Negative electrode active material, negative electrode sheet, battery and electrical device

Abstract

The present application relates to a negative electrode active material, a negative electrode plate, a battery and an electrical device. The negative electrode active material comprises artificial graphite particles and a carbon layer disposed on at least a portion of the surface of the artificial graphite particles. The volume average particle size D of the negative electrode active material is v 50 satisfies: 3μm≤D v 50≤7μm; Volume distribution particle size D of negative electrode active material v 1 satisfied: D v 1≤1.5μm.

Description

Technical Field

[0001] The present application relates to a negative electrode active material, a negative electrode plate, a battery and an electrical device. Background Art

[0002] Batteries are widely used due to their reliable performance, pollution-free operation, and zero memory effect. For example, with increasing attention paid to environmental protection and the growing popularity of new energy vehicles, the demand for power battery cells is expected to experience explosive growth.

[0003] As battery applications become increasingly widespread, the requirements for battery performance are becoming increasingly stringent. In relatively low temperature environments, the battery's fast charging capability is poor, and it usually takes a long time to charge. Summary of the Invention

[0004] The present application provides a negative electrode active material, a negative electrode plate, a battery and an electrical device. When the negative electrode active material is applied to a battery, the low-temperature fast charging capability of the battery can be improved.

[0005] In the first aspect, the present application proposes a negative electrode active material, which includes artificial graphite particles and a carbon layer disposed on at least a portion of the surface of the artificial graphite particles, wherein the volume average particle size D of the negative electrode active material is v 50 satisfies: 3μm≤Dv50≤7μm; volume distribution particle size D of negative electrode active material v 1 satisfied: D v 1≤1.5μm.

[0006] Therefore, the embodiment of the present application adjusts the D v 50 and D v 1. It can simultaneously improve the diffusion capacity of lithium ions in the negative electrode active material and the negative electrode film layer, and can slow down the side reaction between the negative electrode active material and the electrolyte, which is beneficial to significantly improve the charging capacity under low temperature conditions.

[0007] In some embodiments, 0.8 μm ≤ D v 1≤1.5μm; optionally, 0.9μm≤D v 1≤1.3μm; further optionally, 0.9μm≤D v 1≤1.0μm. The negative electrode active material is further regulated by adjusting the volume particle size distribution D v 1. It can further regulate the proportion of fine powder. The active material contains an appropriate amount of fine powder, which is conducive to further improving the charging power under low temperature conditions.

[0008] In some embodiments, D v 99≤18μm; optionally, 12μm≤D v99≤18μm. By volume particle size distribution D v 99 further selection can further improve the low-temperature charging performance of battery cells.

[0009] In some embodiments, the negative electrode active material includes primary particles, and the primary particles account for ≥90% of the negative electrode active material, optionally ≥95%. The smaller size of the secondary particles further shortens the migration path of lithium ions and improves the low-temperature fast charging capability of the battery cell.

[0010] In some embodiments, the negative electrode active material has a gram capacity of 330 mAh / g to 340 mAh / g. The relatively high gram capacity of the negative electrode active material results in a higher energy density for the battery cell. Based on this high energy density, the negative electrode active material can also simultaneously enhance the fast charging capability of the battery cell.

[0011] In some embodiments, the tap density of the negative electrode active material is 0.78 g / cm 3 to 1.2g / cm 3 ; Optional 0.9g / cm 3 to 1.1 g / cm 3 The tap density of the negative electrode active material is within the above range, which enables good contact between the particles in the negative electrode film layer, thereby improving the fast charging capability of the battery cell. Due to the close packing of the particles, the energy density of the battery cell can also be increased.

[0012] In some embodiments, the degree of graphitization of the artificial graphite particles is 90% to 93%, and optionally 91% to 93%. When the degree of graphitization of the artificial graphite particles is within the above range, the particle structure can have a larger interlayer spacing and a lower powder resistance, which can further improve the fast charging capability of the battery cell.

[0013] In some embodiments, the average thickness of the carbon layer is ≥ 2 nm, and can be 2 nm to 20 nm. By coating the artificial graphite particles with a carbon layer, the low-temperature fast charging performance of the battery cell can be further improved.

[0014] In the second aspect, the present application proposes a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes the negative electrode active material of any embodiment of the first aspect of the present application.

[0015] In a third aspect, the present application proposes a battery comprising a positive electrode sheet according to any embodiment of the second aspect of the present application.

[0016] In a fourth aspect, the present application proposes an electrical device, comprising a battery as in any embodiment of the third aspect of the present application, wherein the battery is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0018] Figure 1 It is a schematic diagram of an embodiment of a battery cell of the present application.

[0019] Figure 2 yes Figure 1 An exploded schematic diagram of an embodiment of a battery cell.

[0020] Figure 3 It is a schematic diagram of an embodiment of a battery module of the present application.

[0021] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0022] Figure 5 yes Figure 4 An exploded schematic diagram of an embodiment of a battery pack is shown.

[0023] Figure 6 It is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0024] Figure 7 This is one of the scanning electron microscope (SEM) images of the negative electrode active material in Example 1 of the present application.

