Secondary battery and electric device

Abstract

The application provides a secondary battery and a power consumption device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the compaction density of the negative electrode film layer is greater than or equal to 1.45 g / cm 3 , the liquid absorption rate of the negative electrode active material is 30 ml / 100 g-60 ml / 100 g, and the tortuosity of the negative electrode sheet is less than or equal to 6. The secondary battery provided by the application has high energy density and excellent cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] The market for secondary batteries used for energy storage is experiencing a boom. Energy density and cycle life are crucial parameters for energy storage batteries, especially those used in large-scale energy storage power stations. However, existing technologies face the following challenges: improving the energy density of energy storage batteries often struggles to balance their cycle performance; and improving the cycle performance of secondary batteries often compromises their energy density. Summary of the Invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device, wherein the secondary battery has a high energy density while also having excellent cycle performance.

[0004] The first aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, and the compaction density of the negative electrode film layer is greater than or equal to 1.45 g / cm 3 The liquid absorption rate of the negative electrode active material is 30ml / 100g-60ml / 100g; the tortuosity of the negative electrode plate is less than or equal to 6.

[0005] Under the premise of high compaction density, the liquid absorption rate of the negative electrode active material and the tortuosity of the negative electrode plate are controlled within an appropriate range, so that the electrolyte can fully infiltrate the negative electrode plate during the repeated deintercalation and insertion of lithium at the negative electrode, reducing the possibility of local polarization, making the current of the negative electrode plate uniformly distributed during the cycle, reducing the possibility of side reactions at the negative electrode interface during the cycle, and reducing the impact of the by-products caused by side reactions clogging the pores on the cycle performance and storage performance of the battery.

[0006] The negative electrode plate of the secondary battery of the present application has a high compaction density, and the electrolyte can fully infiltrate the negative electrode plate during the circulation process, which can further improve the battery's cycle performance and storage performance while having a high energy density.

[0007] In any embodiment, the compaction density of the negative electrode film layer is 1.5 g / cm 3 -1.6g / cm 3 .

[0008] The compaction density of the negative electrode film layer is within an appropriate range, which can take into account both high capacity and excellent electrolyte wetting performance of the electrode, thereby helping the secondary battery to take into account high energy density as well as excellent cycle performance and storage performance.

[0009] In any embodiment, the liquid absorption rate of the negative electrode active material is 35 ml / 100 g to 50 ml / 100 g.

[0010] When the negative electrode active material is within an appropriate range and the electrolyte fully infiltrates the negative electrode plate, the impact of side reactions caused by excessive surface activity of the negative electrode active material on the cycle performance and storage performance is reduced, thereby further improving the cycle performance and cycle performance of the battery and extending the service life and storage life of the battery.

[0011] In any embodiment, the tortuosity of the negative electrode plate is 2-5.

[0012] The tortuosity of the negative electrode plate is within an appropriate range, which can take into account both high capacity and excellent electrolyte wetting performance of the electrode plate, thereby helping the secondary battery to achieve both high energy density and excellent cycle performance and storage performance.

[0013] In any embodiment, the negative electrode active material includes primary particles and secondary particles. Based on the total number of primary particles and secondary particles in the negative electrode active material, the number of secondary particles accounts for 25%-75%, and optionally 26%-50%.

[0014] There are pores inside the secondary particles, which have a certain liquid locking ability and can lock the electrolyte that penetrates into the electrode during the cycle, which is beneficial to increase the liquid absorption rate of the negative electrode active material and facilitate the electrolyte to fully infiltrate the negative electrode. At the same time, the primary particles and secondary particles can form pores in the negative electrode film layer, which can improve the permeability of the electrolyte during the cycle and improve the cycle performance of the battery.

[0015] In any embodiment, the particle body of the negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, and the surface region refers to a region extending 30 nm from the surface of the particle body of the negative electrode active material to the interior of the particle, and the surface region includes a disordered layer. Optionally, the thickness of the disordered layer is 1 nm-20 nm.

[0016] The disordered layer structure in the surface area of ​​the negative electrode active material has a relatively large void structure and a certain liquid locking ability, which can increase the liquid absorption rate of the negative electrode active material, improve the electrolyte's wetting ability on the negative electrode sheet, and improve the battery's cycle performance and storage performance.

[0017] In any embodiment, the specific surface area of ​​the negative electrode active material is 1.1 m 2 / g-1.9m 2 / g, optional 1.2m 2 / g-1.8m 2 / g.

[0018] The specific surface area of ​​the negative electrode active material satisfies the above range, so that the liquid absorption rate of the material is within an appropriate range, so that the electrolyte can fully infiltrate the negative electrode plate during the repeated lithium insertion and deinsertion process of the negative electrode, reducing the possibility of local polarization of the negative electrode plate and improving the cycle performance of the battery.

[0019] In any embodiment, the particle size distribution of the negative electrode active material (Dv90-Dv10) / Dv50 is 1.1-1.6, and optionally 1.15-1.55.

[0020] When the particle size distribution of the negative electrode active material falls within the aforementioned range, the negative electrode plate has a low tortuosity, allowing the electrolyte to fully penetrate the negative electrode plate, improving the battery's cycling and storage performance. Furthermore, a small particle size distribution helps increase the concentration of the negative electrode active material particles, reducing the uneven distribution of active ions in the negative electrode active material caused by large particle size variations, and reducing side reactions between smaller particles of negative electrode active material and the electrolyte, thereby improving the secondary battery's cycling and storage performance.

[0021] In any embodiment, the gram capacity of the negative electrode active material is 345 mAh / g-355 mAh / g, optionally 347 mAh / g-353 mAh / g.

[0022] The gram capacity of the negative electrode active material is within an appropriate range, and its particle strength is high, which reduces the possibility of the particles tending to be flat during the cold pressing process of the electrode, avoids the electrolyte transmission path from becoming significantly longer, and is beneficial to reducing the tortuosity of the negative electrode, facilitating the circulation of the electrolyte, and improving the cycle performance of the battery.

[0023] In any embodiment, the volume distribution particle size Dv50 of the negative electrode active material is recorded as A, and the volume distribution particle size Dv50 of the negative electrode active material after cold pressing under a pressure of 20000N is recorded as B, then the negative electrode active material satisfies: B / A ≥ 85%, optionally ≥ 90%.

[0024] The bonding strength of the negative electrode active material particles that meet the above range is relatively high, which reduces the possibility of the particles tending to be flat during the cold pressing process of the electrode, avoids the electrolyte transmission path from becoming significantly longer, is beneficial to reducing the tortuosity of the negative electrode, is beneficial to the circulation of the electrolyte, and improves the cycle performance of the battery.

[0025] In any embodiment, the volume distribution particle size Dv50 of the negative electrode active material is 8.0 μm-12.0 μm.

