Secondary battery and electric device containing the same

Abstract

The present application provides a secondary battery and an electric device containing the same, the secondary battery comprising a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the current collector and including a negative electrode active material and a conductive agent, the negative electrode active material having a powder electrical conductivity σ of 80 S / cm or more and 106 S / cm or less; and the negative electrode film layer having a compaction density of 1.35 g / cm 3 -1.50 g / cm 3 The negative electrode sheet helps to reduce the black spot phenomenon of the secondary battery and improve the cycle performance and kinetic performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a secondary battery and an electric device containing the same. BACKGROUND

[0002] In recent years, secondary batteries are increasingly widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Therefore, higher requirements are put forward for the performance of secondary batteries.

[0003] During use or storage, secondary batteries often exhibit some failure phenomena such as black spots and lithium precipitation due to a series of complex chemical and physical actions inside the battery, which seriously reduces the performance of the secondary battery. The negative active material is one of the important raw materials of the secondary battery and has a great influence on the electrical properties of the secondary battery. The failure of graphite-based negative electrode materials mainly occurs on the surface of graphite, which is generated in the process of electrochemical reaction between the surface of graphite and the electrolyte to form a solid electrolyte interface phase (SEI), and ultimately affects the cycle performance of the secondary battery. Therefore, it is necessary to provide a secondary battery that can improve the black spot phenomenon of the secondary battery. SUMMARY

[0004] The present application provides a secondary battery which has good cycle performance and kinetic performance and can reduce the black spot phenomenon on the surface of the negative electrode of the secondary battery.

[0005] The secondary battery provided by the present application comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer comprising a negative electrode active material arranged on at least one surface of the current collector, and the powder conductivity σ of the negative electrode active material is greater than or equal to 80 S / cm and less than or equal to 106 S / cm under the test conditions of a compaction density of 1.5 g / cm 3 ; and the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.50 g / cm 3 .

[0006] Adjusting the powder conductivity σ of the negative electrode active material and the compaction density of the negative electrode film layer can make the negative electrode active material particles in the negative electrode sheet have good electrical contact and conductive network, slow down the problem of gas generation lag caused by the lag of SEI film generation during the formation process of part of the active material particles and the black spot defect caused by the inability of active ions to be embedded in the active material due to gas blocking, slow down the problem of lithium precipitation caused by the content of active ions in the battery being greater than the acceptable amount of the negative electrode, and help to improve the cycle performance and kinetic performance of the secondary battery.

[0007] In any embodiment, the powder conductivity σ is 83 S / cm-104 S / cm, thereby facilitating further improvement of the conductive performance of the negative active material, improvement of the black spot phenomenon, and improvement of the cycle performance of the secondary battery.

[0008] In any embodiment, the compaction density of the negative electrode film layer is 1.40-1.50 g / cm 3 The energy density of the secondary battery can be further improved.

[0009] In any embodiment, the negative active material satisfies at least one of the following conditions:

[0010] (1) The volume distribution particle size D V 1 is 1.4 μm-3.0 μm, and optionally 1.7 μm-2.7 μm;

[0011] (2) The volume distribution particle size D V 50 is 12 μm-18 μm, and optionally 12.9 μm-14.5 μm;

[0012] (3) The particle size distribution (D V 90-D V 10) / D V 50 is 1.3-1.8, and optionally 1.35-1.70.

[0013] Controlling the volume distribution particle size D V 1 can reduce excessive active sites on the surface of the negative active material due to excessive small particles, and reduce irreversible consumption of active ions; it also helps to improve the conductive network between the negative active material particles, and helps the secondary battery to have good cycle performance and alleviate the black spot phenomenon. Controlling the volume distribution particle size D V 50 helps to obtain sufficient active sites, reduce the inhibition of the de-intercalation rate of active ions, and improve the kinetic performance of the secondary battery; controlling the particle size distribution of the negative active material helps to improve the particle size distribution concentration of the negative active material, reduce the side reactions of the negative active material with excessive large and small particle sizes in the electrochemical reaction, and comprehensively improve the cycle performance and kinetic performance of the secondary battery, and further reduce the black spot phenomenon.

[0014] In any embodiment, the tap density of the negative active material is 1.25 g / cm 3 -1.45 g / cm 3 , and optionally 1.29 g / cm 3 -1.41 g / cm 3The tap density of the negative active material is adjusted, so that the negative active materials with different particle sizes are well dispersed in the negative electrode sheet, the negative active material particles have sufficient contact sites and good electrical contact, the active ions are well intercalated and deintercalated between the negative active materials, and the precipitation of the active ions and the black spot phenomenon of the negative electrode sheet are reduced.

[0015] In any embodiment, the specific surface area of the negative active material is 0.8 m 2 / g-1.4 m 2 / g, and optionally 0.9 m 2 / g-1.3 m 2 / g. Adjusting the specific surface area of the negative active material is beneficial to increase the contact sites and surface active sites between the negative active material particles, increase the electrical conductivity of the negative active material, and improve the transmission performance of the active ions, thereby improving the cycle performance of the secondary battery.

[0016] In any embodiment, the gravimetric capacity of the negative active material is 335 mAh / g-350 mAh / g, and optionally 340.5 mAh / g-347.5 mAh / g, so that the energy density of the secondary battery can be improved and the cycle performance thereof can be improved.

[0017] In any embodiment, the areal density of the negative film layer in the negative electrode sheet is 7 mg / cm 2 -15 mg / cm 2 , so that the energy density of the secondary battery can be improved and the cycle performance thereof can be improved.

[0018] In any embodiment, the negative active material comprises artificial graphite.

[0019] A second aspect of the present application provides an electrical device comprising the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0021] Figure 2 is Figure 1 is an exploded view of the secondary battery according to an embodiment of the present application.

[0022] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0023] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0024] Figure 5 is Figure 4Exploded view of the battery pack according to an embodiment of the present application.

[0025] Figure 6 Schematic view of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0026] Figure 7 Cycle curves of Example 2 and Comparative Example 1 of the present application are shown.