[0025] Figure 8 This is the second scanning electron microscope (SEM) image of the negative electrode active material in Example 1 of the present application.

[0026] The following are the descriptions of the reference numerals:

[0027] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0028] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0029] 53. Cover plate;

[0030] 6. Electrical equipment. DETAILED DESCRIPTION

[0031] Below, the embodiments of the negative electrode active material, negative electrode sheet, battery cell, battery and 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 structure 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.

[0032] " Range " disclosed in this 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 inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. 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.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] 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.

[0035] Unless otherwise specified, all steps S of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps S(a) and (b), which means that the method may include steps S(a) and (b) performed sequentially, or may include steps S(b) and (a) performed sequentially. For example, a method may further include step S(c), which means that step S(c) may be added to the method in any order, for example, the method may include steps S(a), (b) and (c), or may include steps S(a), (c) and (b), or may include steps S(c), (a) and (b, etc.

[0036] The battery cell includes a positive electrode sheet, a negative electrode sheet and a separator. During the charge and discharge process of the battery cell, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet through the electrolyte. The negative electrode sheet includes a negative electrode collector and a negative electrode film layer arranged on at least one side of the negative electrode collector. The negative electrode active material contained in the negative electrode film layer is an important component of the battery cell, and the active ions can be embedded in and released from the negative electrode active material.

[0037] Under low temperature conditions, the conductivity of the electrolyte decreases, and the solid electrolyte interphase (SEI) membrane impedance, charge transfer impedance, and diffusion impedance of active ions in the negative electrode plate all increase, leading to enhanced polarization and poor low-temperature performance of the battery cell. The negative electrode plate is a key factor restricting the low-temperature kinetic performance of the battery cell. To improve the low-temperature kinetic performance of the battery cell, it is usually considered to improve the performance of the negative electrode film layer, such as adjusting the thickness of the negative electrode film layer and reducing the compaction density of the negative electrode film layer. However, the above methods have limited effect on improving the kinetic performance of the battery cell during charging.

[0038] In view of the above problems, the embodiment of the present application provides a negative electrode active material, which regulates the particle size distribution of the negative electrode active material, specifically regulating the volume average particle size D of the negative electrode active material. v 50 and D v 1. The dynamic performance of the battery cell in both the early and late stages of charging can be significantly improved, and rapid charging of the battery cell can be achieved.

[0039] negative electrode active material

[0040] In a first aspect, an embodiment of the present application provides a negative electrode active material.

[0041] The negative electrode active material includes artificial graphite particles and a carbon layer disposed on at least a portion of the surface of the artificial graphite particles.

[0042] The volume average particle size D of the negative electrode active material v50 satisfies: 3μm≤D v 50≤7μm,

[0043] Volume particle size distribution of negative electrode active material D v 1 satisfied: D v 1≤1.5μm.

[0044] When the negative electrode active material meets the above-mentioned particle size distribution conditions, it can improve both the fast charging performance under low temperature conditions and the high temperature cycle performance. The possible reasons are as follows:

[0045] Battery cell charging is the process in which active ions, such as lithium ions and sodium ions, are extracted from the positive electrode active material and embedded in the negative electrode active material. In the battery field, the industry often uses the "state of charge (SOC)" to reflect the capacity of the battery after charging. Its numerical value is defined as the percentage of the existing capacity to the capacity of the battery after full charge, ranging from 0 to 100%. When "SOC = 0", it means that the battery is not charged; when "SOC = 100%", it means that the battery is in a fully charged state; when "0 < SOC < 100%", it means that the battery has been charged and has a certain capacity, but has not been fully charged. In the embodiment of the present application, the early stage of charging is defined as a low SOC state (≤30% SOC), and the late stage of charging is defined as a high SOC state (≥60% SOC).

[0046] At low temperatures, the diffusion rate of active ions, such as lithium ions, between graphite layers is slow, and the kinetics of lithium ion insertion into the negative electrode is relatively slow. This slow kinetics leads to an overpotential that makes the actual potential of graphite lithium insertion close to the potential for lithium metal deposition, which can easily lead to lithium deposition during low-temperature charging and deteriorate the low-temperature charging performance of the battery cell.

[0047] The volume average particle size D of the negative electrode active material v 50 is the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 50%, and the volume average particle size D of the negative electrode active material v When 50 is 3μm to 7μm, the particle size of the negative electrode active material is small, the active area is large, and the active lithium insertion sites are more. The number of lithium ions diffused to the surface of the negative electrode active material increases, and the interface reaction speed of the negative electrode active material is accelerated, which is beneficial to improving the kinetic performance of the battery cell at a low SOC state, thereby improving its fast charging capability. When the battery cell is in a high SOC state, the diffusion speed of lithium ions becomes the limiting step of the charging rate. The negative electrode active material with a small particle size shortens the lithium insertion path and accelerates the diffusion rate of lithium ions inside the negative electrode active material, which can reduce polarization and is beneficial to the low temperature performance of the battery cell. Therefore, the embodiment of the present application adjusts the volume average particle size D v 50 can regulate the diffusion channels and diffusion rates of lithium ions on the surface and inside the negative electrode active material.