[0026] When the volume distribution particle size Dv50 of the negative electrode active material is within an appropriate range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, which is beneficial to the electrolyte infiltration of the electrode sheet and improves the cycle performance of the battery. At the same time, it can also reduce the negative impact of the excessive volume distribution particle size Dv50 of the negative electrode active material on the kinetic performance of the battery, reduce the possibility of lithium plating, and improve the cycle performance and storage performance of the battery.

[0027] In any embodiment, the surface density of the negative electrode film layer is 8 mg / cm 2 -14mg / cm 2 , optional 9mg / cm 2 -12mg / cm 2 .

[0028] The surface density of the negative electrode film layer is within an appropriate range, and the thickness of the negative electrode plate is appropriate. On the one hand, the distance for the electrolyte to laterally infiltrate the plate is relatively short, and the time required for the electrolyte to completely infiltrate the negative electrode plate is also relatively short, reducing the possibility of local polarization and improving the battery's cycle performance and storage performance. On the other hand, the surface density within an appropriate range also ensures that the battery has a certain energy density.

[0029] In any embodiment, the cohesive force of the negative electrode plate is 50 N / m-200 N / m, and can be optionally 60 N / m-150 N / m.

[0030] The high cohesion of the negative electrode plate can reduce plate rebound, reduce the volume of electrolyte required to replenish the pores of the negative electrode plate during cycling, shorten the time required for the electrolyte to fully penetrate the plate, reduce the possibility of local polarization, improve the electrolyte's penetration into the plate, and enhance the battery's cycling and storage performance. At the same time, high cohesion also prevents the plate from powdering and delamination during cycling, which can negatively impact the battery's cycling performance and safety.

[0031] In any embodiment, the rebound rate of the negative electrode plate is 8%-23%, and can be optionally 10%-21%.

[0032] The rebound rate of the negative electrode sheet affects the volume change rate of the pores in the negative electrode sheet during cycling. Specifically, the rebound rate of the negative electrode sheet affects the volume of electrolyte required to be replenished in the pores during cycling. When the rebound rate of the negative electrode sheet is within an appropriate range, the volume of electrolyte required to be replenished in the pores during cycling is relatively small, shortening the time required for the electrolyte to fully soak the sheet. This reduces the likelihood of local polarization and improves the battery's cycling and storage performance. Furthermore, a suitable rebound rate also ensures a certain energy density for the battery.

[0033] A second aspect of the present application provides an electrical device comprising the secondary battery described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of a cross-sectional image of a particle of the negative electrode active material of the present application;

[0035] Figure 2 Schematic diagram of a secondary battery according to one embodiment of the present application.

[0036] Figure 3 yes Figure 1 FIG. 1 is an exploded view of a secondary battery according to an embodiment of the present application.

[0037] Figure 4 Schematic diagram of a battery module according to one embodiment of the present application.

[0038] Figure 5 Schematic diagram of a battery pack according to one embodiment of the present application.

[0039] Figure 6 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0040] Figure 7 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0041] Description of reference numerals:

[0042] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 100 negative electrode active material, 101 surface area, 102 internal area. DETAILED DESCRIPTION

[0043] Below, the embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0049] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0050] In order to improve the energy density of the battery, the method generally adopted is to increase the compaction density of the negative electrode film layer. However, the tortuosity of the negative electrode sheet under high compaction density becomes larger, the transmission path of the electrolyte in the negative electrode film layer becomes significantly longer, and the time required for the electrolyte to infiltrate the negative electrode sheet becomes longer. As a result, some areas of the sheet cannot absorb the discharged electrolyte in time, resulting in the inability of active ions to continue to embed into the negative electrode sheet, local polarization, and uneven current distribution. Black spots appear on the surface of the negative electrode sheet and are accompanied by other side reactions. The accumulation of by-products further blocks the pores, resulting in a decrease in the capacity retention rate of the battery, reducing the battery service life and storage life.

[0051] Therefore, it is difficult for current secondary batteries to achieve both high energy density and excellent cycle performance and storage performance.

[0052] [Negative electrode]

[0053] The present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, and the compaction density of the negative electrode film layer is greater than or equal to 1.45 g / cm 3 The liquid absorption rate of the negative electrode active material is 30ml / 100g-60ml / 100g; the tortuosity of the negative electrode plate is less than or equal to 6.

[0054] In some embodiments, the compaction density of the negative electrode film layer can be selected to be 1.45 g / cm 3 , 1.55g / cm 3 , 1.65g / cm 3 , 1.75g / cm 3 , 1.85g / cm 3 , 1.95g / cm 3 or any value in between.

[0055] The compaction density of the negative electrode film layer can be tested using methods known in the art. As an example, a negative electrode sheet test sample with an area of ​​S is weighed using an electronic balance, with the weight recorded as W1. The thickness of the negative electrode sheet is measured using a caliper to obtain the thickness T1 of the negative electrode sheet. The weighed electrode sheet film layer is then wiped off, the weight of the negative electrode current collector is weighed as W2, and the thickness of the negative electrode current collector is measured using a caliper to obtain the thickness T2 of the negative electrode current collector. The compaction density of the negative electrode film layer is then calculated as PD = (W1-W2) / [(T1-T2)×S].

[0056] In some embodiments, the liquid absorption rate of the negative electrode active material may be 30 ml / 100 g, 35 ml / 100 g, 40 ml / 100 g, 45 ml / 100 g, 50 ml / 100 g, 55 ml / 100 g, 60 ml / 100 g, or any value therebetween.

[0057] As used herein, the term "liquid absorption rate of a negative electrode active material" refers to the volume of electrolyte that can be absorbed by 100 g of the negative electrode active material. For example, a liquid absorption rate of 40 ml / 100 g of the negative electrode active material means that 100 g of the negative electrode active material can absorb 40 ml of electrolyte.

[0058] The liquid absorption rate of the negative electrode active material is affected by the specific surface area of ​​the material, the proportion of secondary particles in the material and the morphology of the material.

[0059] In the present application, the liquid absorption rate of the negative electrode active material can be tested by methods known in the art. As an example, the following example is used: the test electrolyte and material sample are obtained separately, and the torque threshold of the tester is set; the electrolyte is added to the sample in the mixing chamber of the tester at a constant speed. As the liquid absorption rate of the sample increases, the viscosity of the mixture of the sample and the electrolyte continues to increase. When the viscosity of the mixture reaches the torque threshold preset by the tester (for example, 1N), the test is stopped and the volume of the electrolyte absorbed by the unit mass of the sample is calculated. This value is the liquid absorption rate of the sample. The formula of the electrolyte is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 4:3:3 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0060] In some embodiments, the tortuosity of the negative electrode plate can be selected to be 1, 2, 3, 4, 5, 6 or any value therebetween.

