Secondary battery and electric device

Abstract

The invention relates to a secondary battery and a power utilization device. The secondary battery comprises a negative electrode piece, and the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector; the negative electrode film layer comprises a lower region and an upper region, the lower region comprises a first negative electrode active material, and the upper region is located in the negative electrode film layer region far away from the negative electrode current collector and comprises a second negative electrode active material; wherein the second negative electrode active material simultaneously comprises a primary particle carbon material and a secondary particle carbon material, the volume distribution particle size DV50 of the second negative electrode active material is less than or equal to 13 [mu] m, and the powder OI value of the primary particle carbon material is greater than the powder OI value of the secondary particle carbon material. The design is beneficial to improving the low-temperature fast charging performance of the secondary battery.

Description

[0001] Case Analysis This application is a divisional application of application number 202410338654.9, filed on March 22, 2024, entitled "Secondary Battery and Electrical Device". Technical Field

[0002] This application relates to the field of battery technology, and more particularly to secondary batteries and electrical devices. Background Technology

[0003] In recent years, with the development of secondary battery technology, it has been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, and aerospace.

[0004] Because of the widespread use of rechargeable batteries, users have also placed higher demands on their charging capabilities. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery with improved low-temperature fast charging performance and an electrical device using the secondary battery.

[0006] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector; the negative electrode film layer comprising a lower region and an upper region, the lower region comprising a first negative electrode active material, and the upper region comprising a second negative electrode active material; wherein the second negative electrode active material comprises both primary carbon particles and secondary carbon particles, and the volume distribution particle size D of the second negative electrode active material is [specific particle size distribution]. V 50 is less than or equal to 13 μm.

[0007] The aforementioned technical solution utilizes two types of carbon materials (primary and secondary carbon particles) in combination within the negative electrode film layer region (i.e., the upper region) far from the negative electrode current collector. The granulation structure of the secondary carbon particles helps reduce the OI value, thus improving low-temperature fast-charging performance. Simultaneously, the single-particle carbon material (primary particles) increases the active specific surface area and reduces the charge transfer resistance (Rct), further enhancing the battery's low-temperature fast-charging performance. Furthermore, the combination of different carbon particles allows for a controlled volume distribution particle size D of the second negative electrode active material. V The diameter of the electrode is less than or equal to 13 μm, which results in a better porosity distribution in the upper region of the electrode, which is beneficial to improving the transport performance of ions and electrons and further improving the low-temperature fast charging performance of the battery.

[0008] In some embodiments, the volume distribution particle size D of the second negative electrode active material V 50 has a particle size of 8 μm to 13 μm. The volume distribution particle size D of the second negative electrode active material... V Within the above range, 50 is more conducive to the formation of a better pore distribution in the upper region of the electrode, which is more conducive to improving the transport performance of ions and electrons and improving the low-temperature fast charging performance of the battery.

[0009] In some embodiments, the volume distribution particle size D of the primary carbon material is... V The volume distribution particle size D of the carbon material is smaller than that of the secondary particles. V 50; Optionally, the volume distribution particle size D of the primary carbon material is... V 50 is 3.5 μm to 6 μm, more preferably 3.5 μm to 5.0 μm; optionally, the volume distribution particle size D of the carbon material in the secondary particles is... V 50 is available in sizes from 10.0 μm to 14.0 μm, and can also be selected from 10.0 μm to 13.5 μm.

[0010] The above-mentioned technical solution includes carbon material with smaller primary particles and carbon material with larger secondary particles in the negative electrode film layer region far from the negative electrode current collector. The granulation structure of the larger secondary particles is more conducive to reducing the OI value of the material, which is beneficial to the low-temperature fast charging performance. The carbon material with smaller primary particles is more conducive to maintaining a higher active specific surface area, which further improves the low-temperature fast charging performance of the battery.

[0011] In some embodiments, the OI value of the carbon material in the primary particles is greater than the OI value of the carbon material in the secondary particles; optionally, the OI value of the carbon material in the primary particles is 3 to 6; optionally, the OI value of the carbon material in the secondary particles is 2 to 5.

[0012] In the above-described technical solution, the OI value of the primary carbon material powder is greater than that of the secondary carbon material powder, which is beneficial for rapid ion insertion and extraction. Furthermore, by maintaining the OI values ​​of these two carbon materials within the aforementioned range, the material has ion insertion ports in all directions, enabling rapid ion reception and further improving the low-temperature fast-charging performance of the secondary battery.

[0013] In some embodiments, the specific surface area of ​​the carbon material in the primary particles is greater than that in the secondary particles; optionally, the specific surface area of ​​the carbon material in the primary particles is 2.0 m². 2 / g to 3.5 m 2 / g, or 2.0 m 2 / g to 3.2 m2 / g; Optionally, the specific surface area of ​​the carbon material in the secondary particles is 0.6 m². 2 / g to 1.5 m 2 / g, optionally 0.6 m 2 / g to 1.2 m 2 / g.

[0014] In the above-described technical solution, the specific surface area of ​​the primary carbon material particles is greater than that of the secondary carbon material particles. This is beneficial for increasing the proportion of active specific surface area, improving the battery's low-temperature fast-charging performance, and reducing side reactions. Consequently, the battery can achieve both good fast-charging and cycle performance. Furthermore, when the specific surface area of ​​the carbon material is within the aforementioned range, it can increase the ion insertion channels in the upper region of the film layer, promoting the rapid diffusion of ions from the particle surface to the bulk phase.