[0027] Explanation of Reference Numerals:

[0028] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the positive electrode active material and the method for manufacturing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters that are already well known, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0030] The ranges disclosed herein are defined by the lower and upper limits of the range, given that the range is defined by selecting a lower limit and an upper limit, the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing an arbitrarily selected combination of real numbers between "a" and "b," where "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing these combinations of numbers. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0031] If not particularly specified, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0032] If not particularly specified, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0033] If not particularly specified, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0034] If not particularly specified, the "comprise" and "include" mentioned in the present application are open-ended, and can also be closed. For example, the "comprise" and "include" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0035] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": 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 A and B are both true (or exist).

[0036] Generally, a secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charging and discharging of the battery, active ions (e.g., lithium ions, sodium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, while allowing the active ions to pass through.

[0037] During the formation stage of the secondary battery, the negative electrode active material and the electrolyte will undergo an electrochemical reaction to generate a solid electrolyte interface phase (SEI), accompanied by the generation of gas. In this process, part of the negative electrode active material particles have poor electrical contact with the surrounding particles, and the electrochemical reaction between the graphite material and the electrolyte during the formation process is not timely, and the complete SEI film cannot be formed in time, resulting in a lag in the generation of the SEI film and gas. The gas generated by this lag cannot be discharged in time with the formation process and is retained between the negative electrode plate and the separator, hindering the active ions in this area from being discharged from the positive electrode, passing through the separator, and being embedded in the negative electrode, thus appearing as black spot defects. This causes part of the negative electrode active material to be unable to effectively participate in the charge and discharge cycle of the secondary battery, and the content of the positive electrode active ions in the secondary battery is greater than the maximum active ion content that the negative electrode can accept, causing part of the active ions to be deposited on the surface of the negative electrode and lose electrical activity, resulting in a decrease in the capacity of the battery and a rapid decline in the cycle performance.

[0038] [Secondary battery]

[0039] The present application provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material. Wherein the powder conductivity σ of the negative electrode active material is greater than or equal to 80 S / cm and less than or equal to 106 S / cm under the test conditions of a compaction density of 1.5 g / cm 3 and the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.50 g / cm 3 .

[0040] Adjusting the powder conductivity σ of the negative electrode material and the compaction density of the negative electrode film layer so that there is good electrical contact and a conductive network between the active material particles in the negative electrode plate can slow down the gas lag caused by the lag in the generation of the SEI film during the formation process of part of the negative electrode active material particles, and thus reduce the black spot defects caused by the inability of the active ions to be deintercalated due to the gas barrier and reduce the problem of lithium precipitation in the secondary battery, reduce the irreversible consumption of active ions, and improve the cycle performance and kinetic performance of the secondary battery.

[0041] Herein, the powder conductivity σ of the negative electrode active material is the powder conductivity σ measured under the test conditions of a compaction density of 1.5 g / cm 3 , which can be measured using methods known in the art, for example, using the following method:

[0042] At 25°C, using the FT-8100A four-probe method powder testing platform, the sample was prepared according to the four-probe method in GBT 30835-2014 for the determination method of powder conductivity; and 1 g of the test sample powder was placed in a cylindrical metal mold with a height of 25 mm and a diameter of 12 mm; the lower electrode of the mold was pressed, and the upper electrode was pressed to the sample began to be pressed when the upper electrode was pressed to the table surface, and the sample thickness was maintained at 0.147 ± 0.002 after pressure maintaining for 30 s, then the negative electrode active material was determined by the four-probe method powder at 1.50 g / cm 3 The powder conductivity under the compaction density.

[0043] In some embodiments, the powder conductivity σ of the negative electrode active material is 83 S / cm-104S / cm, which is determined under the test condition that the compaction density is 1.5 g / cm 3 In some embodiments, the powder conductivity σ of the negative electrode active material is 85 S / cm-100 S / cm, 90 S / cm-104S / cm, 85 S / cm-104S / cm, or 95 S / cm-100 S / cm, which is determined under the test condition that the compaction density is 1.5 g / cm 3 Adjusting the powder conductivity of the negative electrode active material helps to further improve the electrical contact between the negative electrode active material particles, improve the electrical conductivity of the negative electrode active material, reduce the black spot phenomenon, and improve the cycle performance of the secondary battery.

[0044] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.50 g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.43 g / cm 3 , 1.44 g / cm 3 -1.50 g / cm 3 , 1.41 g / cm 3 -1.50 g / cm 3 , or 1.40 g / cm 3 -1.45 g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.41 g / cm 3 , 1.42 g / cm 3 , 1.44 g / cm 3 , 1.45 g / cm 3 , 1.46 g / cm 3 , 1.47 g / cm 3 , 1.48 g / cm 3 , 1.49 g / cm 3mg / cm2, 8 mg / cm2, 9 mg / cm2, 10 mg / cm2, 11 mg / cm2, 12 mg / cm2, 13 mg / cm2, or any value between any two of the above values. Adjusting the areal density of the negative electrode sheet helps to improve the energy density of the secondary battery and the migration performance of the active ions.

[0045] The compaction density of the negative electrode film layer has the meaning known in the art and can be measured using methods known in the art. As an example, an electronic balance is used to weigh a negative electrode sheet test sample with an area of S, and the weight is recorded as W1, and a micrometer is used to measure the thickness T1 of the negative electrode sheet. Then the above weighed electrode film layer is wiped off, the weight of the negative electrode current collector is weighed and recorded as W2, and the micrometer is used to measure the thickness T2 of the negative electrode current collector. Then the compaction density PD of the negative electrode film layer is (W1-W2) / [(T1-T2) x S].