[0061] In this article, the term "tortuosity of the negative electrode sheet" refers to the ratio of the length of the transmission path of the electrolyte through the pores of the negative electrode film layer of the negative electrode sheet to the thickness of the negative electrode film layer, which determines the diffusion path of the electrolyte inside the negative electrode film layer.

[0062] The tortuosity of the negative electrode sheet is affected by the compaction density of the negative electrode film layer, the uniformity of the particle size of the negative electrode active material, and the particle strength.

[0063] In this application, the tortuosity of the negative electrode plate can be tested by methods known in the art. As an example, (1) a symmetrical battery EIS test is performed: a negative electrode plate with no scratches or creases on the surface is punched into a small disc with a diameter of 14 mm. The negative electrode plates are assembled into a symmetrical battery in a glove box (humidity ≤ 1 ppm) at room temperature. After injecting the electrolyte, the plates are left to stand for more than 12 hours to allow the electrolyte to fully penetrate the plates. The impedance change is detected by EIS test. The test process is: upper limit frequency 1 kHz, lower limit frequency 500 MHz, perturbation voltage 5 mV, symmetrical battery voltage range -1 V to 1 V; the test data are fitted to obtain the ion diffusion impedance Rion. The electrolyte formula is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 4:3:3 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. (2) Calculation of the tortuosity of the pole piece: The area A (1.5386 cm 2 ), the thickness of the small disc d (cm), the electrolyte conductivity k, the porosity ε of the electrode, and the ion diffusion resistance Rion (Ω) are substituted into the following formula to calculate the electrode tortuosity

[0064] In the negative electrode sheet of this application, the compaction density of the negative electrode film layer is greater than or equal to 1.45g / cm 3 The battery has a high energy density, but the high compaction density will increase the tortuosity of the negative electrode plate and lengthen the electrolyte transmission path, which is not conducive to the circulation of the electrolyte, affecting the wettability of the electrolyte to the negative electrode plate and affecting the cycle performance of the battery.

[0065] In order to compensate for the negative impact of high compaction density on wettability, the present application solves this problem from two aspects: shortening the infiltration time and shortening the infiltration path. On the one hand, a negative electrode active material with a liquid absorption rate of 30ml / 100g-60ml / 100g is used, and its liquid absorption rate will affect the diffusion ability of the electrolyte inside the electrode. If the liquid absorption rate of the negative electrode active material is too small, the wettability of the electrolyte and the negative electrode active material will be worse, and it will take longer for the electrolyte to completely infiltrate the negative electrode active material particles and the pores of the negative electrode plate, and the purpose of improving the wettability of the electrode plate will not be achieved; if the liquid absorption rate of the negative electrode active material is too large, the surface activity of the negative electrode active material is too high, which will cause it to consume more active lithium during the cycle, which is not conducive to extending the battery life. On the other hand, by regulating the uniformity of the particle size, particle strength or surface density of the negative electrode active material, the tortuosity of the electrode sheet is controlled to be less than or equal to 6, thereby compensating for the negative impact of high compaction density on the tortuosity of the electrode sheet, shortening the transmission path of the electrolyte in the negative electrode film layer, and achieving the purpose of improving the wettability of the electrolyte to the negative electrode sheet, thereby improving the cycle performance and storage performance of the battery.

[0066] In summary, the negative electrode plate of the present application has a high compaction density, and the electrolyte can fully infiltrate the negative electrode plate during the cycle process, which can improve the cycle performance and storage performance of the battery while having a high energy density.

[0067] In some embodiments, the compaction density of the negative electrode film layer is 1.5 g / cm 3 -1.6g / cm 3 .

[0068] In some embodiments, the compaction density of the negative electrode film layer can be selected to be 1.5 g / cm 3 , 1.52g / cm 3 、1.54g / cm 3 , 1.55g / cm 3 , 1.56g / cm 3 、1.58g / cm 3 , 1.6g / cm 3 or any value in between.

[0069] The compaction density of the negative electrode film layer is within an appropriate range, which can take into account both high capacity and excellent electrolyte wetting performance of the electrode, thereby helping the secondary battery to take into account high energy density as well as excellent cycle performance and storage performance.

[0070] In some embodiments, the liquid absorption rate of the negative electrode active material is 35 ml / 100 g to 50 ml / 100 g. In some embodiments, the liquid absorption rate of the negative electrode active material can be 35 ml / 100 g, 40 ml / 100 g, 45 ml / 100 g, 50 ml / 100 g, or any value therebetween.

[0071] The liquid absorption rate of the negative electrode active material is within the above range. On the premise that the electrolyte fully infiltrates the negative electrode plate, the impact of the side reactions caused by the excessive surface activity of the negative electrode active material on the cycle performance and storage performance is reduced, thereby further improving the cycle performance and storage performance of the battery and extending the battery life.

[0072] In some embodiments, the tortuosity of the negative electrode plate is 2 to 5. In some embodiments, the tortuosity of the negative electrode plate can be 2, 3, 4, 5 or any value therebetween.

[0073] A suitable range of negative electrode tortuosity can further shorten the electrolyte transport path within the negative electrode sheet, improve electrolyte wettability of the negative electrode sheet, and enhance the battery's cycling and storage performance. It also avoids excessively low tortuosity, which can limit the compaction density or surface density of the negative electrode film to a relatively small range, impacting the battery's energy density, or limiting the particle size distribution of the negative electrode active material to a narrow range, increasing the difficulty of material preparation and hindering industrial production.

[0074] In summary, the tortuosity of the negative electrode sheet is within an appropriate range, which not only improves the cycle performance and storage performance of the battery, but also enables the battery to have a high energy density and / or save costs.

[0075] In some embodiments, the negative electrode active material includes primary particles and secondary particles. Based on the total number of primary particles and secondary particles in the negative electrode active material, the number of secondary particles accounts for 25%-75%, and optionally 26%-50%.

[0076] In some embodiments, based on the total number of primary particles and secondary particles in the negative electrode active material, the number of secondary particles may be selected to be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or any value therebetween.

[0077] As used herein, primary particles and secondary particles have meanings well known in the art. "Primary particles" generally refer to non-agglomerated particles. "Secondary particles" refer to particles that are aggregated from two or more primary particles. Agglomeration between particles can be achieved by external pressure or by the aid of additional substances (e.g., sticky chemicals). Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0078] In the present application, the number ratio of secondary particles in the negative electrode active material can be tested according to the following method: randomly select a test sample in the negative electrode film layer, randomly select multiple test areas in the test sample, use a scanning electron microscope to obtain images of the multiple test areas, and count the ratio of the number of negative electrode active material particles with secondary particle morphology in each image to the total number of negative electrode active material particles. The average value of multiple statistical results is the number ratio of secondary particles in the negative electrode active material.