[0015] In some embodiments, the carbon material of the primary particles satisfies the following: the volume distribution particle size D of the carbon material of the primary particles V 10 ranges from 1.0 μm to 3.0 μm.

[0016] In some embodiments, the carbon material of the primary particles satisfies the following: the volume distribution particle size D of the carbon material of the primary particles V 90 ranges from 9 μm to 12 μm.

[0017] When the volume distribution particle size of the primary carbon material is within the above range (Dv10 and / or Dv90), it is beneficial to improve the transport performance of ions and electrons, thereby further improving the fast charging performance of the secondary battery.

[0018] In some embodiments, the carbon material of the primary particles satisfies the following: the particle size distribution (D) of the carbon material of the primary particles V 90-D V 10) / DV50 is 1.1 to 1.8.

[0019] Particle size distribution of primary carbon materials (D) V 90-D V 10) / D V Within this range, 50 indicates a good distribution of carbon material in the primary particles, which is beneficial for the upper region of the negative electrode film to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transport and further improving the fast charging performance of the secondary battery.

[0020] In some embodiments, the carbon material of the primary particles satisfies the following condition: the tap density of the carbon material of the primary particles is 0.8 g / cm³. 3 Up to 1.1 g / cm 3When the tap density is within the above range, the compaction density of the negative electrode film can be increased, thereby achieving both low-temperature fast charging performance and battery energy density.

[0021] In some embodiments, the primary carbon material particles satisfy the following condition: the compacted density of the primary carbon material particles at 20000 N is 1.35 g / cm³. 3 Up to 1.55 g / cm 3 When the powder compaction density is within the above range, the compaction density of the negative electrode film can be increased, thereby achieving both low-temperature fast charging performance and battery energy density.

[0022] In some embodiments, the carbon material of the primary particles satisfies the following condition: the degree of graphitization of the carbon material of the primary particles is 90% to 93%. When the degree of graphitization of the carbon material of the primary particles is within the above range, it is beneficial to improve the ion transport performance of the negative electrode film, thereby enabling the secondary battery to achieve both high energy density and good fast charging performance.

[0023] In some embodiments, the carbon material of the secondary particles satisfies the following: the volume distribution particle size D of the carbon material of the secondary particles V 10 ranges from 4.5 μm to 8.0 μm.

[0024] In some embodiments, the carbon material of the secondary particles satisfies the following: the volume distribution particle size D of the carbon material of the secondary particles V 90 is 18 μm to 24 μm.

[0025] Volume distribution of carbon materials with particle size D V 10 and / or D V Within this range, 90% is conducive to the matching between the carbon material of the secondary particles and the carbon material of the primary particles, which is beneficial to the compaction density and thus to the energy density of the battery.

[0026] In some embodiments, the carbon material of the secondary particles satisfies the following: the particle size distribution (D) of the carbon material of the secondary particles... V 90-D V 10) / D V 50 is 0.9 to 1.3. Particle size distribution of secondary carbon materials (D) V 90-D V 10) / D V Within this range, 50 indicates a good distribution of carbon materials, which is beneficial for the upper region of the negative electrode film to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transport and further improving the fast charging performance of the secondary battery.

[0027] In some embodiments, the carbon material of the secondary particles satisfies the following condition: the tap density of the carbon material of the secondary particles is 0.9 g / cm³. 3 Up to 1.2 g / cm 3 When the tap density is within the above range, it can be well combined with the carbon material of the primary particles to improve the compaction density of the negative electrode film, thereby improving the low-temperature fast charging performance while taking into account the energy density of the battery.

[0028] In some embodiments, the carbon material of the secondary particles satisfies the following condition: the powder compaction density of the carbon material of the secondary particles at 20000 N is 1.55 g / cm³. 3 Up to 1.70 g / cm 3 When the compaction density of the secondary carbon material powder is within the above range, it can be well matched with the primary carbon material to improve the compaction density of the negative electrode film. This allows for both improved low-temperature fast charging performance and adequate battery energy density.

[0029] In some embodiments, the carbon material of the secondary particles satisfies the following condition: the degree of graphitization of the carbon material of the secondary particles is 92% to 95%. This is beneficial for the secondary battery to achieve both high energy density and good fast charging performance.

[0030] In some embodiments, the mass percentage of carbon material in the primary particles is less than the mass percentage of carbon material in the secondary particles, based on the total mass of the second negative electrode active material; optionally, the mass percentage of carbon material in the primary particles is 20% to 40% based on the total mass of the second negative electrode active material; optionally, the mass percentage of carbon material in the secondary particles is 60% to 80% based on the total mass of the second negative electrode active material.

[0031] By setting the mass percentage of carbon material in the primary particles to be less than that in the secondary particles, it is beneficial to improve the low-temperature fast charging performance of the battery while taking into account energy density.

[0032] In some embodiments, the carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

[0033] In some embodiments, the first negative electrode active material includes artificial graphite and / or natural graphite; alternatively, the first negative electrode active material includes both artificial graphite and natural graphite.