[0048] However, only regulating the diffusion capacity of lithium ions in the negative electrode active material cannot effectively improve the low temperature charging performance of the battery. It is also necessary to simultaneously regulate the diffusion capacity of lithium ions in the negative electrode film layer. v 50, also synchronizes and regulates D v 1. Volume particle size distribution D of negative electrode active material v 1 is the particle size corresponding to the cumulative volume distribution percentage of the negative electrode active material reaching 1%, and the D v 1. It can affect the proportion of fine powder in the negative electrode active material by regulating D v 1≤1.5μm. The inclusion of an appropriate amount of fine powder in the negative electrode active material is beneficial for improving charging power under low temperature conditions. The exposed active surface of the negative electrode active material is not excessive, which can slow down the side reactions between the negative electrode active material and the electrolyte. In addition, the risk of agglomeration of the negative electrode active material in the negative electrode film layer is low, which can increase the porosity in the negative electrode film layer and facilitate the diffusion of lithium ions in the negative electrode film layer. In the embodiments of the present application, fine powder refers to particles with a relatively small particle size.

[0049] Therefore, the embodiment of the present application adjusts the D v 50 and D v 1. It can simultaneously improve the diffusion capacity of lithium ions in the negative electrode active material and the negative electrode film layer, and can slow down the side reaction between the negative electrode active material and the electrolyte, which is beneficial to significantly improve the charging capacity under low temperature conditions.

[0050] In some embodiments, the volume particle size distribution D of the negative electrode active material is v 99 satisfied: D v 99≤18μm.

[0051] In addition to regulating the D v 50 and D v 1. D can be further regulated v 99, Volume particle size distribution of negative electrode active material D v 99 is the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 99%. v 99 can basically control the upper limit of the particle size of the negative electrode active material, the volume particle size distribution of the negative electrode active material D v 99 satisfies D v99≤18μm, the upper limit of the particle size of the negative electrode active material is small, and the consistency of the lithium insertion degree of the negative electrode active materials with different particle sizes is improved due to the small difference in particle size, and the polarization degree of the negative electrode plate is further reduced; and by regulating the overall particle size of the negative electrode active material, the negative electrode film layer has a better pore distribution, which can accelerate the diffusion speed of lithium ions in the negative electrode film layer, thereby improving the low-temperature charging performance of the battery cell. In the embodiment of this application, D v When 99≤18μm, the negative electrode slurry coating performance can also be improved. The performance of the negative electrode film layer coated with the negative electrode slurry is more consistent, and it is not easy to produce scratches when thinly coated, which can avoid subsequent interface abnormalities and performance deterioration caused by scratches.

[0052] In summary, the embodiment of the present application further simultaneously controls the volume average particle size D of the negative electrode active material. v 50. D v 1 and D v 99, which increases the active sites on the surface of the negative electrode active material and the channels for lithium ion diffusion; since the lithium ion diffusion path is shorter, its diffusion rate is improved; and the consistency of the lithium insertion degree between the particles is improved, and the polarization degree of the negative electrode plate is reduced; and the diffusion ability of lithium ions in the negative electrode film layer is improved, thereby significantly improving the kinetic performance of the battery cell in the early and late stages of charging, and improving the low-temperature fast charging capability of the battery cell.

[0053] The volume average particle size D of the negative electrode active material v 50 satisfies: 3μm≤D v 50≤7μm, D v 50 can be specifically 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm or a range consisting of any two of the above values. v 50 further selection can further improve the low-temperature charging performance of the battery cell.

[0054] Volume particle size distribution of negative electrode active material D v 1 satisfied: D v 1≤1.5μm, D v 1 can specifically be 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or a range consisting of any two of the above values. Optionally, 0.8 μm ≤ D v 1≤1.5μm; further optionally, 0.9μm≤D v1≤1.3μm; further optionally, 0.9μm≤D v 1≤1.0μm. The negative electrode active material is further regulated by adjusting the volume particle size distribution D v 1. It can further regulate the proportion of fine powder. The active material contains an appropriate amount of fine powder, which is conducive to further improving the charging power under low temperature conditions.

[0055] Volume particle size distribution of negative electrode active material D v 99 satisfied: D v 99≤18μm, D v 99 can specifically be 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, or a range consisting of any two of the above values. Optionally, 12μm≤D v 99≤18μm. By volume particle size distribution D v 99 further selection can further improve the low-temperature charging performance of battery cells.

[0056] In some embodiments, the negative electrode active material includes primary particles.

[0057] Optionally, the primary particles may comprise ≥90% of the negative electrode active material; ≥95%; ≥98%; or ≥99%. When the primary particles comprise 100% of the negative electrode active material, the negative electrode active material is composed of primary particles. The smaller size of the primary particles further shortens the migration path of lithium ions, improving the low-temperature fast charging capability of the battery cell.

[0058] In some embodiments, the negative electrode active material has a gram capacity of 330 mAh / g to 340 mAh / g. The relatively high gram capacity of the negative electrode active material results in a higher energy density for the battery cell. Based on this high energy density, the negative electrode active material can also simultaneously enhance the fast charging capability of the battery cell.