[0046] In some embodiments, the areal density of the negative electrode film layer is 7 mg / cm2 2 -15 mg / cm2 2 , 8 mg / cm2 2 -15 mg / cm2 2 , 9 mg / cm2 2 -15 mg / cm2 2 , 7 mg / cm2 2 -13 mg / cm2 2 In some embodiments, the areal density of the negative electrode sheet is 13.0 mg / cm2 2 , 12 mg / cm2 2 , 11 mg / cm2 2 , 10 mg / cm2 2 , 9 mg / cm2 2 , 8 mg / cm2 2 , 7 mg / cm2 2 or any value between any two of the above values. Adjusting the areal density of the negative electrode sheet helps to improve the energy density of the secondary battery and the migration performance of the active ions.

[0047] In this application, the areal density of the negative electrode film layer has the meaning known in the art and can be tested using methods known in the art. As an example, a negative electrode sheet after cold pressing is punched into a small round piece with an area of S1, and its weight is recorded as M1. Then the negative electrode film layer of the above weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0, and the areal density of the negative electrode film layer is (the weight of the negative electrode sheet M1-the weight of the negative electrode current collector M0) / S1.

[0048] In some embodiments, the volume distribution particle size D V1 is 1.4-3.0 μm, optionally 1.7-2.7 μm, 1.8-2.7 μm, 1.71-2.58 μm. In some embodiments, the volume distribution particle size Dv1 of the negative active material is 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or a range between any two of the values. Adjusting the volume distribution particle size Dv1 of the negative active material can control the content of small particles in the negative active material and make the particle size distribution of the negative active material more concentrated, which is conducive to reducing the irreversible consumption of active ions caused by excessive content of small particles; it is also conducive to improving the conductive network between the particles of the negative active material, which can improve the cycle performance and dynamic performance of the secondary battery. V 1 is 1.6 μm, 2.0 μm, 1.2 μm, 1.5 μm, 1.6 μm, or a range between any two of the values. Small-particle negative active materials have a large specific surface area and many surface active sites, and are more likely to form by-products at the active sites during the cycle process, resulting in increased consumption of active ions and deteriorated cycle performance. Adjusting the volume distribution particle size Dv1 of the negative active material can control the content of small particles in the negative active material and make the particle size distribution of the negative active material more concentrated, which is conducive to reducing the irreversible consumption of active ions caused by excessive content of small particles; it is also conducive to improving the conductive network between the particles of the negative active material, which can improve the cycle performance and dynamic performance of the secondary battery. V 1 helps to reduce the content of small-particle negative active materials, reduce the irreversible consumption of active ions, and improve the cycle performance of the secondary battery. At the same time, adjusting the volume distribution particle size Dv1 of the negative active material can shorten the migration path of active ions, promote the embedding and de-embedding of active ions, and improve the conductivity of the negative active material and the dynamic performance of the secondary battery. V 1 can further improve the diffusion channel of active ions in the secondary battery, improve the migration performance of active ions, and the rapid capacity decay caused by the precipitation of active ions in the later cycle.

[0049] In some embodiments, the volume distribution particle size Dv1 of the negative active material is 1.4-3.0 μm, optionally 1.7-2.7 μm, 1.8-2.7 μm, 1.71-2.58 μm. In some embodiments, the volume distribution particle size Dv1 of the negative active material is 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or a range between any two of the values. V 50 is 12-18 μm, optionally 14-16.5 μm, 12-14 μm, 12.9-14.5 μm. In some embodiments, the volume distribution particle size Dv50 of the negative active material is 12.9 μm, 13 μm, 15 μm, 16 μm, 17 μm, or a range between any two of the values. Adjusting the volume distribution particle size Dv50 of the negative active material can improve the specific surface area of the negative active material and provide sufficient surface active sites, shorten the migration path of active ions, promote the embedding and de-embedding of active ions, and improve the conductivity of the negative active material and the dynamic performance of the secondary battery. V 50 helps to improve the specific surface area of the negative active material and provide sufficient surface active sites, shorten the migration path of active ions, promote the embedding and de-embedding of active ions, and improve the conductivity of the negative active material and the dynamic performance of the secondary battery.

[0050] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the negative active material is 1.3-1.8, optionally 1.35-1.70, 1.35-1.60. In some embodiments, the particle size distribution of the negative active material is 1.4, 1.45, 1.5, 1.55, 1.65, 1.7, 1.75, or a range between any two of the values. Adjusting the particle size distribution of the negative active material can control the content of small particles in the negative active material and make the particle size distribution of the negative active material more concentrated, which is conducive to reducing the irreversible consumption of active ions caused by excessive content of small particles; it is also conducive to improving the conductive network between the particles of the negative active material, which can improve the cycle performance and dynamic performance of the secondary battery. V 90-D V 10) / D V 50 is 1.3-1.8, optionally 1.35-1.70, 1.35-1.60. In some embodiments, the particle size distribution of the negative active material is 1.4, 1.45, 1.5, 1.55, 1.65, 1.7, 1.75, or a range between any two of the values. Adjusting the particle size distribution of the negative active material can control the content of small particles in the negative active material and make the particle size distribution of the negative active material more concentrated, which is conducive to reducing the irreversible consumption of active ions caused by excessive content of small particles; it is also conducive to improving the conductive network between the particles of the negative active material, which can improve the cycle performance and dynamic performance of the secondary battery.

[0051] In the present application, the volume distribution particle size D V 10, D V 50, D V 90 has the meaning known in the art, which respectively represents the particle size corresponding to the cumulative volume distribution percentage of 10%, 50% and 90% of the material, which can be measured by using the instruments and methods known in the art. For example, it can be measured by using a laser particle size analyzer according to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0052] In some embodiments, the tap density of the negative electrode active material is 1.25 g / cm 3 -1.45 g / cm 3 , optionally 1.25 g / cm 3 -1.35 g / cm 3 , 1.29 g / cm 3 -1.41 g / cm 3 , 1.25 g / cm 3 -1.41 g / cm 3 . In some embodiments, the tap density of the negative electrode active material is 1.28 g / cm 3 , 1.30 g / cm 3 , 1.33 g / cm 3 , 1.40 g / cm 3 , 1.42 g / cm 3 or a range between any two numerical values. The tap density of the negative electrode active material is within a suitable range, and the negative electrode active material particles with smaller particle size can be well dispersed between the negative electrode active material particles with larger particle size, filling the voids between the negative electrode active material particles with larger particle size, increasing the contact sites between the negative electrode active material particles, which not only improves the electrical conductivity of the negative electrode active material particles, but also helps the insertion and extraction of active ions in the negative electrode active material, reduces the precipitation of active ions and the black spot phenomenon of the negative electrode sheet, and further improves the cycle performance of the secondary battery.