[0079] The negative electrode active material of this application comprises both primary and secondary particles, achieving both good cycling and kinetic performance. The primary particles have a relatively stable structure, effectively improving the battery's cycling performance. The secondary particles contain pores within them, which provide a certain degree of liquid retention. They can effectively absorb the electrolyte that penetrates the electrode during the cycle, increasing the liquid absorption rate of the negative electrode active material and facilitating the full infiltration of the electrolyte into the negative electrode, thereby improving the battery's kinetic performance.

[0080] In some embodiments, the particle body of the negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, and the surface region refers to a region extending 30 nm from the surface of the particle body of the negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0081] Figure 1 Schematic diagram of a cross-sectional image of a particle of the negative electrode active material 100 of the present application. Figure 1 As shown, the region extending 30 nm inward from the surface of the particle body of the negative electrode active material 100 is the surface region 101 , and the region inside the surface region 101 is the inner region 102 . The surface region 101 includes a disordered layer.

[0082] The disordered layer can be detected through transmission electron microscopy (TEM). Using a focused ion beam (FIB) to slice a 20-50mm thick slice from the center of the negative electrode active material particle, TEM analysis reveals a disordered layer with long-range disorder and short-range order in the surface region, including lattice fringes. The electron diffraction pattern in the disordered layer appears halo-like.

[0083] The disordered layer mainly includes amorphous carbon. The disordered layer has a relatively large porous structure and a certain liquid locking ability, which can increase the liquid absorption rate of the negative electrode active material and improve the wetting ability of the electrolyte to the negative electrode plate. In addition, unlike the disordered layer coated on the surface of the negative electrode active material in the prior art, the disordered layer of the negative electrode active material provided in the embodiment of the present application is located in the particle body of the negative electrode active material. It is derived from the same raw material as the negative electrode active material and is not prepared by post-processing. Therefore, compared with the negative electrode active material obtained by surface coating treatment to obtain a disordered layer, the negative electrode active material has better material consistency, so that the battery exhibits a longer cycle life, and achieves a balance between battery kinetic performance and cycle stability, and is particularly suitable for energy storage batteries with extremely high requirements for cycle life.

[0084] In some embodiments, the thickness of the disordered layer is 1 nm to 20 nm. In some embodiments, the thickness of the disordered layer is 1 nm, 4 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 16 nm, 20 nm, or any range therebetween.

[0085] In the present application, the thickness of the disordered layer can be tested by methods known in the art. As an example, it can be obtained by transmission electron microscopy (TEM) testing. A thin slice with a thickness of about 20-50 mm is cut from the middle of the negative electrode active material particle body by a focused ion beam (FIB), and then the thin slice is subjected to TEM testing to obtain the original TEM test image, and the original image format (xx.dm3) is saved. The original image obtained by the above TEM test is opened in the Digital Micrograph software, and the disordered layer is identified by diffraction stripes or lattice spacing, and its thickness is measured. Normally, the disordered layer has no diffraction stripes, and the lattice spacing is larger than that of the ordered layer, and its thickness is measured.

[0086] The disordered layer with a thickness within the above range has a liquid absorption rate of the negative electrode active material within an appropriate range, which is beneficial for the electrolyte to fully infiltrate the negative electrode sheet and improve the cycle performance of the battery; it will not cause an excessively high degree of side reaction between the active material and the electrolyte, thereby affecting the cycle performance and storage performance.

[0087] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.1 m 2 / g-1.9m 2 In some embodiments, the specific surface area of ​​the negative electrode active material may be 1.1 m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g, 1.9m 2 / g or any value therebetween.

[0088] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.2 m 2 / g-1.8m 2 In some embodiments, the specific surface area of ​​the negative electrode active material may be 1.2 m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g or any value therebetween.

[0089] The specific surface area of ​​the negative electrode active material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0090] The specific surface area of ​​the negative electrode active material satisfies the above range, so that the liquid absorption rate of the material is within an appropriate range, which is conducive to the full infiltration of the electrolyte into the negative electrode sheet and the improvement of the cycle performance of the battery; and does not cause an excessively high degree of side reaction between the active material and the electrolyte, thereby affecting the cycle performance and storage performance.

[0091] In some embodiments, the particle size distribution of the negative electrode active material (Dv90-Dv10) / Dv50 is 1.1-1.6, optionally 1.15-1.55. In some embodiments, the particle size distribution of the negative electrode active material (Dv90-Dv10) / Dv50 can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or any value therebetween.

[0092] The volume distribution particle sizes Dv10, Dv50, and Dv90 of the negative electrode active material are well known in the art and represent the particle sizes corresponding to the 10%, 50%, and 90% cumulative volume distribution percentages, respectively. These can be measured using instruments and methods known in the art. For example, they can be conveniently measured using a laser particle size analyzer, referring to the laser diffraction method for particle size distribution in GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0093] The particle size distribution of the negative electrode active material within the above range helps to improve the concentration of the negative electrode active material particle size, improve the arrangement concentration of the particles, reduce the tortuosity of the negative electrode plate, allow the electrolyte to fully infiltrate the negative electrode plate, and improve the battery's cycle performance and storage performance. At the same time, it can also reduce the uneven distribution of active ions in the negative electrode active material caused by large particle size differences, reduce the side reactions between the smaller particle size negative electrode active material and the electrolyte, and improve the cycle performance and storage performance of the secondary battery. At the same time, the particle size distribution of the negative electrode active material within the above range is good, and its particle packing performance is good, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0094] In some embodiments, the gram capacity of the negative electrode active material is 345 mAh / g-355 mAh / g, optionally 347 mAh / g-353 mAh / g. In some embodiments, the gram capacity of the negative electrode active material can be 345 mAh / g, 347 mAh / g, 349 mAh / g, 351 mAh / g, 353 mAh / g, 355 mAh / g, or any value therebetween.

[0095] The gram capacity can be measured using any method known in the art. For example, a negative electrode active material sample, conductive agent carbon black, and polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an appropriate amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform negative electrode slurry. The negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil, dried, and cold-pressed. An electrolyte is then injected using a metal lithium sheet as the counter electrode and a polypropylene (PP) film as the separator. The electrolyte formulation used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed at a weight ratio of 1:1:1 to form an organic solvent, and LiPF6 is dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the charge capacity was recorded. The ratio of the charge capacity of the button cell to the mass of the negative electrode active material sample is the gram capacity of the negative electrode active material.

[0096] The negative electrode active material's gram capacity is within an appropriate range, and its particle strength is high, reducing the possibility of the particles flattening during the cold pressing process of the electrode sheet. This prevents the electrolyte transmission path from becoming significantly longer, helps reduce the tortuosity of the negative electrode sheet, facilitates the flow of electrolyte, and improves the battery's cycle performance and storage performance. At the same time, the appropriate gram capacity also ensures a high energy density.