[0059] Illustratively, the gram capacity of the negative electrode active material can be 330 mAh / g, 331 mAh / g, 332 mAh / g, 333 mAh / g, 334 mAh / g, 335 mAh / g, 336 mAh / g, 337 mAh / g, 338 mAh / g, 339 mAh / g, 340 mAh / g, or a range consisting of any two of the above values.

[0060] In some embodiments, the tap density of the negative electrode active material is 0.78 g / cm 3 to 1.2g / cm 3; Optional 0.9g / cm 3 to 1.1 g / cm 3 The tap density of the negative electrode active material is within the above range, which enables good contact between the particles in the negative electrode film layer, thereby improving the fast charging capability of the battery cell. Due to the close packing of the particles, the energy density of the battery cell can also be increased.

[0061] For example, the tap density of the negative electrode active material may be 0.78 g / cm 3 , 0.8g / cm 3 , 0.82g / cm 3 , 0.85g / cm 3 、0.88g / cm 3 , 0.9g / cm 3 , 0.92g / cm 3 , 0.95g / cm 3 , 0.98g / cm 3 , 1g / cm 3 , 1.05g / cm 3 , 1.10g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 Or a range consisting of any two of the above values.

[0062] In some embodiments, the degree of graphitization of the artificial graphite particles is 90% to 93%, optionally 91% to 93%. For example, the degree of graphitization of the artificial graphite particles is 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, or a range consisting of any two of these values. When the degree of graphitization of the artificial graphite particles falls within the above range, the particle structure has a larger interlayer spacing and lower powder resistance, further improving the fast charging capability of the battery cell.

[0063] Artificial graphite particles are formed by high-temperature heat treatment of a carbon source. The order of arrangement of carbon atoms in the carbon source may be poor, and is mainly an ordered arrangement in two-dimensional space, that is, a chaotic layer structure. After high-temperature heat treatment, the disordered or two-dimensional ordered arrangement is transformed into a three-dimensional ordered arrangement, that is, from amorphous carbon to graphite. The process of ordering the atomic arrangement is the graphitization process, and the degree of ordering transformation is the degree of graphitization, which can be measured by X-ray diffraction.

[0064] Artificial graphite particles are at least partially coated with a carbon layer, primarily comprising amorphous carbon. Amorphous carbon refers to carbon materials in a non-completely crystalline amorphous region or an amorphous solid. The lattice structure of amorphous carbon tends to be disordered, while the lattice structure of artificial graphite particles tends to be ordered, which can be observed and distinguished using a transmission electron microscope (TEM). By coating the artificial graphite particles with a carbon layer, the low-temperature fast-charging performance of the battery cells can be further improved.

[0065] In some embodiments, the coverage of the carbon layer on the surface of the artificial graphite particles is ≥50%, and can be 60% to 100%. When the coverage of the carbon layer on the surface of the artificial graphite particles is 100%, it can be understood that the carbon layer covers the entire surface of the artificial particles; when the coverage of the carbon layer on the surface of the artificial graphite particles is less than 100%, it can be understood that the carbon layer covers a portion of the surface of the artificial particles.

[0066] In some embodiments, the average thickness of the carbon layer is ≥ 2 nm, optionally 2 nm to 20 nm; for example, 2 nm to 15 nm, 2 nm to 10 nm, or 5 nm to 10 nm.

[0067] In the embodiment of the present application, D of the negative electrode active material v 99.D v 50. D v 1. The test can be performed using equipment and methods known in the art. For example, a certain amount of negative electrode active material is taken as a sample and the volume average particle size D is measured by a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T19077-2016. v 50 and volume particle size distribution D v 99 and volume particle size distribution D v 1, where D v 99 is the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 99%; D v 50 is the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 50%; D v 1 is the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 1%.

[0068] In the embodiment of the present application, the prepared negative electrode active material can be directly taken as a sample for testing, or the negative electrode active material can be prepared into a negative electrode sheet, and the negative electrode sheet is subjected to an ion polishing cross-sectional morphology (CP) test to observe the material type of graphite in the negative electrode active material. As an example, the test method can be: first, the prepared negative electrode sheet is cut into a sample to be tested of a certain size (for example, 2cm×2cm), and the negative electrode sheet is fixed on the sample table by paraffin. Then the sample table is placed in the sample holder, locked and fixed, and the power of the argon ion cross-sectional polisher (for example, IB-19500CP) and the vacuum (for example, 10 -4 Pa), set the argon flow rate (e.g., 0.15 MPa), voltage (e.g., 8 kV), and polishing time (e.g., 2 hours), adjust the sample stage to rocking mode, and begin polishing. For sample testing, refer to JY / T010-1996. Scanning tests can be performed on randomly selected areas of the sample to be tested, and images of the ion-polished cross-sectional morphology (CP) of the negative electrode sheet can be obtained at a certain magnification (e.g., 5000x).