[0053] In the present application, the tap density has the meaning known in the art, which can be measured by using the methods known in the art. For example, it can be measured by using a powder tap density tester (such as Dandong Baiter BT-301) according to GB / T 5162-2006.

[0054] In some embodiments, the specific surface area of the negative electrode active material is 0.8 m 2 / g-1.4 m 2 / g, optionally 0.9 m 2 / g-1.3 m 2 / g, 0.95 m 2 / g-1.1 m 2 / g, 0.97 m 2 / g-1.1 m 2 / g. In some embodiments, the specific surface area of the negative active material is 1.0 m 2 / g, 1.05 m 2 / g, 1.1 m 2 / g, 1.15 m 2 / g, 1.2 m 2 / g, 1.25 m 2 / g, 1.30 m 2 / g, 1.35 m 2 / g or a range between any two values. Adjusting the specific surface area of the negative active material is conducive to improving the degree of overlap between the negative active material particles, increasing the contact sites and surface active sites of the negative active material, improving the electrical conductivity and transport performance of active ions of the negative active material, and improving the cycle performance and power performance of the secondary battery.

[0055] In this context, the term "specific surface area" refers to the sum of the total external surface area of all particles per gram of material. The specific surface area of the graphite material can be measured using instruments and methods known in the art. For example, the specific surface area of the negative active material can be measured by nitrogen adsorption / desorption method using a specific surface area analyzer (American Mac TriStar 3020) according to GB / T 19587-2017 specific surface area determination method: the negative active material is dried in a vacuum drying oven and then loaded into a sample tube, and the specific surface area is measured in the analyzer.

[0056] In some embodiments, the gram capacity of the negative active material is 335 mAh / g-350 mAh / g. In this context, the term "gram capacity" refers to the ratio of the electrical capacity that can be released by the graphite material to the mass of the graphite material. Generally speaking, the higher the gram capacity, the more conducive to improving the energy density of the secondary battery.

[0057] In some embodiments, the gram capacity of the negative active material is 340.5 mAh / g-347.5 mAh / g, for example 344.7 mAh / g, 345.5 mAh / g, 344.9 mAh / g, 345.9 mAh / g, which helps to improve the energy density of the secondary battery and improve the cycle performance of the secondary battery.

[0058] The method for measuring the gram capacity can use any method known in the art. For example, a graphite negative active material sample can be mixed with a conductive agent, carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent NMP to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the surface of a negative electrode current collector copper foil and dried and cold-pressed. Then, a metal lithium sheet is used as a counter electrode, a polypropylene (PP) film is used as a separator film, and an electrolyte is injected, wherein the electrolyte formulation used is as follows: dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. A CR2430 type button cell is assembled in an argon glove box. At 25°C, the button cell prepared above is first discharged at a current of 0.05C to 0.005V, and then discharged at a constant current of 10μA to 0.005V, and then left for 5min, and the first circle discharge capacity of the button cell is recorded. Then, the button cell is charged at a current of 0.1C to 2.0V, and the charge capacity of the button cell is recorded. The ratio of the charge capacity of the button cell to the mass of the graphite negative active material sample is the gram capacity of the graphite negative active material.

[0059] In the present application, the negative active material can be prepared using a method comprising the following steps:

[0060] providing a raw material; processing the raw material to obtain a precursor; subjecting the precursor to graphitization treatment to obtain a graphitized product; removing the magnetic field to obtain the negative active material.

[0061] In some embodiments, the raw material comprises at least one of petroleum coke, needle coke, and pitch coke.

[0062] In the present application, the term "petroleum coke" refers to coke formed by high-temperature carbonization of petroleum residue oil or petroleum pitch.

[0063] In the present application, the term "needle coke" refers to coke with needle-like texture formed by high-temperature carbonization after liquid-phase carbonization of coal tar pitch or petroleum pitch.

[0064] In the present application, the term "pitch coke" refers to solid material formed by high-temperature carbonization of coal tar pitch.

[0065] In some embodiments, the raw material comprises petroleum coke.

[0066] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low graphitization and low expansion graphite materials, and is conducive to the long cycle life of the battery. At the same time, petroleum coke has high compacted density and high gram capacity, which is conducive to improving the energy density of the battery. In addition, the source of petroleum coke is more extensive, which is conducive to industrialized production.

[0067] The above raw material usually includes at least one of mosaic type, regional type and fiber type structure. Generally, according to the morphological characteristics and isochromatic zone size of the coke under a polarizing microscope, the isochromatic zone microstructure with a size less than 30 μm is determined as the mosaic type; the isochromatic zone microstructure with a size greater than 30 μm is determined as the regional type, and the anisotropic strip-shaped isochromatic zone is determined as the fiber type structure.

[0068] In some embodiments of the present application, the volume ratio of the mosaic type and the regional type structure in the raw material is greater than or equal to 60%, and can be 65%-80%, based on the total volume of the structure of the raw material.