[0034] In some embodiments, the first negative electrode active material comprises natural graphite, and the volume distribution particle size (DV50) of the natural graphite is 9 μm to 20 μm. The inclusion of natural graphite in the first negative electrode active material further benefits low-temperature fast-charging performance due to the abundant coating layer on the surface of the natural graphite and its internal porous structure.

[0035] In some embodiments, the first negative electrode active material comprises artificial graphite with secondary particles.

[0036] In some embodiments, the first negative electrode active material comprises artificial graphite, wherein the volume distribution particle size D of the artificial graphite is... V 50 is 12 μm to 17 μm, and can be selected from 13 μm to 16 μm.

[0037] In some embodiments, the first negative electrode active material comprises natural graphite. In some embodiments, the volume distribution particle size D of the natural graphite is... V The particle size distribution D of the natural graphite ranges from 5.0 μm to 12.0 μm. In some embodiments, the volumetric particle size D of the natural graphite is... V 90 represents 20 μm to 30 μm. In some embodiments, the particle size distribution (D) of the natural graphite is... V 90-D V 10) / D V The density is 0.9 to 1.3. In some embodiments, the tap density of the natural graphite is 0.9 g / cm³. 3 Up to 1.2 g / cm 3 In some embodiments, the compacted density of the natural graphite powder at 20000 N is 1.60 g / cm³. 3 Up to 1.90 g / cm 3 In some embodiments, the degree of graphitization of the natural graphite is 96% to 98%.

[0038] In some embodiments, the first negative electrode active material comprises artificial graphite. In some embodiments, the volume distribution particle size D of the artificial graphite is... V 10 is 4 μm to 8 μm. In some embodiments, the volume distribution particle size D of the artificial graphite is... V 90 is 25 μm to 40 μm. In some embodiments, the particle size distribution (D) of the artificial graphite is... V 90-D V 10) / D V 50 is between 1.0 and 1.4. In some embodiments, the tap density of the artificial graphite is 0.95 g / cm³. 3 Up to 1.25 g / cm 3 In some embodiments, the compacted density of the artificial graphite powder at 20000 N is 1.70 g / cm³. 3 Up to 1.90 g / cm 3 In some embodiments, the degree of graphitization of the artificial graphite is 93% to 95%.

[0039] A second aspect of this application also provides an electrical device, including the secondary battery of the first aspect of this application. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0041] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0042] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0043] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0044] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0045] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0046] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0047] The following detailed description discloses embodiments of the secondary battery and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0053] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0054] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0055] In this application, the terms "primary particle" and "secondary particle" have meanings known in the art. A primary particle refers to a non-agglomerated particle. A secondary particle refers to an aggregated particle composed of two or more primary particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0056] In this application, the volume distribution particle sizes "Dv10", "Dv50", and "Dv90" mentioned when referring to materials have meanings known in the art. They represent the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively, and can be measured using instruments and methods known in the art. For example, GB / T 19077 can be referenced. In 2016, a laser particle size analyzer was used for determination. The testing instrument was the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0057] In this application, the term "powder OI value" has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray powder diffractometer (X'pert PRO), and the test can be performed in accordance with JIS K0131. 1996, JB / T 4220 In 2011, the X-ray diffraction pattern of the powder sample was obtained, and the OI value of the powder was calculated according to the formula OI value = I004 / I110. Here, I004 is the integrated area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integrated area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of this application, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, the ray wavelength scanning 2θ angle range is 20° to 80°, and the scanning rate is 4° / min.

[0058] In this application, the term "specific surface area" has a meaning known in the art and can be measured using instruments and methods known in the art. For example, GB / T 19587 can be referenced. The standard for determining the specific surface area of ​​solid materials by gas adsorption BET method in 2004 was tested using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using the Tri Star II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0059] In this application, the term "tap density" as used when referring to materials has a meaning known in the art and can be measured using instruments and methods known in the art. For example, GB / T5162 can be referenced. In 2006, the powder tap density was determined using a powder tap density tester. The testing instrument can be a Dandong Baite BT... 301, the test parameters are as follows: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, vibration number 5000 times, graduated cylinder 25mL.

[0060] In this application, the term "powder compaction density" as used when referring to materials has a meaning known in the art and can be measured using instruments and methods known in the art. For example, GB / T 24533 can be referenced. In 2009, the test was conducted using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine). An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327 cm². 2 In the mold, pressurize to the required pressure, hold the pressure for 30 seconds, release the pressure, hold for 10 seconds, and then record and calculate the compaction density of the powder material under the required pressure.

[0061] In this application, the term "degree of graphitization" has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the test can be referenced in JIS K 0131. 1996, JB / T 4220 In 2011, the average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure was obtained, and then according to the formula g=(0.344 d002) / (0.344 It is calculated using 0.3354)×100%. Wherein, d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure, expressed in nanometers (nm).

[0062] For systems requiring high energy density, thick coatings are typically used, necessitating high electrode compaction density. This hinders ion transport and consequently negatively impacts the low-temperature fast-charging performance of the rechargeable battery. Therefore, how to achieve both high-energy-density batteries and good low-temperature fast-charging performance is a pressing technical problem that needs to be solved.

[0063] As an important component of secondary batteries, the performance of the negative electrode sheet has a crucial impact on the overall performance of the secondary battery.

[0064] In view of this, the inventors ingeniously improved the composition of the negative electrode film, which enables the secondary battery to achieve both high energy density and good low-temperature fast charging performance.