[0097] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is recorded as A, and the volume distribution particle size Dv50 of the negative electrode active material after cold pressing under a pressure of 20,000 N is recorded as B. Then the negative electrode active material satisfies: B / A ≥ 85%, and can optionally be B / A ≥ 90%.

[0098] As used herein, the term "volume distribution particle size Dv50" refers to the particle size corresponding to when the cumulative volume distribution number of particles reaches 50% in the particle size distribution curve.

[0099] In this application, the volume distribution particle size Dv50 of the negative electrode active material can be measured using methods known in the art. As an example, it can be measured using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK. The Dv50 ratio of the powder before and after cold pressing can be calculated by the ratio of the Dv50 of the powder to the Dv50 measured by scraping the electrode after cold pressing.

[0100] In some embodiments, B / A is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any range therebetween.

[0101] The bonding strength of the negative electrode active material particles that meet the above range is relatively high, which reduces the possibility of the particles tending to be flat during the cold pressing process of the electrode, avoids the electrolyte transmission path from becoming significantly longer during the cold pressing process, is beneficial to reducing the tortuosity of the negative electrode, is beneficial to the circulation of the electrolyte, and improves the battery's cycle performance and storage performance.

[0102] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is 8.0 μm-12.0 μm.

[0103] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material may be 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, or any value therebetween.

[0104] The volume distribution particle size (Dv50) of the negative electrode active material affects the interparticle pore size in the negative electrode film, which in turn affects the electrolyte wetting path for the negative electrode plate. A suitable volume distribution particle size (Dv50) of the negative electrode active material facilitates the formation of a reasonable pore structure between the particles in the negative electrode film, facilitating electrolyte wetting of the plate and improving the battery's cycling performance. It also reduces the negative impact of an excessively large volume distribution particle size (Dv50) on the battery's kinetic performance, lowering the likelihood of lithium plating and improving the battery's cycling and storage performance.

[0105] In some embodiments, the surface density of the negative electrode film layer is 8 mg / cm 2 -14mg / cm 2 , optional 9mg / cm 2 -12mg / cm 2 In some embodiments, the surface density of the negative electrode film layer can be 8 mg / cm 2 , 9mg / cm 2 、10mg / cm 2 , 11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 、14mg / cm 2 or any range of values ​​between them.

[0106] The areal density of the negative electrode film can be measured using methods known in the art. For example, a cold-pressed negative electrode sheet is punched into small discs with an area of ​​S1. These discs are weighed and recorded as M1. The negative electrode film is then wiped off the weighed negative electrode sheet and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode film = (M1 - M0) / S1.

[0107] The surface density of the negative electrode film layer is within an appropriate range. On the one hand, the distance for the electrolyte to laterally infiltrate the electrode is relatively short, the tortuosity of the electrode is small, and the time required for the electrolyte to completely infiltrate the negative electrode is also relatively short, reducing the possibility of local polarization and improving the battery's cycle performance and storage performance. On the other hand, the surface density within an appropriate range also ensures that the battery has a certain energy density.

[0108] In some embodiments, the cohesive force of the negative electrode plate is 50 N / m-200 N / m, and can be 60 N / m-200 N / m. In some embodiments, the cohesive force of the negative electrode plate can be 50 N / m, 60 N / m, 70 N / m, 80 N / m, 90 N / m, 100 N / m, 110 N / m, 120 N / m, 130 N / m, 140 N / m, 150 N / m, 160 N / m, 170 N / m, 180 N / m, 190 N / m, 200 N / m, or any value therebetween.

[0109] The cohesion of the negative electrode sheet can be tested using any method and equipment known in the art. For example, after the prepared negative electrode sheet is processed (for example, using a scraper) into a single-sided coated negative electrode sheet, it is cut into long strip samples of a certain length and width (for example, the length can be 200 mm and the width can be 20 mm), and then the negative electrode current collector (for example, copper foil) of the sample is fixed to the aluminum plate with double-sided tape, and the side coated with the negative electrode film layer is attached to the PTE tape; after the sample is prepared, a 180° peeling test is performed using a tensile testing machine (the peeling surface is consistent with the force line of the testing machine), the peeling speed is 50 mm / min, and after complete peeling, the force curve during the peeling process is obtained, and the ratio of the average value of the force in the plateau section to the width of the sample is taken as the cohesion of the negative electrode sheet. To ensure the accuracy of the test results, each negative electrode sheet sample is tested at least three times, and the average value is taken as the test result. The testing instrument can be an Instron 33652 tensile testing machine.

[0110] The negative electrode sheet has high cohesion, which can reduce sheet rebound and the volume of electrolyte required to replenish the pores of the negative electrode sheet during cycling. This reduces the time required for the electrolyte to fully penetrate the sheet, reduces the possibility of local polarization, improves electrolyte penetration of the sheet, and enhances the battery's cycling performance. At the same time, high cohesion also reduces the impact of sheet powder loss and film peeling during cycling on the battery's cycling performance and safety.

[0111] In some embodiments, the rebound rate of the negative electrode plate is 8%-23%, and can be 10%-21%. In some embodiments, the rebound rate of the negative electrode plate can be 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 23%, or any value therebetween.

[0112] In this article, the term "rebound rate of the negative electrode sheet" refers to the rate of change of the thickness of the negative electrode sheet in the empty state (the state of charge SOC is 0%) and the fully charged state (the state of charge SOC is 100%).

[0113] The rebound rate of the negative electrode sheet can be tested by any method in the art, as shown below: the thickness of the cold-pressed negative electrode sheet given in the examples and comparative examples of this application is recorded as H0. Take the secondary batteries given in the examples and comparative examples of this application, and perform charge and discharge tests in an environment of 25°C. At a discharge current of 1.0C (i.e., the current value that completely discharges the theoretical capacity within 1 hour), perform constant current discharge to 2.5V. Then, charge at a constant current of 1.0C to 3.65V, continue constant voltage charging to a current of 0.05C, let the fully charged battery stand for 5 minutes, and then discharge at a constant current of 1.0C to 2.5V. The discharge capacity at this time is recorded as C0. Charge the secondary battery to 3.65V at 25°C, disassemble the secondary battery and test the thickness of the negative electrode sheet at this time, which is recorded as H1. The rebound rate of the negative electrode sheet is: (H1 / H0-1)×100%.

[0114] The rebound rate of the negative electrode sheet is related to the gram capacity of the negative electrode active material and the cohesive force of the electrode sheet.