[0069] In the embodiment of the present application, the structure of the negative electrode active material (such as artificial graphite particles and carbon layer) can be tested using equipment and methods known in the art. As an example, the following step S can be performed: select a microgrid of a certain diameter (such as a diameter of 3 mm), clamp the edge of the microgrid with pointed tweezers, and gently place it on white filter paper with the film surface facing up (the shiny side is the film surface when observed under light); take an appropriate amount of negative electrode active material sample (such as 1 g) and add it to a beaker containing an appropriate amount of ethanol, and perform ultrasonic oscillation for 10 minutes to 30 minutes; use a glass capillary to absorb, and then drop 2-3 drops of the sample to be tested onto the microgrid; after baking in an oven for 5 minutes, place the microgrid with the sample to be tested on the sample stage, and use a transmission electron microscope (such as Hitachi HF-3300SCs-corrected STEM) to test at a certain magnification (such as 60,000 times) to obtain a transmission electron microscope (TEM) image of the sample to be tested.

[0070] In the embodiments of this application, primary particles and secondary particles have meanings well known in the art. Primary particles refer to non-agglomerated particles, while secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be easily distinguished using scanning electron microscope (SEM) images.

[0071] The number ratio of primary particles in the negative electrode active material can be tested by methods known in the art. An exemplary test method is as follows: the negative electrode active material is laid and adhered to the conductive glue to form a sample to be tested with a length × width = 6 cm × 1.1 cm; the particle morphology is tested using a scanning electron microscope (such as ZEISS Sigma300). The test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, multiple (for example, 5) different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, 1000 times), the percentage of the number of primary particles in each area to the total number of particles is calculated, that is, the number ratio of primary particles in the area, and the average value of the test results of multiple test areas is taken as the number ratio of primary particles in the negative electrode active material. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) can be taken to repeat the above test, and the average value of each test sample is taken as the final test result.

[0072] In the embodiments of the present application, the degree of graphitization of the artificial graphite particles in the negative electrode active material is well known in the art and can be tested using methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used, and the test can refer to JIS K0131-1996 and JB / T4220-2011 to measure d 002 The size of the G is then calculated according to the formula G = (0.344-d 002 ) / (0.344-0.3354)×100% to calculate the graphitization degree, where d 002 It is the interlayer distance in the graphite crystal structure expressed in nanometers (nm). In X-ray diffraction analysis, a copper target can be used as the anode target, with CuK α The ray is the radiation source, and the wavelength of the ray is The scanning 2θ angle range is 20° to 80°, and the scanning rate can be 4° / min.

[0073] In the embodiments of the present application, the tap density of the negative electrode active material has a meaning well known in the art and can be measured using methods known in the art. For example, it can be measured using a powder tap density tester in accordance with the standard GB / T5162-2006. For example, a tap density tester model FZS4-4B from the Beijing Iron and Steel Research Institute can be used, with the following test parameters: vibration frequency: 250 ± 15 times / minute, amplitude: 3 ± 0.2 mm, number of vibrations: 5000 times, and a measuring cylinder: 25 mL.

[0074] In the embodiments of the present application, the gram capacity of the negative electrode active material has a meaning well known in the art and can be tested using methods known in the art. An exemplary test method is as follows: the prepared negative electrode active material as the negative electrode active material, the conductive agent carbon black (SuperP), and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a solvent N-methylpyrrolidone (NMP) in a mass ratio of 91.6:1.8:6.6 to form a slurry; the prepared slurry is coated on a copper foil current collector, dried in an oven and set aside. A metal lithium sheet is used as the counter electrode and a polyethylene (PE) film is used as the separator. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L. CR2430 button batteries are assembled in an argon-protected glove box. After standing for 12 hours, the resulting button cell was discharged at a constant current of 0.05C to 0.005V at 25°C. The cell was then allowed to stand for 10 minutes and then discharged again at a constant current of 50μA to 0.005V. The cell was allowed to stand for 10 minutes and then discharged again at a constant current of 10μA to 0.005V. The cell was then charged at a constant current of 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the mass of the negative electrode active material is the gram capacity of the prepared negative electrode active material.

[0075] It should be noted that the above-mentioned various parameter tests on the negative electrode active material can be conducted by directly taking samples of the negative electrode active material for testing, or by taking samples from the battery cell for testing.

[0076] When the test sample is sampled from a battery cell, as an example, the sampling can be performed according to the following step S:

[0077] (1) Discharge the battery cells (for safety reasons, the battery is generally in a fully discharged state); disassemble the battery and remove the negative electrode sheet, and soak the negative electrode sheet in dimethyl carbonate (DMC) for a certain period of time (for example, 2 to 10 hours); then remove the negative electrode sheet and dry it at a certain temperature and time (for example, 60°C, 4 hours), and then remove the negative electrode sheet after drying.

[0078] (2) Bake the negative electrode sheet dried in step S(1) at a certain temperature and time (e.g., 400°C, 2h), and sample the negative electrode active material from any area of ​​the baked negative electrode sheet (sampling can be done by scraping powder with a blade).

[0079] (3) The negative electrode active material collected in step S(2) is sieved (for example, using a 200-mesh sieve) to finally obtain a negative electrode active material sample that can be used to test the various material parameters mentioned above in this application.

[0080] Method for preparing negative electrode active material

[0081] In a second aspect, an embodiment of the present application proposes a method for preparing a negative electrode active material.