[0065] Based on this, this application proposes a secondary battery.

[0066] The term "secondary battery" as used in this article refers to a single battery cell, battery module, or battery pack.

[0067] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0068] The secondary battery provided in the first aspect of this application includes the negative electrode plate as described below.

[0069] [Negative electrode plate] The negative electrode sheet of this application includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector; the negative electrode film layer includes a lower region and an upper region, the lower region includes a first negative electrode active material, and the upper region includes a second negative electrode active material; wherein the second negative electrode active material includes both primary carbon material particles and secondary carbon material particles, and the volume distribution particle size DV50 of the second negative electrode active material is less than or equal to 13 μm.

[0070] The aforementioned technical solution utilizes two types of carbon materials (primary and secondary carbon particles) in combination within the negative electrode film layer region (i.e., the upper region) far from the negative electrode current collector. The granulation structure of the secondary carbon particles helps reduce the OI value and improves low-temperature fast-charging performance. Simultaneously, the single-particle carbon material (primary particles) increases the active specific surface area and reduces the charge transfer resistance (Rct), further improving the battery's low-temperature fast-charging performance. Furthermore, the combination of different carbon particles allows for a controlled volume distribution particle size D of the second negative electrode active material. V The diameter of the electrode is less than or equal to 13 μm, which results in a better porosity distribution in the upper region of the electrode, which is beneficial to improving the transport performance of ions and electrons and further improving the low-temperature fast charging performance.

[0071] In some embodiments, the volume distribution particle size D of the second negative electrode active material V 50 has a particle size of 8 μm to 13 μm. The volume distribution particle size D of the second negative electrode active material... VWithin the above range, 50 is more conducive to the formation of a better pore distribution in the upper region of the electrode, which is more conducive to improving the transport performance of ions and electrons and improving the low-temperature fast charging performance of the battery.

[0072] In some embodiments, the volume distribution particle size D of the primary carbon material is... V The volume distribution particle size D of the carbon material is smaller than that of the secondary particles. V 50. The above technical solution includes carbon material with smaller primary particles and carbon material with larger secondary particles in the negative electrode film layer region far from the negative electrode current collector. The granulation structure of the larger secondary particles is more conducive to reducing the OI value of the material, which is beneficial to the low-temperature fast charging performance. At the same time, the carbon material mixed with small primary particles is more conducive to the active specific surface area, further improving the low-temperature fast charging performance of the battery.

[0073] In some embodiments, the volume distribution particle size D of the primary carbon material is... V 50 is 3.5 μm to 6 μm. In some embodiments, the volume distribution particle size D of the primary carbon material is... V 50 is 3.5 μm to 5.0 μm. In some embodiments, the volume distribution particle size D of the carbon material in the secondary particles is... V 50 is 10.0 μm to 14.0 μm. In some embodiments, the volume distribution particle size D of the carbon material in the secondary particles is... V The particle size of 50 ranges from 10.0 μm to 13.5 μm. By selecting and combining the appropriate particle sizes of the primary and secondary carbon materials, the upper region of the film layer has better porosity, ensuring lithium-ion transport channels and further improving low-temperature fast charging performance.

[0074] In some embodiments, the OI value of the primary carbon material particles is greater than the OI value of the secondary carbon material particles. In some embodiments, the OI value of the primary carbon material particles is 3 to 6. In some embodiments, the OI value of the secondary carbon material particles is 2 to 5.

[0075] With the above design, the material particles have ion insertion ports in all directions, which can quickly receive ions from the positive electrode, thereby further improving the low-temperature fast charging performance of the secondary battery.

[0076] In some embodiments, the specific surface area of ​​the carbon material in the primary particles is greater than that in the secondary particles. By making the specific surface area of ​​the carbon material in the primary particles greater than that in the secondary particles, it is more beneficial to maintain the proportion of active specific surface area in the upper region of the film layer, thereby improving the low-temperature fast charging performance of the battery.

[0077] In some embodiments, the specific surface area of ​​the carbon material in the primary particles is 2.0 m². 2 / g to 3.5 m 2 / g. In some embodiments, the specific surface area of ​​the carbon material in the primary particles is 2.0 m². 2 / g to 3.2 m 2 / g. In some embodiments, the specific surface area of ​​the carbon material in the secondary particles is 0.6 m². 2 / g to 1.5 m 2 / g. In some embodiments, the specific surface area of ​​the carbon material in the secondary particles may be selected as 0.6 m². 2 / g to 1.2 m 2 / g. Therefore, when the specific surface area of ​​the carbon material is within the aforementioned range, ion insertion channels in the upper region of the film can be maintained, promoting the rapid diffusion of ions from the particle surface to the bulk phase.

[0078] In some embodiments, the carbon material of the primary particles satisfies the following: the volume distribution particle size D of the carbon material of the primary particles V The particle size distribution (Dv10) of the primary carbon material ranges from 1.0 μm to 3.0 μm. When the particle size Dv10 is within this range, it is beneficial to improve the transport performance of ions and electrons, thereby further improving the fast-charging performance of the secondary battery.

[0079] In some embodiments, the carbon material of the primary particles satisfies the following: the volume distribution particle size D of the carbon material of the primary particles V The particle size Dv90 ranges from 9 μm to 12 μm. When the volume distribution particle size Dv90 of primary carbon materials is within this range, the particle uniformity is better, which is beneficial to improving the transport performance of ions and electrons.