[0115] The rebound rate of the negative electrode sheet affects the volume change rate of the pores in the negative electrode film layer during the battery cycle, that is, the volume of electrolyte that needs to be replenished in the pores. The greater the rebound rate of the negative electrode sheet, the more electrolyte needs to be removed when the battery is fully charged, and the longer it takes for the electrolyte to re-infiltrate the negative electrode sheet. The electrolyte may not be able to completely infiltrate the sheet during the cycle, affecting the battery's cycle performance. At the same time, a large sheet rebound rate leads to greater stress on the negative electrode sheet during the charge and discharge process, and greater damage to the SEI film of the negative electrode sheet. More active lithium needs to be consumed to repair during the cycle, which will also affect the battery's cycle performance and storage performance. If the rebound rate of the negative electrode sheet is too small, it is necessary to adjust the gram capacity of the negative electrode active material to an excessively small range or the cohesion of the negative electrode sheet to an excessively large range, which is not conducive to improving the battery's energy density.

[0116] In some embodiments, the negative electrode active material includes a graphite material.

[0117] The second aspect of the present application provides a method for preparing a negative electrode active material, comprising the following steps: providing raw materials; processing the raw materials to obtain an intermediate product; graphitizing the intermediate product to obtain a negative electrode active material; the particle body of the negative electrode active material includes an internal region and a surface region that at least partially surrounds the internal region, the surface region refers to a region extending 30 nm from the surface of the particle body of the negative electrode active material to the interior of the particle, and the surface region includes a disordered layer.

[0118] As used herein, the term "graphitization" refers to the high-temperature heat treatment of carbon materials, whereby the carbon material undergoes a transformation from a two-dimensional carbon network structure to a three-dimensional ordered structure through crystallite growth at high temperatures.

[0119] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0120] In some embodiments, the maximum power of the graphitization treatment can be selected as 70%, 75%, 80%, 85%, 90% or any numerical range therebetween of the rated power of the graphitization treatment equipment. It is understood that the graphitization treatment device refers to any device capable of performing graphitization treatment, including but not limited to Acheson furnace, box furnace, internal string furnace, continuous graphitization, electric calcining furnace, medium frequency furnace, tubular furnace and other devices. Among them, the rated power of graphitization treatment equipment produced by different manufacturers may be different, and can be selected according to actual conditions. The maximum power of the graphitization treatment used in this application needs to be lower than the rated power of the graphitization treatment device to achieve uniformity of the thermal field during the graphitization treatment process.

[0121] In some embodiments, the graphitization treatment equipment is an inner string furnace, and the rated power of the inner string furnace is 25000-32000W.

[0122] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000-30,000W.

[0123] In some embodiments, the graphitization process is performed at maximum power for a period of 10 hours to 50 hours.

[0124] In some embodiments, the graphitization treatment is performed at maximum power for 10 h, 13 h, 16 h, 19 h, 22 h, 25 h, 28 h, 31 h, 33 h, 36 h, 39 h, 42 h, 45 h, 48 h, 50 h, or any range therebetween.

[0125] In some embodiments, the graphitization treatment equipment is an internal series furnace, and the graphitization treatment time at maximum power is 10 hours to 30 hours.

[0126] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the graphitization treatment time at maximum power is 30 hours to 50 hours.

[0127] In some embodiments, the temperature of the graphitization treatment is 2600°C to 3000°C.

[0128] In some embodiments, the temperature of the graphitization treatment is 2600° C., 2700° C., 2800° C., 2900° C., 3000° C., or any range therebetween.

[0129] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite negative electrode active material after graphitization, which affects the high-temperature performance; it can also effectively improve the graphitization degree of the graphite negative electrode active material, thereby facilitating the simultaneous improvement of the high-temperature storage and cycle life of the secondary battery.

[0130] In some embodiments, the raw material includes at least one of petroleum coke, needle coke, and pitch coke, and needle coke can be selected.

[0131] In this article, the term "petroleum coke" refers to the coke formed by high-temperature carbonization of petroleum residue or petroleum asphalt.

[0132] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which, after undergoing liquid phase carbonization to generate an anisotropic mesophase, can produce coke with a needle-like texture through processes such as high-temperature carbonization.

[0133] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0134] Needle coke has a range of advantages, including low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high conductivity, and easy graphitization. The graphite anode active material after graphitization can achieve a high ultimate compaction density and a low cyclic expansion rate.

[0135] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the fiber-type structure in the raw material is greater than or equal to 55%, and can be optionally 58%-70%.

[0136] In this article, "fibrous structure" is also called streamlined structure, which refers to the structure of the raw material with obvious fibrous texture observed under a microscope.

[0137] Generally, the microstructure of the raw material can be divided into mosaic, regional, and fibrous types based on its morphological characteristics and the size of the isochromatic zones under a polarizing microscope. Generally, isochromatic zones with a size less than 30 μm are classified as mosaic, those with a size greater than 30 μm are classified as regional, and anisotropic banded isochromatic zones are classified as fibrous.

[0138] In this application, the volume percentage of the fiber structure in the raw material can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw material is crushed to 1mm and mixed, and 40g to 50g is separated. A square hole sieve is used to take 4g to 5g of a 0.07mm to 1.0mm grade sample for film making; according to the provisions of MT 116.1-86, powder coke and block coke optical films are prepared. The diameter of the powder coke optical film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3; the sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, adjust the polarizer and analyzer to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of the first order red; determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3 to 0.5mm and a line spacing of 0.5 to 0.8mm. Starting from one end of the sample, determine the microstructure category at the intersection of the crosshairs, and divide the number of effective measurement points of the fiber-type optical structure by the total number of test points as the volume proportion of the fiber-type structure in the raw material.

[0139] In some embodiments, based on the total volume of the raw material structure, the volume proportion of the fibrous structure in the raw material can be selected to be 55%, 58%, 60%, 65%, 70% or any numerical range therebetween.

[0140] Raw materials with a high volume fraction of fiber-type structures are beneficial for increasing the compaction density and specific capacity of graphite negative electrode active materials, allowing the graphite negative electrode active materials to retain a high degree of integrity during the compaction process, resulting in batteries with both a long cycle life and good energy density. However, an excessively high proportion of fiber-type structures will increase the cost and expansion rate of the graphite negative electrode active materials, affecting kinetic performance. Raw materials with a volume fraction of fiber-type structures within the above range have both lower costs and good specific capacity for the graphite, providing a full lifecycle kinetic window for the battery cell, thereby comprehensively improving the long-term cycle life and electrochemical performance of the battery.

[0141] In some embodiments, the maximum gram capacity that can be achieved by the raw material is greater than the gram capacity of the graphite negative electrode active material.

[0142] By using high-grade raw materials and controlling the degree of graphitization so that the maximum gram capacity that the raw materials can achieve is not fully utilized, a graphite negative electrode active material including a disordered layer in the surface area is obtained, achieving a balance between battery cycle life and kinetic performance.

[0143] In some embodiments, the processing of raw materials specifically includes: crushing, shaping, and grading the raw materials to obtain a first precursor; granulating the first precursor to obtain a second precursor; and low-temperature carbonizing a mixture of the first precursor and the second precursor to obtain the intermediate product.