[0082] Methods include:

[0083] Step S100, providing artificial graphite particles;

[0084] Step S200: coating the artificial graphite particles to form a carbon layer on at least a portion of the surface of the artificial graphite particles to obtain a negative electrode active material.

[0085] The volume average particle size D of the negative electrode active material is v 50 satisfies: 3μm≤D v 50≤7μm,

[0086] Volume distribution particle size D of negative electrode active material v 1 satisfied: D v 1≤1.5μm.

[0087] In some implementations, step S100 may specifically include:

[0088] Step S110, providing coke raw materials;

[0089] Step S120, shaping the focused raw material to obtain a precursor;

[0090] Step S130 , graphitizing the precursor to obtain artificial graphite particles.

[0091] In step S110 , the coke raw material can be directly purchased from a commercial source, or can be obtained by crushing the coke material.

[0092] In some embodiments, the coke material may be pulverized. The coke material may be pulverized using equipment and methods known in the art, such as a jet mill, mechanical mill, or roller mill. The pulverization process often produces a large number of undersized particles, and sometimes also oversized particles. Therefore, after pulverization, classification may be performed as needed to remove undersized and oversized particles from the pulverized powder. After classification, a coke material having the desired particle size distribution can be obtained. Classification can be performed using equipment and methods known in the art, such as a grading screen, gravity classifier, centrifugal classifier, etc.

[0093] The crushing process of coke material can be carried out in a process unit including a crusher, a classifier and an induced draft fan. During the crushing process, the D of the coke raw material can be controlled by adjusting the feeding frequency, crushing frequency, classification frequency and induced draft frequency. v 50. D v 1 and D v99 is within the required range. Compared with the lower classification frequency in the traditional crushing process, the method of the present application can increase the classification frequency, which is beneficial to the removal of too small particles. Compared with the higher induced draft frequency in the traditional crushing process, the method of the present application can reduce the induced draft frequency, which is beneficial to the removal of too large particles. In addition, compared with the traditional crushing process in which the frequency is controlled within a wider range, the method of the present application can also control the main engine frequency, classification frequency, and induced draft frequency within a narrower frequency range, thereby reducing the particle size distribution width of the coke raw material, for example, regulating the particle size of the coke raw material within a narrower range. The feeding frequency can also be synchronously adjusted to control the feed amount, which can further improve the crushing effect of the material.

[0094] In some embodiments, the coke raw material in step S110 may include one or more of petroleum non-needle coke and petroleum needle coke. Alternatively, the coke raw material includes petroleum green coke.

[0095] In some embodiments, in step S120, the coke feedstock may be shaped using equipment and methods known in the art, such as a shaping machine or other shaping equipment.

[0096] In some embodiments, after the coke raw material is shaped, it is further subjected to classification, which can be performed using equipment and methods known in the art, such as a grading screen, a gravity classifier, a centrifugal classifier, etc.

[0097] The shaping and grading treatment can be carried out in a process unit comprising a shaping machine, a grading machine and an induced draft fan. During the shaping and grading treatment process, the particle size of the obtained precursor can be regulated within the desired range by regulating the shaping frequency (for example, the main machine frequency and auxiliary machine frequency of the shaping machine), the grading frequency, and the induced draft frequency. Compared with the traditional shaping and grading process, the method of the present application increases the shaping frequency during the treatment process, appropriately extends the shaping time, and also reduces the grading frequency and induced draft frequency during the treatment process, so that the particle size of the obtained precursor is regulated within the target range.

[0098] In some embodiments, in step S130 , the precursor is graphitized at a temperature of 2800° C. to 3200° C. to obtain artificial graphite with an appropriate degree of graphitization. Alternatively, the graphitization temperature may be 2900° C. to 3100° C.

[0099] In step S130, graphitization can be performed using equipment known in the art, such as a graphitization furnace, and further such as an Acheson graphitization furnace. After the graphitization treatment is completed, a small amount of oversized particles formed by agglomeration during the high-temperature graphitization process can be removed by screening, which is beneficial to the D of the final negative electrode active material. v 50. D v 1 and D v 99 is within the required range.

[0100] In some embodiments, step S200 involves coating the artificial graphite particles with an organic carbon source, and then heat-treating the artificial graphite particles to form an amorphous carbon layer on at least a portion of the surface of the artificial graphite particles to obtain a negative electrode active material.

[0101] As an example, the artificial graphite obtained in step S130 can be mixed with an organic carbon source so that the organic carbon source coats at least a portion of the surface of the artificial graphite. The mixture is then heated at a temperature between 700°C and 1800°C to carbonize the organic carbon source and form an amorphous carbon layer on at least a portion of the surface of the artificial graphite. Alternatively, the heating temperature can be between 1100°C and 1400°C, and the heating time can be between 1 and 5 hours. Alternatively, the mass ratio of the artificial graphite to the organic carbon source can be between 98:2 and 75:25.

[0102] In some embodiments, the organic carbon source can be selected from one or more of asphalt (such as coal tar, petroleum asphalt), phenolic resin, coconut shell, etc., and can further be asphalt.