[0080] In some embodiments, the carbon material of the primary particles satisfies the following: the particle size distribution (D) of the carbon material of the primary particles V 90-D V 10) / D V 50 is 1.1 to 1.8. The particle size distribution (D) of primary carbon materials. V 90-D V 10) / D V Within this range, 50 indicates a good distribution of carbon materials, which is beneficial for the upper region of the negative electrode film to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transport and further improving the fast charging performance of the secondary battery.

[0081] In some embodiments, the carbon material of the primary particles satisfies the following condition: the tap density of the carbon material of the primary particles is 0.8 g / cm³. 3Up to 1.1 g / cm 3 When the tap density is within the above range, the compaction density of the negative electrode film can be increased, thereby achieving both low-temperature fast charging performance and battery energy density.

[0082] In some embodiments, the primary carbon material particles satisfy the following condition: the compacted density of the primary carbon material particles at 20000 N is 1.35 g / cm³. 3 Up to 1.55 g / cm 3 When the powder compaction density is within the above range, the compaction density of the negative electrode film can be increased, thereby achieving both low-temperature fast charging performance and battery energy density.

[0083] In some embodiments, the carbon material of the primary particles satisfies the following condition: the degree of graphitization of the carbon material of the primary particles is 90% to 93%. When the degree of graphitization of the carbon material of the primary particles is within the above range, it is beneficial to improve the ion transport performance of the negative electrode film, thereby enabling the secondary battery to achieve both high energy density and good fast charging performance.

[0084] In some embodiments, the carbon material of the secondary particles satisfies the following: the volume distribution particle size D of the carbon material of the secondary particles V The particle size D of the secondary carbon material ranges from 4.5 μm to 8.0 μm. V Within this range, the carbon material is better matched with the primary carbon material particles, which is beneficial to the compaction density and thus contributes to the energy density of the battery.

[0085] In some embodiments, the carbon material of the secondary particles satisfies the following: the volume distribution particle size D of the carbon material of the secondary particles V 90 is 18 μm to 24 μm.

[0086] In some embodiments, the carbon material of the secondary particles satisfies the following: the particle size distribution (D) of the carbon material of the secondary particles... V 90-D V 10) / D V 50 is 0.9 to 1.3. Particle size distribution of secondary carbon materials (D) V 90-D V 10) / D V Within this range, 50 indicates a good distribution of carbon materials, which is beneficial for the upper region of the negative electrode film to have a suitable pore structure, thereby reducing the difficulty of ion transport in the liquid phase and further improving the fast-charging performance of the secondary battery. In some embodiments, the carbon material of the secondary particles satisfies the following condition: the tap density of the carbon material of the secondary particles is 0.9 g / cm³. 3 Up to 1.2 g / cm3 When the tap density is within the above range, it can be well matched with the primary particles to improve the compaction density of the negative electrode film, thereby achieving both low-temperature fast charging performance and battery energy density.

[0087] In some embodiments, the carbon material of the secondary particles satisfies the following condition: the powder compaction density of the carbon material of the secondary particles at 20000 N is 1.55 g / cm³. 3 Up to 1.70 g / cm 3 When the compaction density of the carbon material powder in the secondary particles is within the above range, it can be well matched with the primary particles to improve the compaction density of the negative electrode film. This allows the battery's energy density to be considered while achieving low-temperature fast charging performance.

[0088] In some embodiments, the carbon material of the secondary particles satisfies the following condition: the degree of graphitization of the carbon material of the secondary particles is 92% to 95%. This is beneficial for the secondary battery to achieve both high energy density and good fast charging performance.

[0089] In some embodiments, the mass percentage of carbon material in the primary particles is less than the mass percentage of carbon material in the secondary particles, based on the total mass of the second negative electrode active material; optionally, the mass percentage of carbon material in the primary particles is 20% to 40% based on the total mass of the second negative electrode active material; optionally, the mass percentage of carbon material in the secondary particles is 60% to 80% based on the total mass of the second negative electrode active material.

[0090] By setting the mass percentage of carbon material in the primary particles to be less than that in the secondary particles, it is beneficial to improve the low-temperature fast charging performance of the battery while taking into account energy density.

[0091] In some embodiments, the carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

[0092] In some embodiments, the first negative electrode active material includes artificial graphite and / or natural graphite; alternatively, the first negative electrode active material includes both artificial graphite and natural graphite.

[0093] In some embodiments, the first negative electrode active material comprises natural graphite, and the volume distribution particle size D of the natural graphite is... V The thickness of the electrode is 9 μm to 20 μm. The first negative electrode active material includes natural graphite, in which the abundant coating layer on the surface of natural graphite and the internal porous structure further benefit the low-temperature fast charging performance. In addition, the specific capacity of natural graphite in the lower region is higher than that of carbon material in the upper region, which is beneficial to meeting the energy density requirements.

[0094] In some embodiments, the first negative electrode active material comprises artificial graphite with secondary particles.

[0095] In some embodiments, the first negative electrode active material comprises artificial graphite, wherein the volume distribution particle size D of the artificial graphite is... V 50 is 12 μm to 17 μm, and can be selected from 13 μm to 16 μm.