[0144] Crushing is the process of reducing the particle size of raw materials. The raw materials can be crushed by any mechanical device such as crusher, mechanical mill, etc.

[0145] Shaping is the process of adjusting the curvature and particle size of the raw materials.

[0146] Classification is the process of adjusting the particle size distribution of the raw materials to obtain a first precursor that meets the particle size requirements. The particle size and particle size distribution of the first precursor can be controlled by adjusting the classification frequency and air flow rate.

[0147] It can be understood that low-temperature carbonization of the first precursor and the second precursor to obtain the intermediate product includes low-temperature carbonization of a mixture of the first precursor and the second precursor to obtain the intermediate product; it also includes low-temperature carbonization of the first precursor and the second precursor separately to obtain the first intermediate product and the second intermediate product respectively.

[0148] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm to 10.0 μm.

[0149] In some embodiments, the Dv50 particle size of the first precursor is 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, or any range therebetween.

[0150] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05-1.75.

[0151] In some embodiments, the particle size distribution of the first precursor (Dv90-Dv10) / Dv50 is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75, or any range therebetween.

[0152] In some embodiments, the tap density of the first precursor is 0.5 g / cm 3 to 0.7 g / cm 3 .

[0153] As used herein, the term "tap density" refers to the mass per unit volume of powder in a container measured after being tapped under specified conditions.

[0154] In this application, the tap density of the first precursor can be measured using methods known in the art. For example, GB / T 5162-2006 can be used for the tap density test using a powder tap density tester. The test instrument can be a Dandong Better BT-301, with the following test parameters: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration count 5000 times, and a 25 mL graduated cylinder.

[0155] In some embodiments, the tap density of the first precursor is 0.5 g / cm3, 0.55 g / cm3, 0.6 g / cm3, 0.65 g / cm3, 0.7 g / cm3, or any range therebetween.

[0156] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm to 15.0 μm.

[0157] In some embodiments, the Dv50 particle size of the second precursor is 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, or any range therebetween.

[0158] The second precursor is obtained by granulating the first precursor, and therefore, the second precursor mainly forms secondary particles in the graphite negative electrode active material.

[0159] Controlling the particle sizes of the first precursor and the second precursor helps to regulate the particle size and particle size distribution of the graphite negative electrode active material and improve the cycle stability of the battery.

[0160] In some embodiments, the crushing, shaping, and grading of the raw materials to obtain the first precursor includes: crushing, shaping, and grading the raw materials to obtain secondary raw materials; removing fine powder accounting for 10%-35% of the total mass of the secondary raw materials to obtain the first precursor; the Dv50 of the fine powder is 3μm-7μm and Dv99 is less than or equal to 30μm, and the particle size distribution of the fine powder (Dv90-Dv10) / Dv50 is greater than 1.6.

[0161] In some embodiments, the temperature of low-temperature carbonization is 900° C.-1300° C., and the time of low-temperature carbonization is 24 hours-240 hours.

[0162] In some embodiments, the temperature of the low-temperature carbonization may be selected to be 900° C., 1000° C., 1100° C., 1200° C., 1300° C., or any range therebetween.

[0163] In some embodiments, the low-temperature carbonization time may be 24 h, 50 h, 75 h, 100 h, 150 h, 200 h, 240 h, or any range therebetween.

[0164] In some embodiments, the first intermediate product is graphitized to obtain primary particles.

[0165] In some embodiments, the second intermediate product is graphitized to obtain secondary particles.

[0166] In some embodiments, the primary particles and the secondary particles are mixed at a mass ratio of 3:7 to 7:3 to obtain the negative electrode active material.

[0167] In some embodiments, the first intermediate product and the second intermediate product are mixed at a mass ratio of 3:7-7:3 to obtain an intermediate product, and the intermediate product is graphitized to obtain the negative electrode active material.

[0168] In some embodiments, the negative electrode current collector has two opposite surfaces in its 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.

[0169] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0170] In some embodiments, the negative electrode film layer may also be one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0171] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0172] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0174] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0175] In one embodiment of the present application, a secondary battery is provided.

[0176] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0177] [Positive electrode]

[0178] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0179] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0180] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0181] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0182] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0183] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0184] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0185] [Electrolytes]

[0186] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0187] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0188] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0189] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0190] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0191] [Isolation film]

[0192] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0193] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0194] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0195] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0196] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0197] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 2 The secondary battery 5 is a square structure as an example.

[0198] In some embodiments, reference Figure 3 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0199] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0200] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0201] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0202] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0203] Figure 5 and Figure 6 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0204] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0205] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0206] Figure 7 This is an example of an electric device. This device is 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, a battery pack or battery module can be used.

[0207] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0208] Example

[0209] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0210] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0211] 1. Preparation method

[0212] Preparation of negative electrode active materials H1-H6

[0213] H1: The needle coke with a fiber structure volume ratio of 61.1% is coarsely crushed, and then the coarsely crushed material is crushed and sieved, and the sieved material is shaped and graded. During the grading process, a certain amount of fine powder is removed to obtain the first precursor, and 21% of the fine powder relative to the total mass of the sieved material is removed. The fine powder refers to particles with a Dv50 particle size of 3-7μm and a particle size distribution of (Dv90-Dv10) / Dv50>1.6. Among them, the Dv50 particle size of the first precursor is 9.0μm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.35, and the tap density of the first precursor is 0.65g / cm 3 .

[0214] The first precursor is granulated and shaped in a reactor to obtain a second precursor with a particle size Dv50 of 14.3 μm;

[0215] The first precursor and the second precursor were placed in a kiln for carbonization at a temperature of 1100°C and a high temperature zone time of 24 hours to obtain a first intermediate product and a second intermediate product. The tap density of the first intermediate product was 0.98 g / cm 3 The tap density of the second intermediate product is 0.91g / cm 3 ;

[0216] The first intermediate product and the second intermediate product were graphitized at a temperature of 2800°C, respectively. The graphitization treatment device was an internal string furnace with a rated power of 28000W. The maximum power of the graphitization treatment was 22400W. The maximum power / rated power × 100% = 80%. The constant power time of the maximum power was maintained for 20 hours, and primary particles and secondary particles were obtained respectively.

[0217] The primary particles and the secondary particles were evenly mixed in a mass ratio of 30%:70%, and the mixture was sieved to obtain the final negative electrode active material H1.

[0218] The preparation process of negative electrode active materials H2-H6 is basically the same as that of negative electrode active material H1. The adjusted parameters are shown in Table 1.

[0219] Table 1

[0220]

[0221] Example 1

[0222] 1) Preparation of negative electrode sheet

[0223] The prepared negative electrode active material H1, conductive agent carbon black Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed in a mass ratio of 96:1:1.2:1.8, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system became uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained after drying, cold pressing, and slitting. The compacted density of the negative electrode film layer was 1.55 g / cm 3 , with a surface density of 9.2 mg / cm 2 .