[0103] During the above preparation process, the coke raw materials usually contain some impurity elements (such as iron, nickel, chromium, zinc, sulfur, silicon, etc.), and the equipment used in the crushing and shaping process will also introduce some impurity elements (such as iron, copper, etc.). Under normal circumstances, the content of impurity elements in the core is very small, generally less than 1ppm.

[0104] In the above preparation process, the organic carbon source used in the coating process and the equipment used for coating will introduce trace amounts of impurity elements into the coating layer.

[0105] Negative electrode

[0106] In a third aspect, embodiments of the present application further provide a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. The negative electrode active material may comprise the negative electrode active material according to any embodiment of the first aspect of the present application, or a negative electrode active material prepared by the method according to any embodiment of the second aspect of the present application. For example, the negative electrode current collector has two surfaces opposing each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0107] In some embodiments, the negative electrode active material may further include at least one of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0108] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present embodiments do not particularly limit the type of negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent based on the total weight of the negative electrode film layer is ≤5%.

[0109] In some embodiments, the negative electrode film layer may also optionally include a negative electrode binder. The present application embodiment does not particularly limit the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder based on the total weight of the negative electrode film layer is ≤5%.

[0110] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, the weight percentage of the other additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0112] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0113] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0114] battery cells

[0115] In a fourth aspect, an embodiment of the present application further provides a battery cell.

[0116] A battery cell, also known as a rechargeable battery or storage battery, is a battery that can be recharged after discharge to activate the active material and continue to be used. Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0117] In some embodiments, the battery cell includes the negative electrode sheet of any embodiment of the third aspect of the present application. Thus, the battery cell of the embodiment of the present application can effectively improve the low temperature fast charging capability of the battery cell.

[0118] [Positive electrode]

[0119] The battery cell includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0120] The positive electrode active material may include, but is not limited to, at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate, and their respective modified compounds. Examples of lithium-containing transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0121] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A fAt least one of a lithium-containing transition metal oxide and a modified compound thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes at least one of N, F, S and Cl.

[0122] As an example, the positive active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0123] In the embodiment of the present application, the modified compound of each positive electrode active material may be a compound that performs doping modification and / or surface coating modification on the positive electrode active material.

[0124] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0125] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0126] In some embodiments, the mass percentage of the positive electrode active material may be 85 wt % to 95 wt % based on the total mass of the positive electrode film layer. Positive electrode active material in this content range can give the positive electrode sheet a higher capacity and better cycle performance.

[0127] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0128] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0129] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0130] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0131] [Electrolyte]

[0132] In some embodiments, the battery cell further includes an electrolyte.

[0133] During the charge and discharge process of a battery cell, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. The present application embodiment does not specifically limit the type of electrolyte, and the electrolyte can be selected based on actual needs.

[0134] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0135] As an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0136] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate, methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0137] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0138] [Isolation film]

[0139] In some embodiments, the battery cell further includes a separator. The embodiments of the present application have no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0141] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0142] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0144] The embodiment of the present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0145] In some embodiments, as Figure 2 As shown, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0146] The preparation methods of the battery cells of the embodiments of the present application are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0147] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0148] Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 3 As shown, in the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0149] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0150] In some embodiments, the battery modules can be assembled into a battery pack, and the number of battery modules in the battery pack can be adjusted according to the application and capacity of the battery pack. Battery cells, battery modules, and battery packs can all be used as examples of batteries.

[0151] Figure 4 and Figure 5 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 4 and Figure 5 As shown, a battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to 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 within the battery box.

[0152] Electrical devices

[0153] In a fifth aspect, embodiments of the present application provide an electrical device, which includes at least one of the battery cells, battery modules, or battery packs of the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop 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, a satellite, an energy storage system, etc.

[0154] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0155] Figure 6 Schematic diagram of an exemplary electric device 6. The electric device 6 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 electric device 6, a battery pack or battery module may be used.

[0156] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0157] Example

[0158] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention 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, and the instruments used in the examples are commercially available.

[0159] Example 1 Preparation of lithium-ion battery

[0160] 1. Preparation of negative electrode sheet

[0161] Preparation of negative electrode active materials

[0162] The petroleum coke is crushed to obtain the coke raw material, and the coke raw material is shaped and graded to obtain the precursor.

[0163] The precursor is graphitized at 3000°C and sieved to produce artificial graphite. The artificial graphite is then coated with pitch, an organic carbon source, and carbonized to produce a negative electrode active material comprising artificial graphite particles and a carbon layer located on at least a portion of the surface of the artificial graphite particles. The negative electrode active material is primary particles.

[0164] Preparation of negative electrode sheet

[0165] The negative electrode active material, conductive agent carbon black (SuperP), thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 96.4:1:1.2:1.4 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, and after drying and cold pressing, the negative electrode sheet is obtained.

[0166] 2. Preparation of positive electrode sheet

[0167] Aluminum foil was used as the positive electrode current collector.

[0168] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent N-methylpyrrolidone NMP in a weight ratio of 90:5:5 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0169] 3. Isolation film

[0170] A porous polyethylene (PE) film is used as the separator.