[0096] In some embodiments, the first negative electrode active material comprises natural graphite. In some embodiments, the volume distribution particle size D of the natural graphite is... V The particle size distribution D of the natural graphite ranges from 5.0 μm to 12.0 μm. In some embodiments, the volumetric particle size D of the natural graphite is... V 90 represents a particle size distribution of 20 μm to 30 μm. In some embodiments, the particle size distribution (D) of the natural graphite is... V 90-D V 10) / D V The density is 0.9 to 1.3. In some embodiments, the tap density of the natural graphite is 0.9 g / cm³. 3 Up to 1.2 g / cm 3 In some embodiments, the compacted density of the natural graphite powder at 20000 N is 1.60 g / cm³. 3 Up to 1.90 g / cm 3 In some embodiments, the degree of graphitization of the natural graphite is 96% to 98%.

[0097] In some embodiments, the first negative electrode active material comprises artificial graphite. In some embodiments, the volume distribution particle size D of the artificial graphite is... V 10 is 4 μm to 8 μm. In some embodiments, the volume distribution particle size D of the artificial graphite is... V 90 is 25 μm to 40 μm. In some embodiments, the particle size distribution (D) of the artificial graphite is... V 90-D V 10) / D V 50 is between 1.0 and 1.4. In some embodiments, the tap density of the artificial graphite is 0.95 g / cm³. 3 Up to 1.25 g / cm 3 In some embodiments, the compacted density of the artificial graphite powder at 20000 N is 1.70 g / cm³. 3 Up to 1.90 g / cm 3 In some embodiments, the degree of graphitization of the artificial graphite is 93% to 95%.

[0098] It should be noted that the above-mentioned tests on various parameters of the first negative electrode active material, the second negative electrode active material, or the negative electrode film can be performed by sampling and testing from the prepared secondary battery according to the following steps.

[0099] Discharge the secondary battery (for safety reasons, the secondary battery is generally left fully discharged); disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2 to 10 hours); then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours); then remove the negative electrode.

[0100] Subsequently, the dried negative electrode sheet is baked at a certain temperature and time (e.g., 400℃ for more than 2 hours). In the baked negative electrode sheet, a region is randomly selected, and the powder scraped off from the upper 1 / 3 thickness film layer is used as the second negative electrode active material, while the powder scraped off from the 1 / 3 H film layer near the copper foil is used as the first negative electrode active material. The collected first and second negative electrode active materials are sieved to obtain first and second negative electrode active material samples that can be used to test the material parameters mentioned above in this application.

[0101] As an example, the test method for the volume distribution particle size Dv50 of the second negative electrode active material can be as follows: The sample is dispersed at a suitable concentration in a suitable liquid (e.g., deionized water) or gas through ultrasonic treatment or other methods. The particle size distribution is then measured using a laser particle size analyzer (e.g., Malvern Master Size 3000). The sample is passed through a monochromatic beam (usually a laser). When the light encounters the particles, it is scattered at different angles. The scattered light is measured by a multi-element detector, and these values ​​related to the scattering pattern are stored for subsequent analysis. Through appropriate optical models and mathematical processes, these quantified scattering data are converted to obtain a series of discrete particle size ranges representing the percentage of particle volume relative to the total particle volume, thus yielding the particle size distribution. The Dv50 particle size represents the particle size corresponding to a cumulative volume distribution percentage of 50% from the smallest particle size side in the particle size distribution.

[0102] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0104] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0106] [Preparation method of negative electrode sheet] This application also provides a method for preparing the negative electrode sheet of this application. The method includes the following steps: A first slurry containing a first negative electrode active material and a second slurry containing a second negative electrode active material are provided; the first slurry is coated on a negative electrode current collector, and then the second slurry is coated, followed by drying and cold pressing to obtain a negative electrode sheet.

[0107] In some embodiments, a first negative electrode active material, along with optional conductive agents, optional binders, and other optional additives, may be dispersed in a solvent (e.g., NMP) to form a first slurry.

[0108] In some embodiments, a second active material, along with optional conductive agents, optional binders, and other optional additives, may be dispersed in a solvent (e.g., NMP) to form a second slurry, wherein the second negative electrode active material comprises both primary particulate carbon material and secondary particulate carbon material.

[0109] The first and second slurries can be coated simultaneously in one step or separately in two steps. In some embodiments, the first and second slurries are coated simultaneously in one step. Simultaneous coating in one step can reduce the negative electrode film resistance, thereby further improving the rate performance and cycle performance of the secondary battery.

[0110] The coating weights of the first and second slurries can be adjusted according to actual conditions.

[0111] The first negative electrode active material and the second negative electrode active material mentioned above can be obtained commercially or prepared by the method described in this application.

[0112] In some embodiments, primary particulate carbon materials can be prepared by crushing and shaping coke raw materials, followed by graphitization treatment to obtain primary particulate carbon materials. Specific examples of coke raw materials may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke. The graphitization temperature may be between 2800°C and 3200°C.

[0113] In some embodiments, the carbon material containing secondary particles can be prepared by crushing and shaping a coke feedstock, then mixing it with a binder for granulation, followed by graphitization treatment, to obtain a carbon-based material containing secondary particles. Specific examples of the coke feedstock may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke. The graphitization temperature may be between 2800°C and 3200°C. Specific examples of the binder may include pitch.