[0224] 2) Preparation of positive electrode sheet

[0225] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone was added. The mixture was stirred in a vacuum mixer until the system was uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheets were obtained after drying, cold pressing, and slitting. The compacted density of the positive electrode film layer is 2.50g / cm 3 , with a surface density of 19.7 mg / cm 2 .

[0226] 3) Preparation of electrolyte

[0227] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Vinylene carbonate (VC) was then added, and the VC content was 2% of the total mass of the electrolyte.

[0228] 4) Isolation film

[0229] Polypropylene film is used as the isolation film.

[0230] 5) Preparation of secondary batteries

[0231] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to play a role of isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping, and other processes, a lithium-ion battery embodiment is obtained.

[0232] Examples 2-8 and Comparative Examples 1-3

[0233] The preparation method of the secondary battery is similar to that of Example 1, except that different negative electrode active materials are used and the surface density or compaction density of the negative electrode film layer is adjusted, as shown in Table 2 for details.

[0234] 2. Performance Testing

[0235] 1. Cycling performance test of secondary batteries at 60°C

[0236] At 60°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 3.65V. They were then charged at a constant voltage of 3.65V to a current ≤ 0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the discharge capacity (C1) of the first cycle was recorded. This charge and discharge cycle was repeated until the battery capacity decayed to 80% of the initial capacity (C1). The test was then stopped, and the number of test cycles was recorded.

[0237] 2. Room temperature storage performance of secondary batteries

[0238] In an environment of 25°C, a charge and discharge test is carried out. The battery is charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of ≤0.05C. The battery is then discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge process. The discharge capacity of the first cycle is recorded, which is the initial discharge capacity, recorded as C0. The battery cell is then fully charged and placed in an environment of 60°C for different periods of time. Every 30 days, it is taken out and tested at 25°C for the remaining capacity C1. This is a storage cycle, and the discharge capacity this time is the discharge capacity after the first storage. Subsequently, the first storage test process is repeated, the discharge capacity value during the storage process is recorded, and the 120-day cycle capacity retention rate is recorded.

[0239] 3. Results

[0240] Table 2

[0241]

[0242] From the comparison between Examples 1-8 and Comparative Examples 1-3, it can be seen that the embodiments of the present application simultaneously meet the requirements that the compaction density of the negative electrode film layer is greater than or equal to 1.45 g / cm 3 The liquid absorption rate of the negative electrode active materials H1-H4 is 30ml / 100g-60ml / 100g, and the tortuosity of the negative electrode sheet is less than or equal to 6. The secondary battery can have good cycle performance and storage performance while having a higher energy density.

[0243] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a negative electrode plate, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material, wherein the negative electrode active material includes a graphite material, and the compaction density of the negative electrode film layer is greater than or equal to 1.45 g / cm 3 The liquid absorption rate of the negative electrode active material is 30ml / 100g-60ml / 100g, the tortuosity of the negative electrode sheet is less than or equal to 6, and the tortuosity , where ε is the porosity of the electrode, k is the electrolyte conductivity, Rion is the ion diffusion impedance, A is the sample area, and d is the sample thickness; The particle body of the graphite material includes an internal region and a surface region that at least partially surrounds the internal region. The surface region refers to a region extending 30 nm from the surface of the particle body of the graphite material to the interior of the particle. The surface region includes a disordered layer.

2. The secondary battery according to claim 1, wherein The compaction density of the negative electrode film layer is 1.5 g / cm 3 -1.6g / cm 3 .

3. The secondary battery according to claim 1 or 2, characterized in that The liquid absorption rate of the negative electrode active material is 35 ml / 100 g to 50 ml / 100 g.

4. The secondary battery according to claim 1, wherein The tortuosity of the negative electrode plate is 2-5.

5. The secondary battery according to claim 1, wherein The negative electrode active material includes primary particles and secondary particles; based on the total number of primary particles and secondary particles in the negative electrode active material, the number of the secondary particles accounts for 25%-75%.

6. The secondary battery according to claim 1, wherein The negative electrode active material includes primary particles and secondary particles; based on the total number of primary particles and secondary particles in the negative electrode active material, the number of the secondary particles accounts for 26%-50%.

7. The secondary battery according to claim 1, characterized in that: The thickness of the disordered layer is 1 nm to 20 nm.

8. The secondary battery according to claim 1, wherein The specific surface area of ​​the negative electrode active material is 1.1 m 2 / g-1.9m 2 / g.

9. The secondary battery according to claim 1, wherein The specific surface area of ​​the negative electrode active material is 1.2 m 2 / g-1.8m 2 / g.

10. The secondary battery according to claim 1, wherein The particle size distribution of the negative electrode active material (Dv90-Dv10) / Dv50 is 1.1-1.

6.

11. The secondary battery according to claim 1, wherein The particle size distribution of the negative electrode active material (Dv90-Dv10) / Dv50 is 1.15-1.

55.

12. The secondary battery according to claim 1, wherein The gram capacity of the negative electrode active material is 345 mAh / g-355 mAh / g.

13. The secondary battery according to claim 1, wherein The gram capacity of the negative electrode active material is 347 mAh / g-353 mAh / g.

14. The secondary battery according to claim 1, wherein The volume distribution particle size Dv50 of the negative electrode active material is recorded as A, and the volume distribution particle size Dv50 of the negative electrode active material after cold pressing under a pressure of 20000N is recorded as B. Then, the negative electrode active material satisfies: B / A≥85%.

15. The secondary battery according to claim 1, wherein The volume distribution particle size Dv50 of the negative electrode active material is recorded as A, and the volume distribution particle size Dv50 of the negative electrode active material after cold pressing under a pressure of 20000N is recorded as B. Then, the negative electrode active material satisfies: B / A≥90%.

16. The secondary battery according to claim 1, wherein The volume distribution particle size Dv50 of the negative electrode active material is 8.0 μm-12.0 μm.

17. The secondary battery according to claim 1, wherein The surface density of the negative electrode film layer is 8 mg / cm 2 -14mg / cm 2 .

18. The secondary battery according to claim 1, wherein The surface density of the negative electrode film layer is 9 mg / cm 2 -12mg / cm 2 .

19. The secondary battery according to claim 1, wherein The cohesive force of the negative electrode plate is 50N / m-200N / m.

20. The secondary battery according to claim 1, wherein The cohesive force of the negative electrode plate is 60N / m-150N / m.

21. The secondary battery according to claim 1, characterized in that The rebound rate of the negative electrode plate is 8%-23%.

22. The secondary battery according to claim 1, wherein The rebound rate of the negative electrode plate is 10%-21%.

23. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 22.

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