[0069] In the present application, the volume ratio of the mosaic type and the regional type structure in the raw material can be tested by the method known in the art. As an example, the raw material is taken according to GB 1997-89, the raw material crushed to 1 mm is mixed, 40 g-50 g is divided, and 4 g-5 g of the sample of 0.07 mm-1.0 mm is taken by a square hole sieve for tablet preparation; the powder coke and block coke optical film are prepared according to MT 116.1-86, the diameter of the powder coke optical film should not be less than 22 mm, and the volume of the cement should be less than 1 / 3; the sample is placed on the slide with cement, flattened, placed on the stage, focused, and adjusted after the microscope is corrected. The polarizer and the analyzer are made orthogonal. Insert the azurite detection plate (1λ), and make the visual field present the first-order red interference color; the step length is determined to ensure that more than 400 effective measuring points are uniformly distributed, and the point distance is 0.3-0.5 mm, and the line distance is generally 0.5-0.8 mm. Starting from one end of the sample, the microstructure category under the intersection of the crosshairs is determined, and the volume ratio of the mosaic type and the regional type structure in the raw material is calculated by dividing the number of effective measuring points of the optical organization of the mosaic type and the regional type structure by the total number of test points.

[0070] In some embodiments, the crushing is a process of reducing the particle size of the raw material, which can be crushed by any mechanical device such as a crusher or a mechanical mill.

[0071] The classification is a process of adjusting the particle size distribution of the raw material to obtain a precursor meeting the particle size requirement. The particle size and the particle size distribution of the precursor can be controlled by adjusting the classification frequency and the air inlet amount. In some embodiments, the classification frequency is 40 Hz-50 Hz, and the damper opening is 20%-70% during the classification process.

[0072] In some embodiments, the D V50 particle size is 10.0 μm-25.0 μm.

[0073] In some embodiments, the precursor has a particle size distribution (D V 50 particle size is 10.0 μm, 13.0 μm, 15.0 μm, 17.0 μm, 20.0 μm, 23.0 μm, 25.0 μm, or any numerical range between any two of them.

[0074] In some embodiments, the precursor has a particle size distribution (D V 90-D V 10) / D V 50 is 1.05-1.75.

[0075] In some embodiments, the precursor has a particle size distribution (D V 90-D V 10) / D V 50 is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75, or any numerical range between any two of them.

[0076] In some embodiments, the precursor has a tap density of 0.5 g / cm 3 -2 g / cm 3 .

[0077] In some embodiments, the precursor has a tap density of 0.5 g / cm 3 , 0.8 g / cm 3 , 1.0 g / cm 3 , 1.2 g / cm 3 , 1.5 g / cm 3 , 1.8 g / cm 3 , or any numerical range between any two of them.

[0078] In some embodiments, a low-temperature carbonization treatment can be further performed before the graphitization treatment. In some embodiments, the low-temperature carbonization treatment is performed at a temperature of 900°C-1300°C for a time period of 24h-240h.

[0079] In some embodiments, the low-temperature carbonization treatment is performed at a temperature of 900°C, 1000°C, 1100°C, 1200°C, 1300°C, or any numerical range between any two of them.

[0080] In some embodiments, the low-temperature carbonization treatment is performed for a time period of 24h, 50h, 75h, 100h, 150h, 200h, 240h, or any numerical range between any two of them.

[0081] In the present disclosure, the term "graphitization treatment" refers to a heat treatment process of carbon materials, in which the carbon materials are subjected to a process of "crystallite" growth from a two-dimensional structure of carbon network to a three-dimensional ordered structure under the action of high temperature.

[0082] In some embodiments, the maximum power of the graphitization treatment is 70-90% of the rated power of the graphitization treatment equipment.

[0083] In some embodiments, the maximum power of the graphitization treatment is 70%, 75%, 80%, 85%, 90% or any numerical range between any two of the rated power of the graphitization treatment equipment. It can be understood that the graphitization treatment equipment 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, tube furnace, etc. Among them, the rated power of the graphitization treatment equipment produced by different manufacturers may be different, which can be selected according to the actual situation.

[0084] In some embodiments, the graphitization treatment equipment is an internal string furnace, and the rated power of the internal string furnace is 25000-32000W. The time of the graphitization treatment can be 10h-30h, and can be selected as 15h-25h.

[0085] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28000-30000W. The time of the graphitization treatment can be 30h-50h, and can be selected as 40h-50h.

[0086] The maximum power of the graphitization treatment adopted in the present application needs to be lower than the rated power of the graphitization treatment equipment, so as to realize the uniformity of the thermal field in the graphitization treatment process.

[0087] In some embodiments, the maximum power of the graphitization treatment can be 20000W-25000W.

[0088] In some embodiments, the maximum power of the graphitization treatment can be selected as 20000W, 21000W, 22000W, 22500W, 23000W, 23500W, 24000W, 25000W or any numerical range between any two of them.

[0089] By controlling the maximum power of the graphitization treatment, the graphitization degree of the graphitic material in the heat treatment process can be effectively controlled, and a uniform disordered layer is formed on the surface of the body while the internal region of the particles of the graphitic material is highly graphitized, which is beneficial to the improvement of the cycle stability of the secondary battery.

[0090] In some embodiments, the constant power duration for maintaining the maximum power in the graphitization process is 10h-50h. In some embodiments, the constant power duration for maintaining the maximum power is 10h, 13h, 16h, 19h, 22h, 25h, 28h, 31h, 33h, 36h, 39h, 42h, 45h, 48h, 50h, or any numerical range between any two of them.

[0091] In some embodiments, the temperature of the graphitization process is 2600℃-3000℃.

[0092] In some embodiments, the temperature of the graphitization process is 2600℃, 2700℃, 2800℃, 2900℃, 3000℃, or any numerical range between any two of them.

[0093] The suitable graphitization process temperature and the suitable graphitization process time neither easily cause the precursor to rearrange excessively, resulting in a high specific surface area of the graphitic material after the graphitization process and deterioration of high-temperature performance, nor effectively improve the graphitization degree of the graphitic material, thereby facilitating the simultaneous improvement of high-temperature storage and cycle life of the secondary battery.

[0094] [Anode electrode sheet]

[0095] As an example of the anode electrode sheet, the anode current collector has two opposite surfaces in the thickness direction thereof, and the anode film layer is provided on any one or both of the two opposite surfaces of the anode current collector.

[0096] In some embodiments, the anode film layer comprises the graphitic material prepared by the method of the first aspect of the present application, thereby enabling the secondary battery to have good cycle performance and kinetic performance.