[0114] The above-described preparation process does not include the step of forming a carbon coating layer on the material surface. As an example, the carbon coating layer on the surface of the carbon material can be formed by carbonization of an organic carbon source. The organic carbon source can be a carbon-containing material known in the art that is suitable for coating, such as one or more of coal tar pitch, petroleum pitch, phenolic resin, coconut shell, etc.

[0115] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0116] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0117] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0119] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0120] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0121] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0124] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0125] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0127] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0128] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0129] [Isolation membrane] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0130] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0131] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0132] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0133] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0135] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0136] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0137] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0138] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0139] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0140] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0141] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0142] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0143] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0144] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0145] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0146] Example 1 The first negative electrode active material, a mixture of artificial graphite and natural graphite 1-1 (see Table 1 for relevant parameters, the mass ratio of the two is 6:4), conductive agent Super P, thickener CMC, and binder SBR are mixed at a mass ratio of 96.4:1:1.2:1.4. Then, deionized water is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous to obtain the first slurry.

[0147] The second negative electrode active material, a mixture of primary and secondary artificial graphite particles 2-1 (see Table 2 for relevant parameters), conductive agent Super P, thickener CMC, and binder SBR are mixed at a mass ratio of 96.4:1:1.2:1.4. Then, deionized water is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous to obtain the second slurry.

[0148] A first slurry is uniformly coated onto the negative electrode current collector copper foil. After drying, a second slurry is coated onto the surface of the first slurry. The resulting negative electrode sheet is obtained after drying and cold pressing. The coating weights of the lower region formed by the first slurry and the upper region formed by the second slurry are 7.6 mg / cm², respectively. 2 "and 5.1 mg / cm" 2 The thickness of the negative electrode monolayer (i.e., the thickness of the single-sided coated layer + the thickness of the copper foil) is 0.077 mm.

[0149] LiFePO4, conductive agent Super P, and binder polyvinylidene fluoride were mixed in a mass ratio of 97.4:0.8:1.8, and then NMP solvent was added and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0150] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a solvent. LiPF6 was then dissolved in the solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0151] A polypropylene film (12µm thick) is used as a separator and is placed in sequence with the positive and negative electrode sheets prepared above, so that the separator is placed between the positive and negative electrode sheets to play a role in isolation. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, aging and other processes, a secondary battery is obtained.

[0152] Examples 2-9 The secondary battery was assembled in the same manner as in Example 1, except that the first negative electrode active material and the second negative electrode active material shown in Table 3 were used.

[0153] Comparative Example 1 The secondary battery was assembled in the same manner as in Example 1, except that the mixture material 2-8 (Dv50 greater than 13μm) was used as the second negative electrode active material (see Table 2 for relevant parameters).

[0154] Comparative Example 2 The secondary battery was assembled in the same manner as in Example 1, except that only the mixture materials 2-9 (carbon materials containing only secondary particles) were used as the second negative electrode active material (see Table 2 for relevant parameters).

[0155] Comparative Example 3 The secondary battery was assembled in the same manner as in Example 1, except that only the mixture material 2-10 (carbon material containing only primary particles) was used as the second negative electrode active material (see Table 2 for relevant parameters).

[0156] Table 1: First Anode Active Material

[0157] In Table 1, " / " indicates that the item does not exist.

[0158] Table 2: Second Anode Active Material

[0159] Secondary battery performance test Low-temperature fast charging performance test At -10°C, the batteries prepared in the examples and comparative examples were fully charged at x C and fully discharged at 1C within the 20%-50% SOC range for 10 cycles. After that, the batteries were fully charged at x C and disassembled to observe whether lithium was deposited on the surface of the negative electrode. If no lithium was deposited on the negative electrode surface, the charging rate x C was increased in increments of 0.1C and the test was repeated until lithium was deposited on the negative electrode surface. The test was then stopped, and the charging rate (x-0.1) C at this point is the maximum charging rate of the battery.

[0160] Table 3 below shows the parameters of the negative electrode sheets of Examples 1-9 and Comparative Examples 1-3 and the test results of the secondary battery performance.

[0161] Table 3:

[0162] As can be seen from Table 3, compared with Comparative Example 1 (Dv50 of the second negative electrode active material is greater than 13), Comparative Example 2 (the second negative electrode active material uses only secondary particles), and Comparative Example 3 (the second negative electrode active material uses only primary particles), in Examples 1-9, by setting the second negative electrode active material to include both primary and secondary carbon particles, the low-temperature fast charging performance of the secondary battery is significantly improved.

[0163] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector; the negative electrode film layer comprising a lower region and an upper region, the lower region comprising a first negative electrode active material, and the upper region being located in a negative electrode film layer region away from the negative current collector and comprising a second negative electrode active material; in, The second negative electrode active material comprises both primary carbon particles and secondary carbon particles, and the volume distribution particle size D of the second negative electrode active material is... V 50 is less than or equal to 13 μm; and The OI value of the carbon material in the primary particles is greater than that of the carbon material in the secondary particles.

2. The secondary battery according to claim 1, characterized in that, The volume distribution particle size D of the second negative electrode active material V 50 is 8 μm to 13 μm.

