material particles.

22. The negative electrode sheet according to claim 21, wherein The first negative active material particles have a mass percentage content of 70% to 95% based on the total mass of the first negative active material particles and the second negative active material particles.

23. The negative electrode sheet according to any one of claims 20 to 22, wherein The compaction density PD of the negative electrode film layer satisfies: 1.0 g / cm 3 ≤ PD ≤ 1.2 g / cm 3 ; The negative film layer satisfies 30%≤P≤60%, P=[1-CW / (d1*PA)]*100%, d1=d2 / (1+E), CW represents a single-sided coating weight of the negative film layer, PA represents a true density of the single-sided negative film layer, E represents a ductility of the negative electrode sheet, and d2 represents a thickness of the single-sided negative film layer.

24. The negative electrode sheet according to claim 23, wherein The negative film layer satisfies 45%≤P≤55%.

25. The negative electrode sheet according to any one of claims 20-22, wherein, The negative film layer further includes a slip increment component, and a ratio of a sum of masses of the first negative active material particles and the second negative active material particles to a mass of the slip increment component is 100:2 to 100:1, and the slip increment component includes one or more of artificial graphite, natural graphite, and graphene.

26. The negative electrode sheet according to any one of claims 1-25, wherein The negative film layer further includes a flexible binder, and the flexible binder includes one or more of a styrene-acrylic emulsion, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and an acrylate, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber.

27. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 26.

28. A battery module comprising the secondary battery according to claim 27.

29. A battery pack comprising the battery module according to claim 28.

30. An electrical device comprising at least one selected from the secondary battery according to claim 27, the battery module according to claim 28, or the battery pack according to claim 29.

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