[0097] In some embodiments, the anode active material comprises one of artificial graphite, natural graphite, soft carbon, hard carbon, and mesocarbon microbeads. In some embodiments, the anode active material comprises artificial graphite.

[0098] In some embodiments, the anode film layer can further comprise other anode active materials in addition to the above-mentioned graphitic material. In some embodiments, the other anode active materials include, but are not limited to, 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 can include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based materials can include one or more of elemental tin, tin oxide, and tin alloy material.

[0099] In some embodiments, the negative current collector can be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0100] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can 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).

[0101] In some embodiments, the negative electrode tab further includes a conductive agent. The conductive agent includes one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the conductive agent includes carbon black. In some embodiments, the conductive agent includes carbon nanotubes. In some embodiments, the conductive agent includes carbon black and carbon nanotubes. The conductive agent is widely available and has excellent conductivity, which is conducive to controlling the manufacturing cost of the secondary battery and improving the conductivity of the negative electrode tab.

[0103] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0104] In some embodiments, the negative electrode tab can be prepared by dispersing the components used to prepare the negative electrode tab, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and then performing processes such as drying, cold pressing, and the like to obtain the negative electrode tab.

[0105] [Positive electrode tab]

[0106] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0107] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0108] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments, the positive electrode active material can employ a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can 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 can be simply referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be simply referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be simply referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be simply referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be simply referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to simply as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0110] In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluorotetrafluoroethylene-propylene terpolymer, a vinylidene-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0111] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., obtaining the positive electrode tab.

[0113] [Electrolyte]

[0114] The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0115] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0116] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0117] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0118] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0119] [Separator]

[0120] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0121] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0122] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly through a winding process or a stacking process.

[0123] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte solution.

[0124] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0125] In addition, the secondary battery, the battery module, the battery pack, and the power consuming device of the present application will be described below with appropriate reference to the accompanying drawings.

[0126] In one embodiment of the present application, a secondary battery is provided.

[0127] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 1is a square structure secondary battery 5 as an example.

[0128] In some embodiments, referring to Figure 2 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can 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 housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person in the art can select according to the specific actual needs.

[0129] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery module.

[0130] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0131] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0132] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery pack.

[0133] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0134] In addition, the application also provides a power utilization device, which comprises at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0135] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0136] Figure 6 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0137] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0138] Embodiment

[0139] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0140] I. Test method

[0141] 1. Particle size test of powder

[0142] Test method: According to GB / T 19077-2016 particle size distribution laser diffraction method, a laser particle size analyzer such as Master Size 3000 of Malvern Instruments Ltd. in the United Kingdom is used to determine the volume distribution particle size D V 10, D V 50, D V 90, and D V 1.

[0143] 2. Test of powder conductivity of powder

[0144] 25℃, using FT-8100A four-probe method powder testing platform, reference GBT 30835-2014 about the four-probe method of sample preparation method for powder conductivity determination; and take 1 g of test sample powder placed in a cylindrical metal mold with a height of 25 mm and a diameter of 12 mm; press the lower electrode of the mold, and the upper electrode is pressed to the sample starts to be pressed when the upper electrode is pressed to the table, and the sample thickness is kept at 0.147±0.002 after 30 s of pressure holding, then the four-probe method is used to measure the carbon material in 1.50g / cm 3 Powder conductivity under powder compaction.

[0145] 3. Specific surface area test of powder

[0146] Referring to GB / T 19587-2017 specific surface area determination method, using specific surface area analyzer (U.S. Mac TriStar 3020) to measure the specific surface area of negative active material by nitrogen adsorption / desorption method: after drying the negative active material in a vacuum drying box, it is loaded into a sample tube, and measured in the analyzer.

[0147] 4. Tap density test of powder

[0148] Referring to GB / T 5162-2006 and GB / T 24533-2009, using powder tap density tester (such as Dandong Bit BT-301), the tap density is determined with the following test parameters: vibration frequency 250±15 times / min, vibration amplitude 3±0.2 mm, vibration times 5000 times, cylinder 25 mL.

[0149] 5. Negative active material specific capacity test

[0150] The measurement method of gram capacity can use any method known in the art. For example, the graphite negative electrode active material sample can be mixed with conductive agent carbon black, polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 in an appropriate amount of solvent NMP to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the surface of the negative electrode current collector copper foil and dried and cold-pressed. Then, a metal lithium sheet is used as the counter electrode, a polypropylene (PP) film is used as the separator film, and an electrolyte is injected, wherein the electrolyte formula used is as follows: dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 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. A CR2430 type button cell is assembled in a glove box under argon protection. At 25°C, the button cell prepared above is first discharged at a current of 0.05C to 0.005V, and then discharged at a current of 10μA to 0.005V, and then rested for 5min, and the first cycle discharge capacity of the button cell is recorded. Then, the button cell is charged at a current of 0.1C to 2.0V, and the charge capacity of the button cell is recorded. The ratio of the charge capacity of the button cell to the mass of the graphite negative electrode active material sample is the gram capacity of the graphite negative electrode active material.

[0151] 6. Test of compaction density of negative electrode film layer

[0152] An electronic balance is used to weigh the negative electrode sheet test sample with an area of S, and the weight is recorded as W1. A micrometer is used to measure the thickness T1 of the negative electrode sheet. Then, the weighed electrode sheet film layer is wiped off, the weight of the negative electrode current collector is measured and recorded as W2, and the micrometer is used to measure the thickness T2 of the negative electrode current collector. The compaction density PD of the negative electrode film layer is (W1-W2) / [(T1-T2)×S].

[0153] 7. Test of high-temperature cycle performance

[0154] At 60°C, the batteries of the above examples and comparative examples are charged at 1C to a voltage of 3.65V, then charged at 3.65V to a current ≤0.05C, and then discharged at 1C to a voltage of 2.5V, which is one charge and discharge cycle. The discharge capacity C1 of the first cycle is recorded. The charging and discharging cycles are repeated until the battery capacity decays to 80% of the initial capacity C1, the test is stopped, and the cycle test number is recorded.