[0171] 4. Preparation of electrolyte

[0172] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents ethylene carbonate EC, ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent. Subsequently, the lithium salt lithium hexafluorophosphate and the electrolyte solvent are mixed to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0173] 5. Preparation of battery cells

[0174] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0175] Comparative Example 1 and Comparative Example 2

[0176] A lithium-ion battery was prepared by a method similar to that of Example 1. The difference from Example 1 was that the particle size of the negative electrode active material in Example 1 was adjusted, especially D v 50.

[0177] Example 2-1 to Example 2-8

[0178] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the particle size of the negative electrode active material was adjusted in Examples 2-1 and 2-3.

[0179] Example 3-1 to Example 3-5

[0180] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 was that the tap density and other factors of the negative electrode active materials in Examples 3-1 to 3-5 were adjusted.

[0181] Example 4-1 to Example 4-3

[0182] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 was that the graphitization degree of the artificial graphite particles of the negative electrode active material in Examples 4-1 to 4-3 was adjusted.

[0183] Example 5-1 to Example 5-2

[0184] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the average thickness of the carbon layer of the negative electrode active material in Examples 5-1 and 5-2 was adjusted.

[0185] The relevant parameters of the embodiments and comparative examples are shown in Table 1 below.

[0186] Performance Testing

[0187] 1. Performance test of lithium-ion batteries

[0188] The lithium-ion batteries prepared in the examples and comparative examples were adjusted to 80% SOC at -10°C, charged at 20C for 5 seconds and discharged at 20C for 5 seconds, and cycled for 500 cycles. The batteries were then fully charged at 0.33C at room temperature and disassembled to observe the lithium deposition on the surface of the negative electrode. A lithium deposition area of ​​less than 5% on the negative electrode surface was considered mild, a lithium deposition area of ​​5% to 40% was considered moderate, and a lithium deposition area of ​​more than 40% was considered severe.

[0189] Test results

[0190] The test results are shown in Table 1.

[0191] Table 1

[0192]

[0193] It can be seen from Table 1 that the D of the negative electrode active material in Comparative Example 1 v 50 and D v 1 are both large. Under low temperature conditions, the polarization of the battery increases, the active specific surface area of ​​the negative electrode interface reaction decreases, and the lithium ions transferred to the surface of the negative electrode cannot participate in the interface reaction in time, resulting in easy lithium precipitation at the interface. In addition, due to D v 50 is larger, the transmission distance of lithium ions increases at high SOC states, and the low-temperature charging capability deteriorates.

[0194] D in Comparative Example 2 v 1 is larger, and the content of fine powder in the negative electrode active material is less, which is not conducive to the rapid transfer of lithium ions and electrons at high SOC state, while D v The larger value of 99 makes the consistency of lithium embedding in particles relatively poor, which easily aggravates the polarization phenomenon and is not conducive to the rapid charging of battery cells.

[0195] Compared with Comparative Examples 1 and 2, and combined with Figure 7 and Figure 8 , the embodiment of the present application adjusts the D of the negative electrode active material v 99.D v 50 and D v1. Within an appropriate range, it can improve the lithium ion diffusion rate while improving the consistency of lithium insertion, thereby improving the low-temperature fast charging performance of the battery cell.

[0196] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A negative electrode active material comprising artificial graphite particles and a carbon layer disposed on at least a portion of the surface of the artificial graphite particles, wherein: The volume average particle size D of the negative electrode active material v 50 satisfies: 3μm≤D v 50≤7μm; The volume distribution particle size D of the negative electrode active material v 1 satisfied: D v 1≤1.5μm; The volume distribution particle size D of the negative electrode active material v 99 satisfied: D v 99≤18μm.

2. The negative electrode active material according to claim 1, wherein 0.8μm≤D v 1≤1.5μm。 3. The negative electrode active material according to claim 1, wherein 0.9μm≤D v 1≤1.3μm。 4. The negative electrode active material according to claim 1, wherein 0.9μm≤D v 1≤1.0μm。 5. The negative electrode active material according to claim 1, wherein 12μm≤D v 99≤18μm。 6. The negative electrode active material according to claim 1, wherein The negative electrode active material includes primary particles, and the primary particles account for ≥90% of the negative electrode active material.

7. The negative electrode active material according to claim 1, wherein The negative electrode active material includes primary particles, and the primary particles account for ≥95% of the negative electrode active material.

8. The negative electrode active material according to claim 1, wherein The gram capacity of the negative electrode active material is 330 mAh / g to 340 mAh / g; and / or The tap density of the negative electrode active material is 0.78 g / cm 3 to 1.2g / cm 3 .

9. The negative electrode active material according to claim 1, wherein The degree of graphitization of the artificial graphite particles is 90% to 93%.

10. The negative electrode active material according to claim 1, wherein The degree of graphitization of the artificial graphite particles is 91% to 93%.

11. The negative electrode active material according to claim 1, wherein The average thickness of the carbon layer is ≥2 nm.

12. The negative electrode active material according to claim 1, wherein The average thickness of the carbon layer is 2 nm to 20 nm.

13. A negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and comprising a negative electrode active material, wherein the negative electrode active material comprises the negative electrode active material according to any one of claims 1 to 12. A battery comprising the negative electrode sheet according to claim 13 .

15. An electrical device comprising the battery according to claim 14.

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