3. The secondary battery according to claim 1 or 2, characterized in that, The volume distribution particle size D of the carbon material in the primary particles V 50 is available in sizes from 3.5 μm to 6 μm, and can also be selected from 3.5 μm to 5.0 μm; and / or The volume distribution particle size D of the carbon material in the secondary particles V 50 is available in sizes from 10.0 μm to 14.0 μm, and can also be selected from 10.0 μm to 13.5 μm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The primary particles of carbon material have an OI value of 3 to 6; and / or The carbon material of the secondary particles has a powder OI value of 2 to 5.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The specific surface area of ​​the carbon material in the primary particles is greater than that in the secondary particles. Optionally, the specific surface area of ​​the carbon material in the primary particles is 2.0 m². 2 / g to 3.5 m 2 / g, or 2.0 m 2 / g to 3.2 m 2 / g; Optionally, the specific surface area of ​​the carbon material in the secondary particles is 0.6 m². 2 / g to 1.5 m 2 / g, optionally 0.6 m 2 / g to 1.2 m 2 / g.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The carbon material of the primary particles also satisfies at least one of the following (1) to (6): (1) The volume distribution particle size D of the carbon material in the primary particles V 10 ranges from 1.0 μm to 3.0 μm; (2) The volume distribution particle size D of the carbon material in the primary particles V 90 is 9 μm to 12 μm; (3) The particle size distribution (D) of the carbon material in the primary particles V 90-D V 10) / D V 50 is between 1.1 and 1.8; (4) The tap density of the carbon material in the primary particles is 0.8 g / cm³. 3 Up to 1.1 g / cm 3 ; (5) The compacted density of the carbon material in the primary particles at 20000N is 1.35 g / cm³. 3 Up to 1.55 g / cm 3 ; (6) The degree of graphitization of the carbon material in the primary particles is 90% to 93%.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The carbon material of the secondary particles also satisfies at least one of the following (1) to (6): (1) The volume distribution particle size D of the carbon material in the secondary particles V 10 ranges from 4.5 μm to 8.0 μm; (2) The volume distribution particle size D of the carbon material in the secondary particles V 90 is 18 μm to 24 μm; (3) The particle size distribution (D) of the carbon material in the secondary particles V 90-D V 10) / D V 50 ranges from 0.9 to 1.3; (4) The tap density of the carbon material in the secondary particles is 0.9 g / cm³. 3 Up to 1.2 g / cm 3 ; (5) The compacted density of the carbon material in the secondary particles at 20000N is 1.55 g / cm³. 3 Up to 1.70 g / cm 3 ; (6) The degree of graphitization of the carbon material in the secondary particles is 92% to 95%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, Based on the total mass of the second negative electrode active material, the mass percentage of carbon material in the primary particles is less than the mass percentage of carbon material in the secondary particles. Optionally, based on the total mass of the second negative electrode active material, the mass percentage of carbon material in the primary particles is 20% to 40%. Optionally, based on the total mass of the second negative electrode active material, the carbon material content of the secondary particles is 60% to 80%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The carbon material of the primary particles and / or the carbon material of the secondary particles is artificial graphite.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The first negative electrode active material includes artificial graphite and / or natural graphite; Optionally, the first negative electrode active material includes both artificial graphite and natural graphite.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first negative electrode active material comprises natural graphite, and the volume distribution particle size D of the natural graphite is... V 50 ranges from 9 μm to 20 μm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The first negative electrode active material includes artificial graphite with secondary particles.

13. The secondary battery according to any one of claims 1 to 12, characterized in that, The first negative electrode active material includes artificial graphite, wherein the volume distribution particle size D of the artificial graphite is... V 50 is 12 μm to 17 μm, and can be selected from 13 μm to 16 μm.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The first negative electrode active material comprises natural graphite, wherein the natural graphite satisfies at least one of the following (1) to (6): (1) The volume distribution particle size D of the natural graphite V 10 ranges from 5.0 μm to 12.0 μm; (2) The volume distribution particle size D of the natural graphite V 90 represents 20 μm to 30 μm; (3) The particle size distribution (D) of the natural graphite V 90-D V 10) / D V 50 ranges from 0.9 to 1.3; (4) The tap density of the natural graphite is 0.9 g / cm³. 3 Up to 1.2 g / cm 3 ; (5) The compacted density of the natural graphite powder at 20000N is 1.60 g / cm³. 3 Up to 1.90 g / cm 3 ; (6) The degree of graphitization of the natural graphite is 96% to 98%.

15. The secondary battery according to any one of claims 1 to 14, characterized in that, The first negative electrode active material comprises artificial graphite, wherein the artificial graphite satisfies at least one of the following (1) to (6): (1) The volume distribution particle size D of the artificial graphite V 10 ranges from 4 μm to 8 μm; (2) The volume distribution particle size D of the artificial graphite V 90 is 25 μm to 40 μm; (3) The particle size distribution (D) of the artificial graphite V 90-D V 10) / D V 50 is between 1.0 and 1.4; (4) The tap density of the artificial graphite is 0.95 g / cm³. 3 Up to 1.25 g / cm 3 ; (5) The compacted density of the artificial graphite powder at 20000N is 1.70 g / cm³. 3 Up to 1.90 g / cm 3 ; (6) The degree of graphitization of the artificial graphite is 93% to 95%.

16. An electrical device comprising a secondary battery as described in any one of claims 1 to 15.

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