[0155] 8. Black spot test

[0156] At 25°C, the batteries of the above examples and comparative examples are charged at 0.33C to a voltage of 3.65V, and then disassembled in a dry room to observe whether there are black spots on the surface of the negative electrode sheet.

[0157] (1) The total area of black spots / the total area of negative electrode sheet ≤ 1%, and the area of black spots in a single electrode sheet / the area of a single electrode sheet ≤ 8% is defined as a first-level black spot;

[0158] (2) 1% < the total area of black spots / the total area of negative electrode sheet ≤ 3%, or 8% < the area of black spots in a single electrode sheet / the area of a single electrode sheet ≤ 15% is defined as a second-level black spot;

[0159] (3) The total area of black spots / the total area of negative electrode sheet > 3%, or the area of black spots in a single electrode sheet / the area of a single electrode sheet > 15% is defined as a third-level black spot.

[0160] 9. Kinetics performance test

[0161] At 25°C, the secondary battery is charged at 0.33C to 3.65V, then charged at constant voltage to a current of 0.05C, and after standing for 5 min, the secondary battery is discharged at 0.33C to 2.50V, and the actual capacity is recorded as C0.

[0162] Then the secondary battery is sequentially charged at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, to 3.5V or the negative electrode cut-off potential of 0V (whichever is reached first), and after each charging is completed, it is discharged at 1C0 to 2.5V, and the negative electrode potential corresponding to 10%, 20%, 30%, …, 80% SOC (State of Charge) at different charging rates is recorded, and the charging rate corresponding to the negative electrode potential of 0V at different SOC states is obtained by drawing the charging rate-negative electrode potential curve at different SOC states and linear fitting, which is the charging window at the SOC state, and is denoted as C 10％SOC , C 20％SOC , C 30％SOC , C 40％SOC , C 50％SOC , C 60％SOC , C 70％SOC , C 80％SOC , and the charging time T (under the premise that the secondary battery does not lithiumize) of the secondary battery from 10% SOC to 80% SOC is calculated according to the formula (60 / C 10％SOC + 60 / C 20％SOC + 60 / C 30％SOC + 60 / C 40％SOC + 60 / C 50％SOC + 60 / C 60％SOC + 60 / C 70％SOC + 60 / C 80％SOC ) x 10% and is in min. The shorter the charging time, the better the fast-charging performance of the secondary battery.

[0163] II. Method for preparing negative active material

[0164] 1. Preparation of negative active material H1

[0165] The petroleum coke with 67% of mosaic and regional structure is coarsely crushed, and then the coarsely crushed material is crushed, sieved, shaped, and classified. In the classification process, the fine powder accounting for 25% of the total mass of the petroleum coke raw material (volume distribution particle size Dv50 of 3-7 μm) is removed by controlling the frequency of the air guide of the classifier, to obtain a precursor. The volume distribution particle size Dv50 of the precursor is 15.2 μm, and the particle size distribution (Dv90-Dv10) / Dv50 is 1.45.

[0166] The precursor is subjected to graphitization treatment in an Acheson furnace. The graphitization treatment temperature is 2800°C, and the maximum power of the graphitization treatment is 21000 W. After 48 h of constant power treatment at the maximum power, the surface temperature of the graphite crucible of the Acheson furnace is cooled to 250°C, to obtain an intermediate product.

[0167] The obtained intermediate product is screened and demagnetized to obtain the negative active material graphite H1.

[0168] 2. Preparation of negative active material H2

[0169] The preparation process of the negative active material H2 is similar to that of H1, except that:

[0170] The same raw material is used, and is subjected to crushing, shaping, and classification treatment. In the classification treatment, the fine powder is not removed. Then, the same graphitization and screening and demagnetization processes are performed to obtain the negative active material H2.

[0171] 3. Preparation of negative active material H3

[0172] The preparation process of the negative active material H3 is similar to that of H1, except that:

[0173] In the classification process, the fine powder accounting for 16% of the total mass of the petroleum coke raw material is removed. Then, the same graphitization and screening and demagnetization processes are performed to obtain the negative active material H3.

[0174] 4. Preparation of negative active material H4

[0175] The preparation process of the negative active material H4 is similar to that of H1, except that:

[0176] In the classification process, the fine powder accounting for 20% of the total mass of the petroleum coke raw material is removed. Then, the same graphitization and screening and demagnetization processes are performed to obtain the active material H4.

[0177] 5. Preparation of negative active material H5

[0178] The preparation process of the negative active material H5 is similar to that of H1, except that:

[0179] In the classification process, 35% of the total mass of the petroleum coke raw material is removed as fine powder, and then the same graphitization and magnetic screening processes are performed to obtain the active material H5.

[0180] The negative active materials H1-H5 were tested using the above method, and the parameter test results are shown in Table 1:

[0181] Table 1

[0182]

[0183] Preparation of the three, secondary batteries

[0184] Example 1

[0185] 1) Preparation of the negative electrode sheet

[0186] The prepared negative active material, conductive agent carbon black Super P, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed in a mass ratio of 96:1:1.2:1.8, and then deionized water was added as a solvent. The mixture was stirred in a vacuum stirrer until the system was uniform, and a negative electrode slurry was obtained. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil, and then dried, cold-pressed, and cut to obtain a negative electrode sheet. The compaction density of the negative electrode sheet was 1.50 g / cm 3 , and the area density was 9.50 mg / cm 2 .

[0187] 2) Preparation of the positive electrode sheet

[0188] The positive active material lithium iron phosphate (LFP), conductive agent Super P, and binder polyvinylidene fluoride were mixed in a mass ratio of 97:1:2, and then N-methylpyrrolidone was added as a solvent. The mixture was stirred in a vacuum stirrer until the system was uniform, and a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on a positive electrode current collector aluminum foil, and then dried, cold-pressed, and cut to obtain a positive electrode sheet. The compaction density of the positive electrode sheet was 2.5 g / cm 3 , and the area density was 19.5 mg / cm 2 .

[0189] 4) Preparation of the electrolyte

[0190] In an argon atmosphere glove box with a water content of <10 ppm, 8% lithium hexafluorophosphate (LiPF6), 2% vinylene carbonate (VC), 30% ethylene carbonate (EC), 30% methyl ethyl carbonate (EMC), and the rest supplemented with diethyl carbonate (DEC) were mixed to obtain the corresponding electrolyte.

[0191] 5) separator film

[0192] The separator film is selected from a polypropylene film.

[0193] 6) preparation of secondary battery

[0194] The above positive electrode sheet, separator film, and negative electrode sheet are stacked in order with the separator film between the positive and negative electrode sheets to serve as a separator, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, electrolyte is injected after drying, and a lithium ion battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0195] Examples 2-6 and Comparative Examples 1-4

[0196] The preparation method of the secondary battery of Examples 2-6 and Comparative Examples 1-4 is similar to that of the secondary battery of Example 1, but the negative active material and the secondary battery preparation parameters are adjusted. The results of the secondary batteries prepared in Examples 1-6 and Comparative Examples 1-4 tested by the above method are shown in Table 2 below:

[0197] Table 2

[0198]

[0199] As can be seen from Examples 1-6, when the powder conductivity σ of the negative active material is greater than or equal to 80 S / cm and less than or equal to 106 S / cm, and the compaction density of the negative film layer is 1.35 g / cm 3 -1.50 g / cm 3 , the black spot phenomenon is effectively improved, and the secondary battery has good cycle number and charging time.

[0200] As can be seen from Examples 1-2 and Comparative Example 1, when the compaction density of the negative film layer is less than 1.35 g / cm 3 , the electrical contact between the negative active material particles becomes poor and the energy density of the secondary battery is low, resulting in a decrease in the cycle number of the secondary battery and an increase in the black spot phenomenon. Figure 7 The cycle curves of Example 2 and Comparative Example 1 are shown, and it can be seen that the cycle performance of the secondary battery of Example 2 is significantly better than that of Comparative Example 1.

[0201] As can be seen from Examples 1-2 and Comparative Example 2, when the compaction density of the negative film layer is greater than 1.50 g / cm 3 , the electrical contact between the active materials in the negative film layer is improved, which can improve the black spot phenomenon; but the increase in the compaction density leads to a significant deterioration in kinetics, a significant extension of the charging time, and thus a rapid decay in the later cycle, which reduces the cycle performance of the secondary battery.

[0202] As can be seen from Examples 1 to 6 and Comparative Example 3, the content of fine powder in the negative active material in Comparative Example 3 is relatively high, resulting in a powder conductivity σ less than or equal to 80 S / cm; although the fine powder in the active material can improve the electrical contact between the active materials, too much fine powder can block the pores, significantly prolong the charging time, and further result in rapid decay in the later cycle stage, affecting the cycle performance of the secondary battery.

[0203] As can be seen from Examples 1 to 6 and Comparative Example 4, the content of fine powder in the negative active material in Comparative Example 4 is relatively low, resulting in a powder conductivity σ greater than 106 S / cm, poor electrical contact and conductive network between the negative active materials, increased irreversible consumption of active ions in the secondary battery, affecting the charge-discharge performance and capacity of the secondary battery, resulting in a significant decrease in the cycle number, and serious black spot phenomenon.

[0204] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the configuration elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the current collector and including a negative electrode active material, characterized in that, The negative electrode active material has a powder conductivity σ of 80 S / cm to 106 S / cm measured under test conditions of a compaction density of 1.5 g / cm 3 3 and a compaction density of the negative electrode film layer of 1.35 g / cm 3 -1.50 g / cm 3 The negative electrode active material has a volume distribution particle size D V 1 of 1.4 μm to 3.0 μm, and includes artificial graphite.

2. The secondary battery according to claim 1, characterized by the powder conductivity σ is 83 S / cm to 104 S / cm.

3. The secondary battery according to claim 1, characterized by The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.50 g / cm 3 .

4. The secondary battery according to claim 1, characterized by the negative electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle diameter Dv of the negative electrode active material V 1 is 1.7 μm - 2.7 μm; (2) the volume distribution particle diameter D of the negative electrode active material V 50 is 12 μm - 18 μm; (3) the particle size distribution (D V 90-D V 10) / D V 50 is 1.3-1.

8.

5. The secondary battery according to claim 1, characterized by The volume distribution particle diameter D of the negative electrode active material V 50 is 12.9 μm - 14.5 μm.

6. The secondary battery according to claim 1, characterized by The particle size distribution (D V 90-D V 10) / D V 50 is 1.35-1.

70.

7. The secondary battery according to any one of claims 1 to 6, characterized by, The tap density of the negative active material is 1.25 g / cm 3 -1.45 g / cm 3 .

8. The secondary battery according to any one of claims 1 to 6, characterized by, The tap density of the negative active material is 1.29 g / cm 3 -1.41 g / cm 3 .

9. The secondary battery according to any one of claims 1 to 6, characterized by, The negative active material has a specific surface area of 0.8 m 2 / g-1.4 m 2 / g.

10. The secondary battery according to any one of claims 1 to 6, characterized by The negative active material has a specific surface area of 0.9 m 2 / g-1.3 m 2 / g.

11. The secondary battery according to any one of claims 1 to 6, characterized by the gram capacity of the negative electrode active material is 335 mAh / g to 350 mAh / g.

12. The secondary battery according to any one of claims 1 to 6, characterized by the gram capacity of the negative electrode active material is 340.5 mAh / g to 347.5 mAh / g.

13. The secondary battery according to any one of claims 1 to 6, characterized by The areal density of the negative electrode sheet is 7 mg / cm 2 - 15 mg / cm 2 .

14. An electrical device, comprising: a secondary battery comprising the negative electrode sheet according to any one of claims 1 to 13.

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